Table of Contents:
Section 1: Introduction ..........................................................................................3
1.1 Purpose .......................................................................................................3
1.2 Project Authority ..........................................................................................3
1.3 Project Location...........................................................................................3
1.4 Methodologies Used for Hydrology and Hydraulics.....................................4
1.5 Acknowledgements .....................................................................................4
1.6 Study Results ..............................................................................................4
Section 2.0 Summary of Key Facts.......................................................................8
2.1: General Information....................................................................................8
2.2: Mapping Information...................................................................................8
2.3: Hydrology ...................................................................................................8
2.4: Hydraulics...................................................................................................8
2.5: Additional Study Information:......................................................................8
Section 3: Survey and Mapping Information .........................................................9
3.1 Field Survey Information .............................................................................9
3.2 Mapping ......................................................................................................9
Section 4: Hydrology...........................................................................................10
4.1 Method description. ...................................................................................10
4.2 Parameter estimation. ...............................................................................10
4.3 Problems encountered during the study. ...................................................20
4.4 Calibration. ................................................................................................20
4.5 Final results. ..............................................................................................20
Section 5: Hydraulics ..........................................................................................24
5.1 Method description. ...................................................................................24
5.2 Work study maps.......................................................................................24
5.3 Parameter estimation. ...............................................................................24
5.4 Cross section description. .........................................................................25
5.5 Modeling considerations............................................................................25
5.6 Floodway modeling ...................................................................................25
5.7 Problems encountered during the study. ...................................................25
5.8 Calibration. ................................................................................................26
5.9 Final results. ..............................................................................................26
Section 6: Erosion and Sediment Transport .......................................................26
Appendix A: References .....................................................................................28
Appendix B: General Documentation & Correspondence ...................................29
Appendix C: Survey Field Notes .........................................................................29
Appendix D: Hydrologic Analysis Supporting Documentation.............................29
Appendix E: Hydraulic Analysis Supporting Documentation ...............................29
Appendix F: Erosion and Sediment Transport Analysis ......................................30

1

List of Figures:

Figure 1.1 –Watershed Map Woodland Wash ......................................................5
Figure 1.2 – Study Limits Woodland Wash ...........................................................6
Figure 1.3 – Zoning Classification Woodland Wash..............................................7
Figure 4.1 – Flow Chart of Mapping Process ......................................................11
Figure 4.2 – Soil Classification Map Woodland Wash.........................................13
List of Tables:

Table 4.1 - Methods used for a Hec-HMS analysis.............................................10
Table 4.2 - Sub-basin Soils & CN Selection........................................................14
Table 4.3 – Summary of TR-55 Time of Concentration Calculations ..................19
Table 4.4 – 100 –yr Discharges at Sub-basin Outlet...........................................20
Table 4.6 – Rainfall Depths Used in Simulation (inches) ....................................21
Table 4.7 – Peak Discharge Values for 100-yr Event .........................................22
Table 4.8 – Peak Discharge Values for 25-yr Event ...........................................22
Table 4.9 – Peak Discharge Values for 500-yr Event .........................................22

2

Section 1: Introduction
1.1 Purpose
The purpose of this study is to provide flood and erosion hazard information for Woodland 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 Woodland Wash (Figure 1.1). The
site includes Sections 13-14, and 22-27 of Township 13 South, Range 15 East, Pima County,
Arizona. Most of the wash is in FEMA Zone X, as shown on the current Flood Insurance Rate

3

Map (FIRM) number 04019C-1670K. The most downstream portion of FEMA A-zone mapping
extends about 1/4 of a mile upstream of the confluence with the Woodland Wash (Figure 1.2).
The limits of this study are also shown on Figure 1.2.
The watershed is approximately 6 square miles at its outlet. The upper portion of the watershed
drains the Catalinas with well-defined and steep channels with an average gradient of 7%. At the
transition to the alluvial fan, flow becomes distributary in places and channel slope becomes
shallower (<1%). Because of the distributary nature of the flow on the alluvial fan split flows
occur that can bring more or less flow into any one channel.
A major split flow occurs at Gibbon Springs Wash, which is modeled as flowing into Woodland
Wash, though some of it does flow into the Tres Lomas Watershed (Figure 1.2).
Most of the watershed is covered in desert brush with small amounts of mountain brush,
herbaceous cover. Xeroriparian B Major zoning classifications of the watershed are SR, SP and
CR-1 (Figure 1.3).

1.4 Methodologies Used for Hydrology and Hydraulics
Topographic, hydrologic and hydraulic analyses were performed to determine drainage
conditions in Woodland wash. ArcGIS, Version 9.3, Pima County Hydrology Procedures (PCHydro), Version 5.3.1, HEC-HMS version 3.3 (HEC-HMS), Hec-RAS Version 4.0 (HEC-RAS),
and HEC-GeoRAS, Version 4.1.1 (HEC-GeoRAS) 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 floodplains for delineation of watersheds greater than one square mile were
delineated at part of this study. The study found several homes at risk for flooding during
the 100-yr flood. The modeled discharge for the Woodland wash at the confluence with
Sabino Wash (near the confluence with Tres Lomas) is 5,841 cfs, where the area is 5.95
square miles.
The channels draining greater than one square mile are not confined. The 100-yr
discharge for all watersheds greater than 1 square mile is greater than 2000 cfs. The
channels are not confined, and in most cases the 100-yr floodplain is about twice as large
as the 25-yr floodplain. One channel with a watershed area of 0.83 square miles and a
discharge of 1940 cfs is mapped. The remaining watersheds smaller than one square mile
will be further refined as part of a future effort to map tributaries smaller than one square
mile using the PC Hydro program to determine discharge.

4

Figure 1.1
Watershed Map
Woodland Wash

WDL_C

!
(

WoodCPs
Channels
Contour 50ft

Subbasins
WDL_B
WDL_C
WDL_D
WDL_B

WDL_E
WDL_F

WDL_E

WDL_G
WDL_H

WDL_G

WDL_I
WDL_J
WDL_K
SABINO CANYON

WDL_L
WDL_I

WDL_D

WDL_N
WDL_O

CP_B
IN
A

!
(

WDL_N

!
(
CP_D
!
(
CP_N
!
(
CP_N1
CP_H
!
(
CP_J
!
(
WDL_L
!
!
(( CP_M
WDL_M

PRINCE
BEAR CANYON

WDL_H

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.

MELPOMENE

HARRISON

CP_A
!
(

Pima County Index Map

WDL_F

SOLDIER

HOUGHTON

WDL_K

WDL_J

Note: Photo is 2007 USDA

CA
TA
L

SNYDER

CLOUD

WDL_M

WDL_O

Pima County Regional Flood Control District

FORT LOWELL

3,000

1,500

0

3,000 Feet

Scale 1:3000

01/2010
\\gislib\rfcd\projects\imd\xavi\mxd\AKITSU\Woodland_wash_Watershed_Fig1_1.mxd

Figure 1.2
Study Limit
Woodland Wash

WDL_C

!
(

WoodCPs
Channels
Subbasins

WDL_B

Existing FEMA Floodplain
ZONE A

WDL_E

ZONE AE
WDL_G

ZONE X - SHADED
Note: Photo is 2007 USDA
SABINO CANYON

Study Limit
WDL_I

WDL_D
WDL_O

Study Limit

IN
A

!
(
SNYDER

WDL_N

WDL_K

WDL_L !
(
CP_H

WDL_M

CLOUD

BEAR CANYON

PRINCE

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.

MELPOMENE

!
(
CP_A

Pima County Index Map

WDL_H

HARRISON

WDL_J CP_J

Study Limit

SOLDIER

!
( CP_N1
!
(
CP_N !
( CP_K
!
(
CP_D
CP_M
(
!
(!

WDL_F

HOUGHTON

Study Limit

CA
TA
L

CP_B

Pima County Regional Flood Control District

775
FORT LOWELL

3,000

387.5
1,500

0

Scale 1:3000

775 Feet
0

3,000 Feet

01/2010
\\gislib\rfcd\projects\imd\xavi\mxd\AKITSU\Woodland_wash_Watershed_Fig1_2.mxd

Figure 1.3
Zoning Classification
Woodland Wash

WDL_C

Subbasins

Pima County Zoning
CB-1
WDL_B

CR-1
IR

WDL_E

SP
WDL_G

SR
SR-2

SABINO CANYON

Note: Photo is 2007 USDA
WDL_I

WDL_D

CA
TA
L

IN
A

WDL_O

SNYDER

WDL_F
Pima County Index Map

SOLDIER

WDL_H

WDL_M

CLOUD

BEAR CANYON

PRINCE

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.

MELPOMENE

WDL_J

HARRISON

WDL_L

WDL_N

HOUGHTON

WDL_K

Pima County Regional Flood Control District

775
FORT LOWELL

3,000

387.5
1,500

0

Scale 1:3000

775 Feet
0

3,000 Feet

01/2010
\\gislib\rfcd\projects\imd\xavi\mxd\AKITSU\Woodland_wash_Watershed_Fig1_3.mxd

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: February, 2010
2.1.6 Study Contractor: Pima County Regional Flood Control District – Evan Canfield
2.1.7 State Technical Reviewer: Not Applicable
2.1.8 Local Technical Reviewer: Suzanne Shields
2.1.9 River or Stream Name: Woodland Wash
2.1.10 Reach Description: Woodland Wash, Gibbon Canyon Wash (a tributary), and five unnamed tributaries
2.1.11 Study Type: Hydrology and Hydraulics study of a Riverene System

2.2: Mapping Information
2.2.1 FIRM Panels: 04019C-1670K
2.2.2 Mapping for Hydrologic Study: Lidar based on 2006 flight for the Catalinas used to
derive 15’ grid and 10’ and 20’ contour interval maps using ARC-GIS 9.3
2.2.3 Mapping for Hydraulic Study: Lidar based on 2006 flight for the Catalinas used to derive
a TIN for use with GeoRAS

2.3: Hydrology
2.3.1 Model or Method Used: HEC-HMS (v. 3.3) model parameterized using methods of RFCD
Draft Tech Policy 018 (October 10, 2008)
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 4.0, 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 critical.

2.5: Additional Study Information:
Floodplains not delineated into recent subdivisions, which should have accurate floodplain maps.
The primary objective of this study was modeling subdivisions platted before 1980.

8

Section 3: Survey and Mapping Information
3.1 Field Survey Information
No field survey was used.

3.2 Mapping
Study used lidar data collected by Sanborn Mapping in 2007 for mapping debris flows and
characterizing flooding of the July 31, 2006 event. 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 2007 Light Detection and Ranging (LiDAR) data collected to support the analysis of the
2006 flooding in the Catalinas provided the topography for this analysis. The LiDAR was used to
derive three different kinds of topographic information. A Digital Elevation Model (DEM)
derived on 15’ centers provided the basis for delineating the watershed and sub-basins (Figure
3.1). Contour maps derived from the DEM 10’ and 20’ con tour allowed modelers to visualize
topographic differences in making decisions on how to model different areas. A triangular
Irregular Network (TIN) derived from data was used to characterize the topography along
channels used for the floodplain mapping process.

9

Section 4: Hydrology
4.1 Method description.
For the floodplain mapping, a 100-yr discharge is required. This analysis followed the guidance
of the District’s Tech Policy 018 (draft of 10/08). Most of the 100-year return interval peak
discharge rates for watersheds were computed by using HEC-HMS (v 3.3). Discharge values
were calculated for each sub-basin as well as for seven different junctions on the watershed.

4.2 Parameter estimation.
Methods are summarized in Table 4.1.
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

The data processing methods are summarized in Figure 4.1
4.2.1 Drainage area boundaries.
The limits of this study are shown in Figure 4.2. The limits of the watershed were determined
using topographic data based on the DEM and contour data.
4.2.2 Watershed work maps
The boundary of the watershed and internal sub-basins were determined using the Hydrology
tools in ARC GIS. Sub-basins were delineated based on internal concentration points. Sub-basins
were further refined visually using the contour maps and orthophotos. 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, crosssections, river banks, culverts, and other physical attributes of the wash were determined by using
a topographic data (TIN and contour maps) and 2002 aerial photo.
Sub-basins were labeled with the prefix WDL, for Woodland Wash followed by a letter (e.g
WDL_C). For the purposes of the hydrologic assessment, stream centerlines extended up into the
sub-basins, so that channel geometry and slope characteristics could be ascertained for
determining Time of Concentration, and discharge storage characteristics of the modified puls
routing.

10

Figure 4.1 – Flow Chart of Mapping Process

Topographic Data Preparation using ArcGIS with
TIN
(watershed boundary, slope break points)

Hydrologic Analysis using HEC
HMS and PC-Hydro

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
(Upstream area)

11

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 for a
point at the corner of Houghton and Snyder Rds (Lat 32.295; Long 110.778). The 3-hr rainfall
data provided the basis for distributing a Type II rainfall using the methods described in Haan et
al (1994). Because the different channels had different drainage areas, discharges were calculated
for 2, 4 and 6 square mile aerial reduction.
4.2.6 Physical parameters.
A soils classification map for the study area is presented in Figure 4.2. In the mountains,
Hydrologic Soil Group D is the dominant soil type, while Hydrologic Soil Group B is the
dominant soil type on the alluvial fan. 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. On the
urbanizing alluvial fan, turf and golf courses are common, so cover density depended on the
relative fractions of desert brush, turf and impervious cover. Impervious cover percentage from
0-20%, were selected based on lot size, the fraction of the sub-basin that is developed and the
tables in the PC Hydro manual. The CN selections and impervious cover selections are
summarized in Table 4.2.

12

Figure 4.2
Soil Classification Map
Woodland Wash

WDL_C

Subbasins
Soils
Soil Group: A (100%),
ARIZO-RIVERWASH COMPLEX, 0 TO 3 PERCENT SLOPES
Soil Group: B (100%),
HAYHOOK SANDY LOAM, 1 TO 5 PERCENT SLOPES
Soil Group: B (100%),
HAYHOOK-SAHUARITA COMPLEX, 1 TO 5 PERCENT SLOPES
Soil Group: B (100%),
PINALENO VERY COBBLY SANDY LOAM, 1 TO 8 PERCENT SLOPES

WDL_B

Soil Group: B (100%),
PINALENO-STAGECOACH COMPLEX, 5 TO 16 PERCENT SLOPES
Soil Group: B (100%),
YAQUI FINE SANDY LOAM, 1 TO 3 PERCENT SLOPES

WDL_E

Soil Group: C (47%) D (53%),
PANTANO-GRANOLITE COMPLEX, 5 TO 25 PERCENT SLOPES
Soil Group: C (50%), D (50%)

WDL_G

Soil Group: C (53%) D (47%),
PALOS VERDES-JAYNES COMPLEX, 2 TO 8 PERCENT SLOPES
Soil Group: D (100%),
CELLAR-LAMPSHIRE-ROCK OUTCROP COMPLEX, 15 TO 60 PERCENT SLOPES

SABINO CANYON

Note: Photo is 2007 USDA

WDL_I

WDL_D

CA
TA
L

IN
A

WDL_O

SNYDER

WDL_F
Pima County Index Map

SOLDIER

WDL_H

WDL_M

CLOUD

BEAR CANYON

PRINCE

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.

MELPOMENE

WDL_J

HARRISON

WDL_L

WDL_N

HOUGHTON

WDL_K

Pima County Regional Flood Control District

1,200
FORT LOWELL

3,000

600
1,500

0

Scale 1:3000

1,200 Feet
0

3,000 Feet

01/2010
\\gislib\rfcd\projects\imd\xavi\mxd\AKITSU\Woodland_wash_Watershed_Fig4-2.mxd

Table 4.2 - Sub-basin Soils & CN Selection

Sub-basin

WDL_B
WDL_C
WDL_D
WDL_E
WDL_F
WDL_G
WDL_H
WDL_I
WDL_J
WDL_K
WDL_L
WDL_M
WDL_N
WDL_O

Area
(Ac)

498.5
280.7
295.1
234.6
181.9
282.2
426.0
390.6
237.2
298.0
54.8
126.2
310.0
188.0

Hydrologic Soils Groups
A
0.0%
0.0%
4.8%
0.0%
0.0%
0.0%
0.0%
0.1%
21.2%
2.0%
4.8%
13.7%
0.3%
0.0%

B
0.3%
0.0%
40.0%
3.2%
99.6%
0.0%
48.2%
45.1%
58.8%
58.5%
44.5%
34.4%
76.5%
79.9%

C
0.0%
0.0%
1.1%
0.0%
0.0%
0.0%
24.1%
0.0%
10.4%
20.2%
23.8%
25.8%
5.3%
0.1%

D
99.7%
100.0%
54.1%
96.8%
0.4%
100.0%
27.7%
54.8%
9.5%
19.3%
26.9%
26.2%
17.8%
20.0%

Cover Type
Desert
Brush
80.7%
20.7%
100.0%
94.9%
100.0%
100.0%
100.0%
100.0%
100.0%
100.0%
100.0%
100.0%
100.0%
100.0%

Mountain
Brush
Herbaceous
10.8%
6.7%
56.2%
11.5%
0.0%
0.0%
2.5%
2.6%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%

CN
Juniper
%
Grass
Impervious
1.7%
2%
11.6%
0%
0.0%
10%
0.0%
2%
0.0%
14%
0.0%
0%
0.0%
10%
0.0%
5%
0.0%
7%
0.0%
10%
0.0%
10%
0.0%
7%
0.0%
10%
0.0%
15%

90.1
87.0
87.4
90.5
83.0
91.0
86.4
87.4
84.3
85.6
86.3
86.4
84.7
84.6

The SCS TR-55 segmental Time of Concentration (TC) methods were 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.
Travel times were the sum of the sheetflow, shallow concentrated flow and channel flow.
Sheetflow and shallow concentrated flow were calculated using the methods described in the TR55 manual (USDA-1986). However, the overland flow travel time was calculated using the
kinematic wave with the travel time for channels used estimates from a HEC-RAS model. The
methods are described in Appendix D. Table 4.3 summarizes the results.

18

Table 4.3 – Summary of TR-55 Time of Concentration Calculations
SubBasin
WDL_B
WDL_C
WDL_D
WDL_E
WDL_F
WDL_G
WDL_H
WDL_I
WDL_J
WDL_K
WDL_L
WDL_M
WDL_N
WDL_O

Area
(sq mi)
0.779
0.439
0.461
0.367
0.284
0.441
0.666
0.610
0.371
0.466
0.086
0.197
0.484
0.294

CN
90.1
87.0
87.4
90.5
83.0
91.0
86.4
87.4
84.3
85.6
86.3
86.4
84.7
84.6

Impervious Area
(%)
2
0
10
2
14
0
10
5
7
10
10
7
10
15

19

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

Lag Time
(min)
9.2
8.5
13.2
13.0
18.0
11.8
22.8
14.0
20.5
19.1
14.0
7.9
15.7
23.0

The lag time was calculated as 0.6 Tc, and used to calculate sub-basin discharge using the 3-hr
Type II storm. A single value of 3.47 inches was used for all sub-basins based on a NOAA 14
estimate near the centroid of the watershed. The SCS unit hydrograph was used to produce
hydrographs at the outlet of the sub-basin in HEC-HMS. Sub-basin discharges are summarized
on Table 4.4.
Table 4.4 – 100 –yr Discharges at Sub-basin Outlet

Element
WDL_B
WDL_C
WDL_D
WDL_E
WDL_F
WDL_G
WDL_H
WDL_I
WDL_J
WDL_K
WDL_L
WDL_M
WDL_N
WDL_O

Area
(mi)
0.78
0.44
0.46
0.37
0.28
0.44
0.67
0.61
0.37
0.47
0.09
0.20
0.48
0.29

Area
(Ac)
498
281
295
235
182
282
426
391
237
298
55
126
310
188

Time to
Peak (hrs)
01:33
01:32
01:37
01:36
01:42
01:35
01:46
01:37
01:44
01:43
01:37
01:32
01:39
01:46

Runoff
Vol (in)
2.35
2.06
2.22
2.38
1.97
2.41
2.14
2.15
1.95
2.08
2.14
2.1
2.02
2.09

Runoff Vol
(ac-ft)
97.5
48.2
54.5
46.6
29.8
56.7
76.1
70.1
38.5
51.8
9.8
22.1
52.2
32.7

Qp (cfs)
2,362
1,223
1,114
970
502
1,237
1,114
1,401
605
851
194
566
966
471

Hydrographs were routed using modified puls. Modified puls routing employed the
methods described in the HMS manual.
4.3 Problems encountered during the study.
None
4.3.1 Special problems and solutions
4.3.2 Modeling warning and error messages
Several minor errors were encountered. A complete list of errors is included in Appendix D.

4.4 Calibration.
No Calibration

4.5 Final results.
4.5.1 Hydrologic analysis results.
HEC-HMS calculated discharges above the reaches. In general, the discharge from the
downstream point was used for the hydraulic analysis. In this way, estimates were conservative.

20

Aerial reduction was used for 2, 4 and 6 square mile watersheds. Discharges were calculated for
25, 100 and 500 year recurrence interval. Rainfall depths used in the analysis are summarized on
table 4.6.
Table 4.6 – Rainfall Depths Used in Simulation (inches)
100-yr
No Reduction
Reduction 2 Sq-mile
Reduction 4 Sq-mile
Reduction 6 Sq-mile

500-yr
3.36
3.09
2.97
2.86

25-yr
4.37
4.02
3.85
3.72

2.61
2.40
2.30
2.20

Calculations were performed on one-minute time step over six hours. Rainfall occurred on a 5
minute time step with rainfall occurring in the first three hours. Woodtrib2 splits off from
Woodland at the transition between reach 1 and 2. Woodtrib 2 then joins back up with Woodland
2 and becomes Woodland reach 3. In order to determine how much flows into each portion of the
split, the splitflow optimization feature of HEC RAS determined how much could flow down
each split. In order to ensure that the value in each split was conservative, flow at the upper end
was increased by 50%. This methodology previously used in splitflow analysis at Diamond Bell
and the southwest. In this case, the analysis showed that Woodland reach 2 could carry most of
the flow.
For the hydraulic analysis the following discharges were used:

21

Table 4.7 – Peak Discharge Values for 100-yr Event
Concentration
Point

Location

Area
(sq
mile)

Rainfall
Depth
(in)

Runoff
Volume
(in)

Q100
HMS
(cfs)

Time
to
Peak

CP_A
CP_B

Woodland at Sabino
Woodland above Split
Tributary 1 Upstream of
Woodland
CatHwy West of Houghton
Woodland Upstream of CatHwy
Woodland West Split
CatHwy East of Harrison
Woodland below Split
Woodland East Split

5.95
0.78

2.86
3.36

1.72
3.3

5778
2362

2:15
1:33

1.29
1.57
3.00
a
2.58
1.70
a

3.36
3.09
2.96

2.22
1.9
1.83

1:50
1:59
1:54

2.96
3.09

1.8
1.94

2650
2196
4146
800
3090
2310
2362

CP_D
CP_H
CP_J
CP_K
CP_M
CP_N
CP_N1

2:10
1:56

Table 4.8 – Peak Discharge Values for 25-yr Event
Concentration
Point

Location

Area
(sq
mile)

Rainfall
Depth
(in)

Runoff
Volume
(in)

Q25
HMS
(cfs)

Time
to
Peak

CP_A
CP_B

Woodland at Sabino
Woodland above Split
Tributary 1 Upstream of
Woodland
CatHwy West of Houghton
Woodland Upstream of CatHwy
Woodland West Split
CatHwy East of Harrison
Woodland below Split
Woodland East Split

5.95
0.78

2.22
2.61

1.18
1.66

3543
1686

2:23
1:33

1.29
1.57
3.00
a
2.58
1.70
a

2.61
2.40
2.30

1.55
1.3
1.26

1:55
1:56
1:56

2.30
2.40

1.24
1.33

1780
1491
2740
330
1957
1503
1686

CP_D
CP_H
CP_J
CP_K
CP_M
CP_N
CP_N1

2:14
1:59

Table 4.9 – Peak Discharge Values for 500-yr Event
Concentration
Point

Location

Area
(sq
mile)

Rainfall
Depth
(in)

Runoff
Volume
(in)

Q500
HMS
(cfs)

Time
to
Peak

CP_A
CP_B

Woodland at Sabino
Woodland above Split
Tributary 1 Upstream of
Woodland
CatHwy West of Houghton
Woodland Upstream of CatHwy
Woodland West Split
CatHwy East of Harrison
Woodland below Split
Woodland East Split

5.95
0.78

3.71
4.37

2.49
3.3

9134
3280

2:09
1:32

1.29
1.57
3.00
a
2.58
1.70
a

4.37
4.23
3.85
4.37
3.85
4.23
4.37

3.15
2.74
2.64

3810
3482
6318
1500
4744
3562
3810

1:48
1:51
1:52

CP_D
CP_H
CP_J
CP_K
CP_M
CP_N
CP_N1

22

2.6
2.79

2:06
1:54

4.5.2 Verification of results.
Results are reasonable when compared with USGS Regression Equation 13 (Thomas et al, 1997)
and other studies. 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.
Concentration
Point

Location

Area
(sq
mile)

Q100
HMS
(cfs)

Q100
RRE 13
(cfs)

CP_A
CP_B

Woodland at Sabino
Woodland above Split
Tributary 1 Upstream of
Woodland
CatHwy West of Houghton
Woodland Upstream of CatHwy
Woodland West Split
CatHwy East of Harrison
Woodland below Split
Woodland East Split

5.95
0.78

5778
2362

3682
1063

1.29
1.57
3.00
a
2.58
1.70
a

2650
2196
4146
2185
3090
2310
800

1489
1689
2504

CP_D
CP_H
CP_J
CP_K
CP_M
CP_N
CP_N1

23

2292
1775

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. The hydraulic analysis
was performed in reaches in subdivisions older than 1980 in order to establish local floodplain
maps. The model ran in subcritical mode with downstream boundary conditions set to critical
flow conditions.

5.2 Work study maps
As described above, geometric data for HEC-RAS including stream centerline, cross-sections,
and river banks, were obtained from HEC-GeoRAS. The locations of cross sections and channels
used for the 100-yr floodplain and 500-yr floodplain maps are show in Exhibit 1. The annotated
Flood Insurance Rate Map is shown in Exhibit 2.

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 2002 aerial photo and field evaluation. Channel roughness varied between 0.03 and
0.05. The roughness used in this study ranges from 0.04 to 0.06 for overbank areas. Bank stations
were originally established in HEC-GeoRAS, and refined by selecting bank stations consistent
with ¼ or ½ of the 100-yr discharge. The discharge that filled the channel in well-defined crosssections was used to select bank stations. The bank-stations were, therefore, selected to match a
channel flow.
Differentiation of channel and overbank ‘n’ values should be done only when channel flow is at
least twice as deep as overbank flow (Phillips and Tadayon, 2006). On the alluvial fans, there are
many reaches that are wide with several flow paths. Rather than assign a channel and overbank
Manning’s n, an average n for the whole cross-section of 0.045 was assigned. Contraction and
expansion coefficients are 0.1 and 0.3 which were obtained from HEC-RAS Hydraulic Reference
Manual. Boundary conditions were based on critical flow conditions.
5.3.2 Expansion and contraction coefficients.
Default HEC RAS expansion (0.3) and contraction (0.1) coefficients were used.

24

5.4 Cross section description.
Cross-sections were placed so as to capture changes in channel geometry, bends and changes in
flow regime.

5.5 Modeling considerations.
5.5.1 Hydraulic Jump and drop analysis.
No Hydraulic Jumps were encountered.
5.5.2 Bridges and culverts.
One bridge is located on Woodland wash at Wolford Rd. Bridges and large culverts are present in
the upper part of the watershed that was not mapped as part of this study.
5.5.3 Levees and dikes.
None.
5.5.4 Islands and flow splits.
One location of split flow was noted on Woodland Wash near Snyder Rd. In order to determine
how much flowed in each part of the split flow, the discharge was increased 50% and the optimal
flow in each split calculated. The additional discharge was used to ensure that conservative
values were selected. In general the flows indicated that the main part of the Woodland Wash
could carry the full flow, while half of this value could flow in the tributary (WoodTrib2).
5.5.5 Ineffective flow areas.
Ineffective flow areas were noted on all reaches. In general these ineffective flow areas were
disconnected overbank areas that would not convey flow to the next downstream cross-section.
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.
None.

25

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 floodplain map for the 100-yr and 500-yr discharge is shown in Exhibit 1.

5.9.2 Verification of results.
Existing floodplain maps are not available except at the downstream end of the study area where
there is an existing FEMA A zone. The new map tends to follow this existing map on the western
boundary, but not extend as wide in the eastern edge. The results suggest that the mapping is
reasonable, and that discrepancies with the existing FEMA A zone are attributable to the
availability of more accurate topographic data, new rainfall data, more accurate soils and land use
maps, and changed land use since the existing FEMA maps.

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.

26

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

27

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.

28

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 Supporting Documentation
D.1 Precipitation data.
From the NOAA 14, Upper 90% atlas Version 4.0 (2006) embedded in PC Hydro v5.3.
D.2 Physical parameter calculations.
D.3 Hydrograph routing data.
Include routing data, confidence checks on results and cross section plots.
D.4 Reservoir routing data.
Include hydraulic calculations and rating curve plots for control structures, and volume
calculations.
D.5 Flow splits and diversions data.
Include hydraulic calculations and rating curve plots used to define each flow split and diversion
table.
D.6 Hydrologic calculations.

Appendix E: Hydraulic Analysis Supporting Documentation
E.1 Roughness coefficient estimation.
Include copies of photographs and calculations.
E.2 Cross section plots.
E.3 Expansion and contraction coefficients.
Include any special data or calibration efforts made for estimation of expansion and contraction
coefficients.
E.4 Analysis of structures.
Include any separate hydraulic modeling of structures used to estimate control data for
floodplain delineation calculations.
E.5 Hydraulic calculations.
Include computer model output for floodplain and floodway hydraulic calculations.

29

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

30

Digital Data

Attach CD Here

31

E121632

E121631

E121536

E121535

E121534

E121533

Exhibit 2
Annotated Flood
Insurance Rate Map
Woodland Wash

WDL_C
!
(
E131503

E131504

E131605

E131606

E131501

E131502

Woodland CPs
Woodland Sub-basin
100-yr floodplain
500-yr floodplain
vector.GISDATA.fp_panel
vector.GISDATA.trs

WDL_B

vector.GISDATA.fp_lomxb
E131510

E131509

E131512

E131511

E131608

E131607

WDL_E

FIRM Panel
1700 of 4700
Community
040019

FIRM Panel
1655 of 4700
Community
040019

K

FIRM Panel
1660 of 4700
Community
040019

HC
I TC

FIRM Panel
1690 of 4700
Community
040019

NE

RA

LH

FIRM Panel
1670 of 4700
Community
040019

ZONE AE
ZONE X - SHADED

GE

FIRM Panel
1665 of 4700
Community
040019

ZONE A

OC

WDL_G

Existing FEMA Floodplain

USDAPimaHARN2007.ecw
WDL_D

E131516

UN

TL

EM

MO

E131618

E131513

E131514

E131515

MO

WDL_I

N

SH

OR

E131617

T

CP_B

!
(

WDL_O

Pima County Index Map

SNYDER

WDL_N

WDL_F

E131521

BEAR CANYON

CA
TA
LI
N

A

WDL_K

E131522

E131523
CP_D

!
(
!
(

CP_K

Index Map Scale 1:1,500,000

!
(
CP_N1
!
(

WDL_H
WDL_L

CP_J CP_M

SOLDIER

CP_N
CP_H

!
(

(
!
( !

WDL_J

E131620

E131619

E131524

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 Department of
Transportation Technical Services Division makes no
claims regarding the accuracy of the information depicted
herein.

WDL_M

This product is subject to the Department of Transportation
Technical Services Division's Disclaimer and Use Restrictions.

CP_A

!
(

Pima County Regional Flood Control District

E131525

E131526

E131630

MELPOMENE

E131527

HOUGHTON

HARRISON

E131528

Scale 1:800

E131629

PRINCE
1,600

800

0

1,600 Feet

Pima County Regional Flood Control
97 East Congress Street - 3rd Floor
Tucson. Arizona 85701-1207
(520)243-1800 - FAX (520)243-1821
http://www.rfcd.pima.gov

02/2010

\\Gislib\rfcd\projects\imd\xavi\mxd\AKITSU\Unnamed 12\48x36_Wodland_wash_AnnotattedFIRM_exh2.mxd