Consultants USA, Inc. July 24, 1997 Tim Morrison, P.E. Supervisor, Floodplain Management Section Pima County Department of Transportation and Flood Control District 201 N. Stone, 4th Floor Tucson, Arizona 85701 RE: EXISTING CONDITIONS DRAINAGE ASSESSMENT FOR NEW TUCSON UNITS 26, 28,29 AND 30, EROSION HAZARD SETBACK MAP ICON JOB #GEDA952 Dear Mr. Morrison: Enclosed with this letter is a copy of the map that contains the erosion hazard setback as you requested . Should you have any questions, please feel free to call us at (520) 798-1 714. Very truly yours, ICON Consultants USA, Inc. ~Artr)ac:M---Eiizab~ ~acias Hydrologist lM:do MORRIS06.1tr EXISTING CONDITIONS DRAINAGE ASSESSMENT FOR NEW TUCSON UNITS 26, 28, 29 & 30 BK. BK. BK. BK. 17 17 17 17 PG. PG. PG. PG. 34 56 85 86 VOLUME I TEXT Prepared for: MR. MOSHE GEDALIA, et al 3936 HILTON HEAD WAY TARZANA, CA 91356 (818) 705-6696 . Prepared By: ICON CONSULTANTS USA, INC. 1870 W . PRINCE ROAD, SUITE 11 TUCSON, ARIZONA 85705 (520) 888-0422 ..:lh2 GlDA9S02.rpl Preliminary • Not for ~onstruction or Recording TABLE OF CONTENTS 1. INTRO DUCTIO N .... .. . .. . .... .. . ... ... ..... . . ... . . . ...... .. 1 1.1 1.2 Project Locati on .. . .. ... . . .. .. .. . . . . . ... . ... .. ... . . .. . .. 1 Project Description . .... . ... .. .......... ........ .. . . . .... 1 2. O BJECTIVES 3. WATERSHED DESCRIPTI ON ..... . ......... . ........ . . . . . . ... .. . 4 3.1 3.2 3.3 3.4 4. O verall Descriptions & Characteristics .... Upstream Conditions ......... . . . .. . . Site Features . . ......... . ... . .... . . Historical Information ... .. ... . .. . . . . ... .. . .. . .. . . . . . . . . . . . . . . . . . . . ... ........ . .. . .. .. ..... . . .. . . . .. . .... . . . .. . .... ...... 4 4 7 7 PROCEDURES .. . . . . ... .. ............. . . . . . .... . .......... . . 8 4. 1 4.2 5. .... .. ......... . .............. ..... ....... . . .. . 3 Hydrologic M ethod ... .. . .... .. .. .. . . . ... . . . ........... . . 8 Hydraulic M ethod ... .. . ........... . . . . . . ........... . ... 8 HYDROLOGIC FINDINGS ........ . ......... .. ..... ... ... . . . .. . 9 5. 1 5.2 Watershed Descripti on ... . ........ . . . . . . . . . . ... . . . . . . . . .. 9 Peak Di scharge Summary . . ... .. . ... . . . . . . . . . ......... .. . . 9 6. CONCLUSION S .... .. ... .. ... . .... . ... . . . . . . . . . .. . ...... . .. 11 7. REFERENCES . .... . . ..... . .. . ... . .. . .. ............ ...... . . . 12 ... ... LIST OF EXHIBITS ... Location Map ................................................... 2 ... Aerial Photo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 ... Offsite Watersheds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 .. .. . .. .. . - - RB:Ih2 G£0A9502.r)JI ii ... 1. ... INTRODUCTION 1 .1 .. . .. This report is being submitted as a description of drainage conditions for the proposed development of portions of the New Tucson Subdivision Units #26, #28, #29, and #30 (Bk. 17 Pg. 34, Bk. 17 Pg.56, Bk. 17 Pg. 85, Bk. 17 Pg. 86) located in the south 1/2 of Sections 9 and 10, Township 17 South, Range 16 East, Gila and Salt River Meridian, Pima County, Arizona. Lots actually owned by our client are limited in number, however, all four units were analyzed in their entirety in order to properly map floodplains . These units are bordered by Broadview Drive and Calle Agassiz to the north, Davidson Road to the east, Sahuarita Road to the south, and on the west by Wentworth Road (please refer to Location Map). This property is dissected by several watercourses which flow northwesterly through the units and are tributary to the Flato, Cuprite, and Fagan Washes which confluence with the Lee Moore Wash along Interstate 19. .. . 1.2 .. ...' . .. .. Project Description Existing zoning on the site is CR-1. These units are proposed to be developed as single family lots in conformance with the recorded approved plats. The street and lot layout for these four units was platted in 1964. The layout largely conforms to the existing drainage patterns and no drainage improvements are proposed at this time . . . .. Project Location RB:Ih2 GEDA9502.rl>f METRO PO LITAN TUCSON ARTERIAL STREETS . 0 1 z • - -- 3 ......... • -- ' _ • • ---- HW! IcON ..,..,.,. ... - ,.q- nJCQ,-- ICON CONSULTANTS USA. INC. 1111 .. (102) - 2 2 ' ""' (102) --3121 LOCATION MAP ~-. · --:- - ... .. 2. OBJECTIVES The objectives of this report are to document the hydrologic and hydraulic assessment of the site and its characteristics. Specifically, this report is intended to document on-site and off-site hydrologic characteristics, quantify existing conditions peak discharges, and define the limits of 100-year on-site floodplains. .. This study has been conducted in accordance with the guidelines of the "Hydrology Manual for Engineering Design and Floodplain Management within Pima County, Arizona, September 1979". The format of this report has been reduced to include only that information necessary for floodplain delineations . r .. ... .. ... . .. . ... ... RB:Ih2 CEDA9502.r;>l 3 ... ... .. .. 3. WATERSHED DESCRIPTION 3.1 As noted previously, this property is dissected by several unnamed washes which are tributary to the Flata, Cuprite, and Fagan Washes per the Mount Fagan U.S.G.S. quad sheet and aerial reconnaissance flown for this study (please refer to attached aerial photo). These washes confluence with the Lee Moore Wash adjacent to Interstate 19. Existing conditions drainage patterns consist primarily of northwesterly channelization of flows through the four units. ,.. .. There are ten watercourses along the upstream property line that generate flows in excess of 100 cubic feet per second (cfs). Of the ten, four of the washes produce flows in excess of 1,000 cfs, however, none of the discharges exceed 5,000 cfs. This property is not mapped within any Federal 100-year floodplains by the Federal Emergency Management Agency (FEMA) per the Flood Insurance Rate Map (FIRM), Community- Panel No. 040073 3475 B, dated February 15, 1983. A copy of this map is attached in Appendix A. On-site vegetation consists of mesquite mixed with some palo verde, white thorn and cat claw acacia, burrow brush, desert broom, creosote, ocotillo, prickly pear, and yucca. This vegetation will remain relatively undisturbed as the proposed development will only consist of streets (previously cleared in past years) and individual lot pads . r . On-site soils consist of Nolam-Tombstone complex (hydrologic soils group B), SasabeCaralampi complex (hydrologic soils groups Band C), Tombstone very gravelly loam (hydrologic soils group B), Riggs silty clay (hydrologic soils group C), and Tanque sandy loam (hydrologic soils group A). The Tanque sandy loam was assumed to be hydrologic soils Group B for purposed of this study . . 3.2 Upstream Conditions Seventeen off-site watersheds impact the four units and are depicted on the attached Offsite Watershed Exhibit. Mount Fagan defines the headwaters of the largest watershed (#2) and all watersheds drain in a northwesterly direction through the units. These unnamed washes are tributary to the Flato, Cuprite, and Fagan Washes which flow westerly toward Interstate 19 where they confluence with the Lee Moore Wash. The upstream watersheds are primarily in undeveloped, mountainous terrain. Dominant soils within the upstream watersheds are as follows: .. . RB:Ih2 GWA9S02.rpl .. Overall Description and Characteristics 4 ,.. ... SCS CLASSIFICATION HYDROLOGIC SOIL GROUP Mabray - Deloro - rock outcrop complex D ... Deloro -Andrada complex D .. Deloro - rock outcrop complex D Caralampi very gravelly sandy loam B Nolam -Tombstone complex B Sasabe - Caralampi complex C&B Arizo - Riverwash complex A Riggs silty clay c ... ... .. 3.3 - Site Features This site generally falls from south to north with a westerly sloping tendency. Watercourses consist of fairly well defined channels with some braiding occurring throughout the four units. This site has no unusual topographic or hydrologic features of interest with respect to existing conditions other than those previously discussed. - - 3.4 Historical Information Very little historical information is available for this area. Aerial photos, stereo photography, site visits, soils mapping, and a site analysis for unit #30 prepared by others were utilized for assessment of the property . ... - - - - IUUt-2 C£0..,9S02.q.< 7 ... - 4. PROCEDURES 4.1 - Hydrologic Method ICON Consultants USA, Inc. (ICON) utilized a computational form of the Pima County method for predicting peak discharges as well as U.S. Army Corps of Engineers HEC-1 Flood Hydrograph Package for analysis of peak flows within the upstream watersheds and subject property. - - Offsite watersheds were mapped on 1" - 2,000' quadrangle maps and were verified through aerial photography interpretation. On-site watersheds were mapped using site generated 1" = 100' topography. Selection of hydrologic parameters were based on site visits and guidelines within the "Hydrology Manual for Engineering Design and Floodplain Management within Pima County, Arizona. Soils data were interpreted based on Soil Conservation Service (SCS) soils mapping in the area. Soils were mapped as hydrologic soils group "B", "C", and "D" through this interpretation . Soils mapped as group "A" were assumed to be part of group "B" for this study. A soils map and key to soil mapping units is included in Appendix A. ... - Selected hydrologic parameters are as follows: Watershed Type: Foothills- Mountain Basin Factor: .034 - .050 - 4.2 Hydraulic Method Hydraulic methods in standard use and practice in southeastern Arizona were utilized for analysis of the four units. Existing conditions floodplains have been mapped utilizing a computational form of the Manning's equation or U.S. Army Corps of Engineers standard step backwater model, HEC-2. Manning's computations and HEC2 output files are included in Appendix B. Floodplain mapping generated with HEC-2 indicates that the maJonty of the watercourses are flowing at critical depth or below. Roughness coefficients within the Manning's computations and HEC-2 profiles were selected based on site visits and interpretation of topography with respect to historical flow widths. Floodplain mapping is depicted on the Drainage Exhibits attached as Appendix C. - RB:Ih2 0:0.0.9502.r~ - 8 - 5. - HYDROLOGIC FINDINGS 5.1 Watershed Description The results of the hydrologic study of these four units are included within the attached hydrologic computation sheets and HEC-1 output in Appendix A. No unusual findings were observed. The watershed is as described above. 5.2 - Peak Discharge Summary Forty-four points of concentration were analyzed. Seventeen points are along the upstream boundary of the four units while the remaining twenty-seven points are along the downstream boundary. A summary of these concentration points is as follows: - - - - ,.. - - .. IUI:Ih2 GEOA%02.rl~ 9 .. UPSTREAM - POINT II .. .. Q 100 (cis) DOWNSTREAM DRAINAGE AREA POINT II Q, 00 (cfs) DRAINAGE AREA (acres) (acres) 1 105 39.5 18 31 7 2 3,302 2,330 19 60 17 3 544 154 20 83 23 4 226 72 21 16 4 5 33 8 22 188 72 5.5 22 5 23 110 35 6 1,353 630 24 128 45 6.5 29 7 25 45 12 7 1,454 753 26 30 8 7.5 29 7 27 62 19 8 452 184 28 25 6 8.1 51 12 29 2,923 1,700 .. 8.2 39 9 30 18 4 9 87 22 31 93 24 .. 10 2,480 1,670 32 16 4 11 182 45 33 399 174 - 12 348 135 34 3,373 2,563 13 32 8 35 12 3 14 32 8 36 33 10 15 465 218 37 18 5 16 90 29 38 67 19 17 2,516 1,720 39 108 42 ... .. . ... .. .. .. .. ,.. ... 11.8:1~2 G£0...9502.tl_. 10 - 6. - CONCLUSIONS Seventeen off-site watersheds enter Units #26, #28, #29 and #30 from the south. Peak discharges were calculated utilizing the Pima County method and the U.S. Army Corps of Engineers HEC-1 Flood Hydrograph Package. Ten points of concentration contain flows in excess of 100 cfs, of which four contain flows in excess of 1,000 cfs. The Army Corps of Engineers HEC-2 and a computational form of the Manning's equation were utilized for defining existing floodplains throughout the four units. The majority of the site drains through well defined channelization. No unusual hydrologic conditions exist on the subject property. - - - - - - ... RS:Ih2 GEOA950l.fl~ 11 -.. - 7. REFERENCES Brater and King; 1976, Handbook of Hydraulics .. Chang, H. H.; October, 1983, River Hydraulics Chow, V. T.; 1959, Open Channel Hydraulics . . . Chow, V. T.; 1964, Handbook of Applied Hydrology Cooper Aerial Survey Co.; june 3, 1987, 1" - 100' topography Federal Emergency Management Agency; February 15, 1983, Flood Insurance Rate Map, Community- Panel No. 040073 3475 B French, Richard; 1985, Open Channel Hydraulics - McClain Harbors Co., Inc.; June 1986, Aerial Photo Guide Tucson & Vicinity - The Ortho Shop- Tucson; 1996, 1" - 100' topography Pima County Department of Transportation and Flood Control District; September, 1979, Hydrology Manual for Engineering Design and Floodplain Management with Pima County, Arizona .. Soil Conservation Service: SCS Soils Map, Mount Fagan, 1" - 2,000' - U.S. Army Corps of Engineers; September, 1990, HEC-2 Water Surface Profiles Users Manual .. U.S. Army Corps of Engineers; September, 1990 HEC-1 Flood Hydrograph Package Users Manual U.S. Department of Agriculture; April, 1979, Soil Survey of Santa Cruz and parts of Cochise and Pima Counties, Arizona .. - - - IUI:Ikl CEOA950l.re< 12