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
Section 2.1: General Information.......................................................................9
Section 2.2: Mapping Information......................................................................9
Section 2.3: Hydrology ......................................................................................9
Section 2.4: Hydraulics......................................................................................9
Section 2.5: Additional Study Information:.........................................................9
Section 3: Survey and Mapping Information .......................................................10
3.1 Field Survey Information ...........................................................................10
3.2 Mapping ....................................................................................................10
Section 4: Hydrology...........................................................................................11
4.1 Method description. ...................................................................................11
4.2 Parameter estimation. ...............................................................................11
4.3 Problems encountered during the study. ...................................................14
4.4 Calibration .................................................................................................15
4.5 Final results ...............................................................................................15
Section 5: Hydraulics ..........................................................................................16
5.1 Method description. ...................................................................................16
5.2 Work study maps.......................................................................................16
5.3 Parameter estimation. ...............................................................................16
5.4 Cross section description. .............................................................................17
5.5 Modeling considerations............................................................................17
5.6 Floodway modeling ...................................................................................17
5.7 Problems encountered during the study. ...................................................18
5.8 Calibration. ................................................................................................18
5.9 Final results. ..............................................................................................18
Section 6: Erosion and Sediment Transport .......................................................18
Section 7: Ratio of the top width of 100-yr and 25-yr floodplain..........................19

2

List of Figures:
Figure 1.1 Watershed Map ...................................................................................6
Figure 1.2 Study Limit ...........................................................................................7
Figure 1.3 Soil Classification.................................................................................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 ....................................15
Table 4.5 – Summary of 25-yr Peak Discharge Values ......................................15
Table 4.6 – Summary of 500-yr Peak Discharge Values ....................................15
Table 4.7 – Comparison of 100-yr Peak Discharge Values ................................16
Exhibit
Exhibit 1 100-yr Floodplain Limit Map
Exhibit 2 Annotated Flood Insurance Rate Map
Attached CD
Old Grandad Tank TDN with supporting models and GIS data.

3

Section 1: Introduction
1.1 Purpose
The purpose of this study is to provide flood and erosion hazard information for the Old
Grandad Tank 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.

4

1.3 Project Location
The study was performed to provide drainage information for the Old Grandad Tank
Wash. The site includes Sections 24, 25, 26, 27, 34, and 35 of Township 13 South, Range
16 East, Sections 3 of Township 14 South, Range 16 East, Pima County, Arizona. The
Old Grandad Tank Wash watershed is in FEMA Zone X and Zone D, as shown on the
current Flood Insurance Rate Map (FIRM) number 04019C-1690 and 2280K.
The watershed is 2.02 square mile. The study watershed was divided into four sub-basins
(Fig.1.1). The study limits for the Old Grandad Tank Wash extends from a confluence
with Tanque Verde Creek to the upstream end of Subbasin A (Fig.1.2).
1.4 Methodologies Used for Hydrology and Hydraulics
Topographic, hydrologic and hydraulic analyses were performed to determine drainage
conditions in the Old Grandad Tank Wash. ArcGIS, Version 9.3.1, HEC-HMS Version
3.4 (HEC-HMS), Hec-RAS Version 4.0 (HEC-RAS), and HEC-GeoRAS, Version 4.2.93
(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 modeled discharge for the Old Grandad Tank Wash at the confluence with the
Tanque Verde Creek is 3942 cfs, where the area is 2.02 square miles.
The Old Grandad Tank Wash watershed is partially located within Federal land (national
forest, FEMA Zone D). The floodplain was mapped in the downstream area of the Old
Grandad Tank Wash.

5

Figure 1.1
Watershed Map
Old Grandad Tank Wash

!
(

Discharge Point
River
Contour 20 foot

Subbasins
OLG A
OLG B
OLG C
OLG D
Photo: Pima Arizona Governmens 2007
Topo: Pima Arizona Government 2008

CP D CP C
!
(
CP B !
(

Pima County Index Map

REDINGTON

WENTWORTH

Index Map Scale 1:5,250,000

CP A

!
(

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

1,000

500

0

1,000 Feet

10/2010
\\gislib\rfcd\projects\imd\xavi\mxd\AKITSU\Old_Gandad\Old_Grandad_TankWatershed_Fig1_1.mxd

Figure 1.2
Study Limit
Old Grandad Tank Wash

(
!

Discharge Point
River
Subbasins

Existing FEMA Floodplain
OLG C

OLG B

ZONE A
ZONE AE
ZONE X - SHADED
Aerial Photo: 2007 Pima Association of Governments

OLG D
CP C

!
(
( CP D
!
CP B

OLG A

Pima County Index Map

REDINGTON

TANQUE VERDE

WENTWORTH

Index Map Scale 1:5,250,000

Study Limit

( CP A
!

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

SPEEDWAY

1,000

500

0

1,000 Feet

10/2010
\\gislib\rfcd\projects\imd\xavi\mxd\AKITSU\Old_Grandad\Old_grandad_TankWatershed_Fig1_2.mxd

Figure 1.3
Soil Classification
Old Grandad Tank Wash

!
(

Discharge Point
Subbasins

Soil Classification
Soil Group: A (100%), ARIZO-RIVERWASH COMPLEX,
0 TO 3 PERCENT SLOPES

OLG C

OLG B

Soil Group: B (50%) C (50%), PALOS VERDES
-SAHUARITA COMPLEX, 2 TO 8 PERCENT SLOPES
Soil Group: C (50%), D (50%)
Soil Group: D (100%), CELLAR-LAMPSHIREROCK OUTCROP COMPLEX, 15 TO 60 PERCENT SLOPES
Soil Group: D (100%), CELLAR-LEHMANS COMPLEX,
5 TO 25 PERCENT SLOPES

Aerial Photo: 2007 Pima Association of Governments

OLG D
CP C

!
( CP D
!
(
CP B

OLG A

Pima County Index Map

RE

G
DIN

N
TO

WENTWORTH

Index Map Scale 1:5,250,000

!
( CP A

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

1,000

500

0

1,000 Feet

10/2010
\\gislib\rfcd\projects\imd\xavi\mxd\AKITSU\Old_Grandad\Old_Grandad_TankWatershed_Fig1_3.mxd

Section 2.0 Summary of Key Facts
Section 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 – Akitsu Kimoto
2.1.7 State Technical Reviewer: Not Applicable
2.1.8 Local Technical Reviewer: Suzanne Shields
2.1.9 River or Stream Name: Old Grandad Tank Wash
2.1.10 Reach Description: Old Grandad Tank Wash
2.1.11 Study Type: Hydrology and Hydraulics study of a Riverene System
Section 2.2: Mapping Information
2.2.1 FIRM Panels: 04019C-1690 and 2280K
2.2.2 Mapping for Hydrologic Study: Lidar based on 2008 flight used to derive 2’
contour interval maps using ARC-GIS 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
Section 2.3: Hydrology
2.3.1 Model or Method Used: HEC-HMS (v. 3.4) 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
Section 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 normal depth.
Section 2.5: Additional Study Information:
None

9

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.

10

Section 4: Hydrology
4.1 Method description.
The 100-year peak discharges for the nine subbasins of the Old Grandad Tank Wash
(OLG A, B, C and D; Figure 1.1) were calculated using U.S. Army Corps of Engineers
Computer Hydrologic Modeling System, (HEC-HMS) version 3.4. The HEC-HMS
model requires 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. The HEC-HMS model is
included in Appendix D.
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

4.2.1 Drainage area boundaries.
The limits of this study are shown in Fig.1.2. The Old Grandad Tank Wash watershed is
partially located within Federal land (national forest, FEMA Zone D), as shown on the
current Flood Insurance Rate Map (FIRM) number 04019C-1690 and 2280K.
The study watershed was divided into four sub-basins (Fig.1.1). The upstream mapping
limits is the upstream end of the Subbasin A, while the downstream limit is the upstream
end of FEMA Zone X-shaded (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 with DEM derived from the 2008 Lidar. 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
11

centerline, cross-sections, culverts, and other physical attributes of the wash were
determined by using the 10-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,
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

12

4.2.3 Gage Data.
None Available
4.2.4 Statistical parameters
None Available
4.2.5 Precipitation.
According to the Tech-018, the 3-hour storm shall be used as rainfall data in the HECHMS model in case that a time of concentration (Tc) is equal or less than three hours. A
3-hour storm was selected for a peak discharge calculation for the Roger Wash, since Tc
was less than 3 hours in all the subbasins.
A point 3-hour rainfall depth at the coordinates of the centroid of the watershed was
obtained from NOAA Atlas 14, upper 90% confidence interval precipitation frequency
estimate (NOAA 14 rainfall). Areal reduction factor was applied to watersheds larger
than 1 square mile, as described in Tech-018.
4.2.6 Physical parameters.
The physical parameters for the subbasins and reaches of the HEC-HMS model were
summarized in Tables 1 and 2. As mentioned in 4.1, all the methods and parameters were
determined following Tech-018. Table 1 summarizes the method used for a HEC-HMS
analysis.
The SCS Curve Number (CN) method was utilized as a rainfall loss method in the HECHMS model. The CN was determined using the Curve Number table associated with the
PC-Hydro User Guide (Arroyo Engineering, 2007) and a Hydrologic Soils Group map.
The CN was not adjusted for rainfall intensity or antecedent moisture conditions. The
SCS Unit Hydrograph method was used as a transform method. Impervious cover was
determined using the 2008 PAG aerial photograph and Table 3 in the PC-Hydro User
Guide (Arroyo Engineering, 2007). The combination of the kinematic wave method and
the U.S. Natural Resources Conservation Service (NRCS) segmented Time of
Concentration (Tc) calculation method (USDA-NRCS, 1986) was used to determine Tc,
following the recommendation on Tech-018. The Tc was calculated by summing the
travel time for sheet flow, shallow concentrated flow and channel flow. The Tc for sheet
flow was estimated using the kinematic wave equation. Manning’s roughness coefficient
for sheet flow was obtained using Table 3-1 in Technical Release 55, Urban Hydrology
for Small Watersheds (USDA-NRCS, 1986). HEC-GeoRAS and HEC RAS were used to
estimate average velocity of channels. The detail of the Tc calculation is included in
Appendix D.

13

Table 4.2 - Sub-basin Characteristics
Sub-Basin
OLG
OLG
OLG
OLG

A
B
C
D

Area
(sq mi)
0.38
0.47
0.68
0.49

CN
90.6
89.5
89.3
90.4

Impervious Area
(%)
7
5
5
5

Vegetation Cover
(%)
30
30
30
30

Lag Time
(min)
13.1
15.9
19.3
12.5

Runoff from subbasins was routed using the Modified-Puls method. Storage discharge
tables for the channel routing were developed using HEC-GeoRAS and HEC-RAS. Six
different discharges were used for storage-discharge relations. The number of subreaches
was calculated using the following method:
Vw = 1.5 * Vave .........eq.1
K=

L
...................eq.2
Vw

Therefore,
K
N = ..................eq.3
Δt
where Vave is average flow velocity, L is reach length, Vw is velocity of flood wave (a
conversion factor of 1.5 is used for natural channels), K is hydrograph travel time, Δt is
the time interval for computations in the model, and N is the number of steps in the reach
routing. Eq.4 was obtained from eq.1, 2, and 3. The detail of the calculation of the
number of subreach is included in Appendix D.
Table 4.3 - Sub-basin discharges

Sub-Basin
OLG
OLG
OLG
OLG

A
B
C
D

Area
(sq mi)
0.38
0.47
0.68
0.49

Rainfall Depth
(in)
3.44
3.44
3.44
3.44

Runoff Volume
(in)
2.37
2.35
2.32
2.41

Peak Discharge
(cfs)
1001
1105
1402
1341

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

14

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
As described above, this study mainly focuses on drainage information in the
downstream of the Old Grandad Tank Wash (Subbasin A). The 100-year peak discharge
at CP A was determined using the HEC-HMS. Six hours were simulated on a 1 minute
time step with rainfall occurring in the first three hours. The following discharges were
obtained from the hydrologic analysis:
Table 4.4 – Summary of 100-yr Peak Discharge Values
Concentration
Point

Location

CP A

Confluence with Tanque Verde Creek

Area (sq Rainfall
Runoff
Q100
mile)
Depth (in) Volume HMS (cfs)
(in)
2.02
3.25
2.18
3942

Time to
Peak
1:45

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

Location

CP A

Confluence with Tanque Verde Creek

Area (sq Rainfall
Runoff
mile)
Depth (in) Volume
(in)
2.02
2.52
1.5

Q25 HMS Q25 RRE
(cfs)
(cfs)
2723

1119

Time to
Peak
1:46

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

Location

CP A

Confluence with Tanque Verde Creek

Area (sq Rainfall
Runoff
Q500
mile)
Depth (in) Volume HMS (cfs)
(in)
2.02
4.22
3.09
5575

Time to
Peak
1:44

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. No regulatory discharge point data is available
along the Old Grandad Tank Wash.

15

Table 4.7 – Comparison of 100-yr Peak Discharge Values
Concentration
Point

Location

CP A

Confluence with Tanque Verde Creek

Area (sq
Q100
Q100
mile)
HMS (cfs) RRE (cfs)
2.02

3942

1976

Section 5: Hydraulics

5.1 Method description.
The hydraulic modeling for the Old Grandad Tank Wash was performed using Hec-RAS,
Version 4.0 (HEC-RAS), HEC-GeoRAS, Version 4.2.93 (HEC-GeoRAS), and ArcGIS,
Version 9.3.1. Normal-depth with a slope of 0.021 was assumed for a downstream
boundary condition.
The locations of the stream centerline, cross-sections, and bank of the Old Grandad Tank
Wash were determined using the 5-ft contour map and 2008 PAG aerial photos. The
geometric data, including stream centerline, flow paths and cross-sections, were digitized
in HEC-GeoRAS. The digitized data was exported to create geospatially referenced
geometric data (cross section, reach profile) in HEC-RAS. Other parameters for the
steady-state analysis in HEC-RAS, such as Manning’s n-values, expansion and
contraction coefficients, boundary condition, and ineffective flow areas were manually
input into HEC-RAS. The hydraulic data obtained from HEC-RAS were imported into
HEC-GeoRAS to delineate a floodplain boundary for the Old Grandad Tank Wash.
5.2 Work study maps
The work study map for the Old Grandad Tank Wash is included 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 channel and the over-bank areas were
determined by using a 2008 aerial photo. Manning’s n value of 0.05-0.055 was assigned
to overbank with desert brush along the Old Grandad Tank Wash, while 0.035-0.045 was
assigned to a channel.

16

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.
5.4 Cross section description.
A 5-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 no culverts along the study reaches of the Old Grandad Tank 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 Old Grandad Tank Wash.
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.

17

5.7 Problems encountered during the study.
5.7.1 Special problems and solutions.
None.
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 Old Grandad Tank 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.

18

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
Section 7: Ratio of the top width of 100-yr and 25-yr floodplain
A map showing the cross sections with the ratio of the topwidth less than 1.25 is included
in Addendum 1. The average ration of 100-yr to 25-yr floodplain topwidth for the study
reach of the Old Grandad Tank Wash is 1.22.

19

31

30

2850
30

2900

3

0
02

90

30

30

70

40

32

0

33

318

33

3230

322

0

11

3210

2990

90
317
0

31

31

32
31

50

V
U

311

2850

281

0

31

2850

4894

303

3050

476 0

V
U

3090

3080

0

2770

V
U

2800.094

0

60

Contour 2 foot

3100

50

20

2870

5057

Discharge Point
Cross Sections

3230

2780

40
31

0

V
U

324

2860

!
(

00

5231

2802.721

0

57

32

V
U

2806.695

0

327

540 9

2810.39

00

50

60

20

3160

0

333

33

0

8

285

33

80

3310

592

V
U
UU
V
V

2815.309

90

40

60

50

32

32

580

U
V
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32

0
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32

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3120

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7

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!
(

3
2.

2800

32

2860

!
(

2820

66
6.5
282

94
4.1
282

2
28

CP B

CP C
!
( CP D

20

Exhibit 1
100-year Floodplain
with cross sections
Old Grandad Tank Wash

40

28

00

Contour 10 foot

4643

2830

6
30

00

2930

Proposed Floodplain

10

0

29

V
U

294

0

28

29

4406

2792.792

70

30
2860

2810

2760

ZONE A

50
29

2880

50

292

U
V
V
U

0

2880
2860

ZONE AE

3881

2781.233

20

291

0

Aerial Photo: 2008 Pima Association of Governments
Topo: 2008 Pima Association of Governments
Vertical Datum: NAVD 1988

2940

30

90

2780

0

29

20
27

2750

2756
.

28

29

2920
10
29

27
27

290

80

2940

0

3301

30

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0

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286

2767.643

40

2930

0
294

295

40

3454

29

2960

00

V
U

2770.653

29

28

2930

3562

50

V
U

70

29

27

50

29

2890

0

2930

2890

290

374 6

2777.925

2773.306

511

28

28

90

2746.344

28

30

242 4

2730

2750

2730

0

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2736

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2770

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ON
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20

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2749.553

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2870

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0

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80

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2752.448

2885

273

0

2910

2780

2760

295

0

70

28

4043

0

2940

90

V
U

2785.135

Floodplain Zone
283

28

28

298

2880

2910
294
0

2900

V
U
4250

2790.121

60

2960

2770

10

29

3010

0

2930

2850

292

2797.9

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.422
2740

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2770

V
U

220 7

.085
2739

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U
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V
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1949

165
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2726

274

Pima County Index Map

8

V
U

149
41
3.8
272

8

V
U

0
273

9

V
U

3
11

27

27

0

98
0.1
272

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272

273

13

2730

0

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2735.074

0

2710

20

V
U
92

58

4

30

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8
.62
07
7
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9

273

0

V
U

Index Map Scale 1:1,500,000

0

27

20

0
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29
5.5

2720

2720

0
27

271

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27

10

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11
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264

270

2720

0

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2700

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94
96.1

200

100

0

Pima County Regional Flood Control District

130

.53
2694

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

2710

CP A

26

0

272

271

0

2720

0
27

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.

V
U
37

9
2691.

91

2690

2700

269

0

2700

2700

2690

2690

2710

27

00

2700

80
26

2680

2680

90

90

26

00

26

27

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

10/2010

\\Gislib\rfcd\projects\imd\xavi\mxd\AKITSU\Old_grandad\Old_Grandad_Tank_wash_exh1.mxd

200 Feet

DE
EP

WE

LL

Exhibit 2
Annotated Flood
Insurance Rate Map
04019C1690 K
Old Grandad Tank Wash
27

28

O
OK
LO

UT

CORONADO NATIONAL FOREST

ZONE D

33

Proposed
100 year
Floodplain

PINZ
CORTE

PIMA COUNTY

34

A
ON RE

EL CAMINO RINCONADO

ZONE X

CAMINO CASCABEL

L

ZONE X

ZONE X

E
AV
DA
NI
RG
SO
O

REDINGTON

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

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

03

04

Streets
FIRM X-Sections

0

275

550

1,100
Feet

ç ç ç ç ç Base Flood Elevations

Proposed Floodplain
LOMRs
Sections
FIRM - Flood Insurance Rate Map
Jurisdictions
Existing Floodplain Zone
A
AE
AO
X
X (SHADED)

Pima County Index Map

gislib\rfcd\projects\imd\xavi\mdx\AKITSU\Old_Grandad\Old_Grandad_TankExh2_Anno_FIRM8X11_1690K.mxd

Exhibit 2
Annotated Flood
Insurance Rate Map
04019C 2280K
Old Grandad Tank Wash

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ç çç çç
çç ç çç

PLACITA CARTAMO

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)

ççç çç çç ççç çç çç ç

09

MI
CA

IL
AD
EB
AC

ççç

AR

PIMA COUNTY

03

"
)

LOMR Case 99-09-1302P
Effective Date 7/24/2000

ç ç ç ç ç ç ç ç ç ç çç ç ç ç ç ç ç

04

O
TEN
CEN

L
ITA E
PLAC

0
ç ç ç2ç ç7
ç ç ç ç ç2ç
çç ç çç çç

ZONE X

ZONE X

2695

INO
EL
CA
M

Proposed
100 year
Floodplain

O
TAM
CAR
INO
CAM

RIN
CO
NA
DO

RED
ING
TON

SPEEDWAY

SAGUARO NATIONAL PARK EAST

10

LOMR Case 99-09-1302P Effective Date 7/24/2000

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

Streets

0

280

560

1,120
Feet

FIRM X-Sections

ç ç ç ç ç Base Flood Elevations
Proposed Floodplain
LOMRs

Sections

FIRM - Flood Insurance Rate Map
Jurisdictions

Existing Floodplain Zone

Pima County Index Map

A

AE
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

AO
X

X (SHADED)

gislib\rfcd\projects\imd\xavi\mdx\AKITSU\Old_Grandad\Old_Grandad_TankExh2_Anno_FIRM8X11_2280K.mxd

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.