ELECTRONIC COPY OF FINAL DOCUMENT ORIGINAL SEALED DOCUMENT WITH ROBERT L. SHAND, P.E. (CIVIL), NO. 24026 FLOODPLAIN STUDY FOR FLECHA CAIDA RANCH ESTATES # 9 INCLUDING PORTIONS OF FLECHA CAIDA RANCH ESTATES #1 AND #2 AND LAS LOMAS DE CATALINA SECTIONS 15 & 22, TOWNSHIP 13 SOUTH, RANGE 14 EAST PIMA COUNTY, ARIZONA Prepared for: Pima County Regional Flood Control District 97 E. Congress Street, 3rd Floor Tucson, Arizona 85701 520-791-4724 By: JE Fuller Hydrology & Geomorphology Inc. 40 East Helen Street Tucson, Arizona 85705 520-623-3112 January 8, 2008 Revised April 8, 2008 EXPIRES 06/30/2010 FLOODPLAIN STUDY – FLECHA CAIDA RANCH ESTATES # 9 TABLE OF CONTENTS I. INTRODUCTION ...............................................................................................................1 Background ..........................................................................................................................1 Purpose.................................................................................................................................3 II. HYDROLOGY ....................................................................................................................5 Valley View Wash ...............................................................................................................5 St Thomas Church................................................................................................................7 III. FLOODPLAIN ANALYSIS................................................................................................8 Regulatory Flood Plain ........................................................................................................8 Flood Prone Structures.......................................................................................................11 Erosion and Sedimentation ................................................................................................14 IV. FLOOD HAZARD MITIGATION....................................................................................16 Flood Prone Structures.......................................................................................................17 Erosion and Sedimentation ................................................................................................18 V. REFERENCES ..................................................................................................................20 LIST OF APPENDICES (Provided on Compact Disk in PDF format) Appendix A Subdivision Plat/Historic Study Excerpts/Historic Study Reports/Exhibits Appendix B NOAA Atlas 2, Volume VIII (1973) Hydrologic Data Sheets Appendix C NOAA Atlas 14, Volume I (2006) Hydrologic Data Sheets Appendix D Development Plans for St. Thomas Church Appendix E 2007 Topographic Survey Sheets (Cardinal Land Surveying, Inc.) Appendix F Scour Computation Sheets Appendix G Guides to Retrofitting Flood Prone Structures i JE Fuller/Hydrology & Geomorphology, Inc. FLOODPLAIN STUDY – FLECHA CAIDA RANCH ESTATES # 9 LIST OF FIGURES Figure 1 Location Map .........................................................................................................21 Figure 2 1941 Aerial Photograph .........................................................................................22 Figure 3 2007 Topography/2007 Aerial Photograph ...........................................................23 Figure 4 Flood Hazard Map .................................................................................................26 Figure 5 1998 Streambed Profile versus 2007 Profile (Ranch Estates #9) ..........................29 LIST OF TABLES Table 2.1 Pre- and Post-Development Hydrology (100-year) .................................................5 Table 2.2 Updated Hydrology (100-year) ...............................................................................6 Table 2.3 Updated Hydrology (multi-frequency) ....................................................................7 Table 3.1a Regulatory Discharges and Water-Surface Elevations for the Main Corridor of the Valley View Wash within Ranch Estates #9.........................9 Table 3.1b Regulatory Discharges and Water-Surface Elevations for the West Channel of the Valley View Wash within Ranch Estates #9 .........................9 Table 3.2 Regulatory Discharges and Water-Surface Elevations for the Valley View Wash Downstream of Ranch Estates #9 ..........................................10 Table 3.3 Lateral Weir Quantities and Hydraulic Properties.................................................11 Table 3.4 Comparison of FFE to W.S. Elevation and Existing Grade within Ranch Estates No. 9....................................................................................12 Table 3.5 Comparison of FFE to W.S. Elevation and Existing Grade within Ranch Estates No. 9....................................................................................13 LIST OF EXHIBITS (Provided in Appendix A5 in PDF format) Revised Drainage Basin Exhibit Flood Plain Comparison Exhibit Streambed Profile Exhibit (Ranch Estates #1 and #2 and Las Lomas de Catalina) ii JE Fuller/Hydrology & Geomorphology, Inc. FLOODPLAIN STUDY – FLECHA CAIDA RANCH ESTATES # 9 I. Page 1 INTRODUCTION Background The development of Flecha Caida Ranch Estates began in 1956. The subdivision plat for the 40-acre parcel currently known as Flecha Caida Ranch Estates #9 was prepared in December 1959 and recorded in February 1960 (Book 14 at Page 44). The subdivision plats for Flecha Caida Ranch Estates #1 (Book 11 at Page 74) and #2 (Book 12 at Page 69) were prepared and recorded in 1956 and 1957, respectively. The subdivision plat for Las Lomas de Catalina was prepared and recorded in 1978. Copies of the recorded plats are included in Appendix A. The subdivisions occupy portions of Sections 15 and 22 of Township 13 South, Range 14 East, Gila River Base and Meridian, Pima County, Arizona. Portions of the four subdivisions are impacted by the Valley View Wash, which is situated between Valley View Road and Pontatoc Road on the west and Swan Road on the east. This floodplain study of the Valley View Wash begins approximately one-half mile south of Sunrise Drive and extends downstream (south) to North Flecha Drive (see Figure 1). Within the study reach, the Valley View Wash is a natural, privately-owned, unprotected watercourse that is subject to periodic flooding. In addition, since most of the soils within the foothills and valley region are unconsolidated alluvium, the Valley View Wash watercourse is subject to natural dynamic forces that cause localized erosion and sedimentation. Within the study reach, Flecha Caida Ranch Estates #9 is the most problematic area. Previous studies have determined that approximately one half of the 24 lots that comprise the subdivision are located in the 100-year flood plain for the Valley View Wash. Consequently, numerous drainage-related problems have been noted over the years. Common problems include overbank flooding, inundation of existing homes and secondary structures, bank erosion and degradation along the primary flow paths, and limited access to some lots during times of flooding. Although isolated portions of Flecha Caida Ranch Estates #1 and #2 and Las Lomas de Catalina have, to a lesser degree, experienced similar problems, the primary focus of this study was the sub-reach of the Valley View Wash that traverses the Ranch Estates #9 subdivision. In response to the concerns of Ranch Estates #9 homeowners following a significant flow event on June 27, 1984, the Pima County Department of Transportation and Flood Control District (the District) commissioned an initial assessment of flooding problems in the subdivision, which was documented in a report prepared by Simons, Li and Associates (SLA) in 1984 (Reference 1). Homeowners at that time were concerned that new commercial developments within the area surrounding the Swan Road-Sunrise Drive intersection had contributed to the flooding observed on June 27th, which was estimated by SLA to be a 5 to 10year storm event (530 cfs). Although SLA noted that the higher density developments had increased the discharge potential during the 100-year event by approximately five percent, the impact on the depth of flooding was minimal. SLA concluded that drainage problems are inherent to the area primarily because a portion of the subdivision was built in the natural flood plain for the Valley View Wash. This is best illustrated by overlaying a 2007 footprint of the subdivision on the 1941 aerial photograph (Figure 2). JE Fuller/Hydrology & Geomorphology, Inc. FLOODPLAIN STUDY – FLECHA CAIDA RANCH ESTATES # 9 Page 2 Recognizing the impact a 5 to 10-year storm event had on the Ranch Estates #9 subdivision, the District commission a second study in 1985 to establish regulatory (100-year) discharges and 100-year flood plain maps for several Catalina foothills washes, including the Valley View Wash. This study was completed by SLA in 1986 (Reference 2). A detailed hydrology study was performed for the study using precipitation depths from Reference 3. A copy of the 1986 floodplain map that covers Ranch Estates #9 is included in Appendix A1 along with copies of the relevant hydrologic data sheets. Between 1985 and 1988, Pima County attempted to address flooding problems on a lot by lot basis and on a regional basis. Two soil-cement berms were constructed along portions of Calle del Pantera and Cerco del Corazon to protect Lots 495, 496, 498, and 499 from all flows up to and including the 5-year event (i.e., the more-frequent flow events). Localized channel improvements, including channel widening, rock riprap bank protection, and two earthen berms were also constructed to provide flood and erosion protection for Lots 500 and 501. Most of these mitigation measures were constructed in 1985 and 1986. To address flooding on a regional basis, the District commissioned a third study in 1988 to evaluate the feasibility of either constructing a regional detention basin within the Tucson Water reservoir site to the north or channelizing a portion of the Valley View Wash to eliminate the flood hazards . This study was the direct result of the 1986 study that identified 15 flood prone structures within the Valley View Wash flood plain, including eight within Ranch Estates #9, five within Ranch Estates #1, and one in Ranch Estates #2. The study also included: (1) a more-detailed analysis of the upstream watershed to determine the relative impact of roadway/storm drain improvements (both existing and proposed) on the flood hazards associated with the subdivision; and (2) a moredetailed floodplain study within the boundary of the subdivision itself. This study was completed by SLA in 1989 (Reference 4). Copies of the revised drainage basin map and the revised floodplain map from the 1989 report for Ranch Estates #9 are included in Appendix A1. Appendices A2 through A4 provide archived copies of the 1984, 1986, and 1989 reports The 1989 study concluded that regional solutions (i.e., detention and/or channelization) were not cost effective and that roadway/storm drain improvements would have little impact on the flooding. Consequently, the primary focus of the study's recommendations was erosion mitigation on a site by site basis and the purchase of residential flood insurance. Long-term degradation was identified as the most significant erosion problem and seven sites were specifically addressed. Two of the sites were upstream of the neighborhood on Tucson Water property, and five of the sites were within the neighborhood. The five sites and the problems noted at each site are summarized as follows: JE Fuller/Hydrology & Geomorphology, Inc. FLOODPLAIN STUDY – FLECHA CAIDA RANCH ESTATES # 9 Site No. 3 4 5 6 7 Description Downstream of Calle del Pantera, adjacent to northwest corner of Lot 498 Downstream of access drive to Lot 501 Downstream of Cerco de Corazon Circle, north boundary of Lot 497 Downstream of access drive to Lot 503 Downstream of Cerco de Corazon Circle, south boundary of Lot 497, north boundary Lot 504 Page 3 Problem Noted 1-foot (or less) drop in streambed profile on downstream side relative to roadway. 1-foot (or less) drop in streambed profile on downstream side relative to roadway. 2 to 3-foot drop in streambed profile on downstream side relative to roadway. 2 to 3-foot drop in streambed profile on downstream side relative to roadway. 2 to 3-foot drop in streambed profile on downstream side relative to roadway. Given the severity of the problems noted and their potential to worsen as a result of their location relative to downstream control points, the order-of-concern was Site 6, 7, 5, 4, and 3. The long-term or ultimate degradation depth associated with each site was eight, seven, three, three, and eleven feet, respectively. The recommended short-term solution at Sites 5 through 7 was a gabion cut-off wall. The long-term solution included the addition of bank protection and aprons to the short-term structures. Gabions were selected as opposed to conventional cut-off walls or plunge basis to facilitate the addition of the long-term components. A wait and see approach was recommended for Sites 3 and 4. It should be noted that between 1984 and 1989, the eastern flow path along Calle del Pantera was considered the primary flow path for the more frequent flow events and the western low-flow channel was considered the secondary flow path. In addition, the 1989 study did not specifically address the home on Lot 502, which was constructed in 1986, since it appears that most of the field data (i.e., topographic information and finish-floor elevations) were collected between 1984 and 1986, and initial development of the St Thomas Apostle church occurred in 1987, with additional improvements in 1997. Subsequent to the 1989 study, some drainage/erosion-mitigation measures were constructed in the neighborhood, including (1) a concrete cut-off wall between Sites 3 and 4; (2) a concrete cut-off wall between the access drive to Lot 502 and 503 (Site 6); (3) a concrete cutoff wall on the downstream side of the access drive to Lot 502; (4) a drainage structure beneath the access drive to Lot 503; and, (5) grouted rock/gunite channel lining immediately downstream of the access drive to Lot 503. It appears that the cut-off wall between Sites 3 and 4 was constructed in conjunction with the 1997 improvements to the church. However, the other mitigation measures appear to have been constructed by the individual property owners. Purpose Recent flooding and erosion within the Ranch Estates #9 subdivision during the 2007 summer monsoon season raised the concerns of numerous homeowners who were not aware of the historical drainage problems inherent to the area. The Pima County Regional Flood Control District commissioned this study to (1) address the impact of recent improvements in the JE Fuller/Hydrology & Geomorphology, Inc. FLOODPLAIN STUDY – FLECHA CAIDA RANCH ESTATES # 9 Page 4 drainage area upstream of the study area; (2) provide updated flood-hazard mapping for the area from just upstream of Calle del Pantera to North Flecha Drive, which is where the Federal Emergency Management Administration (FEMA) flood plain for the Valley View Wash begins; and (3) identify mitigation measures that could be implemented by the affected homeowners to address their flood/erosion hazards. The key elements of the study as outlined in the scope-of-work are summarized as follows: • • • • • Data collection and field investigation. Aerial topographic mapping at 1"=40', one-foot contour interval, including digital aerial photography and ground control. Obtain finish-floor elevations (FFEs) of flood prone structures within the Ranch Estates #9 subdivision. Use the newly acquired topographic information to estimate FFEs for the remaining floodprone structures. Revisit 1984 hydrology using NOAA 14 rainfall depths, including multiple return intervals. Compare results to 1984 study. Remap 100-year flood plain using new topography. Provide a comparison with the expanded mapping completed in 1989. Identify flood prone structures based on FFEs from survey. Identify and evaluate alternative mitigation measures, including their impact on the floodplain. Perform scour analyses as needed, including long-term degradation, to provide preliminary design parameters for the mitigation measures (e.g., floodwalls, bank protection, cut-off walls, etc.). JE Fuller/Hydrology & Geomorphology, Inc. FLOODPLAIN STUDY – FLECHA CAIDA RANCH ESTATES # 9 II. Page 5 HYDROLOGY Valley View Wash In 1984, it was standard engineering practice to conduct hydrologic analyses under the assumption that the upstream drainage area would be fully developed in accordance with the zoning conditions that were in place at the time of the study (i.e., future-conditions hydrology). The 1984 hydrology study performed by SLA was based on future conditions. It included a drainage basin map that outlined the zoning boundaries that were used in the study. Although the majority of the upstream watershed was developed at the time of the study, the most recent (2005) aerial photographs of the watershed were reviewed to determine if these boundaries were still valid. Based on the results of that review, it was noted that three small areas in the watershed were developed at a greater density than previously assumed. An exhibit showing the location of these areas relative to the key concentration points is provided in Appendix A5. To determine the impact of these higher-density developments, the original hydrologic data sheets were revised accordingly. A comparison between the original values and the updated values is shown in Table 2.1. The revised hydrologic data sheets are provided in Appendix B. The three concentration points (CP) included in the comparison were CP 18, 11.1, and 13. CP 18 is located immediately downstream of the area containing the higher density developments. CP 11.1 is located at Sunrise Drive and CP 13 is located at the northern boundary of the Ranch Estates #1 subdivision. Table 2.1 Pre- and Post-Development Hydrology (100-year) Conc. Pt. 11.1 (1986) 13 (1986) 18 (1986) 11.1 (1986 updated) 13 (1986 updated) 18 (1986 updated) Area (ac) 927 1239 610 927 1239 610 nb 0.047 0.045 0.055 0.047 0.045 0.055 I (%) 8 12 3 9 12.8 4.5 Cw 0.65 0.65 0.68 0.66 0.65 0.68 Tc (min.) 38 49 22 38 49 22 Q100 (cfs) 2263 2512 2175 2279 2527 2192 change (%) 0.69% 0.61% 0.81% Description of hydrologic variables: nb (basin factor); I (Impervious Cover); Cw (weighted runoff coefficient); Tc (time of concentration); Q100 (100-year or regulatory discharge). The largest increase (0.81%) occurs immediately downstream of the area containing the higher-density developments. Since the drainage area increases in the downstream direction, the relative impact decreases. The updated analysis clearly shows that the impact associated with the three higher-density developments is not significant. The impact in the immediate vicinity of Ranch Estates #9 is approximately 0.65%. JE Fuller/Hydrology & Geomorphology, Inc. FLOODPLAIN STUDY – FLECHA CAIDA RANCH ESTATES # 9 Page 6 This comparative analysis was based on precipitation depths from Reference 3, which was used in Pima County in 1984. Today, the upper-bound of the 90% confidence interval values from Reference 5 are used in all hydrologic analyses. Therefore, a separate hydrologic analysis was conducted to define new discharge values at the key concentration points, which were used to remap the regulatory or 100-year floodplain. The new regulatory discharge values are shown in Table 2.2. The associated hydrologic data sheets are provided in Appendix C. Table 2.2 Updated Hydrology (100-year) Conc. Pt. 11 11.1 11.3 11.3a 11.3b 11.4 11.4a 13 13.1 18 Area (ac) 908 927 1034 1045 1055 1073 1189 1239 1608 610 nb 0.047 0.047 0.046 0.046 0.046 0.046 0.046 0.045 0.045 0.055 I (%) 9 9 12 12 12 12 12 12.8 12.9 4.5 Cw 0.70 0.70 0.70 0.70 0.70 0.69 0.69 0.69 0.69 0.73 Tc (min.) 35 35 40 42 43 43 44 44 50 19 Q100 (cfs) 2802 2861 2916 2855 2804 2844 3119 3219 3797 2823 Description of hydrologic variables: nb (basin factor); I (Impervious Cover); Cw (weighted runoff coefficient); Tc (time of concentration); Q100 (100-year or regulatory discharge). SLA's 1989 study included runoff concentration points at both the northern and southern boundaries of the Ranch Estates #9 subdivision. These concentration points were CP 11.3 and 11.4, respectively. For the purpose of this study, three additional concentration points were defined. Two (CP 11.3a and 11.3b) are within the subdivision itself, and the third (CP 11.4a) is located immediately downstream of the confluence of the tributary wash that traverses the southern boundary of Lot 505. An exhibit showing the locations of the key concentration points listed in Table 2.2 is provided in Appendix A5. Based on the results of the updated hydrologic analysis, the regulatory discharge associated with CP 11.3 was selected for the floodplain analysis of the sub-reach that traverses the Ranch Estates #9, since the discharge at CP 11.3 exceeds the values associated with CP 11.3a, 11.3b, and 11.4. The downstream reach that traverses Ranch Estates #1 and #2 and Las Lomas de Catalina was analyzed using the discharges associated with CP 11.4, 13, and 13.1. In addition, peak discharges for the more-frequent runoff events were determined at CP 11.3. These are summarized in Table 2.3. The associated hydrologic data sheets are also provided in Appendix C. JE Fuller/Hydrology & Geomorphology, Inc. FLOODPLAIN STUDY – FLECHA CAIDA RANCH ESTATES # 9 Page 7 Table 2.3 Updated Hydrology (multi-frequency) Conc. Pt. 11.3 Return Interval (yr) 2 5 10 25 Tc (min.) 104 71 59 49 Cw 0.31 0.45 0.53 0.61 Q (cfs) 268.00 680.00 1092.00 1740.00 Description of hydrologic variables: Tc (time of concentration); Cw (weighted runoff coefficient); Q (peak discharge). St. Thomas Church As previously noted, the initial development of the St Thomas Apostle church occurred in 1987, with additional improvements in 1997. Copies of the two development plans are included in Appendix D. Since there was some concern that the overall development of the church had increased the magnitude of runoff impacting the subdivision, the pre- and post-developed conditions associated with the church site were evaluated. Based on the results of that evaluation, it was determined that the church has had no significant impact on the hydrology for the Valley View Wash. In addition, some of the improvements associated with the church have actually benefited potions of the subdivision. When the church was initially developed in 1987, four detentions basins were constructed. Two of these basins regulate runoff that ultimately enters the Ranch Estates #9 subdivision. In 1984, approximately 1.6 acres of the church site contributed direct runoff to the subdivision. The associated 100-year peak discharge under Natural/Rural conditions was determined to be approximately 8.3 cfs. Under developed conditions (i.e., post-1997), the drainage area increased to approximately 3.0 acres with a current 100-year runoff potential of 23 cfs. However, approximately 2.2 acres of this area drains to the two detentions basins constructed in 1987. In order to limit the magnitude of runoff impacting the subdivision to 8.3 cfs, a conservative estimate of the required storage volume for these two basins is approximately 0.33 acre-feet. This estimate was made using the procedures outlined in Reference 6. Although it appears that only approximately one-half of the this volume was actually provided, the two basins should effectively reduce the 100-year peak discharge entering the subdivision to approximately 13.6 cfs, which is only 5.3 cfs above the pre-developed condition. Considering the magnitude of runoff associated with Valley View Wash during the 100-year event (2916 cfs), this increase in not significant. It should be noted that the results just discussed are based on the rainfall depths associated with Reference 5. When the church was developed, they would have been permitted to use the values associated with Reference 3 to determine the required storage volume for each detention basin. Therefore, the results are not intended to suggest that they did not meet the requirements in effect at the time of development. JE Fuller/Hydrology & Geomorphology, Inc. FLOODPLAIN STUDY – FLECHA CAIDA RANCH ESTATES # 9 Page 8 A comparison of the 2007 topography versus the 1984 topography was also conducted to determined if either site grading or other site improvements has had an adverse impact on the subdivision. The results indicate that site grading has actually benefited the subdivision by capturing and diverting a small quantity of overbank flow from the Valley View Wash, which slightly reduces the flood hazard associated with Lot 501. It was also noted that a grade-control structure placed just upstream of the northwest corner of Lot 500 and one placed just north of the southwest corner of Lot 498 have effectively stabilized the bed profile along the western boundary of Lots 498 and 499, in addition to protecting the pavement at Calle del Pantera. III. FLOODPLAIN ANALYSIS Regulatory Flood Plain Per Pima County's floodplain ordinance, the regulatory floodplain is defined as "that portion of the geologic floodplain associated with a watercourse….where the 100-year peak discharge is 100 cfs or greater, or those areas that are subject to sheet flooding." It is also important to note that the term 100-year flood or flood plain is a probability reference as opposed to a time period reference. The referenced year is divided into one (i.e., 1/100, or 1 divided by 100) to define the probability of occurrence in any given year. For example, the 100-year flood has a 1% chance of occurring in any given year. The 50-year flood has a 2% chance, the 5-year flood has a 20% chance, and so on. The regulatory or 100-year flood plain within the study area was remapped using ground data from the 2007 topographic survey prepared by Cardinal Land Surveying, Inc. (CLS). A copy of the complete ground survey is provided in Appendix E. The floodplain analysis was performed using the HEC-RAS water-surface profile model (Reference 7). An exhibit showing the 2007 topography, including the 2007 aerial photograph for the study reach, is provided as Figure 3. The locations of the cross sections used in the HEC_RAS analysis are shown on Figure 4. The regulatory (100-year) floodplain boundary and floodprone area is also shown on Figure 4. Sheet 1 of Figure 4 depicts three flood zones; whereas, Sheets 2 and 3 depict only one. This is due to the more-detailed floodplain analysis that was required to accurately map flooding conditions within Ranch Estates #9. The blue shaded area between the eastern and western-most 100-year or regulatory floodplain boundaries (on all sheets) is the approximate wetted portion or special flood hazard area as defined by the base flood elevations (e.g., WS= 2620.13) listed for each cross section. The base flood elevations relative to each cross section within the Ranch Estates #9 sub-reach are summarized in Tables 3.1a and 3.1b. The base flood elevations relative to each cross section within Ranch Estates #1 and #2 and Las Lomas de Catalina are summarized in Table 3.2. It should be noted that high ground or "islands" that may exist between the floodplain boundaries (i.e., locations where the ground is higher than the base flood elevations) were not identified or excluded from the floodprone area. JE Fuller/Hydrology & Geomorphology, Inc. FLOODPLAIN STUDY – FLECHA CAIDA RANCH ESTATES # 9 Page 9 Table 3.1a Regulatory Discharges and Water-Surface Elevations for the Main Corridor of the Valley View Wash within Ranch Estates #9 (as shown on Sheet 1 of Figure 4) Reach Main Corridor Main Corridor Main Corridor Main Corridor Main Corridor Main Corridor Main Corridor Main Corridor Main Corridor Main Corridor Main Corridor Main Corridor Main Corridor Main Corridor Main Corridor Main Corridor Main Corridor Main Corridor Main Corridor Main Corridor Main Corridor Main Corridor Main Corridor Main Corridor Main Corridor Main Corridor Main Corridor River Station (or Cross Section) 1 2 3 4 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 10.5 11 11.5 12 13 14 15 16 17 18 19 20 Q Total (cfs) 3119 3119 1978 1775 1775 Lateral Weir 1816 Lateral Weir 2106 Lateral Weir 2366 Lateral Weir 2458 Lateral Weir 2551 Lateral Weir 2885 Lateral Weir 2916 2916 2916 2916 2916 2916 2916 2916 2916 W.S. Elevation (ft) 2608.88 2612.30 2613.85 2616.12 2620.59 2624.07 2627.85 2631.21 2634.48 2637.65 2641.20 2644.31 2646.94 2650.01 2652.79 2654.67 2656.90 2658.44 2660.90 2662.81 Table 3.1b Regulatory Discharges and Water-Surface Elevations for the West Channel of the Valley View Wash within Ranch Estates #9 (as shown on Sheet 1 of Figure 4) Reach West Overflow West Overflow West Overflow West Overflow West Overflow West Overflow West Overflow West Overflow West Overflow West Overflow West Overflow River Station (or Cross Section) 1 2 3 4 5 6 7 8 9 10 11 Q Total (cfs) 3119 3119 1140 1140 1140 1099 807 551 460 367 31 JE Fuller/Hydrology & Geomorphology, Inc. W.S. Elevation (ft) 2608.88 2612.30 2615.27 2618.00 2620.13 2622.94 2625.59 2629.85 2633.54 2637.10 2640.67 FLOODPLAIN STUDY – FLECHA CAIDA RANCH ESTATES # 9 Page 10 Table 3.2 Requlatory Discharges and Water-Surface Elevations for the Valley View Wash Downstream of Ranch Estates #9 (as shown on Sheet 2 and 3 of Figure 4) Reach Main Channel Main Channel Main Channel Main Channel Main Channel Main Channel Main Channel Main Channel Main Channel Main Channel Main Channel Main Channel Main Channel Main Channel Main Channel Main Channel Main Channel Main Channel Main Channel Main Channel Main Channel Main Channel Main Channel Main Channel River Station (or Cross Section) 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10 0.11 0.12 0.13 0.14 0.15 0.16 0.17 0.18 0.19 0.20 0.21 0.22 0.23 0.24 Q Total (cfs) 3797 3797 3797 3797 3797 3797 3797 3797 3797 3797 3219 3219 3219 3219 3219 3219 3219 3219 3219 3219 3219 3119 3119 3119 W.S. Elevation (ft) 2530.72 2533.42 2536.97 2541.83 2543.86 2545.92 2549.46 2551.01 2553.56 2557.19 2561.73 2565.60 2569.43 2574.09 2578.48 2582.23 2585.84 2589.53 2592.94 2596.39 2599.43 2601.46 2605.49 2608.88 Two water-surface profiles are represented by Tables 3.1a and 3.1b. Table 3.1a applies to the "main corridor" of the Valley View Wash within Ranch Estates #9, and Table 3.1b applies to the "west overflow" channel, which conveys flows that break out of the main corridor between Sections 5 and 12. The location of the drainage divide or "lateral weir" crest is shown on Sheet 1 of Figure 4 as a black-dashed line that extends south from the church's access drive to the house constructed on Lot 503. Breakout flows from the "main corridor" were used to map the flood plain associated with the "west overflow" channel. A section by section breakdown of the discharge associated with each overflow or "lateral weir" section is presented in Table 3.3. Since the average depth of flow over the weir between Section 6 and 10 was approximately one foot, a second flood zone characterized by shallow flooding with average depths equal to one foot was delineated between the weir crest and the eastern boundary of the "west overflow" flood plain. The third delineated flood zone is characterized by shallow flooding with average depths less than one foot. This area is centered along Calle del Pantera in the vicinity of the Cerco del Corazon intersection. JE Fuller/Hydrology & Geomorphology, Inc. FLOODPLAIN STUDY – FLECHA CAIDA RANCH ESTATES # 9 Page 11 Table 3.3 Lateral Weir Quantities and Hydraulic Properties Reach River Station Main Corridor Main Corridor Main Corridor Main Corridor Main Corridor Main Corridor Main Corridor 5.5 6.5 7.5 8.5 9.5 10.5 11.5 Q Leaving (cfs) 42 292 256 91 93 337 31 Max Depth (ft) 0.87 1.38 1.24 1.16 1.65 1.42 0.69 Lateral Weir Avg Depth (ft) 0.45 1.14 1.11 0.67 1.10 1.17 0.42 Min El (ft) 2622.00 2623.20 2627.00 2631.00 2635.00 2637.00 2640.50 W.S. Elevation u/s d/s (ft) (ft) 2624.07 2620.59 2627.85 2624.07 2631.21 2627.85 2634.48 2631.21 2637.65 2634.48 2641.20 2637.65 2643.63 2641.20 It should be noted that the water-surface elevations presented in Tables 3.1 and 3.2 are based on a critical flow regime, as opposed to a subcritical or supercritical flow regime. When the subcritical floodplain analysis defaulted to critical depth, a supercritical profile was evaluated. The results confirmed that critical flow dominates. This is significant in that the computed water-surface elevations are not subject to either upstream or downstream controls. For example, removing the culvert beneath the access drive to Lot 503 (Section 7) will not significantly change the water-surface elevation at either Section 6 or Section 8. In addition to analyzing the 100-year or regulatory flood plain within Ranch Estates #9, a separate model was prepared to evaluate the capacity of the primary low-flow channel, which is currently the western-most watercourse, as opposed to the Calle del Pantera street section. The results indicate that the capacity falls between the 2-year and 5-year peak discharge, which is consistent with the results of the 1989 study. The bifurcation in the main channel located immediately upstream of Calle del Pantera was also evaluated to determine the approximate distribution of flow between the two flow paths. The results indicate that approximately half the flow will be conveyed along both watercourses, especially during high-flow events. During lowflow events, the current tendency is for most of the flow to be conveyed along the western watercourse. However, given the dynamic nature of this alluvial channel, this tendency can change, and there is no way to predict the actual flow path from one flow event to another (i.e., the relative distribution of flow can fluctuate from one event to another). Flood Prone Structures In addition to providing updated topographic information that could be used to remap the Valley View Wash flood plain, Cardinal Land Surveying obtained the finish-floor elevations (FFEs) of all homes within Ranch Estates #9 which were thought to be within the 100-year or regulatory flood plain per the 1989 study. Table 3.4 summarizes the results of their survey, in addition to providing a comparison between the regulatory water-surface elevation and the existing ground elevation (grade) on the upstream side of the structure. The negative sign associated with the values in the "FFE versus WSstructure" column denotes that the regulatory water surface is above the finish-floor elevation. The values in the JE Fuller/Hydrology & Geomorphology, Inc. FLOODPLAIN STUDY – FLECHA CAIDA RANCH ESTATES # 9 Page 12 "WSstructure versus Grade" column denotes the approximate depth of flow adjacent the to upstream side of the structure during a regulatory event. Per Pima County's floodplain ordinance, new homes constructed in or near a flood prone area must have their lowest finish floor elevated a minimum of one foot above the regulatory water-surface elevation on the upstream side of the structure. Only two structures in or near the remapped regulatory flood plain within Ranch Estates #9 meet this requirement – the main structure on Lot 493 and the garage on Lot 504. Although the finish-floor elevation for the structure on Lot 499 is above the computed water-surface elevation, the difference is only 0.45 feet. Table 3.4 Comparison of FFE to W.S. Elevation and Existing Grade within Ranch Estates #9 Lot Description FFE W.S. Elev (ft) 2651.46 2648.78 2643.30 2635.54 2635.16 2632.26 2630.73 2629.55 2622.98 2621.78 2617.90 2630.75 2636.19 2639.71 at Structure (ft) 2652.79 2644.85 2642.85 2635.66 2635.66 2632.31 2631.21 2629.83 2620.17 2622.45 2618.43 2631.78 2636.59 2640.95 No. 498 493 499 496 495 497 504 503 502 501 500 main structure main structure main structure main structure sunken living main structure main structure bedroom addition garage main structure carport main structure main structure main structure FFE versus WSstructure (ft) -1.33 3.93 0.45 -0.12 -0.50 -0.05 -0.48 -0.28 2.81 -0.67 -0.53 -1.03 -0.40 -1.24 Existing Grade at Structure (ft) 2651.30 2649.00 2642.50 2634.50 n/a 2631.80 2630.30 2629.00 2623.00 2621.50 2618.60 2630.30 2635.00 2639.40 WSstructure Grade (ft) 1.49 -4.15 0.35 1.16 n/a 0.51 0.91 0.83 -2.83 0.95 -0.17 1.48 1.59 1.55 versus Since all of the habitable structures within Ranch Estates #1 and #2 and Las Lomas de Catalina, which were thought to be flood prone in 1986, turned out to have FFEs from the 1989 survey that were above the previously defined base flood elevations, new FFEs were not obtained by Cardinal Land Surveying for these structures. Instead, FFEs for the previouslyidentified structures were estimated using the 1989 FFE plus a datum conversion constant. FFEs for any newly identified structures were estimated using the 2007 topographic survey as a guide. Table 3.5 summarizes the results of a comparison between the adjusted and/or estimated FFEs and the new regulatory (100-year) water-surface elevations. JE Fuller/Hydrology & Geomorphology, Inc. FLOODPLAIN STUDY – FLECHA CAIDA RANCH ESTATES # 9 Page 13 Table 3.5 Comparison of FFE to W.S. Elevation and Existing Grade within Ranch Estates #1 and #2 and Las Lomas de Catalina Description Lot No.1 55 12 13 14 16 43 44 45 46 47 48 49 secondary structure main structure main structure guest house east half of lot (split) main structure main structure main structure main structure main structure main structure main structure Finish Floor Elevation (FFE)2 OLD (ft) 2598.70 ----2557.70 2563.60 2553.80 2549.60 -2538.80 -- NEW (ft) 2600.95 2591.50 2589.90 2585.90 2578.25 2559.953 2565.85 2556.05 2551.85 2546.50 2541.05 2536.00 W.S. Elev at Structure (ft) 2602.04 2591.52 2588.28 2584.96 2576.96 2558.90 2566.10 2554.31 2547.78 2544.00 2539.70 2534.36 FFE versus WSstructure (ft) -1.09 -0.02 1.62 0.94 1.29 1.05 -0.25 1.74 4.07 2.50 1.35 1.64 1 Note: Lot 55 is in Flecha Caida Ranch Estates No. 2, Bk 12 Pg 69. Lots 12 and 13 are in Las Lomas de Catalina, Bk 29, Pg 79. The remaining lots are in Flecha Caida Ranch Estates, Bk 11, Pg 74. 2 If applicable, the "Old" FFE (NGVD 29) is from the 1989 SLA report. The "New" FFE (NAVD 88) was computed by adding 2.25 feet to the "Old" FFE. For all lots lacking an "Old" FFE, the "New" FFE was estimated using the topographic survey as a guide. 3 The adjusted FFE for Lot 43 is significantly higher than the topographic mapping suggests As previously noted, structures located in or near the 100-year flood plain are generally considered protected from flooding when their lowest finish floor is elevated a minimum of one foot above the 100-year water-surface elevation on the upstream side of the structure. Only one structure in Ranch Estates #1 (FC1), one in Ranch Estates #2 (FC2), and two in Las Lomas de Catalina (LLdC) do not meet this requirement – the secondary structure on Lot 55 of FC1, the main structure on Lot 55 of FC2, and the main structure on Lot 12 and guest structure on Lot 14 of LLdC. However, the guest structure on Lot 14 of LLdC is close with a difference of 0.94 feet. To verify the potential floodprone status or risk of flooding for these structures, it recommended that the owners have their FFEs surveyed for comparison with the water-surface elevations provided in Table 3.4. In addition, since the FFE for Lot 43 is questionable (see footnote 3 in Table 3.5), it is recommended that the owner contact a land surveyor and arrange to have the FFE determined, such that it can be compared to the elevations provided in Table 3.4. Also, if the owners of any of the remaining lots listed in Table 3.5 are concerned about the potential for flooding, it is recommended that they have their FFEs surveyed to more accurately identify their flood risk. JE Fuller/Hydrology & Geomorphology, Inc. FLOODPLAIN STUDY – FLECHA CAIDA RANCH ESTATES # 9 Page 14 Erosion and Sedimentation In addition to flooding problems, the subdivisions, to a varying degree, are also prone to erosion and sedimentation problems. Long-term degradation, which is the gradual lowing of the channel bed in response to a reduction in the upstream sediment supply, was the primary focus of the 1989 study, since it stood out as the most significant erosion problem. That study identified five problems areas within the Ranch Estates #9 subdivision and discussed the extent of the problem associated with each. The location of these problem areas are shown on a excerpt of the 1989 exhibit, which is provided in Appendix A1 (page 18). The full exhibit is provided in Appendix A4 (page 63). Using the same site numbers referenced in the 1989 study, the five sites are described as follows: Site 3 is located along the west branch immediately downstream of Calle del Pantera; Site 4 is located immediately downstream of the access drive for Lot 501; Site 5 is located just downstream of Cerco de Corazon, near the northwest corner of Lot 497; Site 6 is located immediately downstream of the access drive for Lot 503; and, Site 7 is located within the boundary of Lot 504 immediately downstream of Cerco del Corazon. During the field investigation associated with this 2007 study, it was noted that erosion and/or sedimentation problems still exist at all five locations, with the possible exception of Site 3. As previously noted, two grade-control structures constructed adjacent to Lots 498 and 499 have temporarily checked long-term degradation at Site 3. However, some local erosion near the access drive to Lot 498 was noted. In addition, the installation of a grade-control structure just downstream of the access drive to Lot 502, and the paved access drive itself, which was not considered during the 1989 study, has temporarily mitigated the long-term degradation problem at Site 4. To show the short-term effect both of these structures have had on the streambed profile, Figure 5 was prepared. It compares the 1998 streambed profile along the western watercourse to the 2007 profile. The approximate locations of the three referenced grade-control structures are Stations 5+15, 10+35, and 12+23. It should be noted that the magnitude of degradation in the vicinity of the access drive for Lot 501 is misleading. The difference between the two profiles at this location was due to bank erosion as opposed to channel bed degradation. During the 2007 summer monsoon season, the area experienced a 2-year to 5-year flow event. During this event, the west bank in the vicinity of the access drive eroded between 20 and 30 feet in a southwesterly direction. Bank erosion extended approximately 50 to 60 feet in upstream direction and ceased just downstream of the access drive. As a result, most of the rock riprap bank protection along the upstream reach was lost, and the majority of the sediment removed from the bank was deposited in the area between the wash and the north elevation of the home on Lot 502. Bank erosion was also noted along the east bank in the vicinity of the home on Lot 500. Currently, this structure is located less than ten feet from the top of the eastern bank. However, it does not appear that bank protection in the form of rock riprap has ever been provided along this bank. With the exception of the additional erosion and sedimentation problems noted in the vicinity of Site 4 and the stabilizing effect of the church's grade-control structure relative to Site 3, long-term degradation is still the most significant erosion problem at the remaining sites. The existing slope of the bed along the western channel ranges between 2.15% and 2.45%. The slope of the bed along the eastern channel segment located within the boundary of Lot 497 is JE Fuller/Hydrology & Geomorphology, Inc. FLOODPLAIN STUDY – FLECHA CAIDA RANCH ESTATES # 9 Page 15 approximately 1.4%. The 1989 study estimated an equilibrium bed slope of approximately 1%. However, assuming a conservative sediment reduction factor of 40% relative to the upstream watershed, the equilibrium bed slope was estimated to be approximately 1.5% using the relationship provided in Chapter 6 of Reference 8. The computed equilibrium slope of 1.5% was plotted on Figure 5 at several locations based on appropriate downstream pivot points. Typically, the pivot points around which a channel bed will adjust its grade are channel confluences, grade-control structures, and at-grade roadway crossings. For Sites 6 and 7, the downstream pivot point was the confluence with the eastern tributary channel that traverses the southern boundary of Lot 505. The estimated longterm degradation depth at Sites 6 and 7 were determined to be approximately 5.2 feet and 4.8 feet respectively. This is in addition to the drop height that currently exists, which is 1.0 feet and 2.0 feet, respectively. For the grade-control structure located just downstream of the access drive to Lot 502, the additional degradation depth was determined to be approximately 1.5 feet, with an existing drop of approximately 1.8 feet. Assuming this existing grade-control remains effective (i.e., does not fail), the approximate long-term degradation depth downstream of the access drive to Lot 502 is less than one foot, which is also applicable to the access drive for Lot 501, since the channel bed downstream of the access drive for Lot 501 pivots around the access drive for Lot 502. With respect to the existing grade-control structures at Station 10+35 and 12+23 and the downstream edge of pavement for Calle del Pantera, the long-term degradation depths were determined to be approximately 1.3 feet, 1.0 feet, and 2.5 feet, respectively. Again, these depths are in addition to the drop height that currently exists, which is approximately 2.0 feet, 1.0 feet, and 0.5 feet, respectively. Since the existing slope for the eastern channel is slightly less than the computed equilibrium slope, it is reasonable to assume that this channel is at or near its equilibrium slope; therefore, the existing drop height at Site 5, which is approximately four feet, is not expected to increase significantly. An exhibit similar to Figure 5 was also prepared for the main branch of the Valley View Wash with Ranch Estates 31 and #2 and Las Lomas de Catalina. This exhibit is included in Appendix A5. Since the 2007 profile is very similar to the 1998 profile, long-term degradation does not appear to be a problem along this portion of the study reach. However, given the dynamic nature of alluvial channels, especially when man's activities are factored into the equation, the critical balance between the upstream sediment supply and the downstream sediment transport capacity could be upset at any time. The existing slope along this reach is approximately 2.3%, which is consistent with the existing slope of the west branch channel within Ranch Estates #9. Therefore, the estimated equilibrium bed slope for that reach (1.5%) is also applicable to this reach. Consequently, the long-term degradation depth for this reach is approximately one foot per 125 feet of channel relative to the downstream pivot. In addition to estimating the long-term bed profile for the western channel within Ranch Estates #9, a single-event scour analysis was conducted in accordance with the procedure outlined in Chapter 6 of Reference 8. The associated computation sheets are provided in Appendix F. Based on the results of the scour analysis, the minimum design scour depth is three feet. A similar analysis was conducted for the main channel of the Valley View Wash within Ranch Estates #1 and #2 and Las Lomas de Catalina. Based on the results of that analysis the JE Fuller/Hydrology & Geomorphology, Inc. FLOODPLAIN STUDY – FLECHA CAIDA RANCH ESTATES # 9 Page 16 minim design scour depth is 3.5 feet within Ranch Estates #1 and #2 and 3.3 feet within Las Lomas de Catalina. The associated computation sheets are also provided in Appendix F. Typically, when bank protection is proposed, the minimum scour depth is combined with the long-term depth to determine the design toe-down depth. When protection is proposed in the vicinity of a channel drop and bed protection is not provided, then the design toe-down depth must be increased to account for the depth of local scour on the downstream side of the drop, which is a function of the ultimate drop height. Under existing conditions, the maximum drop height is expected to occur at Site 6 within Ranch Estates #1. Based on an ultimate drop height of 6.2 feet, the maximum local scour depth was determined to be approximately 9.9 feet. Assuming a minimum drop height of three feet (e.g., Site 3), the local scour depth would be approximately 7.3 feet. These depths emphasize the importance of bed protection when excessive drop heights are anticipated or the importance of adequately spaced grade-control structures to stabilize the bed profile. An erosion-hazard setback analysis was also performed in conjunction with the singleevent scour analysis using the procedure outlined in Chapter 7 of Reference 8. Based on the results of that analysis, the average building setback distance was determined to be approximately 73 feet. This value is consistent with the minimum distance (75 feet) specified in Pima County's current floodplain and erosion hazard management ordinance for unprotected banks along natural channels. Currently, the homes on Lots 498, 500, and 501 are within the erosion-hazard area for the western channel. The existing setback distances for these homes are approximately 60 feet, 10 feet, and 20 feet, respectively. Since the home on Lot 498 is located on the inside of the channel bend and approach flows are more dispersed, the existing setback distance (60 feet) may be adequate. However, the potential for bank erosion and/or lateral migration of the channel bank should be a major concern for the owners of Lots 500 and 501. The 75-foot setback specified in Pima County's current floodplain and erosion hazard management ordinance is also applicable to the structures within Ranch Estates #1 and #2 and Las Lomas de Catalina. Currently, the homes on Lots 16B and 43 through 51 (Ranch Estates #1), Lot 55 (Ranch Estates #2), and Lots 11 through 16 (Las Lomas de Catalina) are within the erosion-hazard area for either the main channel or one of the secondary channels. However, the actual potential for bank erosion and/or lateral migration was not evaluated as part of this study. Within the majority of these lots, mitigating factors such as soils, channel-specific discharges, armoring, etc., may result in a reduced potential for bank erosion and/or lateral migrations. IV. FLOOD HAZARD MITIGATION For the most part, the results of this 2007 study are consistent with the results of the 1989 study (see the floodplain comparison exhibit in Appendix A5). The floodplain boundaries are similar, as are the identified erosion hazards, with the possible exception of Site 4 within Ranch Estates #9. The 1989 study addressed the feasibility of regional solutions, including upstream detention and channelization of flows within the subdivision itself and determined that neither was cost-effective. To reduce the economic impact of flooding, flood insurance was recommended. To address long-term degradation, both short-term and long-term solutions in the form of gabion cut-off walls and grade-control structures were recommended. Although cut-off JE Fuller/Hydrology & Geomorphology, Inc. FLOODPLAIN STUDY – FLECHA CAIDA RANCH ESTATES # 9 Page 17 walls and grade-control structures have been provided within Ranch Estates #9, they were not designed in accordance with the recommendations of the study (i.e., concrete cutoff walls, concrete grade-control structures, and grouted rock aprons were installed instead). At the time, bank erosion in the vicinity of Lots 500 and 501 was not discussed, since rock riprap protected berms had already been provided upstream of these lots. However, the loss of this protection must now be addressed and floodproofing options should also be considered, in addition to the purchase of flood insurance. Although long-term degradation continues to be a problem within Ranch Estates #9, particularly at Site 6, the recommendations of the 1989 study are still valid. Since the Valley View Wash along the study reach is a natural watercourse that is subject to periodic flooding and the natural dynamic forces of sedimentation and erosion, mitigation measures will be needed to protect flood/erosion prone structures. However, mitigation measures must be addressed by individual property owners, since the wash is privately owned. Flood Prone Structures As previously recommended, flood insurance should be purchased to reduce the economic impact of any flooding that may occur in the future. At a minimum, flood insurance should be purchased by the owners of all lots identified in Table 3.4 and 3.5, with the possible exception of Lots 493 and 504 (Ranch Estates #1), Lots 45-47 and Lot 49 (Ranch Estates #1), and Lot 13 (Las Lomas de Catalina). However, any lot owner concerned about the potential for flood damage should consider purchasing flood insurance. Since the subdivisions are not shown to be in a special flood hazard area on the effective FIRMs, Zone X insurance (the least expensive) can be purchased. Zone X premiums are significantly lower than Zone AE, Zone A01, or Shaded Zone X premiums. In addition, as along as the policy remains effective, owners who purchase insurance now will continue to qualify for this rate zone, even if the maps are revised to include the subdivision. In addition, the owners should consider flood proofing their homes to minimize damage to the contents and to the structure itself. Floodproofing measures typically fall into to categories – wet and dry floodproofing. However, since wet floodproofing, which allows water to enter the structure, is typically limited to uninhabited parts of a residence, these measures would only apply to a garage or detached storage shed. Dry floodproofing involves sealing the home to prevent water from entering the structure. Typical dry floodproofing measures that are applicable to the flooding conditions that exist within the subdivision include: • • • • Adding a waterproof veneer (approx. two to three feet) along exterior walls Raising electrical system components approximately 1.5 feet Raising or waterproofing HVAC equipment approximately 1.5 feet Installing sewer backflow values See Appendix G for more detailed information. Although elevating, relocating, or demolishing (then rebuilding) the structure are other retrofitting measures, they would not be as cost-effective as simple floodproofing. Berms or low-profile levees and floodwalls are also effective retrofitting measures since they can JE Fuller/Hydrology & Geomorphology, Inc. FLOODPLAIN STUDY – FLECHA CAIDA RANCH ESTATES # 9 Page 18 effectively divert flows around and/or away from structures; however, engineering studies that document the impact of these structures would have to be prepared by each property owner and submitted to the Regional Flood Control District for approval before floodplain-use permits could be issued. These types of structures typically increase the water-surface elevation and/or divert flows onto adjacent properties. Consequently, the Flood Control District needs to be assured that implementation of these types of mitigation measures will not adversely impact adjacent properties. Although some floodproofing measures would still require a floodplain-use permit, they are more likely to be approved without the requirement for a detailed floodplain study, since the impact of encroachment into the flood plain would be minimal. Erosion and Sedimentation The long-term degradation problem associated with Site 4 within Ranch Estates #9 appears to have been addressed, at least for now, by the combined effect of the grade-control structure installed downstream of the access drive to Lot 502 and the access drive itself. However, the loss of the rock riprap bank protection along the west bank should be addressed by the installation of new bank protection. If loss rock riprap protection is provided on a 3:1 (horizontal to vertical) side slope, the D50 diameter of the rock should be one foot, and the thickness of the rock layer should be a minimum of two feet. In addition, filter fabric should be installed under the rock and the toe of the protection should extend below channel bed a minimum of three feet plus the long-term degradation depth (Figure 5). The loss rock riprap bank protection along the east bank adjacent to Lot 500 should also address by the installation of new protection. However, since the existing home is located within 10 feet of the bank, vertical gabion baskets (i.e., wire-tied baskets filled with rock), which can be placed vertically along the bank, would minimize disturbance of the soil in the vicinity of the homes foundation. Loose rock on a 3:1 slope would require 12-15 feet to install. The sedimentation problem associated with Lot 502 appears to be directly related to the recent bank erosion associated with Lot 501. If a portion of the west bank adjacent to Lot 501 is reconstructed and adequately protected, the sediment transport capacity along the reach will be increased and low-flow will be redirected to its pre-Summer 2007 flow path. If desired, the bank between Sections 8 and 10 could be elevated to contain all or a portion of the 100-year discharge that currently breaks out of the western channel in the vicinity of Lots 501 and 502. A separate HEC-RAS model demonstrated that eliminating breakout in this area would not have an adverse impact on either the adjacent or downstream property owners. However, eliminating breakout upstream of Lot 501 could have an adverse impact of Lots 500 and 501. In addition, eliminating breakout downstream of Lot 502 could increase the flood hazard associated with Lot 503. Although elevating the bank in the vicinity of Lots 501 and 502 would eliminate breakout in this area and reduce low-flow hazards, it will not eliminate the high-flow hazards and vehicular access over the berm would have to be addressed. Access during times of flooding is also a problem for the owners of Lots 501 and 502. However, installation of culvert crossing similar to the one installed for Lot 503 would increase the long-term degradation potential for Lot 500 and could undermine the existing grade-control structure installed on the church property. Consequently, crossings should not be provided, JE Fuller/Hydrology & Geomorphology, Inc. FLOODPLAIN STUDY – FLECHA CAIDA RANCH ESTATES # 9 Page 19 unless detailed engineering plans are prepared for review and approval. The plans should include the installation of bank and bed protection and additional grade-control structures upstream of the crossings. It appears that the grade-control structure installed upstream of the access drive for Lot 503 was constructed to minimize the impact on the access drive for Lot 502, since some lowering the streambed would have been required to facilitate the crossing. However, it does not appear that plans were prepared for this crossing; therefore, the long-term stability of the structure is questionable. The long-term degradation problem at Sites 6 and 7 can be addressed in the manner identified in the 1989 study (i.e., the installation of gabion grade-controls structures. Gradecontrol structures could also be constructed along the downstream reach to minimize the longterm degradation potential at these sites. Since the slope of the eastern branch of the Valley View Wash within the boundary of Lot 497 appears to have reached equilibrium, long-term degradation should no longer be a problem for this reach, including Site 5. Therefore, the existing grouted rock bank protection along the east bank should continue to protect the home on Lot 497, which is within 30 feet of the bank. However, the addition of a loose rock riprap apron downstream of the existing grouted rock apron would provide some protection from local scour. Since erosion and sedimentation problem areas were not previously identified in Ranch Estates #1 and #2 and Las Lomas de Catalina, no site specific evaluations or recommendations were prepared as part of this study. JE Fuller/Hydrology & Geomorphology, Inc. FLOODPLAIN STUDY – FLECHA CAIDA RANCH ESTATES # 9 Page 20 V. REFERENCES 1. Pima County Department of Transportation and Flood Control District, Preliminary Assessment of Flooding Problems along Valley View Was in the Vicinity of the Flecha Caida Subdivision, July 26, 1984. 2. Pima County Department of Transportation and Flood Control District, Flecha Caida Flood Improvement Study – Phase I, 100-year Peak Discharge Magnitudes and Floodplain Mapping, January 28, 1986. 3. United States Department of Commerce, National Oceanic and Atmospheric Administration, National Weather Service, Precipitation – Frequency Atlas of the Western United States, Volume VIII, Arizona, NOAA Atlas 2, 1973. 4. Pima County Department of Transportation and Flood Control District, Valley View Wash, Flood and Erosion Control Study for the Calle Del Pantera Area (Phase II, Flecha Caida Flood Improvement Study), February 15, 1989. 5. United States Department of Commerce, National Oceanic and Atmospheric Administration, National Weather Service, Precipitation – Frequency Atlas of the United States, NOAA Atlas 14, Volume I, Version 4, 2004, revised 2006. 6. Pima County Department of Transportation and Flood Control District/City of Tucson, Department of Transportation, Stormwater Detention/Retention Manual, July, 1987. 7. U.S. Army Corps of Engineers, Hydraulic Engineering Center, HEC-RAS River Analysis System, Version 4 Beta, November 2006. 8. City of Tucson, Department of Transportation, Engineering Division, Standards Manual for Drainage Design and Floodplain Management in Tucson, Arizona, prepared by Simons, Li and Associates, Inc., December 1989, last revision, July 1998. JE Fuller/Hydrology & Geomorphology, Inc. Appendix A A1-Subdivision Plat/Historic Study Excerpts A2-1984 SLA-Flooding Problems Report A3-1986 SLA Phase 1-Hydrology and Mapping Report A4- 1989 SLA Flood and Erosion Assessment/Mitigation Report A5- Revised Drainage Basin/Floodplain Comparison Exhibits JE Fuller/Hydrology & Geomorphology, Inc. Appendix B NOAA Atlas 2, Volume VIII (1973) Hydrologic Data Sheets JE Fuller/Hydrology & Geomorphology, Inc. Appendix C NOAA Atlas 14, Volume I (2006) Hydrologic Data Sheets JE Fuller/Hydrology & Geomorphology, Inc. Appendix D Development Plans for St. Thomas Church JE Fuller/Hydrology & Geomorphology, Inc. Appendix E 2007 Topographic Survey Sheets (Cardinal Land Surveying, Inc.) JE Fuller/Hydrology & Geomorphology, Inc. Appendix F Scour Computation Sheets JE Fuller/Hydrology & Geomorphology, Inc. Appendix G Guides to Retrofitting Flood Prone Structures JE Fuller/Hydrology & Geomorphology, Inc. Appendix A through G (digital copies on compact disk) JE Fuller/Hydrology & Geomorphology, Inc. HYDROLOGIC DATA SHEET Watercourse or Project Name: Flecha Caida Flood Improvement Study Drainage Concentration Point: 11 (1986) Watershed Area (A): 908 acres Watershed Type: Mtn (dev)/Foothills(dev) Incremental Changes along Primary Watercourse by Reach Reach Elevations Height Length Slope Basin u/s d/s Hi Li Si Factor limit limit (ft) (ft) (ft/ft) nb 6080 5600 480 1100 0.436 0.047 5600 3800 1800 4000 0.450 0.047 3800 3400 400 2200 0.182 0.047 3400 3200 200 1900 0.105 0.047 3200 2740 460 12500 0.037 0.047 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 Length of Watercourse (Lc): Length to Center of Gravity (Lca): 21700 10850 Storm Event 3-hour 2-hour 1-hour Cover Type(s): Impervious Surfaces: ft ft Mean Slope (Sc): Weighted Basin Factor (nb): Rainfall Data Mapped Computed Values Values (in) (in) n/a 3.25 n/a 3.03 n/a 2.69 Mtn./Desert Brush Mix Percent 8% Hydrologic Group A B C D Weighted Runoff Coefficient (Cw): Time of Concentration (Tc): 0.96 Soils Data Group Curve Number % Normal Adjusted 38 13 49 83 82 90 87.06 86.28 92.52 min. Rainfall Intensity (i) at Tc: 3.71 in/hr Runoff Supply Rate (q) at Tc: 2.42 in/hr 30% (CN constant at 99) Runoff Coefficient 0.55 0.53 0.71 100-year Peak Discharge (Q100): 38 ft/ft Reduced Values (in) 3.25 3.03 2.69 Cover Density (pervious areas): Runoff Coefficient: 0.652 JE Fuller / Hydrology and Geomorphology, Inc. Areal Reduction % 0% 0% 0% 0.0670 0.047 2217 For Return Intervals Other Than Q100 25-year = n/c cfs 10-year = n/c cfs 5-year = n/c cfs 2-year = n/c cfs cfs HYDROLOGIC DATA SHEET Watercourse or Project Name: Flecha Caida Flood Improvement Study Drainage Concentration Point: 11.1 (1986) Watershed Area (A): 927 acres Watershed Type: Mtn (dev)/Foothills(dev) Incremental Changes along Primary Watercourse by Reach Reach Elevations Height Length Slope Basin u/s d/s Hi Li Si Factor limit limit (ft) (ft) (ft/ft) nb 6080 5600 480 1100 0.436 0.047 5600 3800 1800 4000 0.450 0.047 3800 3400 400 2200 0.182 0.047 3400 3200 200 1900 0.105 0.047 3200 2740 460 12500 0.037 0.047 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 Length of Watercourse (Lc): Length to Center of Gravity (Lca): 21700 10850 Storm Event 3-hour 2-hour 1-hour Cover Type(s): Impervious Surfaces: ft ft Mean Slope (Sc): Weighted Basin Factor (nb): Rainfall Data Mapped Computed Values Values (in) (in) n/a 3.25 n/a 3.03 n/a 2.69 Mtn./Desert Brush Mix Percent 8% Hydrologic Group A B C D Weighted Runoff Coefficient (Cw): Time of Concentration (Tc): 0.96 Soils Data Group Curve Number % Normal Adjusted 38 13 49 83 82 90 87.06 86.28 92.52 min. Rainfall Intensity (i) at Tc: 3.71 in/hr Runoff Supply Rate (q) at Tc: 2.42 in/hr 30%/20% (CN constant at 99) Runoff Coefficient 0.55 0.53 0.71 100-year Peak Discharge (Q100): 38 ft/ft Reduced Values (in) 3.25 3.03 2.69 Cover Density (pervious areas): Runoff Coefficient: 0.652 JE Fuller / Hydrology and Geomorphology, Inc. Areal Reduction % 0% 0% 0% 0.0670 0.047 2263 For Return Intervals Other Than Q100 25-year = n/c cfs 10-year = n/c cfs 5-year = n/c cfs 2-year = n/c cfs cfs HYDROLOGIC DATA SHEET Watercourse or Project Name: Flecha Caida Flood Improvement Study Drainage Concentration Point: 13 (1986) Watershed Area (A): 1239 acres Watershed Type: Mtn (dev)/Foothills(dev) Incremental Changes along Primary Watercourse by Reach Reach Elevations Height Length Slope Basin u/s d/s Hi Li Si Factor limit limit (ft) (ft) (ft/ft) nb 6080 5600 480 1100 0.436 0.045 5600 3800 1800 4000 0.450 0.045 3800 3400 400 2200 0.182 0.045 3400 3200 200 1900 0.105 0.045 3200 2740 460 12500 0.037 0.045 2740 2580 160 5600 0.029 0.045 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 Length of Watercourse (Lc): Length to Center of Gravity (Lca): 27300 13650 Storm Event 3-hour 2-hour 1-hour Cover Type(s): Impervious Surfaces: ft ft Mean Slope (Sc): Weighted Basin Factor (nb): Rainfall Data Mapped Computed Values Values (in) (in) n/a 3.25 n/a 3.03 n/a 2.68 Mtn./Desert Brush Mix Percent 12% Hydrologic Group A B C D Weighted Runoff Coefficient (Cw): Time of Concentration (Tc): 0.96 Soils Data Group Curve Number % Normal Adjusted 53 10 37 83 82 90 87.04 86.26 92.50 min. Rainfall Intensity (i) at Tc: 3.11 in/hr Runoff Supply Rate (q) at Tc: 2.01 in/hr 30% (CN constant at 99) Runoff Coefficient 0.55 0.53 0.71 100-year Peak Discharge (Q100): 49 ft/ft Reduced Values (in) 3.25 3.03 2.68 Cover Density (pervious areas): Runoff Coefficient: 0.648 JE Fuller / Hydrology and Geomorphology, Inc. Areal Reduction % 0% 0% 0% 0.0545 0.045 2512 For Return Intervals Other Than Q100 25-year = n/c cfs 10-year = n/c cfs 5-year = n/c cfs 2-year = n/c cfs cfs HYDROLOGIC DATA SHEET Watercourse or Project Name: Flecha Caida Flood Improvement Study Drainage Concentration Point: 18 (1986) Watershed Area (A): 610 acres Watershed Type: Mtn (dev)/Foothills(dev) Incremental Changes along Primary Watercourse by Reach Reach Elevations Height Length Slope Basin u/s d/s Hi Li Si Factor limit limit (ft) (ft) (ft/ft) nb 6080 5600 480 1100 0.436 0.055 5600 3800 1800 4000 0.450 0.055 3800 3400 400 2200 0.182 0.055 3400 3200 200 1900 0.105 0.055 3200 2980 220 4100 0.054 0.055 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 Length of Watercourse (Lc): Length to Center of Gravity (Lca): 13300 7000 Storm Event 3-hour 2-hour 1-hour Cover Type(s): Impervious Surfaces: ft ft Mean Slope (Sc): Weighted Basin Factor (nb): Rainfall Data Mapped Computed Values Values (in) (in) n/a 3.25 n/a 3.03 n/a 2.72 Mtn./Desert Brush Mix Percent 3% Hydrologic Group A B C D Weighted Runoff Coefficient (Cw): Time of Concentration (Tc): 0.96 Soils Data Group Curve Number % Normal Adjusted 8 19 73 83 82 90 87.12 86.34 92.57 min. Rainfall Intensity (i) at Tc: 5.22 in/hr Runoff Supply Rate (q) at Tc: 3.54 in/hr 30%/20% (CN constant at 99) Runoff Coefficient 0.55 0.53 0.72 100-year Peak Discharge (Q100): 22 ft/ft Reduced Values (in) 3.25 3.03 2.72 Cover Density (pervious areas): Runoff Coefficient: 0.677 JE Fuller / Hydrology and Geomorphology, Inc. Areal Reduction % 0% 0% 0% 0.1339 0.055 2175 For Return Intervals Other Than Q100 25-year = n/c cfs 10-year = n/c cfs 5-year = n/c cfs 2-year = n/c cfs cfs HYDROLOGIC DATA SHEET Watercourse or Project Name: Flecha Caida Flood Improvement Study Drainage Concentration Point: 11.1 (1986 updated) Watershed Area (A): 927 acres Watershed Type: Mtn (dev)/Foothills(dev) Incremental Changes along Primary Watercourse by Reach Reach Elevations Height Length Slope Basin u/s d/s Hi Li Si Factor limit limit (ft) (ft) (ft/ft) nb 6080 5600 480 1100 0.436 0.047 5600 3800 1800 4000 0.450 0.047 3800 3400 400 2200 0.182 0.047 3400 3200 200 1900 0.105 0.047 3200 2740 460 12500 0.037 0.047 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 Length of Watercourse (Lc): Length to Center of Gravity (Lca): 21700 10850 Storm Event 3-hour 2-hour 1-hour Cover Type(s): Impervious Surfaces: ft ft Mean Slope (Sc): Weighted Basin Factor (nb): Rainfall Data Mapped Computed Values Values (in) (in) n/a 3.25 n/a 3.03 n/a 2.69 Mtn./Desert Brush Mix Percent 9.0% Hydrologic Group A B C D Weighted Runoff Coefficient (Cw): Time of Concentration (Tc): 0.96 Soils Data Group Curve Number % Normal Adjusted 38 13 49 83 82 90 87.06 86.28 92.52 min. Rainfall Intensity (i) at Tc: 3.72 in/hr Runoff Supply Rate (q) at Tc: 2.44 in/hr 30%/20% (CN constant at 99) Runoff Coefficient 0.55 0.53 0.71 100-year Peak Discharge (Q100): 38 ft/ft Reduced Values (in) 3.25 3.03 2.69 Cover Density (pervious areas): Runoff Coefficient: 0.656 JE Fuller / Hydrology and Geomorphology, Inc. Areal Reduction % 0% 0% 0% 0.0670 0.047 2279 For Return Intervals Other Than Q100 25-year = n/c cfs 10-year = n/c cfs 5-year = n/c cfs 2-year = n/c cfs cfs HYDROLOGIC DATA SHEET Watercourse or Project Name: Flecha Caida Flood Improvement Study Drainage Concentration Point: 13 (1986 updated) Watershed Area (A): 1239 acres Watershed Type: Mtn (dev)/Foothills(dev) Incremental Changes along Primary Watercourse by Reach Reach Elevations Height Length Slope Basin u/s d/s Hi Li Si Factor limit limit (ft) (ft) (ft/ft) nb 6080 5600 480 1100 0.436 0.045 5600 3800 1800 4000 0.450 0.045 3800 3400 400 2200 0.182 0.045 3400 3200 200 1900 0.105 0.045 3200 2740 460 12500 0.037 0.045 2740 2580 160 5600 0.029 0.045 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 Length of Watercourse (Lc): Length to Center of Gravity (Lca): 27300 13650 Storm Event 3-hour 2-hour 1-hour Cover Type(s): Impervious Surfaces: ft ft Mean Slope (Sc): Weighted Basin Factor (nb): Rainfall Data Mapped Computed Values Values (in) (in) n/a 3.25 n/a 3.03 n/a 2.68 Mtn./Desert Brush Mix Percent 12.8% Hydrologic Group A B C D Weighted Runoff Coefficient (Cw): Time of Concentration (Tc): 0.96 Soils Data Group Curve Number % Normal Adjusted 53 10 37 83 82 90 87.04 86.26 92.50 min. Rainfall Intensity (i) at Tc: 3.11 in/hr Runoff Supply Rate (q) at Tc: 2.02 in/hr 30% (CN constant at 99) Runoff Coefficient 0.55 0.53 0.71 100-year Peak Discharge (Q100): 49 ft/ft Reduced Values (in) 3.25 3.03 2.68 Cover Density (pervious areas): Runoff Coefficient: 0.650 JE Fuller / Hydrology and Geomorphology, Inc. Areal Reduction % 0% 0% 0% 0.0545 0.045 2527 For Return Intervals Other Than Q100 25-year = n/c cfs 10-year = n/c cfs 5-year = n/c cfs 2-year = n/c cfs cfs HYDROLOGIC DATA SHEET Watercourse or Project Name: Flecha Caida Flood Improvement Study Drainage Concentration Point: 18 (1986 updated) Watershed Area (A): 610 acres Watershed Type: Mtn (dev)/Foothills(dev) Incremental Changes along Primary Watercourse by Reach Reach Elevations Height Length Slope Basin u/s d/s Hi Li Si Factor limit limit (ft) (ft) (ft/ft) nb 6080 5600 480 1100 0.436 0.055 5600 3800 1800 4000 0.450 0.055 3800 3400 400 2200 0.182 0.055 3400 3200 200 1900 0.105 0.055 3200 2980 220 4100 0.054 0.055 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 Length of Watercourse (Lc): Length to Center of Gravity (Lca): 13300 7000 Storm Event 3-hour 2-hour 1-hour Cover Type(s): Impervious Surfaces: ft ft Mean Slope (Sc): Weighted Basin Factor (nb): Rainfall Data Mapped Computed Values Values (in) (in) n/a 3.25 n/a 3.03 n/a 2.72 Mtn./Desert Brush Mix Percent 4.5% Hydrologic Group A B C D Weighted Runoff Coefficient (Cw): Time of Concentration (Tc): 0.96 Soils Data Group Curve Number % Normal Adjusted 8 19 73 83 82 90 87.12 86.34 92.57 min. Rainfall Intensity (i) at Tc: 5.23 in/hr Runoff Supply Rate (q) at Tc: 3.57 in/hr 30%/20% (CN constant at 99) Runoff Coefficient 0.55 0.53 0.72 100-year Peak Discharge (Q100): 22 ft/ft Reduced Values (in) 3.25 3.03 2.72 Cover Density (pervious areas): Runoff Coefficient: 0.681 JE Fuller / Hydrology and Geomorphology, Inc. Areal Reduction % 0% 0% 0% 0.1339 0.055 2192 For Return Intervals Other Than Q100 25-year = n/c cfs 10-year = n/c cfs 5-year = n/c cfs 2-year = n/c cfs cfs HYDROLOGIC DATA SHEET Watercourse or Project Name: Flecha Caida Flood Improvement Study Drainage Concentration Point: 14 (1986 duplicate effective) Watershed Area (A): 239 acres Watershed Type: Foothills(dev) Incremental Changes along Primary Watercourse by Reach Reach Elevations Height Length Slope Basin u/s d/s Hi Li Si Factor limit limit (ft) (ft) (ft/ft) nb 3000 2800 200 4200 0.048 0.035 2800 2610 190 6600 0.029 0.035 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 Length of Watercourse (Lc): Length to Center of Gravity (Lca): 10800 5000 Storm Event 3-hour 2-hour 1-hour Cover Type(s): Impervious Surfaces: ft ft Mean Slope (Sc): Weighted Basin Factor (nb): Rainfall Data Mapped Computed Values Values (in) (in) n/a 3.17 n/a 2.96 n/a 2.63 Mtn./Desert Brush Mix Percent 15.0% Hydrologic Group A B C D Weighted Runoff Coefficient (Cw): Time of Concentration (Tc): 0.96 Soils Data Group Curve Number % Normal Adjusted 100 83 82 90 86.93 min. Rainfall Intensity (i) at Tc: 5.09 in/hr Runoff Supply Rate (q) at Tc: 3.06 in/hr 20% (CN constant at 99) Runoff Coefficient 0.54 100-year Peak Discharge (Q100): 21 ft/ft Reduced Values (in) 3.17 2.96 2.63 Cover Density (pervious areas): Runoff Coefficient: 0.601 JE Fuller / Hydrology and Geomorphology, Inc. Areal Reduction % 0% 0% 0% 0.0345 0.035 737 For Return Intervals Other Than Q100 25-year = n/c cfs 10-year = n/c cfs 5-year = n/c cfs 2-year = n/c cfs cfs HYDROLOGIC DATA SHEET Watercourse or Project Name: Flecha Caida Flood Improvement Study Drainage Concentration Point: 11 Watershed Area (A): 908 acres Watershed Type: Mtn (dev)/Foothills(dev) Incremental Changes along Primary Watercourse by Reach Reach Elevations Height Length Slope Basin u/s d/s Hi Li Si Factor limit limit (ft) (ft) (ft/ft) nb 6080 5600 480 1100 0.436 0.047 5600 3800 1800 4000 0.450 0.047 3800 3400 400 2200 0.182 0.047 3400 3200 200 1900 0.105 0.047 3200 2740 460 12500 0.037 0.047 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 Length of Watercourse (Lc): Length to Center of Gravity (Lca): 21700 10850 Storm Event 3-hour 2-hour 1-hour Cover Type(s): Impervious Surfaces: ft ft Mean Slope (Sc): Weighted Basin Factor (nb): Rainfall Data Mapped Computed Values Values (in) (in) n/a 3.57 n/a 3.39 n/a 3.00 Mtn./Desert Brush Mix Percent 9% Hydrologic Group A B C D Weighted Runoff Coefficient (Cw): Time of Concentration (Tc): 0.96 Soils Data Group Curve Number % Normal Adjusted 38 13 49 83 82 90 87.63 86.87 92.96 min. Rainfall Intensity (i) at Tc: 4.40 in/hr Runoff Supply Rate (q) at Tc: 3.06 in/hr 30% (CN constant at 99) Runoff Coefficient 0.60 0.58 0.75 100-year Peak Discharge (Q100): 35 ft/ft Reduced Values (in) 3.57 3.39 3.00 Cover Density (pervious areas): Runoff Coefficient: 0.695 JE Fuller / Hydrology and Geomorphology, Inc. Areal Reduction % 0% 0% 0% 0.0670 0.047 2802 For Return Intervals Other Than Q100 25-year = n/c cfs 10-year = n/c cfs 5-year = n/c cfs 2-year = n/c cfs cfs HYDROLOGIC DATA SHEET Watercourse or Project Name: Flecha Caida Flood Improvement Study Drainage Concentration Point: 11.1 Watershed Area (A): 927 acres Watershed Type: Mtn (dev)/Foothills(dev) Incremental Changes along Primary Watercourse by Reach Reach Elevations Height Length Slope Basin u/s d/s Hi Li Si Factor limit limit (ft) (ft) (ft/ft) nb 6080 5600 480 1100 0.436 0.047 5600 3800 1800 4000 0.450 0.047 3800 3400 400 2200 0.182 0.047 3400 3200 200 1900 0.105 0.047 3200 2740 460 12500 0.037 0.047 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 Length of Watercourse (Lc): Length to Center of Gravity (Lca): 21700 10850 Storm Event 3-hour 2-hour 1-hour Cover Type(s): Impervious Surfaces: ft ft Mean Slope (Sc): Weighted Basin Factor (nb): Rainfall Data Mapped Computed Values Values (in) (in) n/a 3.57 n/a 3.39 n/a 3.00 Mtn./Desert Brush Mix Percent 9% Hydrologic Group A B C D Weighted Runoff Coefficient (Cw): Time of Concentration (Tc): 0.96 Soils Data Group Curve Number % Normal Adjusted 38 13 49 83 82 90 87.63 86.87 92.96 min. Rainfall Intensity (i) at Tc: 4.40 in/hr Runoff Supply Rate (q) at Tc: 3.06 in/hr 30%/20% (CN constant at 99) Runoff Coefficient 0.60 0.58 0.75 100-year Peak Discharge (Q100): 35 ft/ft Reduced Values (in) 3.57 3.39 3.00 Cover Density (pervious areas): Runoff Coefficient: 0.695 JE Fuller / Hydrology and Geomorphology, Inc. Areal Reduction % 0% 0% 0% 0.0670 0.047 2861 For Return Intervals Other Than Q100 25-year = n/c cfs 10-year = n/c cfs 5-year = n/c cfs 2-year = n/c cfs cfs HYDROLOGIC DATA SHEET Watercourse or Project Name: Flecha Caida Flood Improvement Study Drainage Concentration Point: 11.3 Watershed Area (A): 1034 acres Watershed Type: Mtn (dev)/Foothills(dev) Incremental Changes along Primary Watercourse by Reach Reach Elevations Height Length Slope Basin u/s d/s Hi Li Si Factor limit limit (ft) (ft) (ft/ft) nb 6080 5600 480 1100 0.436 0.046 5600 3800 1800 4000 0.450 0.046 3800 3400 400 2200 0.182 0.046 3400 3200 200 1900 0.105 0.046 3200 2740 460 12500 0.037 0.046 2740 2660 80 2900 0.028 0.046 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 Length of Watercourse (Lc): Length to Center of Gravity (Lca): 24600 12300 Storm Event 3-hour 2-hour 1-hour Cover Type(s): Impervious Surfaces: ft ft Mean Slope (Sc): Weighted Basin Factor (nb): Rainfall Data Mapped Computed Values Values (in) (in) n/a 3.57 n/a 3.39 n/a 3.00 Mtn./Desert Brush Mix Percent 12% Hydrologic Group A B C D Weighted Runoff Coefficient (Cw): Time of Concentration (Tc): 0.96 Soils Data Group Curve Number % Normal Adjusted 44 12 44 83 82 90 87.63 86.87 92.96 min. Rainfall Intensity (i) at Tc: 4.01 in/hr Runoff Supply Rate (q) at Tc: 2.80 in/hr 30%/20% (CN constant at 99) Runoff Coefficient 0.60 0.58 0.75 100-year Peak Discharge (Q100): 40 ft/ft Reduced Values (in) 3.57 3.39 3.00 Cover Density (pervious areas): Runoff Coefficient: 0.697 JE Fuller / Hydrology and Geomorphology, Inc. Areal Reduction % 0% 0% 0% 0.0590 0.046 2916 For Return Intervals Other Than Q100 25-year = n/c cfs 10-year = n/c cfs 5-year = n/c cfs 2-year = n/c cfs cfs HYDROLOGIC DATA SHEET Watercourse or Project Name: Flecha Caida Flood Improvement Study Drainage Concentration Point: 11.3a Watershed Area (A): 1045 acres Watershed Type: Mtn (dev)/Foothills(dev) Incremental Changes along Primary Watercourse by Reach Reach Elevations Height Length Slope Basin u/s d/s Hi Li Si Factor limit limit (ft) (ft) (ft/ft) nb 6080 5600 480 1100 0.436 0.046 5600 3800 1800 4000 0.450 0.046 3800 3400 400 2200 0.182 0.046 3400 3200 200 1900 0.105 0.046 3200 2740 460 12500 0.037 0.046 2740 2660 80 2900 0.028 0.046 2660 2640 20 770 0.026 0.046 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 Length of Watercourse (Lc): Length to Center of Gravity (Lca): 25370 12685 Storm Event 3-hour 2-hour 1-hour Cover Type(s): Impervious Surfaces: ft ft Mean Slope (Sc): Weighted Basin Factor (nb): Rainfall Data Mapped Computed Values Values (in) (in) n/a 3.57 n/a 3.39 n/a 3.00 Mtn./Desert Brush Mix Percent 12% Hydrologic Group A B C D Weighted Runoff Coefficient (Cw): Time of Concentration (Tc): 0.96 Soils Data Group Curve Number % Normal Adjusted 45 12 43 83 82 90 87.63 86.87 92.96 min. Rainfall Intensity (i) at Tc: 3.89 in/hr Runoff Supply Rate (q) at Tc: 2.71 in/hr 30%/20% (CN constant at 99) Runoff Coefficient 0.60 0.58 0.75 100-year Peak Discharge (Q100): 42 ft/ft Reduced Values (in) 3.57 3.39 3.00 Cover Density (pervious areas): Runoff Coefficient: 0.696 JE Fuller / Hydrology and Geomorphology, Inc. Areal Reduction % 0% 0% 0% 0.0572 0.046 2855 For Return Intervals Other Than Q100 25-year = n/c cfs 10-year = n/c cfs 5-year = n/c cfs 2-year = n/c cfs cfs HYDROLOGIC DATA SHEET Watercourse or Project Name: Flecha Caida Flood Improvement Study Drainage Concentration Point: 11.3b Watershed Area (A): 1055 acres Watershed Type: Mtn (dev)/Foothills(dev) Incremental Changes along Primary Watercourse by Reach Reach Elevations Height Length Slope Basin u/s d/s Hi Li Si Factor limit limit (ft) (ft) (ft/ft) nb 6080 5600 480 1100 0.436 0.046 5600 3800 1800 4000 0.450 0.046 3800 3400 400 2200 0.182 0.046 3400 3200 200 1900 0.105 0.046 3200 2740 460 12500 0.037 0.046 2740 2660 80 2900 0.028 0.046 2660 2640 20 770 0.026 0.046 2640 2620 20 770 0.026 0.046 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 Length of Watercourse (Lc): Length to Center of Gravity (Lca): 26140 13070 Storm Event 3-hour 2-hour 1-hour Cover Type(s): Impervious Surfaces: ft ft Mean Slope (Sc): Weighted Basin Factor (nb): Rainfall Data Mapped Computed Values Values (in) (in) n/a 3.57 n/a 3.39 n/a 3.00 Mtn./Desert Brush Mix Percent 12% Hydrologic Group A B C D Weighted Runoff Coefficient (Cw): Time of Concentration (Tc): 0.96 Soils Data Group Curve Number % Normal Adjusted 46 11 43 83 82 90 87.63 86.87 92.96 min. Rainfall Intensity (i) at Tc: 3.79 in/hr Runoff Supply Rate (q) at Tc: 2.64 in/hr 30%/20% (CN constant at 99) Runoff Coefficient 0.60 0.58 0.75 100-year Peak Discharge (Q100): 43 ft/ft Reduced Values (in) 3.57 3.39 3.00 Cover Density (pervious areas): Runoff Coefficient: 0.696 JE Fuller / Hydrology and Geomorphology, Inc. Areal Reduction % 0% 0% 0% 0.0556 0.046 2804 For Return Intervals Other Than Q100 25-year = n/c cfs 10-year = n/c cfs 5-year = n/c cfs 2-year = n/c cfs cfs HYDROLOGIC DATA SHEET Watercourse or Project Name: Flecha Caida Flood Improvement Study Drainage Concentration Point: 11.4 Watershed Area (A): 1073 acres Watershed Type: Mtn (dev)/Foothills(dev) Incremental Changes along Primary Watercourse by Reach Reach Elevations Height Length Slope Basin u/s d/s Hi Li Si Factor limit limit (ft) (ft) (ft/ft) nb 6080 5600 480 1100 0.436 0.046 5600 3800 1800 4000 0.450 0.046 3800 3400 400 2200 0.182 0.046 3400 3200 200 1900 0.105 0.046 3200 2740 460 12500 0.037 0.046 2740 2660 80 2900 0.028 0.046 2660 2640 20 770 0.026 0.046 2640 2620 20 770 0.026 0.046 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 Length of Watercourse (Lc): Length to Center of Gravity (Lca): 26140 13070 Storm Event 3-hour 2-hour 1-hour Cover Type(s): Impervious Surfaces: ft ft Mean Slope (Sc): Weighted Basin Factor (nb): Rainfall Data Mapped Computed Values Values (in) (in) n/a 3.57 n/a 3.39 n/a 3.00 Mtn./Desert Brush Mix Percent 12% Hydrologic Group A B C D Weighted Runoff Coefficient (Cw): Time of Concentration (Tc): 0.96 Soils Data Group Curve Number % Normal Adjusted 47 11 42 83 82 90 87.63 86.87 92.96 min. Rainfall Intensity (i) at Tc: 3.78 in/hr Runoff Supply Rate (q) at Tc: 2.63 in/hr 30%/20% (CN constant at 99) Runoff Coefficient 0.60 0.58 0.75 100-year Peak Discharge (Q100): 43 ft/ft Reduced Values (in) 3.57 3.39 3.00 Cover Density (pervious areas): Runoff Coefficient: 0.695 JE Fuller / Hydrology and Geomorphology, Inc. Areal Reduction % 0% 0% 0% 0.0556 0.046 2844 For Return Intervals Other Than Q100 25-year = n/c cfs 10-year = n/c cfs 5-year = n/c cfs 2-year = n/c cfs cfs HYDROLOGIC DATA SHEET Watercourse or Project Name: Flecha Caida Flood Improvement Study Drainage Concentration Point: 11.4a Watershed Area (A): 1189 acres Watershed Type: Mtn (dev)/Foothills(dev) Incremental Changes along Primary Watercourse by Reach Reach Elevations Height Length Slope Basin u/s d/s Hi Li Si Factor limit limit (ft) (ft) (ft/ft) nb 6080 5600 480 1100 0.436 0.046 5600 3800 1800 4000 0.450 0.046 3800 3400 400 2200 0.182 0.046 3400 3200 200 1900 0.105 0.046 3200 2740 460 12500 0.037 0.046 2740 2660 80 2900 0.028 0.046 2660 2640 20 770 0.026 0.046 2640 2620 20 770 0.026 0.046 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 Length of Watercourse (Lc): Length to Center of Gravity (Lca): 26140 13070 Storm Event 3-hour 2-hour 1-hour Cover Type(s): Impervious Surfaces: ft ft Mean Slope (Sc): Weighted Basin Factor (nb): Rainfall Data Mapped Computed Values Values (in) (in) n/a 3.57 n/a 3.39 n/a 3.00 Mtn./Desert Brush Mix Percent 12% Hydrologic Group A B C D Weighted Runoff Coefficient (Cw): Time of Concentration (Tc): 0.96 Soils Data Group Curve Number % Normal Adjusted 52 10 38 83 82 90 87.63 86.87 92.96 min. Rainfall Intensity (i) at Tc: 3.77 in/hr Runoff Supply Rate (q) at Tc: 2.60 in/hr 30%/20% (CN constant at 99) Runoff Coefficient 0.60 0.58 0.75 100-year Peak Discharge (Q100): 44 ft/ft Reduced Values (in) 3.57 3.39 3.00 Cover Density (pervious areas): Runoff Coefficient: 0.690 JE Fuller / Hydrology and Geomorphology, Inc. Areal Reduction % 0% 0% 0% 0.0556 0.046 3119 For Return Intervals Other Than Q100 25-year = n/c cfs 10-year = n/c cfs 5-year = n/c cfs 2-year = n/c cfs cfs HYDROLOGIC DATA SHEET Watercourse or Project Name: Flecha Caida Flood Improvement Study Drainage Concentration Point: 13 Watershed Area (A): 1239 acres Watershed Type: Mtn (dev)/Foothills(dev) Incremental Changes along Primary Watercourse by Reach Reach Elevations Height Length Slope Basin u/s d/s Hi Li Si Factor limit limit (ft) (ft) (ft/ft) nb 6080 5600 480 1100 0.436 0.045 5600 3800 1800 4000 0.450 0.045 3800 3400 400 2200 0.182 0.045 3400 3200 200 1900 0.105 0.045 3200 2740 460 12500 0.037 0.045 2740 2580 160 5600 0.029 0.045 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 Length of Watercourse (Lc): Length to Center of Gravity (Lca): 27300 13650 Storm Event 3-hour 2-hour 1-hour Cover Type(s): Impervious Surfaces: ft ft Mean Slope (Sc): Weighted Basin Factor (nb): Rainfall Data Mapped Computed Values Values (in) (in) n/a 3.57 n/a 3.39 n/a 3.00 Mtn./Desert Brush Mix Percent 12.8% Hydrologic Group A B C D Weighted Runoff Coefficient (Cw): Time of Concentration (Tc): 0.96 Soils Data Group Curve Number % Normal Adjusted 53 10 37 83 82 90 87.63 86.87 92.96 min. Rainfall Intensity (i) at Tc: 3.73 in/hr Runoff Supply Rate (q) at Tc: 2.58 in/hr 30% (CN constant at 99) Runoff Coefficient 0.60 0.58 0.75 100-year Peak Discharge (Q100): 44 ft/ft Reduced Values (in) 3.57 3.39 3.00 Cover Density (pervious areas): Runoff Coefficient: 0.691 JE Fuller / Hydrology and Geomorphology, Inc. Areal Reduction % 0% 0% 0% 0.0545 0.045 3219 For Return Intervals Other Than Q100 25-year = n/c cfs 10-year = n/c cfs 5-year = n/c cfs 2-year = n/c cfs cfs HYDROLOGIC DATA SHEET Watercourse or Project Name: Flecha Caida Flood Improvement Study Drainage Concentration Point: 18 Watershed Area (A): 610 acres Watershed Type: Mtn (dev)/Foothills(dev) Incremental Changes along Primary Watercourse by Reach Reach Elevations Height Length Slope Basin u/s d/s Hi Li Si Factor limit limit (ft) (ft) (ft/ft) nb 6080 5600 480 1100 0.436 0.055 5600 3800 1800 4000 0.450 0.055 3800 3400 400 2200 0.182 0.055 3400 3200 200 1900 0.105 0.055 3200 2980 220 4100 0.054 0.055 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 Length of Watercourse (Lc): Length to Center of Gravity (Lca): 13300 7000 Storm Event 3-hour 2-hour 1-hour Cover Type(s): Impervious Surfaces: ft ft Mean Slope (Sc): Weighted Basin Factor (nb): Rainfall Data Mapped Computed Values Values (in) (in) n/a 3.70 n/a 3.50 n/a 3.11 Mtn./Desert Brush Mix Percent 4.5% Hydrologic Group A B C D Weighted Runoff Coefficient (Cw): Time of Concentration (Tc): 0.96 Soils Data Group Curve Number % Normal Adjusted 8 19 73 83 82 90 87.81 87.06 93.10 min. Rainfall Intensity (i) at Tc: 6.30 in/hr Runoff Supply Rate (q) at Tc: 4.59 in/hr 30%/20% (CN constant at 99) Runoff Coefficient 0.61 0.59 0.76 100-year Peak Discharge (Q100): 19 ft/ft Reduced Values (in) 3.70 3.50 3.11 Cover Density (pervious areas): Runoff Coefficient: 0.728 JE Fuller / Hydrology and Geomorphology, Inc. Areal Reduction % 0% 0% 0% 0.1339 0.055 2823 For Return Intervals Other Than Q100 25-year = n/c cfs 10-year = n/c cfs 5-year = n/c cfs 2-year = n/c cfs cfs HYDROLOGIC DATA SHEET Watercourse or Project Name: Flecha Caida Flood Improvement Study Drainage Concentration Point: 11.3 (2-year) Watershed Area (A): 1034 acres Watershed Type: Mtn (dev)/Foothills(dev) Incremental Changes along Primary Watercourse by Reach Reach Elevations Height Length Slope Basin u/s d/s Hi Li Si Factor limit limit (ft) (ft) (ft/ft) nb 6080 5600 480 1100 0.436 0.046 5600 3800 1800 4000 0.450 0.046 3800 3400 400 2200 0.182 0.046 3400 3200 200 1900 0.105 0.046 3200 2740 460 12500 0.037 0.046 2740 2660 80 2900 0.028 0.046 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 Length of Watercourse (Lc): Length to Center of Gravity (Lca): 24600 12300 Storm Event 3-hour 2-hour 1-hour Cover Type(s): Impervious Surfaces: ft ft Mean Slope (Sc): Weighted Basin Factor (nb): Rainfall Data Mapped Computed Values Values (in) (in) n/a 1.53 n/a 1.46 n/a 1.28 Mtn./Desert Brush Mix Percent 12% Hydrologic Group A B C D Weighted Runoff Coefficient (Cw): 0.91 Soils Data Group Curve Number % Normal Adjusted 44 12 44 83 82 90 80.93 79.95 87.82 104 min. Rainfall Intensity (i) at Tc: 0.82 in/hr Runoff Supply Rate (q) at Tc: 0.26 in/hr 30%/20% (CN constant at 99) Runoff Coefficient 0.16 0.14 0.33 2-year Peak Discharge (Q2): Time of Concentration (Tc): ft/ft Reduced Values (in) 1.53 1.46 1.28 Cover Density (pervious areas): Runoff Coefficient: 0.314 JE Fuller / Hydrology and Geomorphology, Inc. Areal Reduction % 0% 0% 0% 0.0590 0.046 268 For Return Intervals Other Than Q100 25-year = n/c cfs 10-year = n/c cfs 5-year = n/c cfs 2-year = n/c cfs cfs HYDROLOGIC DATA SHEET Watercourse or Project Name: Flecha Caida Flood Improvement Study Drainage Concentration Point: 11.3 (5-year) Watershed Area (A): 1034 acres Watershed Type: Mtn (dev)/Foothills(dev) Incremental Changes along Primary Watercourse by Reach Reach Elevations Height Length Slope Basin u/s d/s Hi Li Si Factor limit limit (ft) (ft) (ft/ft) nb 6080 5600 480 1100 0.436 0.046 5600 3800 1800 4000 0.450 0.046 3800 3400 400 2200 0.182 0.046 3400 3200 200 1900 0.105 0.046 3200 2740 460 12500 0.037 0.046 2740 2660 80 2900 0.028 0.046 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 Length of Watercourse (Lc): Length to Center of Gravity (Lca): 24600 12300 Storm Event 3-hour 2-hour 1-hour Cover Type(s): Impervious Surfaces: ft ft Mean Slope (Sc): Weighted Basin Factor (nb): Rainfall Data Mapped Computed Values Values (in) (in) n/a 1.97 n/a 1.89 n/a 1.68 Mtn./Desert Brush Mix Percent 12% Hydrologic Group A B C D Weighted Runoff Coefficient (Cw): Time of Concentration (Tc): 0.93 Soils Data Group Curve Number % Normal Adjusted 44 12 44 83 82 90 83.71 82.82 89.95 min. Rainfall Intensity (i) at Tc: 1.45 in/hr Runoff Supply Rate (q) at Tc: 0.65 in/hr 30%/20% (CN constant at 99) Runoff Coefficient 0.31 0.29 0.49 5-year Peak Discharge (Q5): 71 ft/ft Reduced Values (in) 1.97 1.89 1.68 Cover Density (pervious areas): Runoff Coefficient: 0.451 JE Fuller / Hydrology and Geomorphology, Inc. Areal Reduction % 0% 0% 0% 0.0590 0.046 680 For Return Intervals Other Than Q100 25-year = n/c cfs 10-year = n/c cfs 5-year = n/c cfs 2-year = n/c cfs cfs HYDROLOGIC DATA SHEET Watercourse or Project Name: Flecha Caida Flood Improvement Study Drainage Concentration Point: 11.3 (10-year) Watershed Area (A): 1034 acres Watershed Type: Mtn (dev)/Foothills(dev) Incremental Changes along Primary Watercourse by Reach Reach Elevations Height Length Slope Basin u/s d/s Hi Li Si Factor limit limit (ft) (ft) (ft/ft) nb 6080 5600 480 1100 0.436 0.046 5600 3800 1800 4000 0.450 0.046 3800 3400 400 2200 0.182 0.046 3400 3200 200 1900 0.105 0.046 3200 2740 460 12500 0.037 0.046 2740 2660 80 2900 0.028 0.046 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 Length of Watercourse (Lc): Length to Center of Gravity (Lca): 24600 12300 Storm Event 3-hour 2-hour 1-hour Cover Type(s): Impervious Surfaces: ft ft Mean Slope (Sc): Weighted Basin Factor (nb): Rainfall Data Mapped Computed Values Values (in) (in) n/a 2.31 n/a 2.22 n/a 1.97 Mtn./Desert Brush Mix Percent 12% Hydrologic Group A B C D Weighted Runoff Coefficient (Cw): Time of Concentration (Tc): 0.94 Soils Data Group Curve Number % Normal Adjusted 44 12 44 83 82 90 85.02 84.18 90.96 min. Rainfall Intensity (i) at Tc: 1.99 in/hr Runoff Supply Rate (q) at Tc: 1.05 in/hr 30%/20% (CN constant at 99) Runoff Coefficient 0.39 0.37 0.58 10-year Peak Discharge (Q10): 59 ft/ft Reduced Values (in) 2.31 2.22 1.97 Cover Density (pervious areas): Runoff Coefficient: 0.527 JE Fuller / Hydrology and Geomorphology, Inc. Areal Reduction % 0% 0% 0% 0.0590 0.046 1092 For Return Intervals Other Than Q100 25-year = n/c cfs 10-year = n/c cfs 5-year = n/c cfs 2-year = n/c cfs cfs HYDROLOGIC DATA SHEET Watercourse or Project Name: Flecha Caida Flood Improvement Study Drainage Concentration Point: 11.3 (25-year) Watershed Area (A): 1034 acres Watershed Type: Mtn (dev)/Foothills(dev) Incremental Changes along Primary Watercourse by Reach Reach Elevations Height Length Slope Basin u/s d/s Hi Li Si Factor limit limit (ft) (ft) (ft/ft) nb 6080 5600 480 1100 0.436 0.046 5600 3800 1800 4000 0.450 0.046 3800 3400 400 2200 0.182 0.046 3400 3200 200 1900 0.105 0.046 3200 2740 460 12500 0.037 0.046 2740 2660 80 2900 0.028 0.046 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 Length of Watercourse (Lc): Length to Center of Gravity (Lca): 24600 12300 Storm Event 3-hour 2-hour 1-hour Cover Type(s): Impervious Surfaces: ft ft Mean Slope (Sc): Weighted Basin Factor (nb): Rainfall Data Mapped Computed Values Values (in) (in) n/a 2.78 n/a 2.67 n/a 2.37 Mtn./Desert Brush Mix Percent 12% Hydrologic Group A B C D Weighted Runoff Coefficient (Cw): Time of Concentration (Tc): 0.95 Soils Data Group Curve Number % Normal Adjusted 44 12 44 83 82 90 86.31 85.50 91.94 min. Rainfall Intensity (i) at Tc: 2.74 in/hr Runoff Supply Rate (q) at Tc: 1.67 in/hr 30%/20% (CN constant at 99) Runoff Coefficient 0.49 0.47 0.66 25-year Peak Discharge (Q25): 49 ft/ft Reduced Values (in) 2.78 2.67 2.37 Cover Density (pervious areas): Runoff Coefficient: 0.609 JE Fuller / Hydrology and Geomorphology, Inc. Areal Reduction % 0% 0% 0% 0.0590 0.046 1740 For Return Intervals Other Than Q100 25-year = n/c cfs 10-year = n/c cfs 5-year = n/c cfs 2-year = n/c cfs cfs HYDROLOGIC DATA SHEET Watercourse or Project Name: Flecha Caida Flood Improvement Study Drainage Concentration Point: 13.1 Watershed Area (A): 1608 acres Watershed Type: Mtn (dev)/Foothills(dev) Incremental Changes along Primary Watercourse by Reach Reach Elevations Height Length Slope Basin u/s d/s Hi Li Si Factor limit limit (ft) (ft) (ft/ft) nb 6080 5600 480 1100 0.436 0.045 5600 3800 1800 4000 0.450 0.045 3800 3400 400 2200 0.182 0.045 3400 3200 200 1900 0.105 0.045 3200 2740 460 12500 0.037 0.045 2740 2580 160 5600 0.029 0.045 2580 2540 40 2150 0.019 0.045 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 Length of Watercourse (Lc): Length to Center of Gravity (Lca): 29450 14725 Storm Event 3-hour 2-hour 1-hour Cover Type(s): Impervious Surfaces: ft ft Mean Slope (Sc): Weighted Basin Factor (nb): Rainfall Data Mapped Computed Values Values (in) (in) n/a 3.57 n/a 3.39 n/a 3.00 Mtn./Desert Brush Mix Percent 12.9% Hydrologic Group A B C D Weighted Runoff Coefficient (Cw): Time of Concentration (Tc): 0.96 Soils Data Group Curve Number % Normal Adjusted 64 8 29 83 82 90 87.63 86.87 92.96 min. Rainfall Intensity (i) at Tc: 3.41 in/hr Runoff Supply Rate (q) at Tc: 2.34 in/hr 30% (CN constant at 99) Runoff Coefficient 0.60 0.58 0.75 100-year Peak Discharge (Q100): 50 ft/ft Reduced Values (in) 3.57 3.39 3.00 Cover Density (pervious areas): Runoff Coefficient: 0.686 JE Fuller / Hydrology and Geomorphology, Inc. Areal Reduction % 0% 0% 0% 0.0493 0.045 3797 For Return Intervals Other Than Q100 25-year = n/c cfs 10-year = n/c cfs 5-year = n/c cfs 2-year = n/c cfs cfs HYDROLOGIC DATA SHEET Watercourse or Project Name: Flecha Caida Flood Improvement Study Drainage Concentration Point: 14 (NOAA14) Watershed Area (A): 239 acres Watershed Type: Foothills(dev) Incremental Changes along Primary Watercourse by Reach Reach Elevations Height Length Slope Basin u/s d/s Hi Li Si Factor limit limit (ft) (ft) (ft/ft) nb 3000 2800 200 4200 0.048 0.035 2800 2610 190 6600 0.029 0.035 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 0 0 0 0 0.000 0.000 Length of Watercourse (Lc): Length to Center of Gravity (Lca): 10800 5000 Storm Event 3-hour 2-hour 1-hour Cover Type(s): Impervious Surfaces: ft ft Mean Slope (Sc): Weighted Basin Factor (nb): Rainfall Data Mapped Computed Values Values (in) (in) n/a 3.57 n/a 3.39 n/a 3.00 Mtn./Desert Brush Mix Percent 15.0% Hydrologic Group A B C D Weighted Runoff Coefficient (Cw): Time of Concentration (Tc): 0.96 Soils Data Group Curve Number % Normal Adjusted 100 83 82 90 87.63 min. Rainfall Intensity (i) at Tc: 6.13 in/hr Runoff Supply Rate (q) at Tc: 3.99 in/hr 20% (CN constant at 99) Runoff Coefficient 0.60 100-year Peak Discharge (Q100): 19 ft/ft Reduced Values (in) 3.57 3.39 3.00 Cover Density (pervious areas): Runoff Coefficient: 0.651 JE Fuller / Hydrology and Geomorphology, Inc. Areal Reduction % 0% 0% 0% 0.0345 0.035 962 For Return Intervals Other Than Q100 25-year = n/c cfs 10-year = n/c cfs 5-year = n/c cfs 2-year = n/c cfs cfs Summary of Scour Analysis - Input Parameters and Results Flecha Caida Ranch Estates #1 and #2 and Las Lomas de Catalina (Sections .01-0.10) GENERAL INPUT PARAMETERS This section summarizes the general input parameters that were used in the scour analysis. Additional input parameters (if applicable) are provided on the individual computation sheets. The scour equations are from the "Standards Manual for Drainage Design and Floodplain Management in Tucson, Arizona", City of Tucson, 1989. Hydraulic Data Qtotal = Qch = Ach = Tch = Ymax = Se = TW = n-value = 100-yr 3797 1210 cfs 131.10 sq ft 55.77 feet 5.03 feet 0.0181 ft/ft 0.00 feet 0.040 total discharge channel discharge channel area of flow channel topwidth of flow maximum depth of flow energy slope or channel bed slope tailwater depth (if different than Ymax; otherwise 0) Manning's n-value for channel Note: The energy slope is typically used when the basic hydraulic data is obtained from a HEC-2 or HEC-RAS analysis of the watercourse, and the channel bed slope is typically used when the data is obtained from a normal-depth analysis of the channel section. For a straight reach, the radius of curvature (rc) should be equal to or greater than: Applied rc = 350 feet 557.66 radius of curvature of channel centerline DESIGN SCOUR DEPTH Per COT Drainage Design Manual, Equation 6.3: Zgs = 0.00 feet (general scour) Za = 1.16 feet (anti-dune trough) Zls = 0.00 feet (controlling drop scour not applicable) Zbs = 0.49 feet (bend scour) Zlft = 1.00 feet 2.66 feet (low-flow thalweg) 1.30 3.45 feet (safety factor) (minimum recommended design scour depth) Zt = JE Fuller Hydrology and Geomorphology, Inc. feet Depth of Scour Flecha Caida Ranch Estates #1 and #2 and Las Lomas de Catalina (Sections .01-0.10) GENERAL SCOUR Per COT Drainage Design Manual, Equation 6.4: Vm = Ymax = 9.23 fps 5.03 feet Yh = 2.35 feet Se = 0.0181 ft/ft Zgs = 0.00 feet (if a negative value is calculated, result appears as 0) ANTI-DUNE TROUGH DEPTH Per COT Drainage Design Manual, Equation 6.5: Vm = g= Za = 9.23 fps 32.20 accelaration due to gravity in ft/s 2 1.16 feet LOW-FLOW THALWEG Per COT Drainage Design Manual: Assume thalweg depth (Zlft) is 2.0 feet for regional watercourses and 1.0 feet for all other watercourses, unless field observations dictate otherwise. Zlft = 1.00 feet BEND SCOUR Per COT Drainage Design Manual, Equation 6.6: Vm = 9.23 fps Ymax = 5.03 feet Yh = 2.35 feet Se = 0.0181 ft/ft rc = T= rc/T = 350.00 feet 55.77 feet 6.28 Zbs = 0.49 feet JE Fuller Hydrology and Geomorphology, Inc. (calculated rc/T is limited to 0.5 < rc/T < 10) (using rc/T and substituting Eqn. 6.7 into Eqn. 6.6) Summary of Scour Analysis - Input Parameters and Results Flecha Caida Ranch Estates # 1 and #2 and Las Lomas de Catalina (Sections 0.11-0.21) GENERAL INPUT PARAMETERS This section summarizes the general input parameters that were used in the scour analysis. Additional input parameters (if applicable) are provided on the individual computation sheets. The scour equations are from the "Standards Manual for Drainage Design and Floodplain Management in Tucson, Arizona", City of Tucson, 1989. Hydraulic Data Qtotal = Qch = Ach = Tch = Ymax = Se = TW = n-value = 100-yr 3219 1600 cfs 200.29 sq ft 97.25 feet 3.13 feet 0.0180 ft/ft 0.00 feet 0.040 total discharge channel discharge channel area of flow channel topwidth of flow maximum depth of flow energy slope or channel bed slope tailwater depth (if different than Ymax; otherwise 0) Manning's n-value for channel Note: The energy slope is typically used when the basic hydraulic data is obtained from a HEC-2 or HEC-RAS analysis of the watercourse, and the channel bed slope is typically used when the data is obtained from a normal-depth analysis of the channel section. For a straight reach, the radius of curvature (rc) should be equal to or greater than: 972.47273 feet Applied rc = 350 feet radius of curvature of channel centerline DESIGN SCOUR DEPTH Per COT Drainage Design Manual, Equation 6.3: Zgs = 0.00 feet (general scour) Za = 0.87 feet (anti-dune trough) Zls = 0.00 feet (controlling drop scour not applicable) Zbs = 0.66 feet (bend scour) Zlft = 1.00 feet 2.53 feet (low-flow thalweg) 1.30 3.29 feet (safety factor) (minimum recommended design scour depth) Zt = JE Fuller Hydrology and Geomorphology, Inc. Depth of Scour Flecha Caida Ranch Estates # 1 and #2 and Las Lomas de Catalina (Sections 0.11-0.21) GENERAL SCOUR Per COT Drainage Design Manual, Equation 6.4: Vm = Ymax = 7.99 fps 3.13 feet Yh = 2.06 feet Se = 0.0180 ft/ft Zgs = 0.00 feet (if a negative value is calculated, result appears as 0) ANTI-DUNE TROUGH DEPTH Per COT Drainage Design Manual, Equation 6.5: Vm = g= Za = 7.99 fps 32.20 accelaration due to gravity in ft/s 2 0.87 feet LOW-FLOW THALWEG Per COT Drainage Design Manual: Assume thalweg depth (Zlft) is 2.0 feet for regional watercourses and 1.0 feet for all other watercourses, unless field observations dictate otherwise. Zlft = 1.00 feet BEND SCOUR Per COT Drainage Design Manual, Equation 6.6: Vm = 7.99 fps Ymax = 3.13 feet Yh = 2.06 feet Se = 0.0180 ft/ft rc = T= rc/T = 350.00 feet 97.25 feet 3.60 Zbs = 0.66 feet JE Fuller Hydrology and Geomorphology, Inc. (calculated rc/T is limited to 0.5 < rc/T < 10) (using rc/T and substituting Eqn. 6.7 into Eqn. 6.6) Who The Guide Is For As a homeowner, you need clear information about the options that are available to reduce flood damage to your home – and straightforward guidance on selecting the option that is best for you. Quite often this is a difficult task. The publication described here is for readers who have little or no knowledge of flood protection methods or building construction techniques. You should take action to avoid repetitive flood damage to your house. First, you need to know what damage-reduction methods are available, the degree to which they work, how much they cost, and whether they meet your needs. All of these questions are answered by the guide. In addition, the guide explains how the degree of flood risk varies from one location to another. By knowing the basic questions to ask, you are guided towards the investment in retrofitting that is appropriate for you. Want To Learn More? FEMA-L235 Homeowner’s Guide to Retrofitting: Six Ways To Protect Your House From Flooding is FEMA publication 312. Call 1-800-737-8669 to get a copy of this important guide. For copies of other FEMA publications, including those listed below, call 1-800-480-2520. Related Publications Elevation Wet Floodproofing FEMA 55 Coastal Construction Manual FEMA 257 Mitigation of Flood and Erosion Damage Relocation Homeowner’s Guide to Retrofitting Six Ways To Protect Your House From Flooding FEMA 102 Floodproofing Non-Residential Structures Recommended for Architects and Engineers — FEMA 259 Engineering Principles and Practices for Retrofitting Flood Prone Residential Buildings State and local representatives of emergency management, emergency services, floodplain management, building code, and planning and zoning agencies may have copies of FEMA 312 for immediate distribution. Dry Floodproofing Levees and Floodwalls Demolition You can download FEMA 312, or parts of it, from FEMA’s web site – http://www.fema.gov/mit/rfit/ Some retrofitting techniques may not be used in certain circumstances under state or local laws, ordinances, or regulations. Federal Emergency Management Agency Building a Disaster Resistant Community IMPACT Mitigation Directorate Washington, DC 20472 www.fema.gov What Is “Retrofitting”? Retrofitting means making changes to an existing building to protect it from flooding or other hazards such as high winds and earthquakes. FEMA publication 312, Homeowner’s Guide to Retrofitting: Six Ways To Protect Your House From Flooding, provides information that will help you decide whether your house is a candidate for retrofitting. The guide helps by describing six retrofitting methods that protect your house from flooding. Elevation is raising your house so that the lowest floor is above the flood level. This is the most common way to avoid flood damage. Wet floodproofing makes uninhabited parts of your house resistant to flood damage when water is allowed to enter during flooding. The guide uses photographs and illustrations to help explain how each of the six retrofitting methods works. For example, this series of figures from the guide shows how a house on a basement or crawlspace foundation can be elevated above the flood level on extended foundation walls. A AFTER OPENINGS ARE MADE IN THE FOUNDATION WALLS, STEEL I-BEAMS ARE INSTALLED BELOW THE FLOOR JOISTS EXISTING FLOOR JOISTS EXISTING FLOOR TEMPORARY STEEL SUPPORT BEAMS ORIGINAL GROUND SURFACE TEMPORARY STEEL LIFTING BEAM JACK EXISTING FOUNDATION WALL OPENINGS CUT FOR I-BEAMS B THE HOUSE IS RAISED JACK RAISED ON TEMPORARY CRIBBING Relocation means moving your house to higher ground where the exposure to flooding is eliminated altogether. Dry floodproofing is sealing your house to prevent flood waters from entering. Levee and floodwall protection means constructing barriers to prevent flood waters from entering your house. Demolition means razing your house and rebuilding properly on the same property or buying a house elsewhere. C THE FOUNDATION WALLS ARE EXTENDED AS THE HOUSE IS RAISED, AND PERMANENT OPENINGS FOR FLOODWATERS ARE CREATED NEW PERMANENT OPENINGS FOR FLOODWATERS NEWLY EXTENDED FOUNDATION WALL I-BEAMS OPENINGS FILLED WITH CONCRETE BLOCK D THE FINISHED PROJECT FLOOD LEVEL DEPENDING ON FINAL HEIGHT OF EXTENDED FOUNDATION, AREA UNDER HOUSE MAY BE USED FOR PARKING, STORAGE, OR ACCESS The Next Step Whether or not your house has been damaged by flooding, contact your local floodplain administrator or building official before retrofitting. This contact is the critical next step in reducing your potential flood losses. Local officials know the retrofitting methods that meet state and local government requirements. Financial Assistance The guide provides information on government and non-government financial assistance that can help homeowners with retrofitting projects. Financial assistance means loans, grants, and insurance payments. The assistance goes to individual property owners, communities, and states. For example, under FEMA’s National Flood Insurance Program, a policy holder may qualify for Increased Cost of Compliance (ICC) coverage. If your house is substantially damaged by flooding, ICC coverage may help pay for some types of retrofitting. Other programs, such as the Hazard Mitigation Grant Program and the Flood Mitigation Assistance Program are designed to help financially. The guide describes many government and nongovernment programs, and it explains how you might qualify for assistance. Protecting Your Business From Flooding ARE YOU AT RISK? If you aren’t sure whether your business is at risk from flooding, check with your local floodplain manager, building official, city engineer, or planning and zoning administrator. They can tell you whether you are in a flood hazard area, and they also can tell you how to protect your business from flooding. WHAT YOU CAN DO Protecting your business from flooding can involve a variety of actions, from inspecting and maintaining your buildings to installing protective devices. Most of these actions, especially those that affect the structure of your buildings or their utility systems, should be carried out by qualified maintenance staff or professional contractors licensed to work in your state, county, or city. One example of flood protection is using dry floodproofing techniques to protect buildings in flood hazard areas. DRY FLOODPROOF YOUR BUILDING One way to protect a building and its contents from flood damage is to seal the building so that flood waters cannot enter. This method, referred to as “dry floodproofing,” encompasses a variety of measures (some of which are covered by separate fact sheets – see back of this sheet): • applying a waterproof coating or membrane to the exterior walls of the building • installing watertight shields over doors, windows, and other openings • anchoring the building as necessary so that it can resist floatation • installing backflow valves in sanitary and storm sewer lines • raising utility system components, machinery, and other pieces of equipment so that they are above the flood level • anchoring fuel tanks and other storage tanks to prevent flotation • installing a sump pump and foundation drain system • strengthening walls so that they can withstand the pressures of flood waters and the impacts of floodborne debris FOUNDATION UNDERPINNED TO RESIST FLOTATION LOWER PORTION OF WINDOW PERMANENTLY CLOSED WITH MASONRY SUMP PUMP WATERPROOF COATING ON WALLS REMOVABLE FLOOD SHIELD ACROSS SERVICE BAY BACKFLOW VALVE ON SANITARY SEWER LINE VULNERABLE EQUIPMENT SUSPENDED OR RAISED ABOVE FLOOD LEVEL PROPERLY ANCHORED UNDERGROUND FUEL TANK Protecting Your Business From Flooding Dry Floodproof Your Building TIPS Keep these points in mind when you dry floodproof a building: 9 Dry floodproofing is appropriate primarily for slab-on-grade buildings with concrete or solid masonry walls. Concrete and masonry are easier to seal, more resistant to flood damage, and stronger than other conventional construction materials. 9 If you dry floodproof a “substantially damaged” or “substantially improved” building (as defined by the National Flood Insurance Program regulations) or a newly constructed building, and if the building’s lowest floor (including any basement) is below the Base Flood Elevation (BFE) shown on the Flood Insurance Rate Map (FIRM) for your community, your dry floodproofing must be certified as providing protection from the BFE. To obtain this certification, you must floodproof your building to a height at least 1 foot above the BFE. Check with your local floodplain manager or building official for more information. 9 The height of your dry floodproofing should not exceed 3 feet. The pressures exerted by deeper water can cause walls to buckle or collapse. Before you use dry floodproofing to protect against greater flood depths, have a structural engineer evaluate the strength of your walls. 9 If your dry floodproofing measures require human intervention, such as placing shields over doors and windows before flood waters arrive, you should have an operations and maintenance plan that describes all the actions that must be taken and lists the persons who are responsible. It must also include a schedule of periodic maintenance that states how often the dry floodproofing measures will be inspected and who will perform the inspections. ESTIMATED COST The cost of individual dry floodproofing measures will vary with the size, condition, and use of your building; the dry floodproofing height; and the extent to which you use contractors and engineers. OTHER SOURCES OF INFORMATION Install Sewer Backflow Valves, Protecting Your Property from Flooding, FEMA Hazard Mitigation Fact Sheet, 1998 Anchor Fuel Tanks, Protecting Your Property from Flooding, FEMA Hazard Mitigation Fact Sheet, 1998 Non-Residential Floodproofing – Requirements and Certification for Buildings Located in Special Flood Hazard Areas, FEMA Technical Bulletin 3-93, April 1993 Floodproofing Non-Residential Structures, FEMA 102, 1986 To obtain copies of FEMA documents, call FEMA Publications at 1-800-480-2520. Information is also available on the World Wide Web at http//:www.fema.gov. Protecting Your Property From Flooding ARE YOU AT RISK? If you aren’t sure whether your house is at risk from flooding, check with your local floodplain manager, building official, city engineer, or planning and zoning administrator. They can tell you whether you are in a flood hazard area. Also, they usually can tell you how to protect yourself and your house and property from flooding. WHAT YOU CAN DO Flood protection can involve a variety of changes to your house and property – changes that can vary in complexity and cost. You may be able to make some types of changes yourself; however, complicated or large-scale changes and those that affect the structure of your house or its electrical wiring and plumbing should be carried out only by a professional contractor licensed to work in your state, county, or city. One example of flood protection is adding a waterproof veneer to the exterior walls of your house. This is something that only a licensed contractor should do. ADD WATERPROOF VENEER TO EXTERIOR WALLS Even in areas where flood waters are less than 2 feet deep, a house can be severely damaged if water reaches the interior. The damage to walls and floors can be expensive to repair, and the house may be uninhabitable while repairs are underway. One way to protect a house from shallow flooding is to add a waterproof veneer to the exterior walls and seal all openings, including doors, to prevent the entry of water. As shown in the figure, the veneer can consist of a layer of brick backed by a waterproof membrane. Before the veneer is applied, the siding is removed and replaced with exterior grade plywood sheathing. If necessary, the existing foundation footing is extended to support the brick. Also, because the wall will be exposed to flood water, changes are made to the interior walls as well so that they will resist moisture damage. In the area below the flood level, standard batt insulation is replaced with washable closed-cell foam insulation, and any wood blocking added inside the wall cavity is made of exterior grade lumber. EXISTING BATT INSULATION NEW BRICK VENEER WATERPROOF MEMBRANE CLOSED-CELL FOAM INSULATION EXTENDED FOOTING EXISTING FOUNDATION AND FOOTING Protecting Your Property From Flooding Add Waterproof Veneer to Exterior Walls TIPS Keep these points in mind if you plan to have a waterproof veneer added to the exterior walls of your house: 9 Adding a waterproof veneer is appropriate in areas where the flood depth is less than 2 feet. When flood depths exceed 2 feet, the pressure on waterproofed walls increases greatly, usually beyond the strength of the walls. If greater flood depths are expected, consult with a licensed civil or structural engineer before using this method. 9 Changes to the foundation of your house must be done by a licensed contractor, who will ensure that the work is done correctly and according to all applicable codes. This is important for your safety. 9 If your house is being remodeled or repaired, consider having the veneer added as part of the remodeling or repair work. It will probably be cheaper to combine these projects than to carry them out separately. 9 If your house has brick walls, you can still use this method. The new brick veneer and waterproof membrane are added over the existing brick. 9 If your house is flooded by groundwater entering through the floor, this method will not be effective. ESTIMATED COST If you have a contractor add a waterproof brick veneer to your house, you can expect to pay about $10 per square foot of exterior wall. For example, a 3-foot-high brick veneer on a house measuring 60 feet by 30 feet would cover about 540 square feet and would cost about $5,400. This figure does not include the cost of sealing doors and other openings or extending the foundation. OTHER SOURCES OF INFORMATION Protecting Your Home from Flooding, FEMA, 1994 Repairing Your Flooded Home, FEMA-234, 1992 Flood Emergency and Residential Repair Handbook, FIA-13, 1986 Retrofitting Flood-Prone Residential Structures, FEMA-114, 1986 To obtain copies of these and other FEMA documents, call FEMA Publications at 1-800-480-2520. Information is also available on the World Wide Web at http//:www.fema.gov. Protecting Your Property From Flooding ARE YOU AT RISK? If you aren’t sure whether your house is at risk from flooding, check with your local floodplain manager, building official, city engineer, or planning and zoning administrator. They can tell you whether you are in a flood hazard area. Also, they usually can tell you how to protect yourself and your house and property from flooding. WHAT YOU CAN DO Flood protection can involve a variety of changes to your house and property – changes that can vary in complexity and cost. You may be able to make some types of changes yourself; however, complicated or large-scale changes and those that affect the structure of your house or its electrical wiring and plumbing should be carried out only by a professional contractor licensed to work in your state, county, or city. One example of flood protection is raising the components of your electrical system above the level of the 100-year flood. This is something that only a licensed contractor should do. RAISE ELECTRICAL SYSTEM COMPONENTS Electrical system components, including service panels (fuse and circuit breaker boxes), meters, switches, and outlets, are easily damaged by flood water. If they are inundated for even short periods, they will probably have to be replaced. Another serious problem is the potential for fires caused by short circuits in flooded systems. Raising electrical system components helps you avoid those problems. Also, having an undamaged, operating electrical system after a flood will help you clean up, make repairs, and return to your home with fewer delays. As shown in the figure, all components of the electrical system, including the wiring, should be raised at least 1 foot above the 100-year flood level. In an existing house, this work will require the removal of some interior wall sheathing (drywall, for example). If you are repairing a flood-damaged house or building a new house, elevating the electrical system will be easier. RAISED OUTLETS RAISED SWITCH RAISED WIRING 100-YEAR FLOOD LEVEL RAISED METER RAISED MAIN SERVICE PANEL DASHED LINES SHOW PREVIOUS LOCATIONS (BELOW FLOOD LEVEL) Protecting Your Property From Flooding Raise Electrical System Components TIPS Keep these points in mind when you have your electrical system components raised: 9 Electrical system modifications must be done by a licensed contractor, who will ensure that the work is done correctly and according to all applicable codes. This is important for your safety. 9 Your contractor should check with the local power company about the maximum height that the electric meter can be raised. 9 If your house is equipped with an old-style fuse box or low-amperage service, you may want to consider upgrading to a modern circuit breaker system and higher-amperage service, especially if you have large appliances or other electrical equipment that draws a lot of power. ESTIMATED COST Raising the electrical service panel, meter, and all of the outlets, switches, and wiring in a 1,000square-foot, single-floor house will cost about $1,500 to $2,000. If this work is performed during the repair of a damaged house or construction of a new house, the cost may be much lower. OTHER SOURCES OF INFORMATION Protecting Your Home from Flooding, FEMA, 1994 Repairing Your Flooded Home, FEMA-234, 1992 Flood Emergency and Residential Repair Handbook, FIA-13, 1986 Retrofitting Flood-Prone Residential Structures, FEMA-114, 1986 To obtain copies of these and other FEMA documents, call FEMA Publications at 1-800-480-2520. Information is also available on the World Wide Web at http//:www.fema.gov. Protecting Your Property From Flooding ARE YOU AT RISK? If you aren’t sure whether your house is at risk from flooding, check with your local floodplain manager, building official, city engineer, or planning and zoning administrator. They can tell you whether you are in a flood hazard area. Also, they usually can tell you how to protect yourself and your house and property from flooding. WHAT YOU CAN DO Flood protection can involve a variety of changes to your house and property – changes that can vary in complexity and cost. You may be able to make some types of changes yourself; however, complicated or large-scale changes and those that affect the structure of your house or its electrical wiring and plumbing should be carried out only by a professional contractor licensed to work in your state, county, or city. One example of flood protection is raising the heating, ventilating, and cooling equipment in your house so that it is above the flood level, or surrounding it with a flood wall. These are things that only a licensed contractor should do. RAISE OR FLOODPROOF HVAC EQUIPMENT Heating, ventilating, and cooling (HVAC) equipment, such as a furnace or hot water heater, can be damaged extensively if it is inundated by flood waters. The amount of damage will depend partly on the depth of flooding and the amount of time the equipment remains under water. Often, the damage is so great that the only solution is replacement. In floodprone houses, a good way to protect HVAC equipment is to move it from the basement or lower level of the house to an upper floor or even to the attic. A less desirable method is to leave the equipment where it is and build a concrete or masonry block floodwall around it. Both of these methods require the skills of a professional contractor. Relocation can involve plumbing and electrical changes, and floodwalls must be adequately designed and constructed so that they are strong enough and high enough to provide the necessary level of protection. HVAC COMPONENTS RAISED TO SECOND FLOOR OR ATTIC CONCRETE FLOODWALL AROUND HVAC COMPONENTS BELOW FLOOD LEVEL 100-YEAR FLOOD LEVEL Protecting Your Property From Flooding Raise or Floodproof HVAC Equipment TIPS Keep these points in mind when you have your HVAC equipment raised or floodproofed: 9 Changes to the plumbing, electrical system, and ventilating ductwork in your house must be done by a licensed contractor, who will ensure that the work is done correctly and according to all applicable codes. This is important for your safety. 9 If you are having your existing furnace or hot water heater repaired or replaced, consider having it relocated at the same time. It will probably be cheaper to combine these projects than to carry them out at different times. 9 Similarly, if you have decided to raise your HVAC equipment, consider upgrading to a more energy-efficient unit at the same time. Upgrading can not only save you money on your heating and cooling bills, it may also make you eligible for a rebate from your utility companies. 9 If you decide to protect your HVAC equipment with a floodwall, remember that you will need enough space in the enclosed area for system repairs and routine maintenance. Also, depending on its height, the wall may have to be equipped with an opening that provides access to the enclosed area. Any opening will have to be equipped with a gate that can be closed to prevent flood waters from entering. ESTIMATED COST Having your furnace and hot water heater moved to a higher floor or to the attic will cost about $ 1,500. The cost of a floodwall will depend partly on its height and length. A 3-foot-high wall with a perimeter length of 35 feet would cost about $1,000. OTHER SOURCES OF INFORMATION Protecting Your Home from Flooding, FEMA, 1994 Repairing Your Flooded Home, FEMA-234, 1992 Flood Emergency and Residential Repair Handbook, FIA-13, 1986 Retrofitting Flood-Prone Residential Structures, FEMA-114, 1986 To obtain copies of these and other FEMA documents, call FEMA Publications at 1-800-480-2520. Information is also available on the World Wide Web at http//:www.fema.gov. Protecting Your Property From Flooding ARE YOU AT RISK? If you aren’t sure whether your house is at risk from flooding, check with your local floodplain manager, building official, city engineer, or planning and zoning administrator. They can tell you whether you are in a flood hazard area. Also, they usually can tell you how to protect yourself and your house and property from flooding. WHAT YOU CAN DO Flood protection can involve a variety of changes to your house and property – changes that can vary in complexity and cost. You may be able to make some types of changes yourself; however, complicated or large-scale changes and those that affect the structure of your house or its electrical wiring and plumbing should be carried out only by a professional contractor licensed to work in your state, county, or city. One example of flood protection is installing a backflow valve to prevent sewage from backing up into your house. This is something that only a licensed plumber or contractor should do. INSTALL SEWER BACKFLOW VALVES TYPICAL INSTALLATION OF AN EXTERIOR BACKFLOW VALVE In some floodprone areas, flooding can cause sewage from sanitary sewer lines to back up into houses through drain pipes. These backups not only cause damage that is difficult to repair, but also create health hazards. A good way to protect your house from sewage backups is to install backflow valves, which are designed to block drain pipes temporarily and prevent flow into the house. Backflow valves are available in a variety of designs that range from the simple to the complex. The figure shows a gate valve, one of the more complex designs. It provides a strong seal, but must be operated by hand. So the effectiveness of a gate valve will depend on how much warning you have of impending flooding. Among the simpler valves are a flap or check valves, which open to allow flow out of the house but close when the flow reverses. These valves operate automatically but do not provide as strong a seal as a gate valve. BACKFLOW VALVE PIT BACKFLOW VALVE Í NORMAL DIRECTION OF FLOW (VALVE PREVENTS FLOW IN REVERSE DIRECTION) Protecting Your Property From Flooding Install Sewer Backflow Valves TIPS Keep these points in mind if you have backflow valves installed: 9 Changes to the plumbing in your house must be done by a licensed plumber or contractor, who will ensure that the work is done correctly and according to all applicable codes. This is important for your safety. 9 Some valves incorporate the advantages of both flap and gate valves into a single design. Your plumber or contractor can advise you on the relative advantages and disadvantages of the various types of backflow valves. 9 Valves should be installed on all pipes that leave the house or that are connected to equipment that is below the potential flood level. So valves may be needed on washing machine drain lines, laundry sinks, fuel oil lines, rain downspouts, and sump pumps, as well as sewer/septic connections. 9 If you have a sump pump, it may be connected to underground drain lines, which may be difficult to seal off. ESTIMATED COST Having a plumber or contractor install one backflow valve will cost you about $525 for a combined gate/flap valve or about $375 for a flap valve. These figures include the cost of excavation and backfilling. OTHER SOURCES OF INFORMATION Protecting Your Home from Flooding, FEMA, 1994 Repairing Your Flooded Home, FEMA-234, 1992 Flood Emergency and Residential Repair Handbook, FIA-13, 1986 Retrofitting Flood-Prone Residential Structures, FEMA-114, 1986 To obtain copies of these and other FEMA documents, call FEMA Publications at 1-800-480-2520. Information is also available on the World Wide Web at http//:www.fema.gov. Flood-Resistant Materials Requirements for Buildings Located in Special Flood Hazard Areas in accordance with the National Flood Insurance Program F EDERAL E MERGENCY M ANAGEMENT A GENCY F EDERAL I NSURANCE A DMINISTRATION FIA-TB-2 4/93 Key Word/Subject index: This index allows the user to quickly locate key words and subjects in this Technical Bulletin. The Technical Bulletin User’s Guide (printed separately) provides references to key words and subjects throughout the Technical Bulletins. For definitions of selected terms, refer to the Glossary at the end of this bulletin. Key Word/Subject Breakaway wall materials in V zones, made of flood-resistant materials Page 12 Flood-resistant flooring materials 4 Flood-resistant material, definition of 1 Flood-resistant materials, classifications, use of 2 Flood-resistant wall and ceiling materials 7 Latticework in V zones, made of flood-resistant materials U.S. Army Corps of Engineers “Flood Proofing Regulations” 12 2 Any comments on the Technical Bulletins should be directed to: FEMA/FIA Office of Loss Reduction Technical Standards Division 500 C St., SW, Room 417 Washington, D.C. 20472 Technical Bulletin 2-93 replaces Technical Bulletin 88-2 (draft) “Flood-Resistant Materials.” Graphic design based on the Japanese print The Great Wave Off Kanagawa, by Katsushika Hokusai [1 7601849), Asiatic collection, Museum of Fine Arts, Boston. TECHNICAL BULLETIN 2-93 Flood-Resistant Materials Requirements for Buildings Located In Special Flood Hazard Areas in accordance with the National Flood Insurance Program Introduction The requirement to use construction and finishing materials that are resistant to flood damage in all new and substantially improved buildings in identified Special Flood Hazard Areas (SFHAs) is an important part of the National Flood Insurance Program’s (NFIP’s) flood-damage-resistant design and construction standards. A residential building’s lowest floor is required to be elevated to or above the base flood elevation (BFE). All construction below the lowest floor is susceptible to flooding and must consist of flood-resistant materials. Uses of enclosed areas below the lowest floor in a residential building are limited to parking, building access, and limited storage—areas that can withstand inundation by floodwater without sustaining significant structural damage. The purpose of this Technical Bulletin is to provide data and guidance on what constitute “materials resistant to flood damage” and how and when these materials must be used to improve a building’s ability to withstand flooding. NFIP Regulations Section 60.3(a)(3) of the NFIP regulations requires that the community: “Review all permit applications to determine whether proposed building sites will be reasonably safe from flooding. If a proposed building site is in a floodprone area, all new construction and substantial improvements shall... be constructed with materials resistant to flood damage...” It should be noted that Technical Bulletins provide guidance on the minimum requirements of the NFIP regulations. Community or State requirements that exceed those of the NFIP take precedence. Design professionals should contact the community to determine whether more restrictive local or State regulations apply to the building or site in question. All applicable standards of the State or local building code must also be met for any building in a flood hazard area. Required Use of Flood-Resistant Materials Flood-Resistant Material “Flood-resistant material” is defined as any building material capable of withstanding direct and prolonged contact with floodwaters without sustaining significant damage. The term “prolonged contact” means at least 72 hours, and the term “significant damage” means any damage requiring more than low-cost cosmetic repair (such as painting). 1 As stated previously, all structural and non-structural building materials at or below the BFE must be flood resistant. This requirement applies regardless of the expected or historic flood duration. For example, buildings in coastal areas that experience relatively short-duration flooding (generally, flooding with a duration of less than 24 hours) must be constructed with flood-resistant materials below the BFE. As noted in the tables within this bulletin, only Class 4 and Class 5 materials are acceptable for areas below the BFE in floodprone buildings. In some instances, Class 1,2, and 3 materials may be permitted below the BFE, when specifically required to meet local building code provisions concerning life-safety issues. In belowBFE applications, materials that meet life-safety code requirements and have maximum resistance to damage from flood inundation should be used. This applies to the flood-resistant requirements only. In Zones V, VE, and V 1 -V30, the installation of such materials may create an obstruction. Because obstructions in V zones could result in structural failure of the building, they represent a life-safety issue and shall therefore take precedence over local building codes. Refer to Technical Bulletin 5, “Free of Obstruction Requirements,” for further information. Lowest Floor Under the NFIP, the term “lowest floor” is used to define the lowest level of a building that must be located at or above the BFE as required under Sections 60.3(c)(2) and (3) of the NFIP regulations. The floodplain management regulations, under Section 60.3(c)(5), limit the use of all areas below the lowest floor to parking of vehicles, storage, and building access. These reasonable uses below the BFE are permitted because the amount of damage caused by flooding to these areas can easily be kept to a minimum if design and construction requirements contained in the NFIP regulations are met. Failure to meet the requirements can increase the building’s damage potential and result in the application of higher flood insurance premiums. The requirement to use flood-resistant materials means that all interior wall, floor, and ceiling materials located below the BFE be unfinished and resistant to flood damage. This is meant to exclude the use of materials and finishes normally associated with living areas constructed above the BFE. Flood Insurance Implication An NFIP flood insurance requirement regarding the use of materials in areas below the BFE must also be considered. Flood insurance will not pay a claim for finishing materials (such as clay floor tiles) located in basements or in enclosed areas below the lowest floor of an elevated building, even if such materials are considered to be flood resistant. The NFIP defines finishing materials as anything beyond basic wall construction. Flood-Resistant Classification of Materials The information in this Technical Bulletin is based primarily on the U.S. Army Corps of Engineers (COE) 1992 “Flood Proofing Regulations. ” The following table (Table 1) classifies building materials according to their ability to resist flood damage. 2 Table 1 Flood-Resistant Classification of Materials N F I Class Class Description P A c 5 Highly resistant to floodwater damage. Materials within this class are permitted for partially enclosed or outside uses with essentially unmitigated flood exposure. 4 Resistant to floodwater damage. Materials within this class may be exposed to and/or submerged in floodwaters in interior spaces and do not require special waterproofing protection. 3 Resistant to clean water damage. Materials within this class may be submerged in clean water during periods of intentional flooding. 2 Not resistant to water damage. Materials within this class require essentially dry spaces that may be subject to water vapor and slight seepage. 1 Not resistant to water damage. Materials within this class require conditions of dryness. c E P T A B L E u N A c c E P T A B L E Source: COE 1992 “Floodproofing Regulations” 3 Flooring Materials Table 2 lists flooring materials commonly used in construction that fall within the five classes described in Table 1. Not all available construction and finishing materials are listed. For products not listed herein, manufacturers’ literature should be reviewed for recommended uses. Such recommendations must be complied with fully. All masonry and wood products used in floodprone buildings must comply with the applicable materials standards of the nationally recognized standards organizations, such as the American Society for Testing and Materials (ASTM), the American Concrete Institute (ACI), and the American Wood Products Association (AWPA). Basis for Classification of Flooring Materials The classification of flooring materials is based on their vulnerability to damage from inundation by floodwaters. Class 1,2, and 3 flooring materials are not acceptable for below-BFE applications for one or more of the following reasons: ● Normal suspended-floor adhesives specified for above-grade use are water soluble or are not resistant to alkali or acid in water, including ground seepage and vapor. ● Flooring materials contain wood and wood products. ● Flooring materials are not resistant to alkali or acid in water, ● Sheet-type floor coverings (linoleum, rubber, and vinyl) restrict evaporation from below. ● Flooring materials are impervious but dimensionally unstable. 4 I Table 2 Flooring Materials Classifications for Flood Resistance Classes of Flooring Acceptable Types of Flooring Materials 5 4 Unacceptable 3 2 1 ● Asphalt Tile1 ● With asphaltic adhesives ● Carpeting (glued down type) Cement/bituminous, formed-in-place ● Cement/latex, formed-in-place ● ● Ceramic tile1 ● With acid-and alkali-resistant grout ● Chipboard Clay tile ● Concrete, precast or in-situ ● Concrete tile ● Cork ● Enamel felt-base floor coverings ● ● Epoxy, formed-in-place Linoleum ● Magnesite (magnesium oxychloride) ● Mastic felt-base floor covering ● Mastic flooring, formed-in-place ● Polyurethane, formed-in-place ● PVA emulsion cement ● Rubber sheets1 ● With chemical-set adhesives ● 2,3 ● Rubber tile1 ● With chemical-set adhesives ● Silicone floor, formed-in-place 5 Table 2 Flooring Materials Classifications for Flood Resistance Classes of Flooring Acceptable Types of Flooring Materials 5 4 Unacceptable 3 2 1 ● Terrazo Vinyl sheets (homogeneous) With chemical-set adhesives Vinyl tile (homogeneous) ● 1 ● 2,3 ● 1 ● With chemical-set adhesives Vinyl tile or sheets (coated on cork or wood ● product backings) Vinyl-asbestos tile (semi-flexible vinyl) ● 1 ● With asphaltic adhesives ● Wood flooring or underlay merits ● Wood composition blocks, laid in cement mortar Wood composition blocks, dipped and laid in ● hot pitch or bitumen Pressure-treated lumber, .40 CCA4 ● Naturally decay-resistant lumber 4,5 ● Notes: 1 Using normally specified suspended flooring (i.e., abovegrade) adhesives, including sulfite liquor (Iignin or “linoleum paste”), rubber/asphaltic dispersions, or “alcohol” type resinous adhesives (culmar, oleoresin) 2 Not permitted as Class 2 flooring 3 E.g., epoxy-polyamide adhesives or latex-hydraulic cement 4 Not in the COE list; added by FEMA 5 Refer to local building code for guidance 6 Wall and Ceiling Materials Table 3 lists wall and ceiling materials commonly used in construction that fall within the five classes described in Table 1. Not all available construction and finishing materials are listed. For products not listed herein, manufacturers’ literature should be reviewed for recommended uses. Such recommendations must be complied with fully. All masonry and wood products used in floodprone buildings must comply with the applicable materials standards of the nationally recognized standards organizations, such as the American Society for Testing and Materials (ASTM), the American Concrete Institute (ACI), and the American Wood Products Association (AWPA). Basis for Classification of Wall and Ceiling Materials The classification of wall and ceiling materials is based on their vulnerability to damage from inundation by floodwaters. Class 1, 2, and 3 wall and ceiling materials are not acceptable for below-BFE applications for one or more of the following reasons: ● ● Normal adhesives specified for above-grade use are water soluble or are not resistant to alkali or acid in water, including ground seepage and vapor. Wall and ceiling material contains wood, wood products, gypsum products, or other material that dissolves or deteriorates, loses structural integrity, or is adversely affected by water. ● Wall or ceiling material is not resistant to alkali or acid in water. ● Wall or ceiling material is impervious but is dimensionally unstable. ● Wall or ceiling materials absorb or retain water excessively after submergence. 7 Table 3 Walls and Ceiling Materials Classifications for Flood Resistance Classes of Walls and Ceilings Types of Wall and Ceiling Materials Acceptable 4 5 Asbestos-cement board (and cement board1) ● Brick, face or glazed ● Unacceptable 3 2 1 ● Common ....... ..................... . ......................... . . . . . . . .... . . . . . . . . . . . . . . . . . . . . . . . . . . . ......... Cabinets, built-in ● Wood ● Metal ● Cast stone (in waterproof mortar) . ... .. ... .. ... .. ... .. ... .. ... .. ... .. .. . . . . . ....... . Chalkboards . ● Slate, porcelain glass, nucite glass Cement-asbestos ● Composition, painted ● ● Chipboard ● Exterior sheathing grade .............. Clay tile . . ’. . . . . . . ● Structural glazed ● Ceramic veneer, ceramic wall tile-mortar set ● Ceramic veneer, organic adhesives Concrete ● Concrete block ● ● Corkboard ... Doors Wood hollow ● Wood, lightweight panel construction ● Wood, solid ● ● Metal, hollow ● Metal, Kalamein 8 Table 3 Walls and Ceiling Materials Classifications for Flood Resistance ] Classes of Walls and Ceilings Types of Wall and Ceiling Materials Acceptable I 5 4 . ... .. .. ..... .. .. ... .. .. ..... .. .. ... .. .. . . . ,..:.:.,. ,. :. , , , ,. ,.,.,.:.:.:., ........... Fiberboard panels, vegetable types Unacceptable; 3 2 1 ● Sheathing grade (asphalt coated or impregnated) ● Otherwise Gypsum products ● Gypsum board (including greenboard1 ) ● Keene’s cement of plaster ● Plaster, otherwise, including acoustical ● Sheathing panels, exterior grade ● Glass (sheets, colored tiles, panels) ● Batt or blanket types ● All other types Metals, non-ferrous (aluminum, copper, or zinc tiles) ● Set in water-soluble adhesives I 9 Table 3 Walls and Ceiling Materials Classifications for Flood Resistance Classes of Walls and Ceilings Types of Wall and Ceiling Materials Acceptable 5 4 Unacceptable 3 2 1 ............. Paint Polyester-epoxy and other waterproof types ● All other types Paperboard Partitions, folding ● . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ,.’. . .’.’.’.. .. .. ... .. .. .. .. ... .. .. . . . . . Wood, pressure treated, .40 CCA minimum 1 (if not treated, then material is Class 2) ● ● Metal ● Fabric-covered ....... ........... Partitions, stationary .. . . ... . . ... . . . .. . . . ... . . ... . . . Wood, pressure treated, .40 CCA minimum 1 (if not treated, then material is Class 2) ● Metal ● Glass, unreinforced ● Glass, reinforced ● ● Gypsum, solid or block Rubber, moldings and trim with epoxy polyamide ● adhesive or latex-hydraulic cement ● All other applications Steel, (paneIs, trim, tile) with waterproof applications ● ● With non-waterproof adhesive Stone, natural solid or veneer, waterproof grout ● Stone, artificial non-absorbent solid or veneer, waterproof grout All other applications ● ● Table 3 Walls and Ceiling Materials Classifications for Flood Resistance Classes of Walls and Ceilings Types of Wall and Ceiling Materials Acceptable 5 4 ..... Strawboard unacceptable 3 2 . . . . . . . . . . . . . . . . ........... Exterior grade (asphalt-impregnated kraft paper) ● All other types ● . . .... .. .. .. .. .. .. .. .. .. .. .. . . . . . . . . .’. . . . . Wall covering 1 . . . . . . . . . . . . , . . . . . . . . . . . . . .:.:. Paper, burlap, cloth types Wood ● Solid, standard Solid, naturally decay-resistant1,2 ● Solid pressure treated, .40 CCA minimum1 ● Plywood Marine Grade1 ● Pressure treated, .40 CCA minimum1 ● ● Exterior grade ● Otherwise Note: 1 Not on the COE list; added by FEMA 2 Refer to local building code for guidance Construction Examples Flood-Resistant Materials in Buildings in Zones A, AE, A1-A30, AR, AO, and AH Figure 1 illustrates a building elevated on solid foundation walls, over a crawlspace. The NFIP regulations require that the lowest floor be at or above the BFE. The construction method illustrated in Figure 1 meets this requirement. Note, however, that the flooring materials and supporting wood members are at or below the BFE. Therefore, in Figure 1, all materials supporting the lowest floor, including the flooring itself, must be made of flood-resistant materials. To maximize the use of the area below the lowest floor, it is a common floodplain construction technique to elevate a building a full story (approximately 8 feet), even though the BFE may only be 4 or 5 feet above grade. In such cases, while the NFIP regulations require that Class 4 or 5 building materials be used below the BFE, FEMA strongly recommends that Class 4 or Class 5 materials also be used for the construction of the remainder of the building below the lowest floor. Flood damage from a greater-than-design flood event will thereby be reduced in the lower area. Flood-Resistant Materials in Buildings in Zones V, VE, and V1-V30 All structural and non-structural materials installed below the BFE must be flood resistant . The NFIP regulations require that the bottom of the lowest horizontal structural member of the lowest floor (usually the floor beam or girder) of a building in Zone V, VE, or VlV30 be at or above the BFE. Therefore, all materials below the floor beam(s) must be flood resistant. This includes but is not limited to breakaway wall materials and open latticework. Breakaway walls will remain in place during low-level floods and must be flood resistant, so that they will not deteriorate over time after being soaked by floodwaters. Figure 2, on the next page, illustrates this requirement. Flooring lowest Floor BFE Floor Joists Sub Floor Sill Plate Foundation Wall Foundation Opening Figure 1. Building Elevated on Solid Foundation Walls Meeting the Minimum NFIP Requirements for Zones A, AE, A1-A30, AR, AO, and AH 12 Bottom of the lowest horizontal structural rnernber of the lowest floor I I II II II II II II II II I I ● D . I I I I I . SECTION ELEVATION Figure2. Flood-Resistant Material Requirements for Buildings Elevated in Accordance with NFIP Requirements for Zones V, VE, and V1 -V30 Accessory Buildings Some communities permit the construction of low-cost, small detached accessory buildings (e.g., garages, storage sheds) with a lowest floor elevation below the BFE (Technical Bulletin 5, “Freeof-Obstruction Requirements,” provides definitions of “low-cost” and “small”). The below-BFE portions of such buildings must be constructed of flood-resistant materials so that flood damage will be minimized. Additional construction requirements for these buildings, such as the need to anchor the building to resist flotation, collapse, and lateral movement, also must be met before the building is permitted and built. For additional information about these requirements, contact the community that has permitting jurisdiction. Wet FloodproofIng Wet floodproofing is designing a building to allow floodwaters to enter in order to equalize hydrostatic forces. The NFIP does not allow wet floodproofing in lieu of meeting the lowest 13 floor elevation requirements. However, in situations where the NFIP regulations do not apply, such as voluntary floodproofing of an existing (Pre-FIRM) building not in association with substantial improvements, the use of flood-resistant materials is advisable. Using flood-resistant materials will make cleanup and repair following a flood much easier and less costly than if the floodprone areas are constructed of non-flood-resistant materials. The NFIP The NFIP was created by Congress in 1968 to provide federally backed flood insurance coverage, because flood insurance was generally unavailable from private insurance companies. The NFIP is also intended to reduce future flood losses by identifying floodprone areas and ensuring that new development in these areas is adequately protected from flood damage. The NFIP is based on an agreement between the federal government and participating communities that have been identified as floodprone. FEMA, through the Federal Insurance Administration (FIA), makes flood insurance available to the residents of a participating community provided that the community adopts and enforces adequate floodplain management regulations that meet the minimum NFIP requirements. The NFIP encourages communities to adopt floodplain management ordinances that exceed the minimum NFIP criteria. Included in the NFIP requirements, found under Title 44 of the U.S. Code of the Federal Regulations, are minimum building design and construction standards for buildings located in SFHAS. Through their floodplain management ordinances, communities adopt the NFIP design performance standards for new and substantially improved buildings located in floodprone areas identified on FIA’s FIRMs. Technical Bulletins This is one of a series of Technical Bulletins FEMA has produced to provide guidance concerning the building performance standards of the NFIP. These standards are contained in Title 44 of the U.S. Code of Federal Regulations at Section 60.3. The bulletins are intended for use primarily by State and local officials responsible for interpreting and enforcing NFIP regulations and by members of the development community, such as design professionals and builders. New bulletins, as well as updates of existing bulletins, are issued periodically, as necessary. The bulletins do not create regulations; rather they provide specific guidance for complying with the minimum requirements of existing NFIP regulations. Users of the Technical Bulletins who need additional guidance concerning NFIP regulatory requirements should contact the Natural Hazards Branch of the appropriate FEMA regional office. The “User’s Guide to Technical Bulletins” lists the bulletins issued to date and provides a key word/subject index for the entire series. Ordering Information Copies of the Technical Bulletins can be obtained from the appropriate FEMA regional office. Technical Bulletins can also be ordered from the FEMA publications warehouse. Use of FEMA Form 60-8 will result in a more timely delivery from the warehouse — the form can be obtained from FEMA regional offices and your state’s Office of Emergency Management. Send publication requests to FEMA Publications, P,O. Box 70274, Washington, D.C. 20024. 14 Further Information The following publications provide further information concerning the use of flood-resistant materials: 1. “Answers to Questions About Substantially Damaged Buildings,” FEMA, May 1991, FEMA-213. 2. “Floodproofing Non-Residential Structures,” FEMA, May 1986, FEMA- 102. 3. “Flood Proofing Regulations”, Chapters 9 and 10, U.S. Army Corps of Engineers, March 1992, EP 1165-2-314. 4. “Flood Proofing Systems and Techniques,” U.S. Army Corps of Engineers, December, 1984. 5. “Repairing Your Flooded Home,” FEMA and the American Red Cross, August 1992, FEMA-234, ARC 4477. 6. “Technical Notes for Brick Construction,’’Brick Institute of America, McLean, Virginia, n.d. Glossary Base flood — The flood that has a 1-percent probability of being equaled or exceeded in any given year (also referred to as the 100-year flood). Base Flood Elevation (BFE) — The height of the base flood, usually in feet, in relation to the National Geodetic Vertical Datum of 1929 or other datum as specified. Basement — Any area of a building having its floor subgrade (below ground level) on all sides. Coastal High Hazard Area — An area of special flood hazard extending from offshore to the inland limit of a primary frontal dune along an open coast and any other area subject to highvelocity wave action from storms or seismic sources. Federal Emergency Management Agency (FEMA) — The independent federal agency that, in addition to carrying out other activities, oversees the administration of the National Flood Insurance Program. Federal Insurance Administration (FIA) — The component of FEMA directly responsible for administering the National Flood Insurance Program. Flood Insurance Rate Map (FIRM) — The insurance and floodplain management map issued by FEMA that identifies, on the basis of detailed or approximate analyses, areas of 100- year flood hazard in a community. Floodprone area — Any land area susceptible to being inundated by floodwater from any source. 15 Lowest floor — The lowest floor of the lowest enclosed area of a building, including a basement. Any NFIP-compliant unfinished or flood-resistant enclosure useable solely for parking of vehicles, building access, or storage (in an area other than a basement) is not considered a building’s lowest floor. Special Flood Hazard Area (SFHA) — Area delineated on a Flood Insurance Rate Map as being subject to inundation by the base flood and designated as Zone A, AE, A1-A30, AR, AO, AH, V, VE, or V1-V30. Substantial damage — Damage of any origin sustained by a structure whereby the cost of restoring the structure to its before-damaged condition would equal or exceed 50 percent of the market value of the structure before the damage occurred. Substantial improvement — Any reconstruction, rehabilitation, addition, or other improvement of a structure, the cost of which equals or exceeds 50 percent of the market value of the structure before the “start of construction” of the improvement. This term includes structures that have incurred “substantial damage,” regardless of the actual repair work performed. 16