Section 1 Introduction ........................................................................................................ 4
1.1 Propose ..................................................................................................................... 4
1.2 Project Authority....................................................................................................... 4
1.3 Project Location ........................................................................................................ 4
1.4 Hydrologic and Hydraulic Methods .......................................................................... 5
1.5 Acknowledgment ...................................................................................................... 5
1.5 Study Results ............................................................................................................. 5
Section 2 Local Government Abstract ................................................................................ 9
2.1 Project Contact Information ..................................................................................... 9
2.2 General Information ................................................................................................. 9
2.3 Survey and Mapping Information ............................................................................. 9
2.4 Hydrology ................................................................................................................ 10
2.5 Hydraulics................................................................................................................ 10
Section 3 Survey and Mapping Information ..................................................................... 10
3.1 Digital Projection Information ................................................................................ 10
3.2 Field Survey Information......................................................................................... 10
3.3 Mapping .................................................................................................................. 11
Section 4 Hydrology .......................................................................................................... 11
4.1 Method Description ................................................................................................ 11
4.2 Parameter Estimation ............................................................................................. 13
4.2.1 Drainage Area Boundaries ............................................................................... 13
4.2.2 Watershed Work Maps .................................................................................... 13
4.2.3 Gage Data ......................................................................................................... 13
4.2.4 Spatial Parameters ........................................................................................... 13
4.2.5 Precipitation ..................................................................................................... 13
4.2.6 Physical Parameters ......................................................................................... 13
4.3 Issues Encountered During the Study ..................................................................... 14
4.3.1 Special Problems and Solutions ....................................................................... 14
4.3.2 Modeling Warning and Error Messages .......................................................... 14
4.4 Calibration ............................................................................................................... 14
4.5 Final Results ............................................................................................................ 14
4.5.1 Hydrologic Analysis Results.......................................................................... 14
4.5.2 Verification of results ................................................................................... 15
Section 5 Hydraulics .......................................................................................................... 15
5.1 Method Description ................................................................................................ 15
5.2 Work Study Maps.................................................................................................... 15
5.3 Parameter Estimation ............................................................................................. 16
5.3.1 Roughness Coefficients .................................................................................... 16
5.3.2 Expansion and Contraction Coefficients .......................................................... 16
5.4 Cross-Section Description ....................................................................................... 16
5.5 Modeling Consideration.......................................................................................... 16
5.5.1 Hydraulic Jump and Drop Analysis................................................................... 16
5.5.2. Bridges and Culverts ....................................................................................... 16
2

5.5.3 Levees and Dikes .............................................................................................. 16
5.5.4 Non-Levee Embankments ................................................................................ 16
5.5.5 Island and Flow Splits....................................................................................... 16
5.5.5 Ineffective Flow Areas...................................................................................... 17
5.6 Floodway Modeling................................................................................................. 17
5.7 Problems Encountered ........................................................................................... 17
5.7.1 Special Problems and Solutions ....................................................................... 17
5.7.2 Model Warnings and Errors ............................................................................. 17
5.8 Calibration ............................................................................................................... 17
5.9 Final Results ............................................................................................................ 17
5.9.1 Hydraulic Analysis Results................................................................................ 17
5.9.2 Verification of Results ...................................................................................... 17
Section 6 Erosion and Sediment Transport ...................................................................... 18
Section 7 Draft FIS Report Data ........................................................................................ 18
7.1 Summary of Discharges .......................................................................................... 18
7.2 Floodway Data ........................................................................................................ 18
7.3 Annotated Flood Insurance Rate Map .................................................................... 18
7.4 Flood Profiles .......................................................................................................... 18
List of Tables
Table 1 Methods used for a PC-Hydro analysis ................................................................ 14
Table 2 Subbasin Characteristics ...................................................................................... 14
Table 3 Summary of the Hydrologic Analysis ................................................................... 14
Table 4 Comparison of a peak discharge .......................................................................... 15
List of Figures
Figure 1.1 Watershed Map ................................................................................................. 6
Figure 1.2 Study Limits ........................................................................................................ 7
Figure 1.3 Soil Classification................................................................................................ 8
Figure 4.1 Flow Chart of Mapping Process ....................................................................... 12
Appendix A: References
Appendix B: FEMA MT-2 Forms, General Documentation and Correspondence
Appendix C: Survey Field Notes
Appendix D: Hydrologic Analysis, Supporting Documents
Appendix E: Hydraulic Analysis, Supporting Documents
Appendix F: Erosion Analysis, Supporting Documents
Exhibit
Exhibit 1 100-yr floodplain limit for the Tucson Mountain Unnamed 02 and 03 Washes

3

Section 1 Introduction
1.1 Purpose
The objective of this Technical Data Notebook (TDN) is to provide 100-yr peak
discharges at a Concentration Point (CP A) for the Unnamed 02 and 03 Washes, 100-yr
floodplain boundary and erosion hazard information, using the most up-to-date
topographic, hydrologic, and hydraulic data.
This TDN was prepared in accordance with the “Instructions for Organizing and
Submitting Technical Documentation for Flood Studies” prepared by the Arizona
Department of Water Resources, Flood Mitigation Section (Arizona State Standard, SSA
1-97) and FEMA Guidelines. This is a local study and has not been submitted to FEMA.

1.2 Project Authority
The State of Arizona has delegated the responsibility to each county flood control
district to delineate or require the delineation of floodplains and to regulate
development within floodplains (ARS § 48-3609):
This study has been prepared by the Pima County Regional Flood Control District (RFCD):
Pima County Regional Flood Control District
97 East Congress, Tucson, AZ 85701
The project was prepared by:
Akitsu Kimoto, Principal Hydrologist
Pima County Regional Flood Control District
97 East Congress, Tucson, AZ 85701

1.3 Project Location
The study was performed to provide drainage information for Unnamed 02 and 03
Washes. The site includes Sections 02 and 03 of Township 13 South, Range 12 East, Pima
County, Arizona. The entire watershed of the Unnamed 02 and 03 Washes is in FEMA
Zone X, as shown on the current Flood Insurance Rate Map (FIRM) number 04019C1655L.
The study area for the Unnamed 02 Wash is from Ina Rd. to Stable TR. (Fig.1.1). The
study watershed is 0.25 square miles (Fig.1.2). The study area for the Unnamed 03 Wash

4

is from Silverbell Rd. to ~700 feet east of Paddock Pl. (Fig.1.1). The study watershed is
0.25 square miles (Fig.1.2).

1.4 Hydrologic and Hydraulic Methods
A hydrologic analysis was performed to estimate regulatory discharge rates at Ina Rd.
using PC-Hydro Version 5.4.2 (PC-Hydro). The parameters for PC-Hydro, such as soil,
vegetation, slope, flow path length and roughness were selected in accordance with the
PC-Hydro User Guide (Arroyo Engineering, 2007). The proposed regulatory discharges
are flow rates that have a 1-percent chance of being equaled or exceeded each year
(“100-year” discharge rates). A hydraulic analysis was performed to determine a 100-yr
floodplain boundary using HEC-GeoRAS, Version 10 (HEC-GeoRAS) and HEC-RAS Version
4.1 (HEC-RAS).

1.5 Acknowledgment
This study relied on assistance from RFCD GIS staff, who were integral to the
development of the models and maps.

1.6 Study Results
The 100-yr discharges were calculated for the Unnamed 02 and 03 Washes. Subbasin
boundaries and corresponding CPs are illustrated in Figure 1.2. Hydrologic
characteristics for the studied subbasins are presented in Table 2. Calculated discharges
are summarized in Table 3. The calculated discharges are compared with the USGS
Regional Regression Equation (Table 4). The comparison shows that the peak discharges
calculated in this study are reasonable. This study found one home in the Unnamed 02
Wash watershed at risk for flooding during the 100-yr flood.

5

INA RD

Figure 1.1
Watershed Map
Unnamed 2 Wash
Unnamed 3 Wash

!
(

ER
LV
SI

!
(

BE
LL

!
(

Discharge Points

RD

Contour 5ft.

Watersheds
Unnamed 2
unnamed 3
C
Aerial : 2012 Pictometry Orthophoto Imagery (
Topo: 2008 Pima Association of Governments
Datum: NAVD 1988

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.
Pima County Regional Flood Control District

300

150

0

300 Feet

10/2013
gislib\rfcd\projects\imd\xavi\mdx\AKITSU\Unnamed_2-3\Unnamed_2_&_3_Fig_1.mxd

Section 2 Local Government Abstract
2.1 Project Contact Information
Contact Information:
Akitsu Kimoto
Pima County Regional Flood Control District
97 E. Congress, Tucson, AZ 85705
Akitsu.Kimoto@pima.gov
Local Technical Reviewer:
Terry Hendricks
Pima County Regional Flood Control District
97E Congress, Tucson, AZ 85705
Terry.Hendricks@pima.gov
Date Study Submitted: _________________________
Date Study Approved: __________________________
2.2 General Information
Community: Pima County Regional Flood Control
County: Pima County
River or Stream Name: Tucson Mountain Unnamed 02/03 Wash
Reach Description: Wash in Tucson Mountain
Study Type: Hydrology and Hydraulics study of a Riverine System
Purpose of the Study: To provide regulatory discharges and map floodplain boundaries
Summary of Hydrology and Hydraulic Methods:
Brief Summary Description of the Study Results:
Acknowledgements:

2.3 Survey and Mapping Information
Digital Projection Information: NAD 1983 HARN State Plane Arizona Central
USGS Quad Sheets if available:
Mapping for Hydrologic Study: LiDAR based on 2008 flight used to derive 2-ft contour
interval maps using ArcGIS 10.0, PAG 2012 orthophotos
Mapping for Hydraulic Study: LiDAR based on 2008 flight used to derive a DEM (20-ft
cell size) for use with HEC-GeoRAS, PAG 2012 orthophotos

9

2.4 Hydrology
Model or Method Used: PC-Hydro Version 5.4.2
Storm Duration: Based on 1-hr Rainfall Depth
Hydrograph Type: NA
Frequencies Determined: 100 yr
List of Gages used in Frequency Analysis or Calibration: None
Rainfall Amounts and Reference: NOAA 14 Upper 90% Confidence Interval
Unique Conditions and Problems: None
Coordination of Q’s: Comparison with a USGS Regression Equation
2.5 Hydraulics
Model or Method Used: HEC-GeoRAS, Version 10 (HEC-GeoRAS) and HEC-RAS Version
4.1 (HEC-RAS)
Regime: Modeled as subcritical
Frequencies for which Profiles were computed: 100 yr
Method of Floodway Calculation: Floodway Not Determined in this Study
Unique Conditions and Problems: None
2.6 Erosion, Sediment Transport and Geomorphic Analysis
Summary of Method: NA
Issues Encountered During Study: NA
Summary of Findings: NA
2.7 Additional Study Information
None

Section 3 Survey and Mapping Information
3.1 Digital Projection Information
The data below are included in this TDN (see “GIS” folder)
Projection: State Plane, Arizona Central Zone
Horizontal Datum: NAD 83 HARN
Vertical Datum: NAVD 88
Units: International Feet
Aerial Photo: PAG 2012 Orthophotos
Contour: 2 feet interval
Topographic Data: 20-ft DEM

3.2 Field Survey Information
A survey was not necessary for this study.

10

3.3 Mapping
A Digital Elevation Model (DEM) derived from 2008 Light Detection and Ranging (LiDAR)
data was used for the HEC-RAS analysis. The contour interval of the topographic map is
2 feet.
Following data are included in this TDN (see “GIS” folder):
Aerial Photo: PAG 2012 Orthophotos
Contour: 2 feet interval
Topographic Data: 5-ft DEM

Section 4 Hydrology
4.1 Method Description
Hydrologic analysis was performed using PC-Hydro Version 5.4.3 (PC-Hydro). The PCHydro uses a semi-empirical method, which is similar to the Rational Formula. The
method is unique to Pima County. Pima County has been using the Pima County
Hydrology Procedures (PC-Hydro method) for over 30 years for a floodplain
management. The PC-Hydro method has been accepted by FEMA for prediction of 100yr peak discharges in Pima County (i.e. Friendly Village LOMR, Case # 08-09-0473P). The
PC-Hydro method produces conservative discharge on smaller watersheds and PC-Hydro
is the accepted method for watersheds less than one square mile in Pima County
Regional Flood Control District Technical Policy 018 (Tech-018, Appendix A). The PCHydro model requires the parameters regarding rainfall, topography, soil, and
vegetation to determine peak discharge. Those parameters were determined following
the PC-Hydro User Guide (Arroyo Engineering, 2007). The PC-Hydro output is included in
Appendix D.

11

Figure 4.1 Flow Chart of Mapping Process
Topographic Data Preparation using ArcGIS with TIN
or DEM

Hydrologic Analysis using PC-Hydro

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

Hydraulic Analysis using HEC-RAS
(Manually input the following data; Manning’s n-values,
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 Parameter Estimation
4.2.1 Drainage Area Boundaries
The Unnamed 02 and 03 Washes watersheds are located within FEMA Zone X. The study
area for the Unnamed 02 Wash is from Ina Rd. to Stable TR. (Fig.1.1). The study
watershed is 0.25 square miles (Fig.1.2). The study area for the Unnamed 03 Wash is
from Silverbell Rd. to ~700 feet east of Paddock Pl. (Fig.1.1). The study watershed is 0.25
square miles (Fig.1.2).

4.2.2 Watershed Work Maps
A watershed work map is included in Exhibit 1. The work map includes subbasin
boundaries, concentration points, flow center lines and cross sections with station
numbers and water surface elevations. Soil group boundaries are shown for the
drainage area in Figure 1.3. Concentration point was named as Un_02 CP A for the
Tucson Mountain Unnamed 02 Wash, and Un_03 CP A for the Tucson Mountain
Unnamed 03 Wash.

4.2.3 Gage Data
No gage data were used in this TDN.

4.2.4 Spatial Parameters
No spatial parameters were used in this TDN.

4.2.5 Precipitation
The NOAA 14 Atlas 90% upper confidence rainfall data was used. The rainfall intensity
at the time of concentration is 5.2 in/hr for the Unnamed 02 Wash watershed, and 5.27
in/hr for the Unnamed 03 Wash watershed. No area reduction factor was applied. 1-hr,
100-year storm rainfall is 3.27 in/hr for Unnamed 02 Wash and 3.46 in/hr for Unnamed
03 Wash.

4.2.6 Physical Parameters
The methods used in this study are summarized in Table 1. The PC-Hydro model
calculates runoff coefficients using an adjusted Curve Number (CN) method, which has
been developed based on the results of the USDA-ARS research. This procedure
assumes that high intensity, short duration storms result in raindrop impacts causing the

13

surface of soils to seal up, resulting in reducing infiltration (Caliche Effect). The CN in the
PC-Hydro model increases with increasing rainfall depth and intensity. The detail of the
method is described in PC-Hydro User Guide (Arroyo Engineering, 2007).
Table 1 Methods used for a PC-Hydro analysis

Rainfall Depth
Rainfall Loss
Time of Concentration

Selected Method
NOAA 14, upper 90% Confidence Interval
Adjusted SCS Curve number
Pima County Hydrology Procedure

Table 2 Watershed Characteristics
CP Name
Un_02 CP A
Un_03 CP A

Area
(Acre)
0.23
0.25

Impervious Area
(%)
15
25

Vegetation Cover
(%)
25
25

4.3 Issues Encountered During the Study
4.3.1 Special Problems and Solutions
There were no problems with the hydrologic modeling.

4.3.2 Modeling Warning and Error Messages
None

4.4 Calibration
No calibration was conducted in this study.

4.5 Final Results
4.5.1 Hydrologic Analysis Results
The 100-year peak discharge at CP A (near Ina Rd.) was determined using the PC-Hydro.
The result is summarized Table 3.
Table 3 Summary of the Hydrologic Analysis
CP Name
Un_02 CP A

Location
Silverbell Rd.

Area
(acre)
147

Rainfall
Intensity at
Tc (in/hr)
5.2

Time of Concentration
(min)
20

Q100 (cfs)
485

14

Un_03 CP A

Near Ina Rd.

160

5.27

19.5

558

4.5.2 Verification of results
The estimated peak discharge at CP A was also compared with the peak discharge
obtained from USGS Regression Equation 13 (Thomas et al., 1997) (Table 4). The
comparison showed that the PC-Hydro-derived peak discharge is 12.8% higher than the
one derived from the Regression Equation for the Unnamed 02 Wash, while 21.5% for
the Unnamed 03 Wash.
Table 4 Comparison of a peak discharge
Concentration
Point

Location

Area (sq
mile)

Q100 PCHydro(cfs)

Q100
RRE (cfs)

Un_02 CP A
Un_03 CP A

Silverbell Rd.
Near Ina Rd.

0.23
0.25

485
558

430
459

RRE: USGS Regression Equation 13

Section 5 Hydraulics
5.1 Method Description
Steady flow analysis with HEC-RAS, Version 4.1 was performed to delineate a 100-year
floodplain of the Unnamed 02 and 03 Washes. Normal depth was used as a downstream
boundary condition. Parameters for the hydraulic analysis were selected following the
District Tech Policy 019.
The physical attributes of the wash were digitized in ArcGIS using the HEC-GeoRAS
extension and exported to HEC-RAS to create geospatially referenced geometric data
(cross section, reach profile). Other parameters for the steady-state analysis, such as
Manning’s n-values, expansion and contraction coefficients, boundary condition, and
ineffective flow areas were manually input into HEC-RAS. Normal-depth with a slope of
0.021 was assumed for the downstream boundary condition for the Unnamed 02 Wash,
while 0.135 was used for the Unnamed 03 Wash. The hydraulic data obtained from HECRAS were imported into HEC-GeoRAS to delineate a floodplain boundary for the
Unnamed 02 and 03 Washes.

5.2 Work Study Maps
A work study map is shown in Exhibit 1.

15

5.3 Parameter Estimation
5.3.1 Roughness Coefficients
Manning’s n values were determined by a combination of a site visit and 2012 PAG
aerial photo. Manning’s n value of 0.065 was assigned for the overbank with desert
brush along the Unnamed 02 Wash. The value of 0.06 was used for the Unnamed 03
Wash. The value of 0.035 was assigned to a channel for the both washes.

5.3.2 Expansion and Contraction Coefficients
The expansion coefficient of 0.3 and contraction coefficient of 0.1 were used for the
entire study reach, except immediately upstream and downstream of the three culverts.
The expansion coefficient of 0.5 and contraction coefficient of 0.3 were used at the
upstream and downstream of the culverts along the Unnamed Wash 03.

5.4 Cross-Section Description
A 2-foot interval contour map was used to select the location of cross sections. Crosssection locations were determined primarily based on the channel topography. The
cross-section lines were drawn to be perpendicular to flow paths in HEC-GeoRAS. The
locations of cross sections and channels used for this study are shown in Exhibit 1.

5.5 Modeling Consideration
5.5.1 Hydraulic Jump and Drop Analysis
No hydraulic, drop analyses or adjustment of the floodplain was conducted in this study.

5.5.2. Bridges and Culverts
There are three culverts along the Unnamed 03Wash.

5.5.3 Levees and Dikes
There are no levees or dikes located within the study limit.

5.5.4 Non-Levee Embankments
None.

5.5.5 Island and Flow Splits
There were no islands or flow splits modeled.

16

5.5.5 Ineffective Flow Areas
Ineffective flow option was modeled in the HEC-RAS model. In general these ineffective
flow areas were disconnected overbank areas that would not convey flow to the next
downstream cross-section.

5.6 Floodway Modeling
No floodway modeling was performed in this study.

5.7 Problems Encountered
5.7.1 Special Problems and Solutions
There are no special problems in the study limit.

5.7.2 Model Warnings and Errors
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.

5.8 Calibration
The model was not calibrated in this study.

5.9 Final Results
5.9.1 Hydraulic Analysis Results
The HEC-RAS model is included in Appendix E.

5.9.2 Verification of Results
The results suggest that the proposed floodplain limit is reasonable based on the
topography.

17

Section 6 Erosion and Sediment Transport
No erosion or sediment transport analysis was conducted in this study.

Section 7 Draft FIS Report Data
7.1 Summary of Discharges
Peak discharges at CP A was used for the hydraulic analysis in this study. The estimated
regulatory discharge rates are summarized in Table 3.

7.2 Floodway Data
Not applicable.

7.3 Annotated Flood Insurance Rate Map
Not applicable.

7.4 Flood Profiles
Flood profiles are included in the HEC-RAS model in Appendix E.

18

A.1 Data Collection Summary
Aldridge, B. and J. Garrett. 1973. Roughness Coefficients for Stream Channels in
Arizona. US Department of the Interior Geological Survey. Tucson, AZ.
Arizona Department of Water Resources, Flood Mitigation Section
“Instruction for Organization and Submitting Technical Document for Flood Studies”
SSA1-97, November 1997
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
City of Tucson (COT), Department of Transportation, 1989. Standards Manual for
Drainage Design and Floodplain Management in Tucson, Arizona. Revised in 1998.
National Weather Service. 1984. Depth-Area Ratios in the Semi-Arid Southwest
United States, NOAA Technical Memorandum NWS Hydro-40
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.
Phillips, J., and T. Ingersoll. 1998. Verification of Roughness Coefficients for Selected
Natural and Constructed Stream Channels in Arizona. U.S. Geological Survey
Professional Paper 1584.
Pima County Regional Flood Control District
“Pima County Mapguide Map”, 2008
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). 2003. Geospatial Hydrologic Modeling Extension
HEC-GeoHMS, (v 1.1) CPD-77, 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.

A 2. Referenced Documents
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.
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. Department of Agriculture Natural Resources Conservation Service (NRCS), 1986.
Urban Hydrology for Small Watersheds, Technical Release 55. Washington, DC.

Appendix B FEMA MT-2 Form, General Documentation
and Correspondence
None

Appendix C: Survey Field Notes

Page 1 of 1

Terry Hendricks

From: Curtis, Edward [mailto:Edward.Curtis@dhs.gov]
Sent: Tuesday, November 10, 2009 2:44 PM
To: Manny M. Rosas
Cc: Terry Hendricks; Lucero, Andrew; Caldwell, Jason; Akl, Pascal
Subject: RE: PAG 2008 Orthos/Lidar
Mr. Rosas –
I apologize for the delay in responding to you regarding the Sanborn LiDAR report. Pascal Akl of Michael Baker,
Jr. reviewed the updated July 2009 report on behalf of FEMA and advised me that all of the concerns raised in his
May 18, 2009 memorandum titled “Pima County, CA [sic] Sanborn LiDAR Report Items” were addressed in the
updated report except the comment that the original report lacked a sufficient number of checkpoints in urban
areas and dense vegetation areas. No additional checkpoints were surveyed in such arease to permit analysis of
data accuracy in these land cover categories. However, in the data voids analysis section of the updated report
(p. 16), Sanborn states the following: "Specific areas, dense vegetation or undergrowth near small streams, for
example, prevents the LiDAR pulses to fully penetrate to the true ground surface. Thus, for mapping products
such as floodplain or contour mapping, LiDAR data must often be manually supplemented with breaklines and
mass-points to accurately model the terrain surface." As long as the data is used with caution and supplemented
with additional ground survey data where necessary in accordance with this statement, I am satisfied that the
terrain data meets FEMA standards for use in detailed flood studies.
Please contact me if you have any questions regarding our review and comments.
Ed Curtis, P.E., CFM
Risk Analysis Branch
FEMA Region IX
(510) 627-7207 - office
(510) 295-5249 - mobile

2/25/2010

Appendix D: Hydrologic Analysis Supporting
Documentation
(models, spreadsheets and supporting information is provided digitally in the TDN disk)

Appendix E: Hydraulic Analysis and As-Built Drawings
for Hydraulic Structures
(models, spreadsheets and supporting information is provided digitally in the TDN disk)

Appendix F: Erosion and Sediment Transport Analysis
Supporting Documentation
None