FLOODPLAIN ANALYSIS FOR THE MIDDLE CREEK WATERSHED
A Project
Presented to the faculty of the Department of Civil Engineering
California State University, Sacramento
Submitted in partial satisfaction of
the requirements for the degree of
MASTER OF SCIENCE
in
Civil Engineering
by
Jeremy P. Hill
FALL
2012
© 2012
Jeremy P. Hill
ALL RIGHTS RESERVED
ii
FLOODPLAIN ANALYSIS FOR THE MIDDLE CREEK WATERSHED
A Project
by
Jeremy P. Hill
Approved by:
__________________________________, Committee Chair
Dr. Saad Merayyan
_______________________________
Date
iii
Student: Jeremy P. Hill
I certify that this student has met the requirements for format contained in the University
format manual, and that this project is suitable for shelving in the Library and credit is to
be awarded for the project.
____________________________, Department Chair
Dr. Kevan Shafizadeh, P.E., PTOE
Department of Civil Engineering
iv
___________________
Date
Abstract
of
FLOODPLAIN ANALYSIS FOR THE MIDDLE CREEK WATERSHED
by
Jeremy P. Hill
Levees in California’s Central Valley currently face an unacceptable high level of
risk. Many agencies are now attempting to analyze the probability of levee failure and the
resulting flooding and damages. The California Department of Water Resources (DWR)
is currently evaluating the flood risk associated with the approximately 1,600 miles of
State Plan of Flood Control levees throughout California’s Central Valley. The objective
of this study is to present a methodology for determining floodplains associated with
various potential levee breaches. Middle Creek and its tributaries contain 13.5 miles of
levees that protect the town of Upper Lake in Northern California. According to DWR’s
Flood Control System Status Report, many of these levees have a high potential for
failure. This study will utilize the most current topographical and survey data that is
available from DWR to develop the hydraulic models.
v
The modeling software used for this study includes the United States Army Corps
of Engineers Hydrologic Engineering Center- River Analysis System (HEC-RAS) and
FLO-2D, developed by FLO-2D Software, Inc. These softwares are used to model the
one-dimensional channel flows and two-dimensional overland flood flows caused by
levee breaches. The popularity of two-dimensional hydraulic models has grown
substantially in recent years. These two-dimensional models have benefitted from
increased computing power which has resulted in faster simulation times and lower
project costs.
The hydraulic models for this study were developed to be consistent with the
recommendations made by the DWR Hydrology and Hydraulics Coordination Work
Group, which is a team of leading hydraulic modelers in California. The results of the
model simulations are presented as water surface profiles and floodplain depth and
velocity maps for the 100- and 500-year flood events.
_________________________, Committee Chair
Dr. Saad Merayyan
_________________________
Date
vi
ACKNOWLEDGEMENTS
I would like to thank my advisor, Professor Saad Merayyan for allowing me to pursue
this study. I would also like to thank the following:

My family and friends for constantly supporting me.

All of my professors that have motivated me to become an engineer.

My colleagues at the Department of Water Resources for encouraging me to
pursue a Master of Science Degree.
vii
TABLE OF CONTENTS
Acknowledgements ……………………………………………………………....… vii
List of Tables ………………………………………………………………..……..… x
List of Figures …………………………………………………………………...….. xi
Chapter
1. INTRODUCTION .……………………………………..……….……….….…… 1
1.1 Description of Study Area …………………………………….…….…… 3
2. LITERATURE REVIEW ………………………………..……………….………. 6
2.1 Historic Flood Events ………………………………………………........ 6
2.2 US Army Corps of Engineers Middle Creek Project ……………….….... 6
2.3 FEMA Flood Insurance Study …………………………........................... 7
2.4 Middle Creek Flood Damage Reduction and Ecosystem Restoration …... 7
2.5 DWR Central Valley Floodplain Evaluation and Delineation ……........... 8
3. MODEL BACKGROUND ………………………………………………………10
3.1 HEC-RAS Governing Equations ……………………………………..… 10
3.2 FLO-2D Governing Equations ……………………………………...….. 12
4. METHODS OF ANALYSIS ……………………………………………...….….. 16
4.1 Hydrologic Analysis …………………………………………………..... 16
4.2 Hydraulic Modeling ……………………………………………….…… 19
4.3 Topographical Data …………………………………………………….. 21
4.4 Geotechnical Data ……………………………………………………… 22
5. HYDRAULIC ANALYSIS USING HEC-RAS ………...………..................… 26
5.1 Model Development ………………………………………………..….. 26
5.2 Boundary Conditions ……………………………………………..……. 35
viii
5.3 Model Simulations …………………………………………………..…. 36
5.4 Model Calibration and Verification ………………………………….… 39
5.5 Model Results ……………………………………………………..…… 40
6. FLOOD INUNDATION USING FLO-2D ………….…………………………. 48
6.1 Model Development ……………………………………………………. 48
6.2 Boundary Conditions …………………………………………………… 55
6.3 Model Simulations ………………………………………………..……. 55
6.4 Model Calibration and Verification ……………..…………………..…. 60
6.5 Model Results …………………………………………………….……. 61
7. DISCUSSION OF RESULTS …………………………………...…………..…. 66
8. CONCLUSIONS …………………………………………………………….…. 70
Appendix A. Cross Sections Table …………………………………………………. 72
Appendix B. Photos for Determining Manning’s n-values ……….……..…………. 79
Appendix C. Lateral Structures Table ……………………………………………… 83
Appendix D. Storage Area Curves …………………………………………………. 86
Appendix E. HEC-RAS Sensitivity Analysis Results ………………………..….…. 90
Appendix F. HEC-RAS Water Surface Profiles …………………...……...……..… 94
Appendix G. Levee Breach Hydrographs ……………………………………….... 113
Appendix H. FLO-2D Levee Breach Simulation Results …………………...……. 123
References …………………………………………………………………………. 133
ix
LIST OF TABLES
Tables
Page
1.
Peak Flow Rate Estimates from Various Models …………………………… 17
2.
Model Reaches ……………………………………………………….……… 28
3.
In-Line Structures ……………………………………………..……..……… 32
4.
Upstream Boundary Conditions- Peak Flows ……………………….……… 35
5.
Unsteady Calculation Options and Tolerances ……………………………… 37
6.
100-Year Levee Freeboard Assessment ……….……………………….…… 41
7.
500-Year Levee Freeboard Assessment …………………………….….…… 42
8.
100-Year Levee Breach Locations ………………………………………..… 46
9.
500-Year Levee Breach Locations ……………………………………..…… 47
10.
FLO-2D Overland Roughness Coefficient by Land Use Type ………..……. 51
11.
100-Year Levee Breach Simulation Results ………………………………... 58
12.
500-Year Levee Breach Simulation Results …………………………….….. 59
13.
ARF and WRF Sensitivity Results Summary (for 500-Year Flood) …...…… 61
14.
Number of Structures Inundated from 100-Year Levee Breach Scenarios …. 65
15.
Number of Structures Inundated from 500-Year Levee Breach Scenarios …. 65
x
LIST OF FIGURES
Figures
Page
1.
Middle Creek Watershed Map ………………………………….……….…… 4
2.
Study Area Map ………………………………………………….…………… 5
3.
100-Year Inflow Hydrographs ………………………………………….…… 18
4.
500-Year Inflow Hydrographs ………………………………………….…… 18
5.
Levee Failure Probability Curve …………………………….…………….… 24
6.
Reliable Levee Height Elevation Determination ……………………….…… 25
7.
Hydraulic Model Layout ………………………………………………….… 27
8.
Pipe Breach Failure ………………………………………………………….. 44
9.
Uncontrolled Overtopping Failure …………………………………..……… 44
10.
Terrain Map ………………………………………………………..……..… 49
11.
Land Use Map ………………………………………………………………. 50
12.
FLO-2D Model Layout ………………………………………………...…… 52
13.
100-Year Levee Breach Scenario Locations ………………………….…..… 56
14.
500-Year Levee Breach Scenario Locations ……………………………...… 57
15.
100-Year Composite Floodplain Map ……………………………….……… 63
16.
500-Year Composite Floodplain Map ………………………………….…… 64
xi
1
Chapter 1
INTRODUCTION
The purpose of this study is to evaluate the flood risk located behind levees in the
Middle Creek watershed in Northern California. The California Department of Water
Resources (DWR) is currently evaluating the flood risk associated with the
approximately 1,600 miles of State Plan of Flood Control (SPFC) levees in the state. The
SPFC system includes levees, weirs, and channels located in the Sacramento River and
San Joaquin River drainage basins for which the DWR has provided assurances of
nonfederal cooperation to the United States required for the project (DWR, 2010).
The SPFC levees were initially built by rudimentary methods to protect mostly
agricultural lands. Now, the SPFC protects a population of over one million people,
major freeways, railroads, airports, water supply systems, utilities, and other
infrastructure of statewide importance, including $69 billion in assets (DWR, 2011).
Although the levees have decreased the frequency of flooding, the risk has increased due
to the urbanization that has occurred behind the levees.
According to the DWR’s Flood Control System Status Report, about 60% of the
1,230 miles of SPFC non-urban levees have a high potential for failure at their design
water surface elevation (DWR, 2011). There have been 70 levees that have overtopped or
failed in California since 1983. In the 1986 levee break in the Linda and Olivehurst areas,
the damages were over $2.7 billion (DWR, 2012).
2
The Hurricane Katrina disaster made the entire nation re-think the potential risks
of levee failure. Many levee segments in California were de-accredited during the Federal
Emergency Management’s (FEMA) Map Modernization Project. The de-accredited
levees were determined to no longer provided protection from the 100-year (or 1%
probability of exceedance) flood. FEMA mapped the areas behind non-accredited levees
using a “without-levee” approach, which did not consider any of the flood reduction
benefits of the de-accredited levees (FEMA, 2011). FEMA has proposed a new
methodology for mapping behind levees which is described in Analysis and Mapping
Procedures for Non-Accredited Levees: Proposed Approach for Public Review (FEMA,
2011).
When analyzing levee failure risk, FEMA uses a deterministic approach that is
based on a median 100-year water surface elevation. FEMA analyzes the levees based on
geotechnical stability criteria and a minimum freeboard (typically 3 feet) (DWR 2012).
The United States Army Corps of Engineers (USACE) uses a combined probabilistic and
deterministic approach that considers uncertainty in the water surface elevation (DWR,
2012).
DWR’s Central Valley Floodplain Evaluation and Delineation (CVFED) study
will use a method similar to FEMA’s deterministic approach. However, DWR will
consider geotechnical evaluations data to prescribe various levee breach scenarios. The
geotechnical data was not available at the time of preparing this report and therefore will
not be considered for this study.
3
The objective of this study is to present a methodology for determining the water
surface elevations for a river system and the extent of flooding behind levees due to
potential levee breaches. This report will review the hydraulic modeling software used
for the study and describe how the models were developed.
1.1. Description of Study Area
The Middle Creek watershed is in the western portion of Lake County in Northern
California (about 100 miles north of San Francisco). At the southern end of the watershed
there are levees which transport the flood flows around the town of Upper Lake and
discharge into Clear Lake. The watershed, which is 195 square miles, is shown in
Figure 1.
As shown in Figure 2, the streams in the area include: Middle Creek, Scotts
Creek, Alley Creek, and Clover Creek. Levees were built by farmers between 1900 and
1940 to reclaim about 1,200 acres of lake bottom and shoreline wetlands for agriculture
(Lake County, 2010). In the 1958, the USACE began building levees to improve on the
existing makeshift levees in the area and reclaim an additional 200 acres. Levees were
built along Middle Creek and portions of Scotts Creek, Alley Creek, and Clover Creek. In
addition to the levees, a diversion channel was built to carry the flood water from Clover
and Alley Creek around the town of Upper Lake and discharge it into Middle Creek
instead of traveling through the town of Upper Lake.
4
FIGURE 1. MIDDLE CREEK WATERSHED MAP
5
FIGURE 2. STUDY AREA MAP
6
Chapter 2
LITERATURE REVIEW
2.1. Historic Flood Events
There have been many floods around Clear Lake and along its tributaries. The
floods of 1938, 1958, 1970, 1983, 1986, and 1998 are considered the most damaging
(DWR, 2005). In 1958, approximately 4,000 acres of residential, commercial, and
agricultural lands were flooded to a depth of about two feet. In 1983 about 300 homes
and 60 businesses were damaged by the flooding. About 1,900 people were evacuated
and one person was killed (DWR, 2005). The levees in some areas have settled up to
three feet below design elevation, and are prone to slope failure (Lake County, 2010).
2.2. US Army Corps of Engineers Middle Creek Project
The Middle Creek project was authorized by the Flood Control Act of 1954
(USACE, 1961). The project, completed in 1967, included the improvement of levees and
channels to provide 100-year flood protection to the town of Upper Lake and
approximately 4,000 acres of agricultural land. The 100-year flows were documented in
the USACE General Design Memorandum No. 1- Hydrology for the Middle Creek
Project (USACE, 1956). The USACE did not use the recorded stream flow data for
Middle Creek and its tributaries, because the data was only available for a period of eight
years (from 1948 to 1956). Instead, the USACE used flow frequency data from several
7
nearby streams, including Putah Creek at Guenoc station where intermittent flow records
were available from 1904 to 1956. The USACE developed a regional envelope curve of
drainage area versus peak runoff to derive the flood frequencies for the Middle Creek
project streams.
2.3. FEMA Flood Insurance Study
FEMA performs Flood Insurance Studies (FIS) to identify flood hazards for
communities that participate in the National Flood Insurance Program (NFIP). The FIS
for Lake County (incorporated and unincorporated areas) was initially completed in 1976.
The study includes the water surface profiles for portions of Middle Creek and its
tributaries for the 10-, 50-, 100-, and 500-year flood events. The peak flows were
computed using the USACE HEC-1 program in conjunction with the Log-Pearson Type
III statistical analysis of the available stream flow gage data. The available stream flow
gage data for Middle Creek (from 1963 to 1973) and Scotts Creek (from 1949 to 1968)
were used for the analysis. The water surface elevations were computed using the
USACE HEC-2 step-backwater program (FEMA, 2005).
2.4. Middle Creek Flood Damage Reduction and Ecosystem Restoration
Of the approximately 9,000 acres of historic wetlands in the Clear Lake area,
7,500 acres have been lost or severely damaged (DWR, 2005). The development of the
Clear Lake watershed has led to anthropogenic eutrophication of the lake and the
8
proliferation of blue-green algae. In the early 1991, the University of California at Davis
determined that the cause of the blue-green algae growth was excess phosphorousprimarily delivered from watershed sediment (DWR, 2005). Since, the Middle and Scotts
Creek watersheds contribute an estimated 57 percent of the total inflow and 71% of the
phosphorous loading to Clear Lake, these watersheds have been targeted for potential
restoration projects.
In 1999, the USACE performed a feasibility study that evaluated three
alternatives to restore portions of the floodplain. The three alternatives described different
extents of the floodplain to be restored. The project calls for the reconnection of Scotts
Creek and Middle Creek to their historic floodplain by breaching the existing levee
system near Clear Lake (DWR, 2005). The primary goals of the project are to restore the
wetland habitat, and enhance the wildlife and fish habitat. The secondary restoration
goals include: preserve existing habitat resources, improve lake water quality, enhance
recreation and tourism, reduce flood risk, and reduce maintenance costs and
responsibility (DWR, 2005).
2.5. DWR Central Valley Floodplain Evaluation and Delineation
The Central Valley Floodplain Evaluation and Delineation (CVFED) project will
determine the 10-, 50-, 100-, 200-, and 500-year floodplains associated with the
approximately 1,600 miles of SPFC levees. The CVFED project is studying about 9,000
square miles in the Central Valley (Hegedus, 2011). The CVFED project is subdivided
9
into six study areas: Upper Sacramento River, Lower Sacramento River, Upper San
Joaquin River, Lower San Joaquin River, North Fork Feather River, and Middle Creek.
ESRI’s Geographic Information System (GIS) is being used to assist in the development
of the hydraulic models. For the hydraulic modeling and floodplain mapping, the HECRAS one-dimensional model is being used in conjunction with the FLO-2D twodimensional model (Hegedus, 2011).
The topographic data for the CVFED study areas was obtained from LiDAR
surveys. LiDAR is an acronym for “Light Detection and Ranging.” LiDAR is an active
laser system, which measures the time of flight of the emitted signal returned from the
target. Using semi-automated techniques the “raw” LiDAR is processed to generate the
“bare-earth” terrain model, in which trees, vegetation, and manmade structures have been
edited out. LiDAR offers many advantages over traditional photogrammetric surveys.
These include high vertical accuracy, fast data collection and processing, and robust data
sets with many uses (Fugro Earthdata, Inc., 2011). LP 360, developed by Q Coherent
Inc., is a tool that can be used to view the LiDAR data within GIS and perform accuracy
checks.
10
Chapter 3
MODEL BACKGROUND
Two modeling softwares were used for this project: HEC-RAS (Hydraulic
Engineering Center’s River Analysis System) and FLO-2D. HEC-RAS was created by
the USACE to primarily simulate one-dimensional flow. FLO-2D, created by FLO-2D
Software, Inc., is used to simulate two-dimensional flows. Both of the modeling
softwares are based on physical governing equations that describe fluid dynamics.
3.1. HEC-RAS Governing Equations
HEC-RAS contains four one-dimensional components: steady flow water surface
profile computations, unsteady flow simulation, movable boundary sediment transport
computations, and water quality analysis (USACE, 2010).
The steady flow component is intended for computing water surface profiles for
steady gradually varied flow. The basic computation procedure is based on the solution of
the one-dimensional energy equation (USACE, 2010):
𝑌2 + 𝑍2 +
∝2 𝑉22
2𝑔
= 𝑌1 + 𝑍1 +
where:
Y1, Y2 = depths at cross sections
∝1 𝑉12
2𝑔
+ ℎ𝑒
Eq. 1
11
Z1, Z2 = elevations of the main channel inverts
V1, V2 = average velocities
α1, α2 = velocity weighting coefficients
g
= gravitational acceleration
he
= energy head loss
Energy losses are evaluated by friction (Manning’s equation) and contraction and
expansion (coefficient multiplied by the change in velocity head). The momentum
equation is used in situations when the water surface profile is rapidly varied. The
unsteady flow component is intended primarily for subcritical flow regime calculations
(USACE, 2010).
The unsteady flows are governed by the principle of conservation of mass
(continuity), and the physical laws of the principle of conservation of momentum. The
continuity equation is as follows:
∂A
∂t
∂Q
+ ∂x − 𝑞𝑙 = 0
where:
A = cross sectional area
Q = flow rate
ql = lateral inflow per unit length
Eq. 2
12
The conservation of momentum for a control volume states that the net rate of
momentum entering the volume (momentum flux) plus the sum of all external forces
acting on the volume be equal to the rate of accumulation of momentum. Three forces are
considered in HEC-RAS: pressure, gravity, and boundary drag (or friction force)
(USACE, 2010).
𝜕𝑄
𝜕𝑡
+
𝜕𝑄𝑉
𝜕𝑥
𝜕𝑧
+ 𝑔𝐴 (𝜕𝑥 + 𝑆𝑓 ) = 0
Eq. 3
where:
Sf = friction slope
The one-dimensional unsteady flow equations are solved using a four-point
implicit finite difference scheme, also known as a box scheme. Space derivatives and
flow are calculated at internal points (USACE, 2010).
3.2. FLO-2D Governing Equations
FLO-2D uses the same basic governing equations as HEC-RAS, but applies them
differently to compute a two-dimensional solution. FLO-2D is a simple volume
conservation model which uses the continuity equation and the full dynamic wave
equation to define the progression of a flood wave. The differential momentum equation
is solved using an explicit finite difference method. (FLO-2D, 2009) The flood wave
progression is controlled by topography and resistance to flow. Flood routing is
13
accomplished through a numerical integration of the momentum equation and the
conservation of fluid volume (FLO-2D, 2009).
∂h
∂t
+
S𝑓𝑥 = S𝑜𝑥 −
∂hVx
∂x
∂h
∂t
−
=𝑖
V𝑥 ∂V𝑥
g ∂x
Eq. 4
−
Vx ∂V𝑥
g ∂x
1 ∂V𝑥
−g
∂t
Eq. 5
The equations of motion in FLO-2D are better defined as quasi two-dimensional.
(FLO-2D User’s Manual) The momentum equation is solved by computing the average
flow velocity across a grid element boundary one direction at a time. There are eight
potential flow directions- the four cardinal directions (North, South, East, West) and four
diagonal directions (Northwest, Northeast, Southeast, Southwest). The stability of this
explicit numerical scheme is based on specific criteria to control the size of the variable
computational time step (FLO-2D, 2009).
The solution in the FLO-2D domain is discretized into uniform, square grid
elements. Many of the hydraulic parameters are estimated by taking the average between
two adjacent grid elements: velocity, Manning’s n-value, flow area, slope, water surface
elevation, and wetted perimeter (FLO-2D, 2009). Flow velocity is calculated from the
solution of the momentum equation. The discharge across the grid element boundary is
computed by multiplying the velocity times the cross sectional flow area. After the
discharge is computed for all eight directions, the net change in discharge (sum of the
discharge in the eight flow directions) in or out of the grid element is multiplied by the
time step to determine the net change in the grid element water volume (FLO-2D, 2009).
14
The FLO-2D flood routing scheme proceeds on the basis that the time step is
sufficiently small to insure numerical stability (i.e. there is no numerical surging). The
key to efficient finite difference flood routing is that numerical stability criteria limits the
time step to avoid surging and yet allows large enough time steps to complete the
simulation in a reasonable time (FLO-2D, 2009). FLO-2D has a variable time step that
varies depending on whether the numerical stability criteria are exceeded or not. The
numerical stability criteria are checked for every grid element on every time step to
ensure that the solution is stable. If the numerical stability criteria are exceeded, the time
step is decreased (FLO-2D, 2009).
Most explicit schemes are subject to the Courant-Friedrich-Lewy (CFL) condition
for numerical stability (FLO-2D, 2009). The CFL condition relates flood wave celerity to
the model time and spatial increments. The physical interpretation of the CFL condition
is that a particle of fluid should not travel more than one spatial increment Δx in one time
step Δt (FLO-2D, 2009).
𝐶∆𝑥
∆𝑡 = 𝑣+𝑐
where:
C = Courant number (C≤1.0)
x
= square element width
v
= computed average cross section velocity
Eq. 6
15
c
= computed wave celerity
The primary limitation of the FLO-2D model is the discretization of the
floodplain topography into a system of square grid elements. Each grid element is
represented by a single elevation and roughness (FLO-2D, 2009). The basic inherent
assumptions in a FLO-2D simulation are:

Steady flow for the duration of the time step;

Hydrostatic pressure distribution;

Hydraulic roughness is based on steady, uniform turbulent flow resistance;

A channel element is represented by uniform channel geometry and roughness.
16
Chapter 4
METHODS OF ANALYSIS
4.1. Hydrologic Analysis
The inflow hydrographs for the 10-, 50-, 100-, 200-, and 500-year flood events
were obtained from Hydrologic Analysis for Middle Creek Study Area in Lake County,
California- Draft Technical Memorandum (Hill, 2012). For the hydrology study, a HECHMS model was developed using synthetic rainfall data. There were no stream flow and
rainfall gage data with coincident periods of record within the watershed to derive unit
hydrographs. Therefore, the National Oceanic and Atmospheric Administration (NOAA)
Atlas 14 for California was used for the rainfall. The NOAA Atlas 14 synthetic 10-day
storms were input into the HEC-HMS model following the guidelines in the Central
Valley Hydrology Study: Ungaged watershed analysis procedures (USACE, 2011). The
initial loss rates were estimated from Table 5-1 of the Sacramento City/ County Drainage
Manual Volume 2: Hydrology Standards and the constant loss rates were estimated from
the NRCS soil survey data (USACE 2011). The s-graph method, which was developed by
the USACE and used extensively in the Central Valley, was used for the direct runoff
transform (USACE, 2011). The Muskingum-Cunge flow routing method was selected
based on the Guidelines for selecting a channel routing method (USACE, 2010).
The resulting storm hydrographs were validated by comparing them to the USGS
regional regression equations. Also, statistical flood frequency analysis was performed at
two stream flow gages on Scotts and Middle Creeks, following the Water Resources
17
Council (WRC) Bulletin 17B method, using the USACE’s HEC-SSP (Statistical
Software Package). The flood frequency analysis peak flows were compared to the HMS
model hydrographs. The HMS results were also compared to previous hydrologic studies
by FEMA and the USACE as shown in Table 1. The resulting hydrographs from the
HMS model are shown in Figures 3 and 4.
Table 1 – Peak Flow Rate Estimates from Various Models
Location
Middle Creek
near Upper
Lake Gage
Scott Creek
near Lakeport
Gage
Clover Creek
Upstream of
Alley Creek
Confluence
USACE
GDM
(1956)
FEMA
FIS
(1976)
HMS
Model
Flood
Frequency
Model
USGS
Regional
Regression
12,400
11,320
10,910
9,750
11,600
11,500
13,200
12,630
12,500
12,100
4,300
3,790
4,650
(No gage data)
4,630
18
FIGURE 3. 100-YEAR INFLOW HYDROGRAPHS
25,000
Middle Creek
20,000
Alley Creek
Flow (cfs)
Clover Creek
15,000
Scotts Creek
10,000
5,000
0
0
1
2
3
4
5
6
Time (day)
7
8
9
10
FIGURE 4. 500-YEAR INFLOW HYDROGRAPHS
35,000
Middle Creek
30,000
Alley Creek
Flow (cfs)
25,000
Clover Creek
Scotts Creek
20,000
15,000
10,000
5,000
0
0
1
2
3
4
5
Time (day)
6
7
8
9
10
19
4.2. Hydraulic Modeling
The hydraulic models chosen for this study are consistent with those used for the
DWR CVFED project. The goal of the CVFED project is to have a consistent modeling
approach across the six study areas. HEC-RAS was chosen to model the unsteady onedimensional flow in the channels and FLO-2D was chosen to model the two-dimensional
flows. HEC-RAS is the most widely used one-dimensional hydraulic model and is the
advancement from the HEC-2 model. HEC-RAS now has the capability to model
unsteady flows. HEC-RAS is a free program that is made available to the public from the
USACE Hydrologic Engineering Center (HEC). The limitation of HEC-RAS is its
inability to accurately model two-dimensional flows. These two-dimensional flows can
occur whenever the flow gets out of the channel, either by overtopping its banks,
overtopping a levee, or breaching a levee.
FEMA and other agencies are now eager to find cost-effective ways to use twodimensional models where they previously used one-dimensional models out of
necessity. FEMA has recently formed a workgroup to develop a new procedure for
mapping floodplains behind non-accredited levees, which will benefit from twodimensional modeling. Hydraulic engineers and computer programmers have taken notethere are a multitude of two-dimensional programs that have been developed (or are
being developed currently). Two-dimensional models include RiverFLO-2D, TU-FLOW,
MIKE21, RMA2, ADH, HIVEL-2D, SRH-2D, and FLO-2D.
20
FLO-2D (v.2009.06) has been approved by FEMA to use for flood insurance
studies. Using two-dimensional models for floodplain mapping is becoming increasingly
popular. The main reason for their popularity is that computing power continues to
improve, so now two-dimensional models can be run in a matter of hours instead of days.
For this study, HEC-RAS was used to determine the locations of potential levee
failures and FLO-2D was used to simulate the resulting inundations. In the current study,
HEC-RAS was used to produce a levee breach hydrograph which then is input into the
FLO-2D model grid at the levee breach location.
Levee failures can be a result of :

Overtopping leading to a breach channel;

Underseepage resulting in internal erosion;

Slope stability failure;

Levee structural collapse due to water force or high pore water pressure;

Piping;

Wave attack;

Animal burrows, cracking, or other structure defects;

Earthquake soil liquefaction.
Historically, most of the Central Valley levees are initiated by slope instability or
piping including underseepage. These failures occur rapidly whereas levee overtopping
failures tend to progress more slowly (FLO-2D/ Riada Engineering, Inc., 2010).
21
The floodplains developed will be composites of the various predicted levee
breach scenarios. Floodplains will be delineated for the 100- and 500-year recurrence
interval floods.
4.3. Topographical Data
For the CVFED project, LiDAR was collected with a nominal post-spacing of 3.2
feet. This point spacing produces an accuracy of approximately one foot. The information
produced from the LiDAR survey includes:

LiDAR raw point file;

Bare earth digital elevation model (DEM);

Top of levee and toe of levee breaklines;

Delineation of obscured areas (buildings and road overpasses), low-confidence
areas, marshland, and water;

Obscured area polygons.
The topography was used to define the geometry of the levees as lateral weirs and
bridge decks. Other geometric features of structures, such as bridge piers and culverts,
could not be obtained from the LiDAR survey. Therefore, the needed dimensions were
measured in the field. Prior to the field visit, the available as-built drawings were
obtained from the California Department of Transportation (Cal-Trans) and Lake County.
For the bridges with as-builts, the accuracy of the as-builts was verified during the field
22
survey. There were not any differences between the as-builts and the surveyed
dimensions.
The LiDAR survey points do not penetrate the water surfaces. Therefore,
bathymetric surveys were conducted to obtain the needed cross sections. In order to
determine which cross sections had portions wetted, LP 360 was used. The portions of
the LiDAR capture area that had few returns or flat cross sections indicate the presence of
water. The lower Middle Creek near Clear Lake and Scotts Creek had water during the
LiDAR survey and needed bathymetric surveys.
4.4. Geotechnical Data
DWR is evaluating 470 miles of Urban levees (ULE Program) and 1500 miles of
Non-Urban levees (NULE Program) in the Sacramento and San Joaquin river basins for
defects (DWR, 2011). The levees in the study area are non-urban levees, because they
protect the town of Upper Lake which is non-urban area with a population of 1,052 (US
Census Bureau, 2010). The criterion for an urban area is a population of 10,000 or more
(DWR, 2011). Non-urban levees are being assessed based on potential failure from
underseepage, landslide stability, through-seepage, or erosion (DWR, 2011).
The collected geotechnical data and analysis will be used to produce levee failure
probability curves, which are plots of the probability of failure [P(f)] vs. water surface
elevation [WSE] for each levee segment. An example of a levee failure probability curve
23
is shown in Figure 5. The P(f)=5.0% is used to determine the water surface elevation at
the reliable levee height (DWR, 2012). This means that the safe water surface elevation is
defined as the level at which the levee has a 5% chance of failure. An example of the
reliable levee height elevation determination is shown in Figure 6.
In the current study, freeboard criterion was the only consideration to determine
the threshold condition for levee breaches. The geotechnical analyses (DWR’s NULE
Project) that will determine the other elevation thresholds were not yet determined at the
time of preparing this report.
24
FIGURE 5. LEVEE FAILURE PROBABILITY CURVE
California Department of Water Resources. (2012). CVFED Levee Reliability Data.
25
FIGURE 6. RELIABLE LEVEE HEIGHT ELEVATION DETERMINATION
California Department of Water Resources. (2012). CVFED Levee Reliability Data.
𝑅𝐻𝐸 = 𝑇𝑂𝐿 − 𝑅𝐻
where:
RHE = reliable height elevation
TOL = top of levee
RH = reduction height (computed)
Eq. 7
26
Chapter 5
HYDRAULIC ANALYSIS USING HEC-RAS
The hydraulic analysis portion of the project for Middle Creek and its tributaries
was conducted using the HEC-RAS one-dimensional unsteady-state model.
5.1. Model Development
The LiDAR DEM raster grid was used as the surface for HEC-GeoRAS version
10 (GeoRAS) computations. GeoRAS was used within GIS to setup the RAS model by
creating stream centerlines, bank lines, flow paths, cross sections, updated cross sections,
lateral structures, and storage areas. The hydraulic model layout is shown in Figure 7.
27
FIGURE 7. HYDRAULIC MODEL LAYOUT
28
The model includes Middle Creek and three tributaries streams. Clover Creek and
Alley Creek meet to the Northeast of the town of Upper Lake. The Diversion channel
carries the flow from Alley Creek and Clover Creek to the west where it meets Middle
Creek. There are outlet culverts on the Diversion channel which allow flow to discharge
into Old Clover Creek, which travels through the town of Upper Lake before it meets
Middle Creek. These culverts were assumed to be closed in order to have conservative
water surface values in the leveed reaches. Downstream of the confluence of Middle
Creek and Old Clover Creek, Scotts Creek meets Middle Creek. Middle Creek continues
until it meets Clear Lake. The model reaches were created using GeoRAS. The model
reaches were connected with junctions. The junction hydraulics was solved by the
unsteady flow model using the “Energy Balance Method.” The model reach details are
shown in Table 2.
Table 2 - Model Reaches
River
Reach
Upstream Downstream Length
Station
Station
(ft)
Middle
Crk
1
30506
24384
6,122
Middle
Crk
2
24384
18007
6,376
Middle
Crk
3
18007
13816
4,190
Description
(from Upstream to
Downstream)
Beginning of SPFC
Levees to confluence
with Diversion
Confluence with
Diversion to
confluence with Old
Clover Creek
Confluence with Old
Clover Creek to
confluence with
Scotts Creek
29
River
Upstream Downstream Length
Reach
Station
Station
(ft)
Middle
Crk
4
13816
0
13,816
Alley Crk
1
2964
0
2,964
Clover
Crk
1
1249
0
1,249
Diversion
1
4836
0
4,836
Old
Clover
Crk
1
1493
0
1,493
Scotts Crk
1
7264
0
7,264
Description
(from Upstream to
Downstream)
Confluence with
Scotts Creek to Clear
Lake
Beginning of SPFC
Levees to confluence
with Clover Creek
and beginning of
Diversion
Beginning of SPFC
Levees to confluence
with Alley Creek and
beginning of
Diversion
Confluence of Alley
Creek and Clover
Creek to confluence
with Middle Creek
Highway 20 bridge to
confluence with
Middle Creek
Beginning of SPFC
Levees to confluence
with Middle Creek
The cross sections were initially spaced based on Samuel’s equation (Brunner,
2011):
∆𝑥 =
0.15 𝐷
𝑆0
where:
Δx = cross section spacing
D = average bank full depth of the channel
Eq. 8
30
S0 = average bed slope
Based on the equation, it was determined that the cross sections should be spaced
at approximately 500 foot intervals. Cross sections were spaced at larger intervals where
the channel appeared to be prismatic and linear. Additional cross sections where added
where the river curved and near junctions. Cross sections were placed immediately
upstream and downstream of in-line structures. Cross sections were placed between inline structures. These initial cross sections were developed using limited topographical
information. When the final LiDAR data was provided, the cross sections were updated
to ensure that they were drawn perpendicular to the direction of flow and did not extend
up hillsides. Also, cross sections were trimmed to the top of levee breaklines. Effort was
taken to ensure that the updated cross sections were not moved off of the field survey
points. The updated cross sections used in the model are shown in Appendix A.
Additional cross sections were created at upstream and downstream extents of
reaches with lateral structures. These additional cross sections were created so that the
unsteady flow model would run. The cross section cutlines were created using GeoRAS.
The cross sections profiles were created based on the terrain grid. The river, reach, and
station identifiers, bank stations, and downstream reach lengths were also developed
using GeoRAS. Bank stations were adjusted in RAS to accurately define the channel and
overbank sections.
For the portions of the streams that contained water when the LiDAR was flown,
field surveys were conducted to obtain underwater channel points. The cross sections
31
with field surveys points were updated using the “Update Elevations” tool in GeoRAS.
The updated profiles were checked to make sure that the points were correctly updated.
Manning’s n-values were based on Manning’s n-values for Channels, Closed
Conduits Flowing Partially Full, and Corrugated Metal Pipes (Chow, 1959). The field
conditions were determined from field survey photos and aerial imagery. The
representative field photos and ranges of Manning’s n-values are shown in Appendix B.
The sensitivity of the model was tested by adjusting the Manning’s n-values. The
sensitivity analysis is included in Chapter 5 and Appendix E.
Ineffective flow areas are used to define areas of the channel cross sections where
water will pond and the velocity will be close to zero. Ineffective flow areas were
specified for many cross sections in areas that would not normally convey flow. These
ineffective flow areas are not permanent, and therefore will convey flows if the
ineffective flow area elevation criteria is exceeded. Obstructed areas are used to
completely block out areas within cross sections from conveying any flow. Obstructed
areas were used at bridge abutments that would permanently constrict the flow.
In-line structures were created directly in HEC-RAS. The bridges’ top deck
profiles were created using the LiDAR top of structure points. The pier, deck, and rail
details were obtained from field survey notes and drawings, photographs, and as-builts (if
available). Bridge rail geometry is typically not included in floodplain analysis or the
thickness of the bridge deck may be increased to account for the rails (Klenzendorf, et. al,
2010). This either overestimates or underestimates the weir flow over a bridge deck with
32
a railing. For simplicity, the Hydrology and Hydraulics Coordination Work Group’s
(HHCWG) Hydraulic Model Technical Guidance states that “rails that are greater than
50% open may be modeled as open and rails with less than 50% open shall be modeled
with obstructed areas.” The rails on the structures in the study areas are mostly open and
therefore were modeled as open. Debris blockages were also not included as per the
HHCWG guidance.
For the bridge modeling approach in HEC-RAS, the highest energy answer
method was used for computing the low flow through the bridges. The bridge modeling
approach is selected within the Geometry Data Editor. The highest energy answer
computation considers the energy (standard step), momentum, and Yarnell methods. The
inputs for the momentum and Yarnell methods require coefficients based on the pier
geometry. The HEC-RAS Hydraulic Reference Manual was used to determine the values
of these coefficients. For the high-flow modeling approach, each bridge was looked at
separately to determine whether the pressurized or weir flow would occur for the
simulated flows. The seven in-line structures are listed in Table 3.
Table 3: In-Line Structures
River
Reach
Alley Crk
1
Diversion
1
Upstream Downstream
Cross
Cross
Section
Section
780
2960
741
2912
Structure
Type
Description
Data
Source
Bridge
Pitney Ln
Field
Survey
Bridge
Elk
Mountain
Rd
Field
Survey
33
River
Middle
Crk
Middle
Crk
Middle
Crk
Old
Clover
Scotts
Crk
Reach
Upstream Downstream
Cross
Cross
Section
Section
Structure
Type
Description
1
27078
27051
Bridge
Rancheria
Rd
2
19842
19747
Bridge
Highway 20
4
387
211
Bridge
1
1217
1175
Bridge
1
4587
4510
Bridge
NiceLucerne
Cutoff Rd/
Co Rd 407
Bridge
Arbor N
State Route
29
Data
Source
Field
Survey
AsBuilt
AsBuilt
Field
Survey
AsBuilt
Lateral structures are features that exchange flow to the overbank floodplain when
they are overtopped. The levees were modeled as lateral structures to connect
overtopping flows to the storage areas The LiDAR top of levee breaklines were used to
create three-dimensional polylines for the lateral structures. GeoRAS was used to create
the lateral structure features from the three-dimensional polylines. The lateral structures
were split at inline structures and stream confluences. HEC-RAS does not allow lateral
structures to span junctions. Lateral structures were limited to 5,000 feet per the lateral
structure guidance provided by the HHCWG. The lateral structure stationing was input
into HEC-RAS to ensure that the distances between cross sections were accurate.
In addition to the levees, lateral structures were created along the high ground left
bank of Alley Creek and right bank of Clover Creek. These high ground lateral structures
were created because during high flows the water will overtop the non-leveed banks of
both Alley Creek and Clover Creek, flooding the land between the two creeks. The lateral
34
structures allow flows to overtop the banks into a storage area that will flow back into the
creeks near the downstream end where the Diversion channel begins. A lateral weir was
also created between Middle Creek and the inlet to Highline Slough. A storage area was
created to model the dead storage in Highline Slough.
The lateral structure weir coefficients were taken from the HHCWG guidance, as
shown below:

Inline weir coefficients: 2.6

Engineer design levee: 2.0

Railroad and road embankments connecting to storage areas: 1.0

Natural high ground: 0.5
The lateral structures are listed in Appendix C.
Storage areas were defined in overbank areas to simulate the ponding that would
occur due to levee overtopping or breaching. Storage areas were connected to the lateral
structures. Storage areas are connected to one another with storage area connections. The
storage area rating curves are shown in Appendix D.
Contraction and expansion coefficients were used at confining bridges. Suggested
values were obtained from the HEC-RAS v4.1 Reference Manual Table 3-3 (USACE,
2010). Contraction coefficients of 0.3 were used upstream of the bridges and expansion
coefficients of 0.5 were used downstream of the bridges.
35
5.2. Boundary Conditions
Inflow hydrographs were input as the upstream boundary conditions for each of
the stream reaches. Hydrographs for the 100- and 500-year flow events were modeled.
The peak flows for the 100- and 500-yr recurrence interval floods are shown in Table 4.
Table 4- Upstream Boundary Conditions- Peak Flows
Flooding Source and Location
Alley Creek at beginning of SPFC
levees
Clover Creek at beginning of SPFC
levees
Middle Creek at beginning of SPFC
levees
Old Clover Creek upstream of beginning
of SPFC levees
Scotts Creek at beginning of SPFC
levees
Tributary
Area
(mi2)
100-yr
Peak Flow
(cfs)
500-yr
Peak Flow
(cfs)
12.4
4,900
6,200
13.9
5,500
6,900
48.6
11,700
15,000
0.9
300
400
104.9
23,000
29,100
In order to help stabilize the model when there are low flows, minimum flows
were set for each of the inflow hydrographs. Minimum flows were set at 5% of each of
the peak flows. These initial conditions were input into the Unsteady Flow Data Editor.
The downstream boundary is located where Middle Creek flows into Clear Lake.
The model extends to the lakeshore of Clear Lake, where there is backwater influence
from the lake. The maximum water surface elevation of Clear Lake was obtained from
the USGS Water Data Report 2011 for Station 11450000 Clear Lake at Lakeport, CA
(USGS, 2012). The maximum water surface elevation, which occurred on February 24,
36
1998, was obtained from the report and converted from NGVD 1929 to NAVD 1988
using the USACE Corpscon v.6.0.1 program. The water surface elevation in NAVD 1988
is 1332.20 feet.
5.3. Model Simulations
The RAS model was run with steady flows to make sure the model was running
correctly. Approximate 100- and 500-year flows were input into the model. Based on
these runs, several locations had potential levee overtopping during the 100-year or
greater flood events.
The hydraulic tables were inspected to make sure that the rating curves extended
high enough to capture the maximum 500-year flows. For many of the cross sections, the
rating curves had to be extended vertically.
Once the final LiDAR was obtained, the model geometry was updated. The
design hydrographs from the Central Valley Hydrology Study (CVHS) were input as
upstream boundary conditions. The model was adjusted in order to stabilize the model
and improve the accuracy. The initial time step was based on the Courant condition
formula (Brunner, 2011):
∆𝑡
𝐶𝑟 = 𝑉 𝑤 ∆𝑥 ≤ 1.0
where:
Vw = flood wave velocity
Eq. 9
37
Δt = computational time step
Δx = distance between cross sections
The flood wave velocity can be approximated by the following equation (Brunner, 2011):
𝑉𝑤 =
3
2
𝑉̅
Eq. 10
where:
𝑉̅ = average velocity
Based on the Courant criteria, a one minute computational time step was used for the
model simulation.
HEC-RAS allows the user to set some computation options and adjust default
settings for the calculation tolerances. These tolerances are used in the solution of the
unsteady flow equations. Table 5 shows the calculation options and tolerances used
during the unsteady flow run. These calculation options and tolerances follow the
guidelines recommended by the HHCWG.
Table 5- Unsteady Calculation Options and Tolerances
Unsteady Flow Options
Value
Theta (implicit weighting factor) [0.6-1.0]:
0.6
Theta for warm up (implicit weighting factor) [0.6-1.0]:
0.6
Water surface calculation tolerance (ft):
0.02
Storage Area elevation tolerance:
0.05
38
Unsteady Flow Options
Value
Maximum number of iterations [0-40]:
20
Number of warm up time steps [0-200]:
0
Time step during warm up period (hrs):
0
Minimum time step for time slicing [hrs]:
0
Maximum time step for time slices:
20
Lateral Structure flow stability factor [1.0-3.0]:
1
Inline Structure flow stability factor [1.0-3.0]:
1
Weir flow submergence decay exponent [1.0-3.0]:
1
Gate flow submergence decay exponent [1.0-3.0]:
1
DSS Messaging Level (1 to 10, Default = 4):
4
The guidelines developed by the HHCWG were used to define the possible sources of
model instability, as follows:

Computed error in water surface elevation greater than 0.2 feet

Program runs to maximum number of iterations of 40 for one or more time steps
with large errors

Oscillations in the computed stage and flow hydrographs

Sudden changes in the following hydraulic parameters including:
o flow
o depth
o area
o storage
39

Flow inconsistency between the overbanks and the main channel.
After running the model simulations, the model was reviewed to verify that it was stable
and producing reasonable results. The maximum computed water surface elevation error
was less than 0.1 feet for all simulations.
5.4. Model Calibration and Verification
The stream flow gage records for the one gage within the model (Middle Creek
Near Upper Lake) were collected. Since the gage just represents one stage- flow
relationship near the upstream end of the project, it cannot be used to calibrate the model.
Instead, the sensitivity of the unknown parameters was analyzed, such as Manning’s nvalues.
The range of Manning’s n-values, provided in “Manning’s n-values for Channels”
(Chow, 1959), was used to analyze the sensitivity of the model. Separate unsteady
simulations were performed with minimum values, normal values, and maximum values
for Manning’s n-values. The results of the sensitivity analysis are shown in Appendix E.
Based on the sensitivity analysis, the average increase in water surface elevation
was 0.5 feet for Middle Creek, when using the maximum Manning’s n-values. The
average decrease in water surface elevation was 1.0 feet for Middle Creek, when using
the minimum Manning’s n-values. The variation in water surface elevation gives a sense
of the inherent uncertainty in the model results.
40
5.5. Model Results
The water surface profiles for the 100- and 500-year simulations are shown in
Appendix F. Many of the levees overtopped during both the 100- and 500-year events.
The overtopping of the levees is calculated in the model as a broad crested weir flow
equation (Roberson, et. al, 1998):
𝑄 = 𝐶𝐿𝐻 3/2
Eq. 11
where:
C = weir coefficient
L = length of weir
H = hydraulic head
The water surface profiles were used to determine where there are freeboard
deficiencies in the levees. The water surface profiles are shown in Appendix F. The
assumption used for this study is that the levees will begin to fail (by piping) when the
water surface elevation becomes greater than three feet lower than the top of levee for
more than 30 minutes or greater than two feet below the levee for any duration. The levee
freeboard assessments are shown in Tables 6 and 7.
41
Table 6- 100-Year Levee Freeboard Assessment
ID
DIV4717R
DIV4716L
DIV2912L
DIV2911R
MID30340L
MID30277R
MID27282L
MID25431R
MID24181R
MID24180L
MID22351R
MID19747R
MID19746L
MID17916L
MID17917R
MID13944L
MID8778L
MID3910L
River
Reach
From
Cross
Section
To
Cross
Section
Freeboard
Deficient?
(Y/N)
Overtop?
(Y/N)
Diversion
1
4717
2960
N
N
Diversion
1
4717
2960
N
N
Diversion
1
2912
256
N
N
Diversion
1
2912
256
N
N
1
30078
27452
N
N
1
30078
27029
Y
N
1
27029
24712
Y
N
1
25120
24712
Y
N
2
24181
19842
Y
N
2
24181
19842
Y
N
2
19747
18393
Y
Y
2
19747
18393
Y
Y
2
19747
18393
Y
Y
3
17917
14030
Y
N
3
17917
14030
Y
Y
4
13692
11022
Y
N
4
11022
4769
Y
Y
4
4769
387
Y
Y
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
42
Table 7- 500-Year Levee Freeboard Assessment
ID
DIV4717R
DIV4716L
DIV2912L
DIV2911R
MID30340L
MID30277R
MID27282L
MID25431R
MID24181R
MID24180L
MID22351R
MID19747R
MID19746L
MID17916L
MID17917R
MID13944L
MID8778L
MID3910L
River
Reach
From
Cross
Section
Diversion
1
4717
2960
Y
N
Diversion
1
4717
2960
Y
N
Diversion
1
2912
256
Y
N
Diversion
1
2912
256
Y
N
1
30078
27452
Y
N
1
30078
27029
Y
N
1
27029
24712
Y
N
1
25120
24712
Y
N
2
24181
19842
Y
Y
2
24181
19842
Y
N
2
19747
18393
Y
Y
2
19747
18393
Y
Y
2
19747
18393
Y
Y
3
17917
14030
Y
Y
3
17917
14030
Y
Y
4
13692
11022
Y
Y
4
11022
4769
Y
Y
4
4769
387
Y
Y
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
To
Cross
Section
Freeboard
Deficient?
(Y/N)
Overtop?
(Y/N)
43
The HEC-RAS models were re-run to simulate the levee breaches based on piping
failures in the levees. HEC-RAS allows the user to perform levee breach analysis by
specifying the levee breach parameters and failure mode. Either piping or overtopping
failure can be modeled in HEC-RAS. Levees in the Central Valley typically fail due to
piping or seepage (including underseepage) (FLO-2D/ Riada Engineering, Inc., 2010).
The modeler must specify the station of the prescribed breach along with the geometry of
the breach (final bottom width, final bottom elevation, side slopes, etc.) as well as the
initial piping elevation. The failure can be triggered by a specified water surface elevation
occurring for a total duration or a water surface elevation only. Figures 8 and 9 show the
two failure modes considered for this study: piping and uncontrolled overtopping.
44
FIGURE 8. PIPE BREACH FAILURE
FLO-2D/ Riada Engineering, Inc. (2010).
FIGURE 9. UNCONTROLLED OVERTOPPING FAILURE
FLO-2D/ Riada Engineering, Inc. (2010).
45
For this study, the centerline station was obtained from the observed water surface
profiles, based on where the levees did not have the required three feet of freeboard. The
final bottom width was assumed to be between 500 and 1000 feet based on the length of
the levee freeboard encroachment. The piping elevation was set at the elevation three feet
below the top of levee elevation. The final bottom elevation was set at one foot below the
initial piping elevation and the side slopes were assumed to be 1:1 (horizontal: vertical).
The piping will began when the water surface elevation exceeds the initial piping
elevation for a cumulative 30 minutes. Piping failures typically occur quickly and will
lead to roof collapse, transforming them to channel flows (FLO-2D/ Riada Engineering,
Inc., 2010). Therefore, the full formation time was set at one hour.
These prescribed breaches are preliminary scenarios. The geotechnical
information obtained from the Urban Levee Elevations and Non-urban Levee Evaluations
will eventually be made available for use in this study and other CVFED studies. Once
that information is obtained, the prescribed failure locations, trigger water surface
elevations, and modes of failure can be adjusted to reflect the geotechnical data.
The resulting levee breach hydrographs are shown in Appendix G. These levee
breach hydrographs were saved and then input into the FLO-2D model as various failure
scenarios. The levee breaches downstream of the confluence of Middle Creek and Scotts
Creek were not modeled for this study, because those levee segments are expected to be
removed as part of the Middle Creek Flood Damage Reduction and Ecosystem
Restoration Project (Lake County, 2010).
46
Table 8- 100-Year Levee Breach Locations
Breach
Scenario
Levee
ID
River
Reach
Breach
Station
(Centerline)
Trigger
Failure
Elevation
Peak
Flow
(cfs)
1
MID24180L
Middle
Crk
2
3400
1347
6,0511
2
MID22351R
Middle
Crk
2
1600
1347
6,0291
3
MID17916L
Middle
Crk
3
2500
1341
15,2711
4
MID8778L
Middle
Crk
4
N/A2
N/A2
N/A2
5
MID3910L
Middle
Crk
4
N/A2
N/A2
N/A2
1
Levee breach hydrographs are shown in Appendix G.
2
Levee breach was not modeled for this study because the levee segment is to be
removed for the Middle Creek Flood Damage Reduction and Ecosystem Restoration
project.
47
Table 9- 500-Year Levee Breach Locations
Breach
Scenario
Levee
ID
River
Reach
Breach
Station
(Centerline)
Trigger
Failure
Elevation
Peak
Flow
(cfs)
1
MID27028L
Middle
Crk
1
1800
1364
2,3031
2
DIV2911R
Diversion
1
1600
1362
1,6211
3
DIV2912L
Diversion
1
1500
1363
4,7481
4
MID24180L
Middle
Crk
2
3400
1347
12,2081
5
MID22351R
Middle
Crk
2
1600
1347
8,6051
6
MID17916L
Middle
Crk
3
2500
1341
16,7121
7
MID8778L
Middle
Crk
4
N/A2
N/A2
N/A2
8
MID3910L
Middle
Crk
4
N/A2
N/A2
N/A2
1
Levee breach hydrographs are shown in Appendix G.
2
Levee breach was not modeled for this study because the levee segment is to be
removed for the Middle Creek Flood Damage Reduction and Ecosystem Restoration
project.
48
Chapter 6
FLOOD INUNDATION USING FLO-2D
The FLO-2D model was used to model the flows that would result from levee
breaches due to piping. The levee breach hydrographs were determined using the HECRAS model, as shown in Appendix G.
6.1. Model Development
The LiDAR DEM raster grid was used as the surface within the PRIMER pre- and
post-processor program developed by Civil Solutions, Inc. PRIMER was used to setup
and calculate the grid elevations. The terrain elevation map is shown in Figure 10.
Manning’s n-values were assigned using FLO-2D’s Grid Developer System
(GDS). Land use survey data from DWR was used as the basis for land use
classifications. Each land use classification was attributed to a roughness coefficient as
determined by the HHCWG. The land use classifications and Manning’s n-values are
shown in Figure 11 and Table 10. The land use shapefile was overlaid with aerial
imagery to verify the accuracy of the land use classifications. It was determined that the
land use classifications were appropriate and no adjustments were made.
49
FIGURE 10. TERRAIN MAP
50
FIGURE 11. LAND USE MAP
51
Table 10 - FLO-2D Overland Roughness Coefficient by Land Use Type
Land Use Type
Manning’s n-values
Citrus and Subtropical
Deciduous Fruits and Nuts
Field Crops
Grain and Hay Crops
Idle
Pasture
Rice
Truck, Nursery, and Berry Crops
Vineyards
Entry Denied
Barren and Wasteland
Riparian Vegetation
Not Surveyed
Native Vegetation
Water Surface
Semi-agricultural and Incidental to Agriculture
Urban
Commercial
Industrial
Urban Landscape
Residential
Vacant
0.200
0.200
0.200
0.200
0.200
0.200
0.100
0.120
0.120
0.150
0.100
0.250
0.100
0.250
0.040
0.040
0.040
0.040
0.040
0.040
0.040
0.100
A 100-foot grid cell size was selected based on the relatively small size of the
model grid. Based on this grid size, there are 22,906 grids. During the test flow model
runs, it was determined that the run times using the 100-foot grid cell size were
reasonable. The model layout is shown in Figure 12.
52
FIGURE 12. FLO-2D MODEL LAYOUT
53
The model grids were setup using PRIMER. The grid elevations were calculated
using PRIMER also. PRIMER calculates the average elevation of each grid cell based on
the input raster grid. Exclusion polygons were delineated in GIS to specify the areas that
would be eliminated from the grid elevation calculations because they would otherwise
bias the grid cell elevations. Exclusion polygons were delineated around the SPFC levees
and other levee-like embankments. The extents of the levees were determined from the
LiDAR LAS files and the toe of levee breaklines. The updated grid elevations were
compared with the biased model grid elevations to check that the elevations were being
correctly updated. It was determined that the updated grid elevations were appropriate.
Area Reduction Factors (ARF’s) and Width Reduction Factors (WRF’s) are used
to reflect the loss of floodplain storage and conveyance in FLO-2D. The LiDAR obscured
area polygons were used to represent the obstructions in the floodplain created by
buildings. According to the HHCWG guidance, “Engineering judgment should be used to
“clean-up” the obscured area polygons to remove non-building polygons and supplement
with [LiDAR] low-confidence area polygons as needed.” The obscured area polygons
were reviewed and some issues were identified that would require revisions to the
dataset. Vegetation, water bodies, and bridges were often erroneously included in the
obscured polygon dataset. Also, many structures were missing from the dataset. Most of
these structures were single family homes or detached garages. The obscured area dataset
was revised by removing the polygons representing vegetation, water bodies, or bridges.
Polygons were added to represent structures that were significantly large (1,000 square
feet or larger) and were not included in the obscured area dataset.
54
The SPFC levees were included in the model. According to the HHCWG
recommendations, levee-like features that are greater than two feet tall can be included as
levees in the two-dimensional model, if they alter the progression of the overland flood
wave. LP 360 was used along with two foot contours generated from the LiDAR to
identify the levee-like features within the model. The SPFC levees were initially
identified from the California Levee Database (CLD). The alignment of the top of levee
was created from the LiDAR breaklines. Three-dimensional polylines were created along
the levee-like embankments.
The levees were imported in FLO-2D using the PRIMER tool. PRIMER takes the
average elevation of each levee octagonal segment. The levee alignment and elevations
are computed from the three-dimensional polylines which were generated from the
LiDAR top of levee breaklines. PRIMER was also used to calculate the width reduction
factor for each levee octagonal segment. This tool provides a more accurate
representation of the length of each levee segment, which is important for levee
overtopping flow calculations (Plummer, 2012).
The aerial imagery was used to verify that there are not any structures in the
floodplain that are hydraulically significant. No streets were included in the model
because the major streets in the study area will not convey flows. Infiltration was not
considered per the guidance of the HHCWG.
55
6.2. Boundary Conditions
Floodplain outflow elements were placed at the southern boundary of the model
domain, which is physically the lakeshore boundary of Clear Lake. FLO-2D will not run
if the outflow nodes are not lower than the upstream grid elevations. PRIMER’s Outflow
Node Elevation tool was used to adjust the outflow elements to be at a lower elevation.
The inflow elements were placed on the dry-side of levee at the location of the
levee breach. The inflow hydrographs were obtained from HEC-RAS. FLO-2D runs
slower when the peak inflow is large when compared to the surface are of the grid
element containing the inflow. The suggested criterion is as shown below (FLO-2D,
2009):
𝑄𝑝𝑒𝑎𝑘
𝐴𝑠𝑢𝑟𝑓𝑎𝑐𝑒 𝑎𝑟𝑒𝑎
<1
𝑐𝑓𝑠
𝑓𝑡 2
Eq.12
In cases where the peak inflow was greater than 10,000cfs, the inflow hydrograph was
split over two grid cells.
6.3. Model Simulations
The FLO-2D program was used exclusively to model the two-dimensional flows
that result from levee failures due to piping. The levee breach hydrographs were obtained
from HEC-RAS. The locations of the levee breach scenarios are shown in Figures 13 and
14.
56
FIGURE 13. 100-YEAR LEVEE BREACH SCENARIO LOCATIONS
57
FIGURE 14. 500-YEAR LEVEE BREACH SCENARIO LOCATIONS
58
Three levee breach scenarios were simulated for the 100-year flood and six
different levee breach scenarios were simulated for the 500-year flood. The results of the
levee breach scenarios are shown in Tables 11 and 12, and in Appendix H.
Table 11 – 100-Year Levee Breach Simulation Results
1
No. of
Buildings
Inundated
Average
Flood
Depth for
Buildings
(ft)
Test
Flow
Scenario
River
Station
Peak
Flow
(cfs)
Maximum
Inundation
Area
(Acres)
1
Middle
Crk
21700
(Left)
6,051
1493.8
351
2.3
2
Middle
Crk
21700
(Right)
6,029
954.9
44
3.2
3
Middle
Crk
17400
(Left)
15,271
2337.2
72
4.5
4
Middle
Crk
8800
(Left)
N/A1
N/A1
N/A1
N/A1
5
Middle
Crk
2100
(Left)
N/A1
N/A1
N/A1
N/A1
Levee breach was not modeled for this study because the levee segment is to be
removed for the Middle Creek Flood Damage Reduction and Ecosystem Restoration
project.
59
Table 12 – 500-Year Levee Breach Simulation Results
1
Station
Peak
Flow
(cfs)
Maximum
Inundation
Area
(Acres)
No. of
Buildings
Inundated
Average
Flood
Depth for
Buildings
(ft)
Middle
Crk
25600
(Left)
2,303
219.6
19
3.1
2
Diversion
Channel
2500
(Right)
1,621
115.6
19
4.0
3
Diversion
Channel
2500
(Left)
4,748
1042.5
404
1.9
4
Middle
Crk
21700
(Left)
12,208
2411.0
393
2.9
5
Middle
Crk
21700
(Right)
8,605
1729.0
48
1.1
6
Middle
Crk
17400
(Left)
16,712
2442.9
90
4.4
7
Middle
Crk
8800
(Left)
N/A1
N/A1
N/A1
N/A1
8
Middle
Crk
2100
(Left)
N/A1
N/A1
N/A1
N/A1
Test
Flow
Scenario
River
1
Levee breach was not modeled for this study because the levee segment is to be
removed for the Middle Creek Flood Damage Reduction and Ecosystem Restoration
project.
The HHCWG recommended using the limiting Froude number to test and debug
the preliminary FLO-2D models. By setting the limiting Froude number, the model is
allowed to adjust the flow roughness values when the limiting Froude number is
60
exceeded. A limiting Froude number of 0.5 was applied for the model domain. The
resulting n-value modifications were reviewed for reasonableness.
The depth variable roughness is used to improve the timing of the flood wave
progression and to reduce numerical surging. In the model, the Manning’s n-values are
adjusted based on the flood depths and the “shallow n” parameter. The “shallow n” value
was set to 0.2.
The Courant Number (or Courant-Friedrich-Lewy), DEPTOL, and WAVEMAX
parameters are used in FLO-2D for numerical stability. The Courant Number relates the
flood wave movement to the model discretization in time and space (FLO-2D, 2009).
Since the model resulted in reasonable velocities on the floodplain and the runtime was
not excessive, the default values for these stability parameters were used.
6.4. Model Calibration and Verification
There are no high water marks in the model domain. Therefore, no calibration of
the model can be performed. Instead, the sensitivity of the unknown parameters was
performed, such as ARF and WRF values.
The simulations were run both with and without the ARF’s and WRF’s to test the
sensitivity of the model to those parameters. Two scenarios where analyzed to determine
whether the extent of the floodplain or the number of inundated buildings were sensitive
to the two parameters. The two scenarios were selected for the analysis because they
61
resulted in the largest number of structures being inundated in the floodplain. The results
of the sensitivity analysis are summarized in Table 13.
Table 13 - ARF and WRF Sensitivity Results Summary (for 500-Year Flood)
Test
Flow
Scenario
Max. Inundation
Area Without
Obscured Area
Polygons
(Acres)
Max. Inundation
Area With
Obscured Area
Polygons
(Acres)
No. of Inundated
Structures
Without
Obscured Area
Polygons
No. of
Inundated
Structures
With Obscured
Area Polygons
3
1,059.2
1,042.5
399
404
4
2,203.2
2,411.0
388
393
Based on the sensitivity analysis, it was determined that the application of the
ARF and WRF values does not greatly impact the overall flooding extents. This is
because the flooding is primarily slow moving and deep. If the flooding was primarily
shallow sheet flow with high velocities, the inclusion of the ARF and WRF values would
be expected to increase the inundated area.
6.5. Model Results
The model output files for each scenario were reviewed to identify potential
sources of error. The simulations ran to completion, and volume conservation within each
of the flow scenarios was within the range recommended by the FLO-2D Reference
Manual (FLO-2D, 2009). Each flow scenario model was reviewed to identify and note
62
any excessive time decrements caused by “sticky” cells. Levee features were also
reviewed for performance.
The maximum flood depth and velocity results for each of the scenarios and
recurrence interval flood events are shown in Appendix H. Figures 15 and 16 depict the
composite floodplain resulting from these scenarios. Tables 14 and 15 show the number
of structures that were inundated at various depths for each levee breach scenario.
63
FIGURE 15. 100-YEAR COMPOSITE FLOODPLAIN MAP
64
FIGURE 16. 500-YEAR COMPOSITE FLOODPLAIN MAP
65
Table 14 – Number of Structures Inundated from 100-Year Levee Breach Scenarios
Flood Depths
(ft)
0-0.5
0.5-1
1-2
2-3
3-4
4-5
5-6
6-8
8-10
10-12
Total No. of
Structures
Breach
Scenario
1
59
37
66
68
80
22
14
5
0
0
Breach
Scenario
2
6
1
8
8
5
6
8
1
1
0
Breach
Scenario
3
4
3
11
9
5
12
3
14
11
0
351
44
72
Table 15 – Number of Structures Inundated from 500-Year Levee Breach Scenarios
Flood
Depths
(ft)
0-0.5
0.5-1
1-2
2-3
3-4
4-5
5-6
6-8
8-10
10-12
Total No. of
Structures
Breach
Breach
Breach
Breach
Breach
Breach
Scenario Scenario Scenario Scenario Scenario Scenario
1
2
3
4
5
6
1
0
56
43
13
8
2
1
56
29
11
9
5
3
114
77
18
10
2
3
108
52
5
12
3
2
48
79
0
7
4
2
16
63
1
8
2
1
5
27
0
8
0
5
1
23
0
10
0
0
0
0
0
17
0
0
0
0
0
1
19
19
404
393
48
90
66
Chapter 7
DISCUSSION OF RESULTS
The results of the hydraulic model are consistent with DWR’s Flood Control
System Status Report, which shows that the levees in the Middle Creek area are at
moderate or high risk of levee failure (DWR, 2011). As was expected, the levees nearest
Clear Lake have the highest risk of failure due to the high water surface elevations that
result from the incoming flood flows combined with a high lake level. The HEC-RAS
model shows that the 100-year flood will overtop the levees by a maximum of 1.1 feet.
This flooding would not impact many structures because the land in this area is
agricultural and there are only 40 structures between Clear Lake and the confluence of
Middle Creek and Scotts Creek. Based on the Middle Creek Flood Damage Reduction
and Ecosystem Restoration Project, it is more cost-effective to relocate the families than
to repair and maintain the levees, which would cost an estimated $2.5 million a year
(Andersen, 2005). Because of the impending restoration project, this report focused on
the flood risk upstream of the confluence of Middle Creek and Scotts Creek.
It was determined that portions of Middle Creek upstream of Scotts Creek may
also be susceptible to overtopping during both 100- and 500-year flood events. The HECRAS model results show that the levee along Middle Creek Reach 3 (immediately
upstream of the confluence with Scotts Creek) will be overtopped by a maximum of 1.4
feet for the 100-year flood. This flooding would impact the town of Upper Lake. The
levee along the Diversion channel is not overtopped in the HEC-RAS model but was
67
assumed to fail due to piping because the 500-year water surface elevation is within 1.9
feet of the top of the levee. This potential levee failure would also result in a large portion
of the town of Upper Lake becoming inundated. As expected, the breach scenarios that
occur closest to the town of Upper Lake resulted in the largest number of flooded
structures. The simulated breach on the south levee of the Diversion channel (500-year
breach scenario 3) results in 404 structures being inundated. The simulated breach on the
east levee of Middle Creek Reach 2 (500-year breach scenario 4) results in 393 structures
being inundated. These levee breach scenarios result in average flood depths of 1.9 feet
for the 500-year breach scenario 3 and 2.9 feet for the 500-year breach scenario 4.
There are many assumptions made when performing the hydrologic analysis and
developing the hydraulic models for this study. The methodology presented in this report
follows the guidelines for DWR’s CVHS and CVFED projects. The hydrologic analysis
is based on more updated data than the previous studies by FEMA and the USACE.
Although rainfall gage data was not available for this study, the NOAA Atlas 14
precipitation data was used for producing synthetic hyetographs for the HMS model. This
study also benefitted from 40 years of stream flow gage data for Middle Creek. The
results of the HMS model were compared to flood frequency analysis and USGS regional
regression equations. The HMS model resulted in higher peak flows than the flood
frequency analysis- 11.9% higher for Middle Creek and 1.0% higher for Scotts Creek.
The HMS model resulted in lower peak flows than the USGS regional regression- 5.9%
lower for Middle Creek and 4.4% lower for Scotts Creek. Even though the data and
68
assumptions are much different, the peak flows from the HMS model were within 12% of
the previous FEMA and USACE studies.
A major difference between this study and previous studies is the unsteady flow
analysis. The unsteady flow analysis is advantageous for this study which considers levee
overtopping and breaches and therefore must account for the routing of flows through
storage areas. The unsteady flow analysis requires additional effort compared to a steady
flow analysis, especially when considering model instabilities. This report described the
geometric model elements and the calculation options and tolerances used for the model.
The resulting stable unsteady flow model is a result of adjustments made to these
geometric elements and calculation options.
The second main difference between this study and previous studies is the
analysis of potential levee breaches. For this study, the assumption was made that the
levees will not be able to convey water above the design water surface elevation (i.e.
three feet below the top of levee). The HEC-RAS water surface profiles were used to
determine where the freeboard criterion was not met. Then the levee breach scenarios
were simulated at these locations. The peak flows for the levee breach hydrographs vary
from 6,029 to 15,271 cfs for the 100-year scenarios, and from 1,621 to 16,712 cfs for the
500-year scenarios. The peak flows are primarily a function of the water surface elevation
versus the levee breach elevation.
The third main difference between this study and previous studies is the use of a
two-dimensional model, FLO-2D, in conjunction with the one-dimensional HEC-RAS
69
model. FLO-2D produces a better result for the overland flows which cannot be
accurately modeled as one-dimensional. The HEC-RAS breach hydrographs were input
into the FLO-2D model grid to simulate the overland flows. The resulting FLO-2D
inundation areas vary from 945.9 to 2,337.2 acres for the 100-year breaches, and from
115.6 to 2,442.9 acres for the 500-year breaches. These variations in inundation areas are
based on the volume of the levee breach hydrographs and the topography.
70
Chapter 8
CONCLUSIONS
The purpose of this study was to evaluate the flood risk behind levees within the
Middle Creek watershed. This study followed the methodology that is being used for
DWR’s CVFED project to evaluate the flood risk associated with SPFC levees. This
report described the process for developing the one-dimensional HEC-RAS model and
the two-dimensional FLO-2D model. HEC-RAS was used to model the riverine
hydraulics and FLO-2D was used to model the overland flows from levee breaches.
The results of the study indicate that the levees along Middle Creek could be
susceptible to levee breaches because they do not have adequate freeboard for both the
100- and 500-year flood events. The levees nearest to Clear Lake are the most at risk of
flooding due to high lake stages combined with high inflows from Middle Creek.
Because there are relatively few structures in the floodplain near Clear Lake, the Middle
Creek Flood Damage Reduction and Ecosystem Restoration project seeks to relocate the
residents and restore the historic floodplain. The levees along the Diversion channel also
could be susceptible to levee failure as they do not the meet the freeboard criteria for the
500-year flood event. These levees could potentially fail before reaching the design water
surface elevation as a result of piping or underseepage. The probability of these failure
modes will be assessed further for DWR’s CVFED project.
The hydraulic models used for this study were developed using the latest spatial
datasets and GIS processing tools. Those tools allow hydraulic modelers to develop
71
complex flood models rather quickly. The integration of one-dimensional and twodimensional models represents a new method to model riverine flooding and levee
breaches. The advantage of this method is the ability to simulate various individual levee
breach scenarios. The disadvantage of this method is that it does not consider internal
drainage flooding that may contribute to the levee breach flows.
The methodology presented in this report can be used for similar floodplain
analysis studies without calibration data. The results of the hydrologic analysis produced
very consistent results with other methods and previous studies. For the hydraulic
models, sensitivity analyses were performed on the unknown parameters. The results of
the sensitivity analyses show that the water surface elevation could vary up to one foot
when adjusting the Manning’s n-values. Future flood studies would benefit from
additional rain and stream flow gages for calibrating hydrologic and hydraulic models.
The results of the FLO-2D simulations were combined to create the composite
floodplain maps for the 100- and 500-year flood events, as was shown in Figures 15 and
16. The floodplain maps can be refined by incorporating the geotechnical data from
DWR’s Levee Evaluations project. The geotechnical data will be used to generate levee
failure probability curves and reliable levee height elevations. DWR should set guidelines
for the levee breach characteristics which can greatly affect the resulting floodplains.
72
APPENDIX A
Cross Sections Table
73
Station
River
Reach
LOB
nvalues
Channel
n-values
ROB
nvalues
3000.00
Alley Crk
1
0.1
0.045
0.1
2901.21
Alley Crk
1
0.1
0.045
0.1
2356.98
Alley Crk
1
0.1
0.045
0.1
1741.93
Alley Crk
1
0.1
0.045
0.1
1138.84
Alley Crk
1
0.1
0.045
0.1
780.04
Alley Crk
1
0.1
0.045
0.1
741.28
Alley Crk
1
0.1
0.045
0.1
391.77
Alley Crk
1
0.1
0.045
0.1
137.16
Alley Crk
1
0.1
0.045
0.1
100.00
Alley Crk
1
0.1
0.045
0.1
1200.00
Clover
Crk
1
0.1
0.045
0.1
1
0.1
0.045
0.1
1
0.1
0.045
0.1
1
0.1
0.045
0.1
1
0.1
0.045
0.1
1169.96
885.05
584.90
192.07
Clover
Crk
Clover
Crk
Clover
Crk
Clover
Crk
100.00
Clover
Crk
1
0.1
0.045
0.1
4800.00
Diversion
1
0.06
0.03
0.06
4717.89
Diversion
1
0.06
0.03
0.06
4241.91
Diversion
1
0.06
0.03
0.06
3463.80
Diversion
1
0.06
0.03
0.06
2960.58
Diversion
1
0.06
0.03
0.06
Data
Source
Copied
from ALL0030
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
Copied
from ALL0001
Copied
from CLO0010
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
Copied
from CLO0001
Copied
from DIV0040
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
Bathymetry?
(Y or N)
N/A
N
N
N
N
N
N
N
N
N/A
N/A
N
N
N
N
N/A
N/A
N
N
N
N
74
Station
River
Reach
LOB
nvalues
Channel
n-values
ROB
nvalues
2912.81
Diversion
1
0.06
0.03
0.06
2174.43
Diversion
1
0.06
0.03
0.06
1396.74
Diversion
1
0.06
0.03
0.06
611.08
Diversion
1
0.06
0.03
0.06
256.67
Diversion
1
0.06
0.03
0.06
200.00
Diversion
1
0.06
0.03
0.06
1
0.1
0.045
0.1
1
0.1
0.045
0.1
1
0.1
0.045
0.1
1
0.1
0.045
0.1
1
0.1
0.045
0.1
1
0.1
0.045
0.1
1
0.1
0.045
0.1
1
0.1
0.045
0.1
1
0.1
0.045
0.1
1
0.1
0.045
0.1
1
0.1
0.045
0.1
1
0.1
0.045
0.1
1
0.1
0.045
0.1
1
0.1
0.045
0.1
1
0.1
0.045
0.1
1
0.1
0.045
0.1
1
0.1
0.045
0.1
30391.90
30078.20
29808.10
29449.80
29096.30
28799.00
28506.50
28162.20
27852.50
27452.40
27078.00
27029.70
26703.30
26414.00
26012.90
25613.90
25120.40
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Data
Source
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
Copied
from DIV0001
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
Bathymetry?
(Y or N)
N
N
N
N
N
N/A
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
75
Station
River
Reach
LOB
nvalues
Channel
n-values
ROB
nvalues
24712.40
Middle
Crk
1
0.1
0.045
0.1
24700.00
Middle
Crk
1
0.1
0.045
0.1
24200.00
Middle
Crk
2
0.1
0.045
0.1
2
0.1
0.045
0.1
2
0.1
0.045
0.1
2
0.1
0.045
0.1
2
0.1
0.045
0.1
2
0.1
0.045
0.1
2
0.1
0.045
0.1
2
0.1
0.045
0.1
2
0.1
0.045
0.1
2
0.1
0.045
0.1
2
0.1
0.045
0.1
2
0.1
0.045
0.1
2
0.1
0.045
0.1
24181.70
23632.70
22974.50
22352.80
21716.50
20995.10
20312.20
19842.00
19748.00
19278.30
18907.20
18393.80
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
18300.00
Middle
Crk
2
0.1
0.045
0.1
18000.00
Middle
Crk
3
0.1
0.045
0.1
3
0.1
0.045
0.1
3
0.1
0.045
0.1
3
0.1
0.045
0.1
3
0.1
0.045
0.1
17917.60
17412.80
16861.90
16156.00
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Data
Source
TO 20
LiDAR
Copied
from MID0170
Copied
from MID0165
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
Copied
from MID0115
Copied
from MID0110
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
Bathymetry?
(Y or N)
N
N/A
N/A
N
N
N
N
N
N
N
N
N
N
N
N
N/A
N/A
N
N
N
Y
76
Station
River
Reach
LOB
nvalues
Channel
n-values
ROB
nvalues
15378.60
Middle
Crk
3
0.1
0.045
0.1
3
0.1
0.045
0.1
3
0.1
0.045
0.1
14601.20
14030.10
Middle
Crk
Middle
Crk
14000.00
Middle
Crk
3
0.1
0.045
0.1
13700.00
Middle
Crk
4
0.1
0.045
0.1
4
0.1
0.045
0.1
4
0.1
0.045
0.1
4
0.1
0.045
0.1
4
0.1
0.045
0.1
4
0.1
0.045
0.1
4
0.1
0.045
0.1
4
0.1
0.045
0.1
4
0.1
0.045
0.1
4
0.1
0.045
0.1
4
0.1
0.045
0.1
4
0.1
0.045
0.1
4
0.1
0.045
0.1
4
0.1
0.045
0.1
4
0.1
0.045
0.1
4
0.1
0.045
0.1
4
0.1
0.045
0.1
4
0.1
0.045
0.1
13692.50
12749.40
11840.90
11022.70
10129.60
8778.08
7771.26
6947.00
6311.73
5596.91
4769.48
3476.81
2108.15
1121.49
387.85
211.01
80.30
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Middle
Crk
Data
Source
Interpolate
d Cross
Section
TO 20
LiDAR
TO 20
LiDAR
Copied
from MID0085
Copied
from MID0080
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
Bathymetry?
(Y or N)
N/A
Y
Y
N/A
N/A
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
77
Station
1370.11
1217.28
1175.88
745.70
344.45
River
Old
Clover
Old
Clover
Old
Clover
Old
Clover
Old
Clover
Reach
LOB
nvalues
Channel
n-values
ROB
nvalues
1
0.1
0.045
0.1
1
0.1
0.045
0.1
1
0.1
0.045
0.1
1
0.1
0.045
0.1
1
0.1
0.045
0.1
300.00
Old
Clover
1
0.1
0.045
0.1
7200.00
Scotts Crk
1
0.1
0.045
0.1
7112.52
Scotts Crk
1
0.1
0.045
0.1
6784.75
Scotts Crk
1
0.1
0.045
0.1
6369.89
Scotts Crk
1
0.1
0.045
0.1
5980.73
Scotts Crk
1
0.1
0.045
0.1
5410.52
Scotts Crk
1
0.1
0.045
0.1
4913.55
Scotts Crk
1
0.1
0.045
0.1
4587.76
Scotts Crk
1
0.1
0.045
0.1
4510.74
Scotts Crk
1
0.1
0.045
0.1
3724.58
Scotts Crk
1
0.1
0.045
0.1
3159.01
Scotts Crk
1
0.1
0.045
0.1
Data
Source
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
Copied
from OLD0001
Copied
from SCO0070
TO 13
LiDAR +
USGS 10m
DEM
TO 13
LiDAR +
USGS 10m
DEM
TO 13
LiDAR +
USGS 10m
DEM
TO 13
LiDAR +
USGS 10m
DEM
TO 13
LiDAR +
USGS 10m
DEM
TO 13
LiDAR +
USGS 10m
DEM
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
Bathymetry?
(Y or N)
N
N
N
N
N
N/A
N/A
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
78
Station
River
Reach
LOB
nvalues
Channel
n-values
ROB
nvalues
2717.21
Scotts Crk
1
0.1
0.045
0.1
2059.26
Scotts Crk
1
0.1
0.045
0.1
1485.47
Scotts Crk
1
0.1
0.045
0.1
937.00
Scotts Crk
1
0.1
0.045
0.1
525.56
Scotts Crk
1
0.1
0.045
0.1
500.00
Scotts Crk
1
0.1
0.045
0.1
Data
Source
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
TO 20
LiDAR
Copied
from SCO0001
Bathymetry?
(Y or N)
Y
Y
Y
Y
Y
N/A
79
APPENDIX B
Photos for Determining Manning’s n-values
80
Alley Creek
Channel
0.045 (0.035 – 0.05) Winding channel, weeds and stones
Overbank 0.10 (0.07- 0.16) Medium to dense brush, in summer
Diversion Channel
Channel
Overbank
0.03 (0.025 – 0.033) Winding earth channel, grass and some weeds
0.06 (0.04 – 0.08) Light brush and trees, in summer
81
Middle Creek
Channel
Overbank
0.045 (0.035 – 0.05) Winding channel, weeds and stones
0.10 (0.07- 0.16) Medium to dense brush, in summer
82
Scotts Creek
Channel
Overbank
0.045 (0.035 – 0.05) Winding channel, weeds and stones
0.10 (0.07- 0.16) Medium to dense brush, in summer
83
APPENDIX C
Lateral Structures Table
84
River
Reach
Location
Structure
Description
From
Cross
Section
To
Cross
Section
Connection
Weir
Coefficient
Alley
Crk
1
Right
Overbank
Levee
2901
780
Storage
Area 1
2.0
Alley
Crk
1
Left
Overbank
High Ground
2901
780
Storage
Area “AlleyClover”
0.5
Alley
Crk
1
Right
Overbank
Levee
741
137
Storage
Area 1
2.0
Alley
Creek
1
Left
Overbank
High Ground
741
Storage
Area “AlleyClover”
0.5
Clover
Crk
1
Right
Overbank
High Ground
1169
192
Storage
Area “AlleyClover”
0.5
Clover
Crk
1
Left
Overbank
Levee
1169
192
Out of the
System
2.0
Diversio
n
1
Right
Overbank
Levee
4717
2960
Storage
Area 1
2.0
Diversio
n
1
Left
Overbank
Levee
4717
2960
Out of the
System
2.0
Diversio
n
1
Left
Overbank
Levee
2912
256
Out of the
System
2.0
Diversio
n
1
Right
Overbank
Levee
2912
256
Storage
Area 1
2.0
Middle
Crk
1
Left
Overbank
Levee
30078
27452
Storage
Area 1
2.0
Middle
Crk
1
Right
Overbank
Levee
30078
27029
Out of the
System
2.0
Middle
Crk
1
Left
Overbank
Levee
27029
24712
Storage
Area 1
2.0
Middle
Crk
1
Right
Overbank
Levee
25120
24712
Storage
Area 2
2.0
Middle
Crk
2
Right
Overbank
Levee
24181
19842
Storage
Area 2
2.0
137
85
River
Reach
Location
Structure
Description
From
Cross
Section
To
Cross
Section
Connection
Weir
Coefficient
Middle
Crk
2
Left
Overbank
Levee
24181
19842
Out of the
System
2.0
Middle
Crk
2
Right
Overbank
Levee
19747
18393
Storage
Area 4
2.0
Middle
Crk
2
Left
Overbank
Levee
19747
18393
Out of the
System
2.0
Middle
Crk
3
Right
Overbank
Levee
17917
14030
Out of the
System
2.0
Middle
Crk
3
Left
Overbank
Levee
17917
14030
Storage
Area 4
2.0
Middle
Crk
4
Left
Overbank
Levee
13692
11022
Out of the
System
2.0
Middle
Crk
4
Left
Overbank
Levee
11022
4769
Out of the
System
2.0
Middle
Crk
4
Left
Overbank
Overflow to
Rodman
Slough Inlet
4769
3476
Storage
Area 9
2.0
Middle
Crk
4
Left
Overbank
Levee
4769
387
Out of the
System
2.0
Old
Clover
1
Right
Overbank
Levee
1175
344
Out of the
System
2.0
Old
Clover
1
Left
Overbank
Levee
1175
344
Out of the
System
2.0
Scotts
Crk
1
Left
Overbank
Levee
7112
5410
Storage
Area 3
2.0
Scotts
Crk
1
Left
Overbank
Levee
4510
525
Storage
Area 4
2.0
86
APPENDIX D
Storage Area Curves
87
Storage Area 1: Elevation-Storage Curve
1376
1374
1372
Elevation
(ft)
1370
1368
1366
1364
1362
1360
1358
1356
0
500
1000
1500
Storage
(AC-ft)
2000
2500
3000
Storage Area 2: Elevation-Storage Curve
1360
1358
1356
1354
Elevation
(ft)
1352
1350
1348
1346
1344
1342
1340
1338
0
200
400
600
800
Storage
(AC-ft)
1000
1200
1400
1600
88
Storage Area 3: Elevation-Storage Curve
1348
1346
1344
1342
Elevation
(ft)
1340
1338
1336
1334
1332
1330
1328
1326
0
100
200
300
400
500
Storage
(AC-ft)
600
700
800
900
800
900
Storage Area 4: Elevation-Storage Curve
1344
1342
Elevation
(ft)
1340
1338
1336
1334
1332
1330
0
100
200
300
400
500
Storage
(AC-ft)
600
700
89
Storage Area 9: Elevation-Storage Curve
1333
1332
Elevation
(ft)
1331
1330
1329
1328
1327
1326
0
20
40
60
Storage Area
(AC-ft)
80
100
120
Storage Area "Alley-Clover":
Elevation-Storage Curve
1373
1372
1371
Elevation
(ft)
1370
1369
1368
1367
1366
1365
1364
1363
0
20
40
60
80
Storage
(AC-ft)
100
120
140
90
APPENDIX E
HEC-RAS Sensitivity Analysis Results
91
Middle
Creek
Station
(ft)
WSE using
Min n-values
(ft, NAVD88)
WSE using
Normal
n-values
(ft, NAVD88)
WSE using
Max
n-values
(ft, NAVD88)
Change in
WSE When
Using Min
n-values
(ft)
Change in
WSE When
Using Max
n-values
(ft)
30391.88
1377.25
1379
1379.88
-1.75
0.88
30078.18
1375.62
1377.53
1378.48
-1.91
0.95
29808.09
1374.12
1376.24
1377.24
-2.12
1
29449.83
1373.36
1375.25
1376.26
-1.89
1.01
29096.26
1371.83
1373.93
1375.04
-2.1
1.11
28798.98
1372.35
1374.06
1375.06
-1.71
1
28506.48
1371.94
1373.69
1374.72
-1.75
1.03
28162.22
1370.66
1372.6
1373.72
-1.94
1.12
27852.46
1370.37
1372.18
1373.27
-1.81
1.09
27452.36
1368.62
1370.61
1371.72
-1.99
1.11
27078
1367.72
1369.6
1370.58
-1.88
0.98
27029.69
1367.6
1369.45
1370.42
-1.85
0.97
26703.25
1367.52
1369.12
1370.02
-1.6
0.9
26414.03
1366.08
1367.81
1368.75
-1.73
0.94
26012.88
1363.47
1365.71
1366.72
-2.24
1.01
25613.91
1363.99
1365.54
1366.29
-1.55
0.75
25120.45
1362.86
1364.41
1365.16
-1.55
0.75
24712.4
1362.37
1363.75
1364.46
-1.38
0.71
24700
1361.2
1362.58
1363.31
-1.38
0.73
24200
1361.2
1362.58
1363.31
-1.38
0.73
24181.68
1359.29
1360.89
1361.71
-1.6
0.82
23632.67
1358.06
1359.46
1360.26
-1.4
0.8
22974.49
1355.39
1357.21
1358.08
-1.82
0.87
22352.82
1354.46
1355.97
1356.79
-1.51
0.82
21716.47
1352.94
1354.47
1355.31
-1.53
0.84
20995.11
1351.04
1352.5
1353.22
-1.46
0.72
20312.19
1349.58
1350.71
1351.17
-1.13
0.46
19842.03
1348.99
1349.85
1350.3
-0.86
0.45
19747.95
1348.93
1349.73
1350.16
-0.8
0.43
19278.34
1348.14
1348.72
1348.89
-0.58
0.17
18907.21
1347.92
1348.38
1348.52
-0.46
0.14
18393.84
1347.13
1347.66
1347.77
-0.53
0.11
18300
1346.06
1346.57
1346.63
-0.51
0.06
18000
1346.06
1346.57
1346.63
-0.51
0.06
17917.56
1345.42
1345.89
1345.96
-0.47
0.07
92
Middle
Creek
Station
(ft)
WSE using
Min n-values
(ft, NAVD88)
WSE using
Normal
n-values
(ft, NAVD88)
WSE using
Max
n-values
(ft, NAVD88)
Change in
WSE When
Using Min
n-values
(ft)
Change in
WSE When
Using Max
n-values
(ft)
17412.79
1344.36
1344.89
1345.03
-0.53
0.14
16861.88
1343.7
1344.12
1344.29
-0.42
0.17
16156.02
1343.33
1343.74
1343.96
-0.41
0.22
15378.6
1343.07
1343.53
1343.77
-0.46
0.24
14601.22
1342.5
1343.11
1343.45
-0.61
0.34
14030.05
1342.29
1342.94
1343.31
-0.65
0.37
14000
1342.15
1342.83
1343.23
-0.68
0.4
13700
1342.15
1342.83
1343.23
-0.68
0.4
13692.47
1340.45
1341.21
1341.67
-0.76
0.46
12749.36
1339.3
1339.79
1340.14
-0.49
0.35
11840.94
1336.83
1337.43
1337.77
-0.6
0.34
11022.69
1335.74
1336.06
1336.21
-0.32
0.15
10129.56
1335.21
1335.45
1335.52
-0.24
0.07
8778.084
1334.49
1334.67
1334.69
-0.18
0.02
7771.263
1334.25
1334.32
1334.29
-0.07
-0.03
6946.997
1334.02
1334.08
1334.06
-0.06
-0.02
6311.727
1333.9
1333.92
1333.87
-0.02
-0.05
5596.913
1333.8
1333.78
1333.7
0.02
-0.08
4769.478
1333.59
1333.56
1333.49
0.03
-0.07
3476.813
1333.19
1333.16
1333.09
0.03
-0.07
2108.146
1332.89
1332.82
1332.76
0.07
-0.06
1121.488
1332.71
1332.63
1332.57
0.08
-0.06
387.8525
1332.48
1332.42
1332.39
0.06
-0.03
211.0086
1332.25
1332.25
1332.25
0
0
80.29996
1332.2
1332.2
1332.2
0
0
93
94
APPENDIX F
HEC-RAS Water Surface Profiles
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
APPENDIX G
Levee Breach Hydrographs
114
115
116
117
118
119
120
121
122
123
APPENDIX H
FLO-2D Levee Breach Simulation Results
124
125
126
127
128
129
130
131
132
133
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