Table of Contents:
Section 1: Introduction ..........................................................................................4
1.1 Purpose .......................................................................................................4
1.2 Project Authority ..........................................................................................4
1.3 Project Location...........................................................................................5
1.4 Methodologies Used for Hydrology and Hydraulics.....................................5
1.5 Acknowledgements .....................................................................................5
1.6 Study Results ..............................................................................................5
Section 2.0 Summary of Key Facts.......................................................................9
2.1 General Information.....................................................................................9
2.2 Mapping Information....................................................................................9
2.3 Hydrology ....................................................................................................9
2.4 Hydraulics....................................................................................................9
2.5 Additional Study Information:.....................................................................10
Section 3: Survey and Mapping Information .......................................................10
3.1 Field Survey Information ...........................................................................10
3.2 Mapping ....................................................................................................10
Section 4: Hydrology...........................................................................................10
4.1 Method description. ...................................................................................10
4.2 Parameter estimation. ...............................................................................10
4.3 Problems encountered during the study. ...................................................14
4.4 Calibration. ................................................................................................15
4.5 Final results. ..............................................................................................15
Section 5: Hydraulics ..........................................................................................17
5.1 Method description. ...................................................................................17
5.2 Work study maps.......................................................................................17
5.3 Parameter estimation. ...............................................................................17
5.5 Modeling considerations............................................................................18
5.6 Floodway modeling ...................................................................................18
5.7 Problems encountered during the study. ...................................................18
5.8 Calibration. ................................................................................................19
5.9 Final results. ..............................................................................................19
Section 6: Erosion and Sediment Transport .......................................................19

List of Figures:
Figure 1.1 Watershed Map ..................................................................................6
Figure 1.2 – Study limit .........................................................................................7
Figure 1.3 –Soil Classification Map.......................................................................8
Figure 4.1 – Flow Chart of Mapping Process......................................................12
List of Tables:
Table 4.1 - Methods used for a HEC-HMS analysis............................................11
Table 4.2 - Sub-basin Characteristics .................................................................14
Table 4.3 - Sub-basin discharges .......................................................................14
Table 4.4 – Summary of 100-yr Peak Discharge Values ....................................16
Table 4.5 – Summary of 25-yr Peak Discharge Values ......................................16
Table 4.6 – Summary of 500-yr Peak Discharge Values ....................................16
Table 4.7 – Comparison of 100-yr Peak Discharge Values ................................16
Exhibit
Exhibit 1 100-yr and 500-yr Floodplain Limit Map for the Race Track Wash
Addendum
Hydrologic and Hydraulic analyses for Tributaries
Attached CD
Race Track TDN with supporting models and GIS data.

Section 1: Introduction
1.1 Purpose
The purpose of this study is to provide flood and erosion hazard information for Race
Track Wash for use by the Pima County Regional Flood Control District (District) in
floodplain use permitting and floodplain management. More specifically, it provides:
 discharge values for sub-basins and important concentration points;
 hydrographs for use with floodplain mapping;
 floodplain mapping for channels with contributing areas greater than 1 square
mile, and channels with 100-yr discharges greater than 2000 cfs, which are treated
differently under the Pima County Ordinance.
1.2 Project Authority
The State of Arizona has delegated the responsibility to each county flood control district
to adopt floodplain regulations designed to promote the public health, safety and general
welfare of its citizenry as provided under the Arizona Revised Statutes, Title 48, Chapter
21, Article 1, Sections 48-3601 through 3627. More specifically, A.R.S. 3609 directs
county flood control districts to adopt floodplain regulations that:
A. Regulate all development of land, construction of residential, commercial or
industrial structures or uses of any kind which may divert, retard or obstruct flood
water and threaten public health or safety or the general welfare; and
B. Establish minimum flood protection elevations and flood damage prevention
requirements for uses, structures and facilities which are vulnerable to flood
damage; and
C. Comply with state and local land use plans and ordinances, if any.
In conformance with A.R.S. 3609, this ordinance provides for protection of the
public health safety and welfare by regulation of flood and erosion hazard areas to
control flood hazards and prevent repetitive loss from flood damage.
D. The flood hazard areas of Pima County are subject to periodic inundation
which may result in loss of life and property, create health and safety hazards,
disrupt commerce and governmental services, require extraordinary public
expenditures for flood protection and relief, and impair the tax base, all of which
adversely affect the public health, safety, and general welfare.
E. These flood losses are caused by the cumulative effect of obstructions in areas
of special flood hazards which increase flood heights, flow velocities, and cause
flood and erosion damage. Uses that are inadequately flood-proofed, elevated, or
otherwise protected from flood damage, also contribute to the flood loss. (Ord.
2005 FC-2 § 2 (part), 2005).
Section 16 of the Pima County Ordinance describes the provisions for floodplain
regulation in Pima County.

1.3 Project Location
The study was performed to provide drainage information for Race Track Wash. The site
includes Sections 5, 7, 18, and 19 of Township 13 South, Range 14 East, Sections 24 of
Township 13 South, Range 13 East, Pima County, Arizona. Entire watershed of the Race
Track Wash is in FEMA Zone X, as shown on the current Flood Insurance Rate Map
(FIRM) number 04019C-1630, 1635, and 1637K.
The watershed is 1.38 square miles. The study watershed was divided into three subwatersheds (Fig.1.1). The study limits for the Race Track Wash extends from River Rd.
to the south of Sunrise Dr. (Fig.1.2).
1.4 Methodologies Used for Hydrology and Hydraulics
Topographic, hydrologic and hydraulic analyses were performed to determine drainage
conditions in Race Track wash. ArcGIS, Version 9.3.1, HEC-HMS version 3.4 (HECHMS), Hec-RAS Version 4.0 (HEC-RAS), and HEC-GeoRAS, Version 4.2.93 (HECGeoRAS) were used for the analyses.
1.5 Acknowledgements
This study relied on assistance of RFCD GIS staff, who were integral to the development
of the models and maps.
1.6 Study Results
The modeled discharge for the Race Track Wash on River Rd. is 1883 cfs, where the area
is 1.38 square miles.
Floodplain boundary for areas less than one square mile is mapped as part of a future
effort to map tributaries smaller than one square mile using the PC Hydro program to
determine discharge.
The floodplains for delineation of watersheds greater than one square mile were
delineated at part of this study. The study found some homes at risk for flooding during
the 100-yr flood. In-general, the footprint of the 500-yr floodplain is slightly wider than
the 100-yr floodplain.

ORA C

LE

Figure 1.3
Soil Classification Map
Race Track Wash

INA

INA

(
!

Concentration Point
Subbasins

Soil Classification

RAT C

Soil Group: A (100%)
Soil Group: B (100%)
Soil Group: B (82%) C (18%)
Soil Group: C (47%) D (53%)

CP C

(
!
SKYLINE

ORANGE GROVE

RAT B

SU
N

Aerial Photo:
2008 Pima Association of Government

RI
SE

SU N
E

1ST

RIS

CP B
BE
MP
CA

RAT A

LL

(
!
Pima County Index Map

Index Map Scale 1:5,250,000

The information depicted on this display is the result
of digital analyses performed on a variety of databases
provided and maintained by several governmental agencies.
The accuracy of the information presented is limited to
the collective accuracy of these databases on the date
of the analysis. The Pima County Regional Flood Control
Department makes no claims regarding the accuracy of the
information depicted herein.
This product is subject to the Department of Transportation
Technical Services Division's Use Restriction Agreement.

RIVER

0

1,000

Pima County Regional Flood Control District

CP A
N
ST O

ORACLE

RIV E R

(
!

E

07/2010
\\gislib\rfcd\projects\imd\xavi\mxd\AKITSU\Race_Track\Race_Track_Fig1_3.mxd

2,000
Feet

Figure 1.2
Study Limit Map
Race Track Wash
with FEMA Floodplains
INA

INA

!
(

Concentration Point
Study Limit
Main Subbasins

Existing FEMA Floodplain

RAT C

ZONE A
LE
ORAC

ZONE AE
ZONE X - SHADED

CP C

!
(
SKYLINE

ORANGE GROVE

RAT B

SU
NR
I

Aerial Photo:
2008 Pima Association of Government

SE

1ST

E
RIS
SUN

CP B
CA
MP

RAT A

BEL

L

!
(
Pima County Index Map

Index Map Scale 1:5,250,000

The information depicted on this display is the result
of digital analyses performed on a variety of databases
provided and maintained by several governmental agencies.
The accuracy of the information presented is limited to
the collective accuracy of these databases on the date
of the analysis. The Pima County Regional Flood Control
Department makes no claims regarding the accuracy of the
information depicted herein.
This product is subject to the Department of Transportation
Technical Services Division's Use Restriction Agreement.

RIVER

1,000

500

0

Pima County Regional Flood Control District

CP A
NE
STO

ORACLE

RIVER

!
(
07/2011
\\gislib\rfcd\projects\imd\xavi\mxd\AKITSU\Race_Track\Race_Track_Fig1_2.mxd

1,000 Feet

Section 2.0 Summary of Key Facts
2.1 General Information
2.1.1 Community: Pima County Regional Flood Control
2.1.2 Community Number: NFIP Community Number 04019C
2.1.3 County: Pima
2.1.4 State: Arizona
2.1.5 Date Study Accepted: Not Accepted
2.1.6 Study Contractor: Pima County Regional Flood Control District
2.1.7 State Technical Reviewer: Not Applicable
2.1.8 Local Technical Reviewer: Suzanne Shields
2.1.9 River or Stream Name: Race Track Wash
2.1.10 Reach Description: Race Track Wash
2.1.11 Study Type: Hydrology and Hydraulics study of a Riverene System
2.2 Mapping Information
2.2.1 FIRM Panels: 04019C-1630, 1635 and 1637K
2.2.2 Mapping for Hydrologic Study: Lidar based on 2008 flight used to derive 2’
contour interval maps using ArcGIS 9.3.1
2.2.3 Mapping for Hydraulic Study: Lidar based on 2008 flight used to derive a DEM
(5-ft cell size) for use with GeoRAS
2.3 Hydrology
2.3.1 Model or Method Used: HEC-HMS model parameterized using methods of RFCD
Draft Tech Policy 018
2.3.2 Storm Duration: 3-hr
2.3.3 Hydrograph Type: SCS Unit Hydrograph
2.3.4 Frequencies Determined: 100 yr
2.3.5 List of Gages used in Frequency Analysis or Calibration: None
2.3.6 Rainfall Amounts and Reference: SCS Type II, NOAA 14 Upper 90%
Confidence Interval
2.3.7 Unique Conditions and Problems: None
2.3.8 Coordination of Q’s: Comparison with previous studies on file with RFCD and
discharge estimates
2.4 Hydraulics
2.4.1 Model or Method Used: HEC-RAS, GeoRAS to parameterize
2.4.2 Regime: Modeled as subcritical
2.4.3 Frequencies for which Profiles were Computed: 100 yr
2.4.4 Method of Floodway Calculation: No Floodway
2.4.5 Unique Conditions and Problems: Boundary set at normal depth.

2.5 Additional Study Information:
None

Section 3: Survey and Mapping Information
3.1 Field Survey Information
No field survey was used.
3.2 Mapping
The 2008 Light Detection and Ranging (LiDAR) data was used for the analysis.
Coordinates were in Pima County projection:
Projection = State Plane, Arizona Central Zone
Datum = NAD83 HARN
Units = International Feet
North American Vertical Datum of 1988 (NAVD, 1988)
The LiDAR was used to derive a Digital Elevation Model (DEM) and a contour map.
DEM derived on 5’ centers provided the basis for delineating the watershed and subbasins. DEM was also used to characterize the topography along channels used for the
floodplain mapping process. Contour map derived from the DEM allowed modelers to
visualize topographic differences in making decisions on how to model different areas.

Section 4: Hydrology
4.1 Method description.
For the floodplain mapping, a 100-yr discharge is required. The 100-year peak discharges
for the sub-basins of the Race Track Wash (RAT A, B, and C; Figure 1.1) were
calculated using U.S. Army Corps of Engineers Computer Hydrologic Modeling System,
(HEC-HMS) version 3.1.0. The HEC-HMS morel requires the parameters regarding
rainfall, topography, soil, vegetation, and channel characteristics to determine runoff
volume and peak discharge. Those parameters were determined according to the Pima
County Regional Flood Control District Technical Policy 018 (Tech-018). Tech-018 is
included in Appendix A.
4.2 Parameter estimation.
Methods are summarized in Table 4.1. The data processing methods are summarized in
Fig. 4

Table 4.1 - Methods used for a HEC-HMS analysis

Rainfall Depth
Rainfall Distribution
Rainfall Loss
Time of Concentration
Transform
Routing

Selected Method
NOAA 14, upper 90% Confidence Interval
3-hr SCS Type II Storm
SCS Curve number
SCS Segmental Method
SCS Unit Hydrograph
Modified-Puls and Kinematic Wave

4.2.1 Drainage area boundaries.
The limits of this study are shown in Fig.1.2. The site includes Sections 5, 7, 18, and 19
of Township 13 South, Range 14 East, Sections 24 of Township 13 South, Range 13
East, Pima County, Arizona. The entire watershed of the Race Track Wash is in FEMA
Zone X, as shown on the current Flood Insurance Rate Map (FIRM) number 04019C1630, 1635, and 1637K.
The watershed is 1.38 square mile. The study watershed was divided into three subwatersheds (Fig.1.1). The upstream study limits is Sunrise Dr, while the downstream
limit is River Rd (Fig.1.2).
4.2.2 Watershed work maps
The boundary of the watershed and internal sub-basins were determined using Hydrology
function in ArcGIS (Fig.1.1) with DEM derived from the 2008 Lidar. Study reach
includes only a main channel. The sub-basins reflected predominant topographic, soils,
cover and development conditions, so that the sub-basins would represent hydrologic
response from the sub-basin. The locations of the stream centerline, cross-sections,
culverts, and other physical attributes of the wash were determined by using the 2-ft
interval contour map and 2008 aerial photo.

Figure 4.1 – Flow Chart of Mapping Process

Topographic Data Preparation using ArcGIS with
DEM

Hydrologic Analysis using HECHMS

Geometric Data Preparation using
ArcMap and Hec-GeoRAS
(stream network, stream centerlines,
cross sections, river banks, culverts,
and/or block obstruction)

Hydraulic Analysis using HEC-RAS
(Manually input the following data; Manning’s nvalues, culvert data, expansion and contraction
coefficients, normal depth boundary condition,
ineffective flow areas, adjustment of reach length if
necessary)

Floodplain Delineation using HecGeoRAS

4.2.3 Gage Data.
None Available
4.2.4 Statistical parameters
None Available
4.2.5 Precipitation.
Rainfall depth was selected from the NOAA 14 Upper 90% rainfall data used in PC
Hydro. The point rainfall depth for the 3-hour storm was obtained, based on the
coordinates of the centroid of the watershed (Latitude: 32.317, Longitude: 110.945).
Areal reduction factor was applied to watersheds larger than 1 square mile as noted in
Tech-018. The 3-hr, SCS Type II rainfall distribution described in Haan et al (1994) was
used.
4.2.6 Physical parameters.
A hydrologic soils group map for the study watershed is presented in Fig.1.3. The study
watershed is covered with Desert brush. Hydrologic Soil Groups B and C are the
dominant soil types in the Race Track Wash watershed. The SCS Curve Number was
determined using maps obtained from NRCS (http://soildatamart.nrcs.usda.gov/) as a
basis for preparing a Hydrologic Soil Group Map for Pima County. The CN charts in the
PC Hydro Manual (Arroyo Engineering, 2007) were the basis for CN selection. A
vegetation cover density of 30% was used to select the SCS Curve Number for the
hydrologic calculation of the mountainous watersheds. Impervious cover percentage of
10% was selected based on lot size, the fraction of the sub-basin that is developed and the
tables in the PC Hydro manual. Sub-basin characteristics are summarized in Table 4.2
The detail of the CN calculation is included in Appendix D.

Table 4.2 - Sub-basin Characteristics
Sub-Basin
RAT A
RAT B
RAT C

Area
(sq mi)
0.45
0.24
0.69

CN
84.0
83.9
88.3

Impervious Area
(%)
10.0
10.0
10.0

Vegetation Cover
(%)
30
30
30

Lag Time
(min)
34.1
27.1
16.1

The SCS TR-55 segmental Time of Concentration (Tc) method with a combination of
kinematic wave method was used. The hydraulically most distant point on the sub-basin
was identified. The length of sheetflow was estimated at 100’, the distance from the end
of the sheetflow to a well-defined channel was selected as the shallow concentrated
portion of the flow path, and the channel portion was the path from the well-defined
channel to the sub-basin outlet was the ‘channel flow’ portion of the flow path.
Tc is the sum of the travel time for sheetflow, shallow concentrated flow and channel
flow. The travel time for sheetflow was calculated using kinematic wave method. The
travel time for shallow concentrated flow was calculated using the methods described in
the TR-55 manual (USDA-1986). The travel time for channels used estimates from a
HEC-RAS model. The lag time was calculated as 0.6 Tc. The detail of the Tc calculation
is included in Appendix D.
The SCS unit hydrograph method was used to produce hydrographs at the outlet of the
sub-basin in HEC-HMS. Runoff from sub-basins was routed using the Modified-Puls
method. A storage discharge table for the channel routing was developed using the cross
sections and slopes derived from HEC-HMS. Modified puls routing employed the
methods described in the HMS manual. The detail of the calculation of the number of
subreach is included in Appendix D. Sub-basin discharges are summarized on Table 4.3.
Table 4.3 - Sub-basin discharges
Sub-Basin
RAT A
RAT B
RAT C

Area
(sq mi)
0.45
0.24
0.69

Rainfall Depth
(in)
3.29
3.29
3.29

Runoff Volume
(in)
1.75
1.75
2.1

4.3 Problems encountered during the study.
None
4.3.1 Special problems and solutions
4.3.2 Modeling warning and error messages

Peak Discharge
(cfs)
465
293
1445

The time interval of the rainfall data used in this study is 5 minutes, while the simulation
time interval is 1 minute. The HEC-HMS model interpolated the 5-minute time interval
of the rainfall data to 1-minute time interval.
4.4 Calibration.
No Calibration
4.5 Final results.
4.5.1 Hydrologic analysis results
The 100-year peak discharges at the concentration points along the Race Track Wash
were determined using the HEC-HMS. Six hours were simulated on a 1 minute time step
with rainfall occurring in the first three hours. For the hydraulic analysis the following
discharges were used:

Table 4.4 – Summary of 100-yr Peak Discharge Values
Concentration
Point

Location

CP A
CP B

River Rd.
Between Camino Paore Isidoro and Calle de la Culebra

Area
(sq
mile)
1.38
0.93

Rainfall Runoff
Depth Volume
(in)
(in)
3.16
1.81
3.29
2.01

Q100
HMS
(cfs)
1883
1680

Time to
Peak

Q25
RRE
(cfs)
887
691

Time to
Peak

Q500
HMS
(cfs)
2830
2420

Time to
Peak

2:06
1:49

Table 4.5 – Summary of 25-yr Peak Discharge Values
Concentration
Point

Location

CP A
CP B

River Rd.
Between Camino Paore Isidoro and Calle de la Culebra

Area
(sq
mile)
1.38
0.93

Rainfall Runoff
Depth Volume
(in)
(in)
2.45
1.22
2.55
1.37

Q25
HMS
(cfs)
1211
1130

2:09
1:51

Table 4.6 – Summary of 500-yr Peak Discharge Values
Concentration
Point

Location

CP A
CP B

River Rd.
Between Camino Paore Isidoro and Calle de la Culebra

Area
(sq
mile)
1.38
0.93

Rainfall Runoff
Depth Volume
(in)
(in)
4.13
2.66
4.13
2.9

2:02
1:49

4.5.2 Verification of results.
Results are reasonable when compared with USGS Regression Equation 13 (Thomas et
al, 1997, Table 4.7). The equation 13 results were generally lower than the HMS results,
which would be expected, because these steep watersheds could be expected to produce
higher than average discharge on average. Existing regulatory peak discharge for the
Race Track Wash is 2100 cfs at First Ave (downstream of CP A). The proposed
discharge is around 10% smaller than the existing regulatory peak discharge.
Table 4.7 – Comparison of 100-yr Peak Discharge Values
Concentration
Point

Location

CP A
CP B

River Rd.
Between Camino Paore Isidoro and Calle de la Culebra

Area (sq
Q100
Q100
mile)
HMS (cfs) RRE (cfs)
1.38
0.93

1883
1680

1555
1199

Section 5: Hydraulics
5.1 Method description.
Steady flow analysis was performed to determine 100-year water surface elevations in the
study area by using HEC-RAS with the discharge obtained from HEC-HMS.
5.2 Work study maps
As described above, geometric data for HEC-RAS including stream centerline, crosssections, and culverts, were obtained from HEC-GeoRAS. The locations of cross sections
and channels used for the 100-yr floodplain analysis are show in Exhibit 1. The 100-yr
and 500-yr floodplain limits are also shown in Exhibit 1.
5.3 Parameter estimation.
The watershed was modeled using methods consistent with District Tech Policy 019.
5.3.1 Roughness coefficients.
Manning’s roughness coefficients for the main channel and the over-bank areas were
determined by using a 2008 aerial photo. The roughness used in this study is 0.055 for
overbank areas and 0.035-0.04 for a channel. Bank stations were refined by selecting
bank stations based on the topography and a 2008 aerial photo.
5.3.2 Expansion and contraction coefficients.
Default HEC RAS expansion (0.3) and contraction (0.1) coefficients were used for the
most cross sections. The expansion coefficient of 0.5 and contraction coefficient of 0.3
were used for the cross sections immediately upstream or downstream of culverts.

5.4 Cross section description.
A 2-foot interval contour map derived from 2008 LiDAR data was used to select the
location of cross sections. Cross-section locations were determined primarily based on
the channel topography. The cross-section lines were drawn to be perpendicular to flow
paths in Geo-RAS and ArcGIS.
5.5 Modeling considerations.
5.5.1 Hydraulic Jump and drop analysis.
No Hydraulic Jumps were encountered.
5.5.2 Bridges and culverts.
There are four culverts along the study reach of the Race Track Wash.
5.5.3 Levees and dikes.
None.
5.5.4 Islands and flow splits.
None.
5.5.5 Ineffective flow areas.
Ineffective flow areas were noted on the study reach of the Race Track Wash.
In general these ineffective flow areas were disconnected overbank areas that would not
convey flow to the next downstream cross-section or immediately upstream or
downstream of culverts.
5.5.6 Supercritical flow.
No supercritical reaches.
5.6 Floodway modeling
No encroachment calculations were performed.
5.7 Problems encountered during the study.
5.7.1 Special problems and solutions.

Lateral structures were used for the cross sections where containment is lost (Reach C2,
station# 1865, reach B station# 5289, 5109, 5081). The HEC-RAS model includes the
tributaries (RAT A1, B1, C1, C2, C3, C4, C5, and C6). The methods and results of the
tributaries were summarized in Addendum.
5.7.2 Modeling warning and error messages.
No errors occurred. The following warning messages occurred:
Divided flow
Energy loss greater than 1.0
Energy equation could not be balanced and defaulted to critical.
Cross-section extended vertically.
Multiple critical depths calculated.
Conveyance ratio is less than 0.7 or greater than 1.4.
Inspection indicated that the modeling is accurate given the steep channel conditions.
Most of these errors force a critical solution which is reasonable for these steep
watercourses. A summary of errors is available in Appendix E.
5.8 Calibration.
None.
5.9 Final results.
5.9.1 Hydraulic analysis results.
The HEC-RAS modeling results were summarized in Appendix E.
5.9.2 Verification of results.
Existing floodplain maps are not available along the Race Track Wash. The new map
tends to follow the floodplain topography. The results suggest that the mapping is
reasonable.
Section 6: Erosion and Sediment Transport
6.1 Method description.
None – not applicable
6.2 Parameter estimation.
None – not applicable
6.4 Modeling considerations.
None – not applicable
6.5 Problems encountered during the study.

6.5.1 Special problems and solutions.
None – not applicable
6.5.2 Modeling warning and error messages.
None – not applicable
6.6 Calibration.
None – not applicable.
6.7 Final results.
6.7.1 Erosion and sediment transport analysis results.
None – not applicable
6.7.2 Verification of results.
None – not applicable

Appendix A: References
A.1 Data collection summary.
Include a list of previous studies, other applicable studies, published and unpublished
historical
flood information, and research contacts.
A.2 Referenced documents.
Arizona Department of Water Resources, Flood Mitigation Section
“Requirements for Flood Study Technical Documentation” SS1-97, November 1997
Arroyo Engineering. 2007. PC-Hydro User Guide. Pima County Regional Flood Control
District
Eychaner, J.H., 1984. Estimation of magnitude and frequency of floods in Pima County,
Arizona, with comparisons of alternative methods: U.S. Geological Survey WaterResources Investigations Report 84-4142, 69 p.
Haan, C.T., Barfield, B.J., Hayes, J.C. 1994. Design Hydrology and Sedimentology for
Small Catchments, Academic Press.
National Weather Service. 1984. Depth-Area Ratios in the Semi-Arid Southwest
United States, NOAA Technical Memorandum NWS Hydro-40
NOAA, 2006. NOAA Atlas 14, Precipitation Frequency Atlas for the United States:
Volume 1 - Version 4.0 The Semiarid Southwest. National Weather Service,
Hydrometeorological Design Studies Center. Available on the internet at:
http://hdsc.nws.noaa.gov/ hdsc/pfds/sa/az_pfds.html
Phillips, J., and S. Tadayon. 2006. Selection of Manning’s roughness coefficient for
natural and constructed vegetated and non-vegetated channels, and vegetation
maintenance plan guidelines for vegetated channels in central Arizona: U.S. Geological
Survey Scientific Investigations Report 2006–5108, 41 p.
Thomas, B.E., H.W. Hjalmarson, and S.D. Waltemeyer. 1997. Methods for Estimating
Magnitude and Frequency of Floods in the Southwestern United States. USGS Water
Supply Paper 2433. 195 p.
U.S. Army Corps of Engineers (COE). 1998. HEC-1 Flood Hydrograph Package, Users
Manual, CPD-1A, Hydraulic Engineering Center, Davis, CA.
U.S. Army Corps of Engineers (COE). 2001. HEC-RAS, River Analysis System,
Hydraulic Reference Manual, CPD-69, Hydraulic Engineering Center, Davis, CA.

U.S. Army Corps of Engineers (COE). 2006. HEC-HMS, Hydrologic Modeling System
User’s Manual, (v. 3.1.0) CPD-74A, Hydraulic Engineering Center, Davis, CA.
U.S. Department of Agriculture Natural Resources Conservation Service (NRCS), 1986.
Urban Hydrology for Small Watersheds, Technical Release 55. Washington, DC.

Appendix B: General Documentation & Correspondence
B.1 Special Problem Reports.
B.2 Contact (telephone) reports.
Provide copies of correspondence documenting notification of the client and the methods
of addressing any special problems described in Sections 4.4.1, 5.5 and 6.5.
B.3 Meeting minutes or reports.
B.4 General Correspondence.
B.5 Contract Documents.
Provide a copy of the contract Scope of Work, not financial documents.

Appendix C: Survey Field Notes
C.1 Survey field notes for aerial mapping control.
C.2 Survey field notes for hydrologic modeling.
C.3 Survey field notes for hydraulic modeling.

Appendix D:
Hydrologic Analysis

Appendix F: Erosion and Sediment Transport Analysis
(None – no sediment transport analysis in this report)

Addendum

Floodplain Analysis for Race Track Wash Tributaries
Introduction
Preliminary floodplain boundaries for areas less than one square mile were shown in the
main part of the report. The peak discharge for the Race Track Wash main channels was
determined using HEC-HMS. This addendum provides drainage information for the Race
Track Wash tributaries. Peak discharge for the tributaries was obtained using Pima
County Hydrology Procedures (PC-Hydro, Arroyo Engineering, 2007), Version 5.3.1.
Floodplain limits for “regulatory washes” will be shown in this addendum. The
assumption that regulatory washes have drainage areas greater than 20 acre was used to
determine the upstream end the tributaries.

Description of the watershed
The three subbasins used for HEC-HMS analysis (RAT A, B, and C) were further divided
into smaller subbasins to determine peak discharge for the tributaries using PC-Hydro.
The eight subbasins (RAT A1, B1, and C1-C6) were delineated for the PC-Hydro
analysis (Fig. A1). Study limits are shown on Fig. A2. Hydrologic Soil Map is shown on
Fig. A3.

Data processing procedures
ArcGIS, Version 9.3.1, PC-Hydro, Version 5.3.1, HEC-RAS, Version 4.0, and HECGeoRas, Version 4.1.1 were used for the analyses. As mentioned in the main part of the
report, the 2008 Light Detection and Ranging (LiDAR) data and 2008 PAG aerial photo
were used for the analysis. Slope break points were determined using the contour lines.
The locations of the stream centerline, cross-sections, river banks, culverts, and other
physical attributes of the wash were determined by using a topographic map and aerial
photo (Exhibit A1).

Hydrologic analysis
The 100-year return interval peak discharge rates for the eight subbasins were computed
by using PC-Hydro. NOAA Atlas 14 Upper 90% Confidence Interval rainfall data were
used for the analysis. Hydrologic soils group map is shown in Fig. A3. The watercourse
was divided into segments (Reaches) using slope break points. The basin factor for each
segment was determined by using a 2008 PAG aerial photo. Basin Factors were based on
the tables in the PC Hydro User Guide. The Basin Factor ranges from 0.034 to 0.036
which corresponds to Suburban-Foothills (< 1 house/acre). A vegetation cover density of
30% was used to select the SCS Curve Number for the hydrologic calculation of the
study watershed. Impervious cover percentage was 10%, which was determined using a
2008 PAG aerial photo. The results were summarized in Table A2.

-1-

Table A1. Subbasin Characteristics
Sub-Basin
RAT A1
RAT B1
RAT C1
RAT C2
RAT C3
RAT C4
RAT C5
RAT C6

Area
(acre)
72.5
45.1
118.7
52.1
75
9.4
120.7
67.6

Impervious Area
(%)
10.0
10.0
10.0
10.0
10.0
10.0
10.0
10.0

Vegetation Cover
(%)
30
30
30
30
30
30
30
30

Time of Concentration
(min)
14.6
13.3
10.2
17.8
8.2
12.9
11.1
8

Table A2. Summary of the results
CP
A1
B1
C1
C2
C3
C4
C5
C6

Area
(acre)
72.5
45.1
118.7
324.8
75
197.7
120.7
67.6

Q100 PC-Hydro
(cfs)
305
191
673
1305
491
1058
702
447

Q100 RRE
(cfs)
238
156
361
785
245
542
366
224

Hydraulic analysis
Steady flow analysis was performed to determine 100-year water surface elevation for the
Race Track Wash by using HEC-RAS. There are three culverts in subbasin RAT C1, and
two culverts in subbasins RAT A, C2, and C6. No floodplain was mapped between
Skyline Dr. and Orange Grove Rd. because there are no outlets between the roads and the
flow stays underground.
Manning’s roughness coefficients for the main channel and the over-bank areas were
determined by using a 2008 PAG aerial photo. The roughness coefficient of 0.04 was
assigned for the channel while 0.055 was assigned for the overbank area. Entrance loss
coefficient and Manning’s roughness coefficient of the culverts are obtained from HECRAS Hydraulic Reference Manual version 3.1. Contraction and expansion coefficients
are 0.3 and 0.5 for just upstream and downstream of culverts, and 0.1 and 0.3 for other
cross sections, which were obtained from HEC-RAS Hydraulic Reference Manual.
Normal depth with a slope of 0.028 at the downstream end of the study area for the main
channel (River Rd.) was used as a boundary condition for the steady flow analysis. A
floodplain limit was shown in Exhibit A1. There are a few houses mapped in a floodplain
along the tributaries (Exhibit A1).

-2-

References
HEC-RAS Hydraulic Reference Manual version 3.1, US Army Corps of Engineering
Center, November 2002.
PC-Hydro User Guide, PC-Hydro V5 Pima County Hydrology Procedures, A couputer
program for predicting peak discharge of surface runoff from small semi-arid watersheds
in Pima County, Arizona, Arroyo Engineering, LLC, 2007
Phillips J., and Tadayon, S., Selection of Manning’s Roughness Coefficient for Natural
and Constructed Vegetated and Non-Vegetated channels, and Vegetation Maintenance
Plan Guidelines for Vegetated Channels in Central Arizona, Flood Control District of
Maricopa County, Scientific Investigations Report 2006-5108.

-3-

ORA C

LE

Figure A3
Soil Classification Map
Tributaries Race Track Wash

INA

INA

RAT C5

RAT C3

!
(

RAT C2

CP C6
CP C5

(
!

Main Concentration Point
Main Subbasins

!
(
(
!

Soil Classification

RAT C4

Soil Group: B (100%)
RAT C1

CP C1
CP C2

Tributaries Concentration Point
Tributaries Subbasins

RAT C6

RAT C
CP C4
CP C3

(
!

Soil Group: B (82%) C (18%)

CP C

Soil Group: C (47%) D (53%)

!
(
(
!
SKYLINE

ORANGE GROVE

RAT B

SU
N

RAT B1

Aerial Photo:
2008 Pima Association of Government

RI
SE

RAT A1
CP B1
SU N

(
!

E

1ST

RIS

CP B2

CP B
BE
MP
CA

RAT A

LL

(
!
!
(
Pima County Index Map

Index Map Scale 1:5,250,000

The information depicted on this display is the result
of digital analyses performed on a variety of databases
provided and maintained by several governmental agencies.
The accuracy of the information presented is limited to
the collective accuracy of these databases on the date
of the analysis. The Pima County Regional Flood Control
Department makes no claims regarding the accuracy of the
information depicted herein.
This product is subject to the Department of Transportation
Technical Services Division's Use Restriction Agreement.

RIVER

0

1,000

Pima County Regional Flood Control District

CP A
N
ST O

ORACLE

RIV E R

(
!

E

07/2010
\\gislib\rfcd\projects\imd\xavi\mxd\AKITSU\Race_Track\Race_Track_Fig_A3.mxd

2,000
Feet

ORA C

LE

Figure A2
Study Limit Map
Tributaries Race Track Wash
with FEMA Floodplains

INA

INA

RAT C5

(
!

Concentration Point
Study Limit

RAT C3

Tributaries Subbasins

RAT C6

Main Subbasins

RAT C

CP C3 CP C4
CP C6
RAT C2
RAT C4 CP C5

!
(

!
(

Existing FEMA Floodplain

ORA C

ZONE A

RAT C1

LE

ZONE AE

CP C2 CP C1

!
(

ZONE X - SHADED
SKYLINE

ORANGE GROVE
SU
N

RAT B
RAT B1

Aerial Photo:
2008 Pima Association of Government

RI
SE

RAT A1
CP B1
SU N

(
!

E

1ST

RIS

CP B2

MP
CA

RAT A

BE

LL

(
!
Pima County Index Map

Index Map Scale 1:5,250,000

The information depicted on this display is the result
of digital analyses performed on a variety of databases
provided and maintained by several governmental agencies.
The accuracy of the information presented is limited to
the collective accuracy of these databases on the date
of the analysis. The Pima County Regional Flood Control
Department makes no claims regarding the accuracy of the
information depicted herein.
This product is subject to the Department of Transportation
Technical Services Division's Use Restriction Agreement.

0

1,000

Pima County Regional Flood Control District

RIV E R

N
ST O

RIV

E

ER

07/2010
\\gislib\rfcd\projects\imd\xavi\mxd\AKITSU\Race_Track\Race_Track_Fig A2.mxd

2,000
Feet

Figure A1
Race Track Tributaries
Watershed Map

INA

(
!

INA

Concentration Point
Contour 10 Foot
Main Subbasins

Tributaries Subbasins
RAT A1

CP C4 CP C5 CP C6
(
(
!
( CP !
!
C3

RAT B1

ORAC

RAT C1

LE

RAT C2

CP C2 CP C1
(
!

RAT C3
SKYLINE

ORANGE GRO VE
SU

NR

IS

RAT C4
RAT C5

E

SU

NR

RAT C6
IS

E

Aerial Photo: 2008 Pima Association of Government

CP B1

CP B2
MP
BE
LL

(
!

Pima County Index Map

CA

1ST

(
!

Index Map Scale 1:5,250,000

ORACLE

The information depicted on this display is the result
of digital analyses performed on a variety of databases
provided and maintained by several governmental agencies.
The accuracy of the information presented is limited to
the collective accuracy of these databases on the date
of the analysis. The Pima County Regional Flood Control
Department makes no claims regarding the accuracy of the
information depicted herein.
This product is subject to the Department of Transportation
Technical Services Division's Use Restriction Agreement.
Pima County Regional Flood Control District

STONE

RIVER
RIV ER

1,800

900

0

1,800 Feet

07/2010
Gislib\rfcd\projects\imd\xavi\mxd\AKITSU\Race_Track\Race_Track_FigA1.mxd