Technical Memorandum Limitations: This document was prepared solely for CEMEX Construction Materials, Inc. in accordance with professional standards at the time the services were performed and in accordance with the contract between CEMEX Construction Materials, Inc. and Brown and Caldwell dated September 13, 2013. This document is governed by the specific scope of work authorized by CEMEX Construction Materials, Inc.; it is not intended to be relied upon by any other party except for regulatory authorities contemplated by the scope of work. We have relied on information or instructions provided by CEMEX Construction Materials, Inc. and other parties and, unless otherwise expressly indicated, have made no independent investigation as to the validity, completeness, or accuracy of such information. 701 Pike Street, Suite 1200 Seattle, WA 98101 Phone: 206-624-0100 Fax: 206-749-2200 Prepared for: CEMEX Construction Materials, Inc. Project Title: Eliot Facility Reclamation Plan Amendment, Surface Mining Permit 23, CA Mine 91-01-0009 Project No.: 144718 Technical Memorandum 1 Subject: Hydraulic Modeling of Arroyo del Valle Date: February 12, 2014 To: Ronald D. Wilson, Manager, Land Use Permits: Pacific Region From: Nathan Foged, Supervising Engineer Copy to: Andrew Kopania, EMKO Environmental Karen Spinardi, Spinardi Associates Prepared by: Nathan Foged, Supervising Engineer California Civil Engineer C66395, Exp. June 2014 Reviewed by: Bill Faisst, Vice President California Civil Engineer C29146, Exp. March 2015
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Transcript
Technical Memorandum
Limitations:
This document was prepared solely for CEMEX Construction Materials, Inc. in accordance with professional standards at the time the services were
performed and in accordance with the contract between CEMEX Construction Materials, Inc. and Brown and Caldwell dated September 13, 2013.
This document is governed by the specific scope of work authorized by CEMEX Construction Materials, Inc.; it is not intended to be relied upon by any
other party except for regulatory authorities contemplated by the scope of work. We have relied on information or instructions provided by CEMEX
Construction Materials, Inc. and other parties and, unless otherwise expressly indicated, have made no independent investigation as to the validity,
completeness, or accuracy of such information.
701 Pike Street, Suite 1200 Seattle, WA 98101 Phone: 206-624-0100 Fax: 206-749-2200
Prepared for: CEMEX Construction Materials, Inc.
Project Title: Eliot Facility Reclamation Plan Amendment, Surface Mining Permit 23, CA Mine 91-01-0009
Project No.: 144718
Technical Memorandum 1
Subject: Hydraulic Modeling of Arroyo del Valle
Date: February 12, 2014
To: Ronald D. Wilson, Manager, Land Use Permits: Pacific Region
From: Nathan Foged, Supervising Engineer
Copy to: Andrew Kopania, EMKO Environmental Karen Spinardi, Spinardi Associates
Prepared by: Nathan Foged, Supervising Engineer California Civil Engineer C66395, Exp. June 2014
Reviewed by: Bill Faisst, Vice President California Civil Engineer C29146, Exp. March 2015
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Table of Contents
List of Figures ........................................................................................................................................................... iii
List of Tables ............................................................................................................................................................. iii
List of Abbreviations ................................................................................................................................................. iv
2.1 Site Description ........................................................................................................................................ 2
2.1.1 Livermore-Amador Valley ................................................................................................................... 2
2.1.2 Arroyo del Valle .................................................................................................................................. 3
Section 3: Model Development ............................................................................................................................... 5
3.1 Data Collection ......................................................................................................................................... 5
3.1.2 Modeling by Local Agencies .............................................................................................................. 6
3.2 Baseline Model Build ............................................................................................................................... 6
3.3 Modifications for Proposed Conditions ................................................................................................. 10
3.3.1 Realigned Channel and Floodplain ................................................................................................. 10
3.3.2 Lake A Diversion .............................................................................................................................. 10
4.1.1 Bed Sediments ................................................................................................................................. 12
4.1.2 Flow Magnitude and Frequency ...................................................................................................... 13
4.2.1 Realigned Channel and Floodplain ................................................................................................. 19
4.2.2 Lake A Diversion .............................................................................................................................. 22
Attachment C: Baseline Profiles at Lakes A and B .............................................................................................. C-1
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List of Figures
Figure 1. Location of CEMEX’s Eliot Facility ............................................................................................................ 2
Figure 2. GIS tools were used to import new cross-section data into HEC-RAS ................................................... 7
Figure 3. Development of a land use coverage for spatially varied Manning’s roughness ................................. 9
Figure 4. Restored Arroyo del Valle corridor geometry from Amendment (Spinardi, 2013) .............................. 10
Figure 5. Right bank modifications at proposed Lake A diversion structure ...................................................... 11
Figure 6. Correlation of average daily discharge data at USGS gauges ............................................................ 13
Figure 7. Flow duration curve for Arroyo del Valle based on average daily flows at AVL (2002–13) ............... 14
Figure 8. Frequency of flows in Arroyo del Valle based on average daily flows at AVL (2002–13) .................. 15
Figure 9. Relation between applied stress and frequency of occurrence in geomorphic processes ............... 16
Figure 10. Annual sediment load profiles for baseline and proposed conditions ............................................. 17
Figure 11. Baseline water surface profiles displayed in HEC-RAS ...................................................................... 18
Figure 12. 100-year flood inundation along Study Reach based on baseline HEC-RAS modeling results ...... 19
Figure 13. Example cross-section at Station 144+00 ........................................................................................ 20
Figure 14. Comparison of 100-year profiles for baseline and proposed conditions along restored corridor .. 20
Figure 15. 100-year water surface increases upstream of restored corridor .................................................... 21
Table 4. Bed Material Data from Zone 7 Stream Management Master Plan ..................................................... 13
Table 5. Arroyo del Valle Peak Discharge Frequency ........................................................................................... 18
Table 6. Comparison of Hydraulic Parameters along the Restored Corridor ...................................................... 21
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List of Abbreviations
ACCDA Alameda County Community Development Agency
Amendment SMP-23 Reclamation Plan Amendment
AVL Arroyo del Valle at Livermore
AVP Arroyo del Valle at Pleasanton
BC Brown and Caldwell
CEMEX CEMEX Construction Materials, Inc.
cfs cubic foot/feet per second
County Alameda County, California
d depth
DFIRM Digital Flood Insurance Rate Map
DTM digital terrain model
FEMA Federal Emergency Management Agency
FIRM Flood Insurance Rate Map
FIS Flood Insurance Study
ft foot/feet
ft/s foot/feet per second
GIS geographic information systems
GUI graphical user interface
HEC Hydrologic Engineering Center
LAVQAR Livermore-Amador Valley Quarry Area Reclamation
mm millimeter(s)
NAIP National Agriculture Imagery Program
NAVD88 North American Vertical Datum 1988
NDVI Normalized Difference Vegetation Index
NFIP National Flood Insurance Program
NGVD29 National Geodetic Vertical Datum 1929
Q-1 Alameda County Quarry Permit 1
Q-76 Alameda County Quarry Permit 76
SFEI San Francisco Estuary Institute
SFHA Special Flood Hazard Area
SMP-23 Surface Mining Permit 23
Spinardi Spinardi Associates
Site authorized mining area
Specific Plan LAVQAR Specific Plan
Study evaluation of hydraulic impacts and design feasibility related to Arroyo del Valle
Study Reach 5.4-mile-long reach of Arroyo del Valle addressed in this technical memorandum
TIN triangulated irregular network
USACE U.S. Army Corps of Engineers
USGS U.S. Geological Survey
V velocity
Zone 7 Zone 7 of the Alameda County Flood Control and Water Conservation District
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Section 1: Introduction CEMEX Construction Materials, Inc. (CEMEX) owns and operates the Eliot Facility, a sand and gravel mining
operation located between the cities of Pleasanton and Livermore within the unincorporated area of
Alameda County (County), California. CEMEX is seeking the approval of an amendment to its existing
Reclamation Plan, which was originally approved in 1987 under Surface Mining Permit 23 (SMP-23).
In June 2013, Spinardi Associates (Spinardi) prepared the SMP-23 Reclamation Plan Amendment
(Amendment) and submitted it to the Alameda County Community Development Agency (ACCDA). ACCDA
provided comments on the Amendment in a July 8, 2013, letter from James Gilford to Ron Wilson, titled
“Completeness Review of Application to Amend Surface Mining Permit and Reclamation Plan No. 23.” The
letter requested additional technical evaluations including the following two comments (summarized here):
• Hydraulic impacts: Conduct technical analyses (e.g., hydraulic modeling) to demonstrate that the
restored channel will remain stable, and that neither the channel modifications nor the diversion
structure will increase flood risk to neighboring properties and infrastructure.
• Design feasibility: Present a complete design concept (e.g., schematic plans) and demonstrate that the
elements of the reclamation plan designed to address diversion and conveyance into the Chain of
Lakes1 can be feasibly constructed in compliance with known regulatory requirements.
In response to these comments, CEMEX retained Brown and Caldwell (BC) to evaluate design options and to
analyze hydraulic impacts along affected reaches of Arroyo del Valle (Study). This document, Technical
Memorandum 1, addresses hydraulic impacts (i.e., channel stability and flood risk) as described in the
above comment. A separate document, Technical Memorandum 2, addresses design feasibility.
Technical Memorandum 1 addresses the following Study objectives:
• develop a baseline hydraulic model representing the existing conditions of the Arroyo del Valle channel
and floodplain
• modify the baseline hydraulic model to represent the proposed (reclaimed) conditions along the affected
reaches of Arroyo del Valle
• evaluate channel stability impacts by comparing long-term sediment transport capacities for baseline
and proposed (reclaimed) conditions
• evaluate flooding impacts by comparing 100-year water surface profiles and potentially inundated areas
for baseline and proposed (reclaimed) conditions
Technical Memorandum 1 includes the following five sections:
1. Introduction: This section provides a brief introduction to the Reclamation Plan Amendment, describes
the purpose of the Study, and lists specific objectives addressed by this document.
2. Background: This section provides background information regarding the project site, Arroyo del Valle,
and the development of the reclamation plan amendment.
3. Model Development: This section discusses the development of input data for the existing-conditions
and proposed-conditions hydraulic models, including an existing-conditions terrain model, bridge data,
and new water conveyance features.
1 The original SMP-23 Reclamation Plan was developed in accordance with the Specific Plan for Livermore-Amador Valley Quarry
Area Reclamation (LAVQAR Specific Plan), adopted by the County in November 1981. The LAVQAR Specific Plan describes a “Chain of Lakes” reclamation concept that calls for the creation of a series of excavated lakes to be used for storage and groundwater recharge. See Section 2.2 for more information.
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4. Hydraulic Evaluations: This section describes the hydraulic modeling approach, flow scenarios, key
assumptions, and simulation methods.
5. Conclusions: This section summarizes the hydraulic modeling results and draws conclusions with
respect to the evaluation objectives.
Section 2: Background This section provides background information regarding the project site (Section 2.1) and the development
of the reclamation plan amendment (Section 2.2).
2.1 Site Description
The CEMEX Eliot Facility is located in the
Livermore-Amador Valley (Valley) between
the cities of Pleasanton and Livermore,
California (see Figure 1). Mining
operations at the Eliot Facility are vested
under Alameda County Quarry Permit 1 (Q-
1) and Quarry Permit 76 (Q-76) granted in
1957 and 1969, respectively. The
authorized mining area (Site) covers
approximately 975 acres of land between
Stanley Boulevard and Vineyard Avenue.
The Shadow Cliffs Regional Recreation
Area is located directly west of the Site,
Vulcan’s sand and gravel operation is
located to the north and east, and the
Ruby Hill subdivision is located across
Vineyard Avenue to the south. The
evaluations presented in this technical
memorandum address a 5.4-mile-long
reach (Study Reach) of Arroyo del Valle,
stretching from 1,000 feet downstream of
Bernal Avenue to roughly 3,000 feet
upstream of Vallecitos Road. Map 1
(Attachment A) shows a detailed view of
the Site, Study Reach, and surrounding
area.
2.1.1 Livermore-Amador Valley
The Valley is a wide depression in the Diablo Range, bounded by the East Bay Hills to the west and the
Altamont Hills to the east. The valley’s western portion is the Amador Valley; it includes the city of
Pleasanton. The valley’s eastern portion is the Livermore Valley; it includes the city of Livermore. The two
valleys together form the Valley.
According to the San Francisco Estuary Institute (SFEI, 2013), the Valley was formed by geological processes
and provides a wide space for streams to spread and sink. Numerous streams that drain out of the
surrounding hills have deposited sediments over thousands of years and filled the Valley (SFEI, 2013).
Figure 1. Location of CEMEX’s Eliot Facility
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Arroyo Mocho and Arroyo del Valle are two major streams draining into the southern portion of the Valley.
Historically, these were wide and braided streams that deposited large amounts of coarse sediment
transported from their headwaters in the Diablo Range (SFEI, 2013). Sand and gravel mining has occurred
along the Arroyo Mocho and Arroyo del Valle alluvial formations since the late 1800s, including the areas
around the Eliot Facility. Over the years, mining and development activities have rerouted and channelized
much of the lower reaches of Arroyo Mocho and Arroyo del Valle. Arroyo del Valle’s existing channel flows
along the southern portion of the Site. Section 2.2 discusses proposed mining and reclamation activities and
potential impacts to Arroyo del Valle. Section 2.1.2 provides an overview of the Arroyo del Valle hydrology
and geomorphology.
2.1.2 Arroyo del Valle
Arroyo del Valle is located in the upper Alameda Creek watershed. The arroyo drains an area of
approximately 172 square miles before it discharges to Arroyo de la Laguna west of Pleasanton. Arroyo de la
Laguna flows south and discharges into Alameda Creek near the town of Sunol. Alameda Creek then flows
west through the East Bay Hills before discharging into San Francisco Bay.
Approximately 85 percent (146 square miles) of the Arroyo
del Valle basin is located upstream of Del Valle Reservoir,
constructed in 1968 to serve as off-channel storage for
water delivered through the South Bay Aqueduct (part of
the California State Water project) and for flood control.
Zone 7 is one of three water agencies served by the South
Bay Aqueduct; Table 1 shows the annual entitlements for
each agency. Zone 7 also uses a small portion of Del Valle
Reservoir capacity to store runoff from the local
watershed2. Although Del Valle Reservoir primarily serves
as water supply storage, a portion of its 77,100-acre-foot
capacity is normally reserved for flood control.
Del Valle Reservoir has altered the hydrologic flow regime in the lower reaches of Arroyo del Valle (Kamman,
2009). Peak flows have decreased and large-magnitude flood flows have been virtually eliminated. Managed
releases during the dry season have resulted in perennial flow conditions along the valley floor rather than
the historical intermittent flow conditions when the arroyo would become dry in the summertime (Kamman,
2009; LSA, 2013). Altered flows have also contributed to changes in Arroyo del Valle channel; the once
actively braided channel network along the valley floor now has shifted to a more defined central channel
system (Kamman, 2009).
Directly downstream of the dam, Arroyo del Valle flows through a narrow, sinuous canyon until it reaches the
valley floor about 1 mile downstream, near the Veterans Administration hospital. At this point, the channel
and floodplain become wider and, in the past, more active and braided. Sycamore Grove Park is an
important community park that preserves mature Western Sycamore trees along this reach of the historical
Arroyo del Valle floodplain. This park stretches approximately 2 miles from the hospital to Vallecitos Road.
The Eliot Facility Site is located just downstream of Sycamore Grove Park. Arroyo del Valle flows along the
southern portion of the Site adjacent to Lakes A and B (see Section 2.2, Reclamation Planning). The arroyo
flows through two small lakes along the south side of the Shadow Cliffs Regional Recreation Area and then
continues west through the city of Pleasanton. Several small streams drain into Arroyo del Valle between the
dam and its confluence with Arroyo de la Laguna (see Map 2, Attachment A).
2 Del Valle Reservoir data are available on the Zone 7 Web site: http://www.zone7water.com/water-supply/48-del-valle-reservoir.
Table 1. Water Agencies Served by the South Bay
Aqueduct
Water agency Annual entitlement
(acre-feet)
Zone 7 46,000
Alameda County Water District 42,000
Santa Clara Valley Water District 100,000
Total 188,000
Source: California Department of Water Resources (1968,
2001).
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2.2 Reclamation Planning
The SMP-23 Reclamation Plan (1987) was developed in accordance with the Specific Plan for Livermore-
Amador Valley Quarry Area Reclamation (LAVQAR Specific Plan, or Specific Plan), which was adopted by the
County in November 1981. The LAVQAR Specific Plan describes a “Chain of Lakes” reclamation concept,
where excavated gravel quarries are to be converted into a series of open lakes and used for storage and
groundwater recharge. After mining is completed and quarry sites are reclaimed, the Chain of Lakes are to
be dedicated to Zone 7 of the Alameda County Flood Control and Water Conservation District (Zone 7) for
use in managing the groundwater basin. According to the SMP-23 Reclamation Plan (1987), and consistent
with the LAVQAR Specific Plan, mining at the Site will result in the formation of two lakes:
• Lake A will be located north of Vineyard Avenue, between Isabel Avenue (State Route 84) and Vallecitos
Road.
• Lake B will be located north of Vineyard Avenue, between Isabel Avenue (State Route 84) and the
Shadow Cliffs Regional Recreation Area.
The SMP-23 Reclamation Plan (1987) indicates that excavation at Lakes A and B will extend as far south as
Vineyard Avenue, and that Arroyo del Valle will flow into and through the pits during active mining operations.
Two large concrete spillways would be constructed to control flows into each pit, one at Vallecitos Road and
one at Isabel Avenue. Outflow from Lake B would occur over a rock-lined overflow weir at the west end of the
lake, returning to Arroyo del Valle. The SMP-23 Reclamation Plan (1987) does not include provision for the
restoration or re-construction of the channel for Arroyo del Valle, indicating that the arroyo would be routed
through Lakes A and B and the spillways would remain in place after mining was completed.
The proposed SMP-23 Reclamation Plan Amendment (June 2013) reconfigures the footprints of both Lakes
A and B to maintain the channel for Arroyo del Valle separate from Lakes A and B. Lake A would no longer be
excavated as far south as Vineyard Avenue such that the existing Arroyo del Valle channel could remain
intact. Lake B still would extend south through the currently disturbed Arroyo del Valle channel alignment,
but a new channel alignment would be constructed closer to Vineyard Avenue to restore the initial hydraulic
and biological function of the arroyo. Given that the channel would no longer flow through Lakes A and B, the
reclamation plan would no longer need to include large concrete spillways at Vallecitos Road and Isabel
Avenue, or the large rock-lined overflow weir at the west end of Lake B.
After reviewing the Amendment that was submitted to the County in June 2013, ACCDA sent a letter to
CEMEX dated July 8, 2013, with several comments that focused on the following two issues related to the
water diversion and conveyance facilities:
• Hydraulic impacts: Conduct technical analyses (e.g., hydraulic modeling) to demonstrate that the
restored channel will remain stable, and that neither the channel modifications nor the diversion
structure will increase flood hazards.
• Design feasibility: Present a complete design concept (e.g., schematic plans) and demonstrate that the
elements of the reclamation plan designed to address diversion and conveyance into the Chain of Lakes
can be feasibly constructed in compliance with known regulatory requirements. For example, the
proposed diversion structure would require a bypass flow feature (e.g., fish ladder) and a screen
cleaning system to be in compliance with current fish habitat requirements.
The remainder of this document addresses the “hydraulic impacts” comment. The “design feasibility”
comment is addressed in Technical Memorandum 2.
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Section 3: Model Development To address the ACCDA comment regarding hydraulic impacts, as described above, BC developed a hydraulic
model of the Arroyo del Valle Study Reach using HEC-RAS software (Version 4.1, 2010). HEC-RAS is a one-
dimensional step backwater flow model developed by the Hydrologic Engineering Center (HEC) of the U.S.
Army Corps of Engineers (USACE). Standard hydraulic simulations require two types of input data: (1)
geometric data, consisting of cross-sections, stream reach lengths, and bridge/culvert dimensions; and (2)
flow data, consisting of flow rates and boundary conditions. The following sections describe the geometric
data development. Flow data development is described in Section 4.
3.1 Data Collection
The hydraulic model developed for this analysis will be used not only to evaluate the proposed conditions of
the Amendment, but also likely for future design and permitting. Therefore, it is important that this modeling
effort use existing data sources, and that the modeling methodology be in accordance with accepted
modeling guidelines.
3.1.1 FEMA Flood Modeling
BC started the data collection effort by researching flood hazard information from the Federal Emergency
Management Agency (FEMA), which administers the National Flood Insurance Program (NFIP)3. BC
purchased the current Flood Insurance Study (FIS) for Alameda County (FEMA, 2009), effective Flood
Insurance Rate Maps (FIRMs) covering the Study Reach, and the associated Digital Flood Insurance Rate
Maps (DFIRM) data from FEMA’s Map Services Center4.
Map 3 (Attachment A) shows the current effective flood hazard mapping for Arroyo del Valle based on the
DFIRM data. The entire reach of Arroyo del Valle from Arroyo de la Laguna to Del Valle Dam is mapped as a
Special Flood Hazard Area (SFHA). The area shown to be within the SFHA is equivalent to the area that could
be inundated by the “base flood.”5 The SFHA along Arroyo del Valle is divided into the following two flood
hazard designations:
• Zone AE is a riverine flooding hazard with established base flood elevations; the delineated areas and
flood profiles are based on detailed hydraulic modeling.
• Zone A is a riverine flooding hazard with no base flood elevations; these areas are delineated by
approximate methods that may not have included any detailed modeling.
Two reaches of Arroyo del Valle are shown as Zone AE. The first reach begins at the confluence with Arroyo
de la Laguna and ends approximately 1,300 feet upstream of Bernal Avenue. The second reach begins at
Isabel Avenue and ends at Del Valle Dam. The connecting Zone A reach covers approximately 3 miles,
including areas adjacent to Shadow Cliffs Regional Recreation Area and Lake B of the Eliot Facility.
3 FEMA provides flood insurance to the residents of communities participating in the NFIP, provided that each community adopts
and enforces floodplain regulations that meet or exceed FEMA minimum requirements (http://www.fema.gov/national-flood-insurance-program). Alameda County, the City of Pleasanton, and the City of Livermore are each participating communities.
4 FEMA provides current flood hazard mapping data at the Map Service Center: https://msc.fema.gov/.
5 The base flood is a flooding event with a 1 percent annual chance of exceedance, or a 100-year flood.
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BC submitted an official data request to the FEMA Engineering Library6 to obtain the supporting technical
data for the two detailed studies along Arroyo del Valle. FEMA was able to provide images of the HEC-27
modeling files for the lower reach (i.e., the reach from Arroyo de la Laguna to just upstream of Bernal
Avenue). FEMA developed the HEC-2 model as part of the original FIS for the city of Pleasanton in 1983. The
HEC-2 input data include cross-sections and basic bridge configurations (most notably, Bernal Avenue).
FEMA was not able to locate any information for the reach upstream of Isabel Avenue.
3.1.2 Modeling by Local Agencies
Zone 7 is responsible for flood control along Arroyo del Valle and has conducted several studies along the
Arroyo del Valle corridor. BC met with Zone 7 on August 1, 2013, to discuss the objectives of the study
presented in this technical memorandum and to request data from Zone 7’s current modeling activities.
Zone 7 provided the following data:
• Topographic survey and aerial imagery: A digital terrain model (DTM) was developed from a 2006 aerial
survey flown using LiDAR remote sensing technology. The DTM was provided by Zone 7 on September
27, 2013, in a triangulated irregular network (TIN) format, which is a vector-based three-dimensional
representation of the physical land surface that is compatible with geographic information systems
(GIS). Zone 7 also provided aerial imagery covering the entire Site and Study Reach.
• Preliminary hydraulic model: Zone 7 provided a preliminary HEC-RAS model covering approximately 7.5
miles of Arroyo del Valle from the confluence with Arroyo de la Laguna to Vallecitos Avenue on October 8,
2013. Zone 7 labeled its model a “work in progress,” subject to change as Zone 7 continues to develop
the model. No documentation was available related to model development; however, correspondence
with Zone 7 confirmed that the model cross-sections were based on the 2006 LiDAR survey.
BC contacted the City of Livermore floodplain coordinator regarding the availability of hydraulic modeling
data for Arroyo del Valle. The floodplain coordinator passed the inquiry on to one of the City’s engineering
contractors, Schaaf & Wheeler, which had recently conducted a flood study on portions of Arroyo Mocho,
Arroyo Las Positas, and Arroyo del Valle. However, that study covered only a few thousand feet of Arroyo del
Valle near the confluence with Arroyo de la Laguna. BC did not use these data because they are located
downstream of the relevant Study Reach.
3.2 Baseline Model Build
BC reviewed Zone 7’s preliminary hydraulic model and found that it would not be sufficient for design and
permitting evaluations without significant modification. The following issues were noted at the time the
information was received:
• The Zone 7 model did not extend upstream of Vallecitos Road; modeling would require additional cross-
sections to evaluate potential flooding impacts in Sycamore Grove Park.
• In some locations, the Zone 7 model sections did not extend far enough laterally to include all of the
Arroyo del Valle floodplain.
• The bridge data were extremely coarse, which suggests that they were based on limited information
rather than surveys or as-built drawings.
• The 100-year flow data in the Zone 7 model did not match the data in the Alameda County FIS (FEMA,
2011); there was no citation as to the source of the 100-year flow data and no information as to why the
flow deviates from the current FEMA study.
6 Supporting technical data for detailed mapping studies can be obtained through the FEMA Engineering Library:
9 ArcGIS is a desktop GIS application developed by ESRI of Redlands, California: http://www.esri.com/software/arcgis.
Figure 2. GIS tools were used to import new cross-section data into HEC-RAS
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Expansion and contraction coefficients were increased from the default values (0.1 for contraction and 0.3
for expansion) to 0.3 and 0.5 for cross-sections near bridges and abrupt transitions.
Bridges. The baseline geometric data input file was augmented to include the three bridges located within
the Study Reach. Table 2 lists the sources and summarizes the input data for each bridge.
Table 2. Bridge Input Data
Bridge Source Input data summary
Bernal Avenue
Station 11+50
HEC-2 model from City of Pleasanton FIS (1983)
• Top of roadway elevation of 367.9 feet NAVD88a
• Low chord of bridge elevation of 360.2 feet NAVD88a
• Total width of obstructions = 7.0 feet (assumed to be two 3.5-foot piers)
• Drag coefficient for pier loss = 2.00
• Abutments were placed185 feet apart and centered over the channel
• The longitudinal width of the deck/roadway was assumed to be 100 feet based on aerial images
• The channel geometry through the bridge was based on upstream and downstream cross-sections cut from the 2006 LiDAR survey described previously
Isabel Avenue
Station 193+00
Baseline conditions: As-built plans by Creegan and D’Angelo (1983)
Proposed conditions: Preliminary plans for widening project (URS, 2013)
• Top of roadway elevation of 422.7 feet NAVD88a
• An additional 2 feet was added to the top of the bridge deck to represent the concrete barrier
• Low chord of bridge elevation of 418.2 feet NAVD88a
• A 1.5-foot-wide pier was added at mid-span
• Abutments were placed120 feet apart and centered over the channel
• The longitudinal width of the deck/roadway was set to 40 feet for baseline conditions
• The longitudinal width of the deck/roadway was increased to 112 feet for proposed conditions to reflect the widening project including the pedestrian bridge to be added parallel to the roadway bridge (93.5 + 18.5 = 112)
• The channel geometry through the bridge was based on upstream and downstream cross-sections cut from the 2006 LiDAR survey described previously
Vallecitos Road
Station 256+60
Preliminary HEC-RAS model developed by Zone 7 (2013)
• Top of roadway elevation of 454.0 feet NAVD88
• Low chord of bridge elevation of 451.0 feet NAVD88
• The channel geometry through the bridge was based on upstream and downstream cross-sections cut from the 2006 LiDAR survey described previously
• Abutments were placed 230 feet apart, roughly equivalent to the top width of the channel shown in the 2006 topography
• The longitudinal width of the deck/roadway was assumed to be 40 feet based on aerial images
a. Original data with elevations based on the National Geodetic Vertical Datum 1929 (NGVD29) were converted to North American Vertical Datum
1988 (NAVD88) using a +2.69-foot conversion factor obtained from http://www.ngs.noaa.gov/cgi-bin/VERTCON/vert_con.prl.
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Manning’s Roughness. BC developed a spatially varied land use coverage in GIS to assign horizontally varied
Manning’s roughness values to the cross-sections during the GeoRAS input data development process. To
do this, BC obtained near-infrared ortho-imagery from the National Agriculture Imagery Program (NAIP)10. BC
used numerical values for visual red and near-infrared to evaluate the density of vegetation using a
Normalized Difference Vegetation Index (NDVI) method11. The NDVI values were visually parsed into three
primary land cover categories: water, earth/impervious, and vegetated. The NDVI raster data set was then
processed into generalized polygon coverage areas (see Figure 3). Manning’s roughness coefficients were
assigned to each area based on values presented in Chow (1959) for excavated channels and floodplain
areas (see Table 3).
(a) NAIP true color (b) NAIP near-infrared (c) NDVI land cover categories (d) generalized polygon
coverage areas
Figure 3. Development of a land use coverage for spatially varied Manning’s roughness
Table 3. Manning’s Roughness Values
Land cover category Manning’s n
Water 0.020
Earth/impervious 0.035
Vegetated 0.080
Selected values based on Chow (1959).
10 NAIP images contain intrinsic data for four color bands: red, green, blue, and near-infrared. The first three are the typical color
ranges used to display true color images. The fourth, near-infrared band can be used to assess vegetative cover. Information about NAIP imagery can be found here https://www.fsa.usda.gov/FSA/apfoapp?area=home&subject=prog&topic=nai. Data can be downloaded via the National Map data server: http://nationalmap.gov/.
11 NDVI is a commonly used remote sensing technique for quantitatively evaluating vegetation density. The formula is given as,
NDVI = (NIR – VIS)/(NIR + VIS); where NIR = spectral reflectance measurement for the near-infrared band, and VIS = spectral reflectance measurement for the visual red band. For general information, go to the following Web site from the NASA Earth Observatory: http://earthobservatory.nasa.gov/Features/MeasuringVegetation/measuring_vegetation_2.php.
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3.3 Modifications for Proposed Conditions
BC modified the baseline model to reflect changes associated with the Amended Reclamation Plan
(Spinardi, 2013). The following sections describe the modifications.
3.3.1 Realigned Channel and Floodplain
The Arroyo del Valle channel and floodplain (i.e., the alluvial corridor, or “corridor”) located along the south
edge of Lake B will be reconstructed and restored along a new alignment parallel to Vineyard Avenue. The
new alignment will span approximately 6,500 feet between Stations 108+98 and 175+65 in the baseline
model. The longitudinal slope of the new channel and floodplain was calculated to be 0.6 percent based on
the upstream and downstream tie-in elevations of 353.6 and 392.4 feet, respectively. The Amendment calls
for a floodplain corridor width of roughly 200 feet with 3 (horizontal)-to-1 (vertical) side slopes extending up
to a depth of approximately 10 feet (see Figure 4). In addition, a 10-foot-wide by 2-foot-deep low-flow
channel would be embedded within the floodplain.
Figure 4. Restored Arroyo del Valle corridor geometry from Amendment (Spinardi, 2013)
The corridor geometry described above was spliced into each of the affected baseline cross-sections at the
approximate lateral location between Vineyard Avenue and the proposed future location of Lake B. Note that
the cross-sections were not modified to reflect the Lake B geometry because BC assumed that all flow will
be contained within the corridor and Lake B would not contribute to flood flow conveyance.
According to the Amendment (Spinardi, 2013) the restored channel and floodplain would be enhanced with
native vegetation and a complex/varied streambed to provide riparian habitat. A Manning’s roughness value
of 0.045 was assigned to the low-flow channel and a value of 0.080 was conservatively assumed for the
floodplain areas, given the potential for dense woody vegetation.
3.3.2 Lake A Diversion
The Amendment currently calls for the construction of a diversion structure on Arroyo del Valle near the
upstream end of Lake A. The structure would divert water out of the channel and into a conduit to Lake A. In
addition to the lateral diversion facilities (screen, piping, etc.) an in-channel structure (e.g., inflatable dam or
Obermeyer gate) has been proposed to generate controlled hydraulic head for the diversion system. Cross-
sections 246+03 and 249+52 were modified by increasing the height of the right bank to an elevation of
450 feet (see Figure 5b), which is necessary to construct diversion facilities and that contain ponded water.
An in-line weir obstruction was added at Station 245+00 for a series of simulations designed to evaluate the
potential backwater flooding impacts resulting from the installation of an inflatable dam (see Figure 5c).
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While the actual design and size of the diversion structure may vary from what is assumed here, the
increased bank height and in-stream obstruction height are considered to be conservative, near worst-case
assumptions in terms of the effects on channel hydrology. Therefore, the model results will provide a very
conservative (i.e., protective of cultural and biological resources) assessment of the potential backwater
flooding impacts related to diversion of water into Lake A.
(a) Cross-section plot at Station 246+03 for baseline conditions model
(b) Cross-section plot at Station 246+03 for proposed conditions model (no obstruction)
(c) Cross-section plot at Station 246+03 for proposed conditions model (6-foot obstruction)
Figure 5. Right bank modifications at proposed Lake A diversion structure
0 500 1000 1500 2000400
410
420
430
440
450
460
470
Station (ft)
Ele
vatio
n (
ft)
Legend
Ground
Ineff
Bank Sta
0 500 1000 1500 2000400
410
420
430
440
450
460
470
Station (ft)
Ele
vatio
n (
ft)
Legend
Ground
Ineff
Bank Sta
0 500 1000 1500 2000400
410
420
430
440
450
460
470
Station (ft)
Ele
vati
on (ft
)
Legend
Ground
Ineff
Bank Sta
LAKE A
LAKE A
LAKE A
ARROYO DEL VALLE
ARROYO DEL VALLE
ARROYO DEL VALLE
OBSTRUCTION
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Section 4: Hydraulic Evaluations BC used the HEC-RAS hydraulic model described in Section 3 to address hydraulic impacts along Arroyo del
Valle, including potential impacts to channel stability (Section 4.1) and flooding (Section 0).
4.1 Channel Stability
Alluvial channels form and continually shift in response to temporal sequences of flow rate and sediment
supply. Over periods of many years, channels adjust to flow and sediment regimes through changes in
geometry (e.g., planform, cross-sectional dimensions, and longitudinal slope). Given a period with a relatively
constant flow regime and sediment supply, a channel approaches a stable geometry and is considered to be
in “dynamic equilibrium.” Dynamic equilibrium does not mean that the channel is static, but rather that
morphological responses to extreme events would only be temporary. Furthermore, the system’s long-term
formative conditions continually would continually restore a more stable morphology over time. Lane’s
Principle, or Lane’s Balance (1955), qualitatively represents this geomorphic concept of disturbance,
channel adjustment, and dynamic equilibrium qualitatively as:
����� ∝ ���
where:
Qs is sediment load
D50 is the 50th percentile of the sediment grain size distribution
Qw is the stream discharge
S is the slope
The relationship represented by Lane’s Principle suggests that a long-term shift in any of these factors would
destabilize the system and initiate a compensatory response in one or more of the other factors as the
system attempts to restore equilibrium. Dynamic equilibrium for a stream reach can be conceptualized in
terms of sediment continuity, where sediment loads flowing into the reach effectively equal the reach
sediment transport capacity. Thus, when sediment loads carry through the reach, the stream reach neither
aggrades nor degrades and the overall slope remains constant.
BC evaluated the restored stream corridor stability by analyzing the sediment loads balance along the entire
Study Reach for both baseline and proposed conditions. Section 4.1.1 discusses bed sediment composition
(D50). Section 0 discusses long-term stream discharges (Qw). Section 4.1.3 discusses sediment loads (Qs) based on calculated sediment transport capacities for the given geometric configuration of the channel; i.e.,
cross-section and slope (S). 4.1.1 Bed Sediments
BC collected no Arroyo del Valle bed sediment data for this study. However, BC did not need site-specific
data for this channel stability analysis because we compare baseline and proposed conditions in relative
terms. Furthermore, BC assumes that the bed sediments used to restore the Arroyo del Valle corridor under
proposed conditions will be similar to the baseline bed sediment composition. Therefore, parameters used
to characterize the bed sediments remain the same for both baseline and proposed conditions.
Zone 7 completed several studies related to geomorphic and sediment transport conditions in the Valley as
part of the development of the Stream Management Master Plan (RMC, 2006). Appendix C of that plan
describes detailed sediment transport modeling of Arroyo las Positas, Arroyo Mocho, and Arroyo de la
Laguna. Although the Zone 7 study did not include Arroyo del Valle explicitly, BC assumed that some study
information would apply to Arroyo del Valle for this study. In particular, BC assumed that Arroyo del Valle bed
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sediment would be similar to bed sediment data collected for Arroyo Mocho. Table 4 shows two Arroyo
Mocho bed sediment data sets taken from Appendix E of the technical memorandum, included as Appendix
C of the Zone 7 Stream Management Master Plan (RMC, 2006). BC used the average of these two data
points for the Arroyo del Valle sediment transport analyses (Section 4.1.3).
Table 4. Bed Material Data from Zone 7 Stream Management Master Plan
Data obtained from Appendix E of the technical memorandum included as Appendix C of the Zone 7 Stream Management
Master Plan (RMC, 2006).
4.1.2 Flow Magnitude and Frequency
Two U.S. Geological Survey (USGS) stream gauging stations on Arroyo del Valle provide observed streamflow
data:
• Arroyo del Valle at Livermore (AVL), USGS
111176500: average daily discharge available
from 1912 to present; located just
downstream of Del Valle Reservoir and
upstream of the Study Reach
• Arroyo del Valle at Pleasanton (AVP), USGS
111176600: average daily discharge available
from 1957 to 1986; located just downstream
of Main Street in the City of Pleasanton and
downstream of the Study Reach
Construction of Del Valle Reservoir in 1968
substantially altered the hydrologic flow regime
(i.e., frequency and duration of flows) in Arroyo del
Valle (Kamman, 2009). Therefore, BC considered
only streamflow data from 1968 onward as
relevant for analyses described herein.
Figure 6 shows a correlation comparison of the
average daily discharge data for each of the USGS
stream gauges based on concurrent data ranging
from 1968 to 1985. The two gauges show a high level of correlation (i.e., R-squared = 0.96), likely due to the
dominance of regulated flow releases from Del Valle Reservoir. Although the AVL gauge is located upstream
of the AVP gauge, the average flow at AVL was about 11 percent greater than the average flow at AVP,
suggesting that the reach in between has a net flow loss. Thus, the AVL gauge provides a more conservative
estimate of flows for evaluating erosion potential. The AVL gauge also provides more recent data records.
BC visually examined the average daily discharge data for the AVL gauge and found that the 12 most recent
water years (from 2002 to 2013) had a consistent pattern of seasonal flow releases. Therefore, BC assumed
Figure 6. Correlation of average daily discharge data at
USGS gauges 11176500 (AVL) and 11176600 (AVP)
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that these data were most representative of dam current operations. Using the 2002 through 2013 data, BC
calculated a flow duration curve (Figure 7) and constructed a flow frequency distribution chart (Figure 8) to
characterize typical flows in Arroyo del Valle. Figure 8 data exhibit a bimodal distribution with a typical
winter/springtime baseflow around 0.5 cubic feet per second (cfs) and a summer/autumn flow release
around 10 cfs.
Figure 7. Flow duration curve for Arroyo del Valle based on average daily flows at AVL (2002–13)
0.01
0.10
1.00
10.00
100.00
1,000.00
10,000.00
0% 20% 40% 60% 80% 100%
DIS
CH
AR
GE
(C
FS
)
PERCENT TIME EXCEEDED
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Figure 8. Frequency of flows in Arroyo del Valle based on average daily flows at AVL (2002–13)
4.1.3 Sediment Load Balance
BC used bed sediment data described in Section 4.1.1, the flow frequency data described in Section 0, and
hydraulic rating tables from HEC-RAS to calculate sediment transport capacities along the Study Reach. BC’s
calculations used the same bed load sediment transport function used for the sediment analysis conducted
for the Zone 7 Stream Management Master Plan (RMC, 2006). Ayres Associates (2001) developed the
transport function (provided below) based on a regression analysis, the Meyer-Peter and Muller bed load
equation, and the Zeller and Fullerton Power Function (RMC, 2006):
�� = 0.000157���.����.������.����.��
where:
qs = unit width total load transport capacity (cfs/ft)
Gr = gradation coefficient of the bed material = �� �
!" #$+ #$ &'(
V = average flow velocity (ft/s)
D50 = bed material size of which 50 percent of the sediment by weight is smaller (mm)
d = hydraulic depth (ft)
0
5
10
15
20
25
30
0.01 0.10 1.00 10.00 100.00 1000.00 10000.00
FR
EQ
UE
NC
Y (
DAYS
PE
R Y
EA
R)
DISCHARGE (CFS)
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BC estimated sediment loads in Arroyo del Valle using the above equation. BC obtained the bed sediment
variables in the above equation (D50 and Gr) from the Table 4 average values. BC obtained the average flow
velocity (V) and hydraulic depth (d) from hydraulic rating tables generated using the HEC-RAS model
described in Section 3. Rather than selecting a single discharge for performing these calculations, BC
performed a magnitude-frequency analysis, where sediment transport capacities are calculated for a full
range of stream discharges and then multiplied by the frequency of occurrence.
The magnitude-frequency concept stems from a theory
developed by Wolman and Miller (1960). They
described how the geomorphic evolution of landscapes
is strongly influenced by the amount “work” done by the
forces acting on the system (e.g., shear forces caused
by flowing water), and how the relative amount of work
done depends on both the magnitude of the force and
the frequency of occurrence.
Figure 9 is a graphical representation of the magnitude-
frequency concept, where the frequency of occurrence
is log-normally distributed and the magnitude of the
influencing force (i.e., applied stress) increases in
accordance with a power function. The product of the
frequency of the occurrences and the magnitude of the
influencing force result in an “effective work” curve. For
an alluvial system, the frequency of flows multiplied by
the sediment transport capacity results in a sediment
loading curve. The integral of the sediment loading
curve is the total sediment load.
BC performed the following steps to calculate average annual sediment loads at each cross-section for both
baseline and proposed conditions:
1. Run 100 steady-state hydraulic simulations using flow rates ranging from near zero to slightly more than
1,000 cfs (the largest average daily discharge recorded at the AVL gauge since 2002 is 1,070 cfs) to
create hydraulic rating tables. BC based flow rates used for these simulations on the logarithmically
distributed flow bins used to generate the frequency distribution shown in Figure 8.
2. Calculate sediment transport capacities for each of the 100 hydraulic profiles using the sediment
transport function developed by Ayres Associates (2001), thereby creating a sediment rating curve.
3. Multiply sediment transport capacities by the frequency of occurrence, based on the average number of
days per year the flows within each flow bin were observed at the AVL gauge, thereby creating an
average annual sediment loading curve.
4. Sum incremental sediment loads calculated for each flow bin to estimate the total annual sediment
loading.
Figure 10 shows the calculated annual sediment loads for baseline and proposed conditions. BC added a
15-point moving average to the plot to remove some of the variation and illustrate the general trend.
Figure 9. Relation between applied stress and
frequency of occurrence in geomorphic processes
Image obtained from Wolman and Miller (1960).
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Figure 10. Annual sediment load profiles for baseline and proposed conditions
(a) Arroyo del Valle flows through two lakes along the Shadow Cliffs Regional Recreation Area; sediment
loading rates (i.e., carrying capacities) in this reach are lower than the sediment loadings in up-
stream reaches, which means this reach is likely depositional.
(b) Estimated sediment loading rates along the restored corridor of Arroyo del Valle are roughly equiva-
lent to the average sediment loading rates in the upstream reaches, which means this reach is likely
stable.
The results presented in Figure 10 indicate that the sediment loadings are roughly equivalent in both the restored and upstream reaches, and also that the average sediment loadings are similar under both base-line and proposed conditions. In other words, the restored corridor will maintain sediment continuity, and therefore it is not likely to experience substantial aggradation or degradation.
1.E-01
1.E+00
1.E+01
1.E+02
1.E+03
1.E+04
1.E+05
1.E+06
0 5000 10000 15000 20000 25000 30000
AN
NU
AL S
ED
IME
NT L
OA
D (
T/Y
R)
STREAM STATION
Baseline
Proposed
15 per. Mov. Avg. (Baseline)
15 per. Mov. Avg. (Proposed)
(a) (b)
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4.2 Flood Impacts
BC evaluated flood hazard impacts by performing steady-state hydraulic simulations of peak flood flows to
calculate peak water surface elevations and delineate potentially inundated areas.
As described in Section 3.1.1, FEMA has performed detailed flood
studies on Arroyo del Valle. FEMA’s current FIS for Alameda County
(2011) provides peak discharges for the 10-, 50-, 100-, and 500-
year floods (see Table 5). As noted previously, operations at Del
Valle Reservoir highly regulate flood flows in Arroyo del Valle. The
100-year flood flow of 7,000 cfs corresponds to a managed flood
release from the dam (USACE, 1978).
BC used the peak discharges shown in Table 5 as inflows to the
upstream end of the Study Reach in the HEC-RAS model. The model
automatically calculates upstream and downstream water surface
boundaries using normal depth calculations. Our analyses estimated
the upstream slope for the normal depth calculation to be 0.6
percent, while the downstream slope would be 0.5 percent12.
BC calculated hydraulic profiles (e.g., peak water surface elevations) along the Study Reach using the
baseline geometric model described in Section 3. Figure 11 shows an overview of the calculated water
surface profiles. Detailed output tables and profile plots are provided in Attachment B.
Figure 11. Baseline water surface profiles displayed in HEC-RAS
12 Note that if this model is later used for FEMA flood hazard map revisions, the upstream and downstream boundary conditions
may need to be adjusted to tie into the effective base flood elevations at each boundary.
0 5000 10000 15000 20000 25000340
360
380
400
420
440
460
480
Main Channel Distance (ft)
Ele
vation
(ft)
Table 5. Arroyo del Valle Peak Discharge
Frequency
Recurrence interval
(years) Peak discharge (cfs)
10 1,860
50 4,150
100 7,000
500 9,080
At Arroyo de la Laguna (FEMA, 2011).
100-YEAR W.S.
500-YEAR W.S.
50-YEAR W.S.
10-YEAR W.S.
ISA
BE
L A
VE
VA
LLE
CIT
OS
RD
BE
RN
AL
AV
E
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As discussed in Section 3.1.1, FEMA uses the 100-year flood as its base flood. Local communities typically
use the 100-year flood for the management and regulation of floodplains. Therefore, BC used the 100-year
flood scenario to evaluate flood impacts. BC developed baseline flood inundation mapping using the
following steps:
1. Export the HEC-RAS results from the baseline 100-year scenario to ArcGIS using HEC-GeoRAS, which
attributes water surface elevations to modeled cross-section transects.
2. Convert the cross-section transects in a three-dimensional TIN surface representing the hydraulic profile
along the arroyo, then convert to a gridded raster surface with 5-foot resolution.
3. Convert the 2006 LiDAR survey data into a raster surface representing existing terrain topography on the
same 5-foot grid as the water surface raster.
4. Subtract the terrain surface from the water surface grid to obtain an elevation difference raster where
the positive values represent the potential inundation depth.
5. Examine potentially inundated areas for connectivity with the main channel; then remove areas not
directly connected.
Figure 12 shows the baseline 100-year inundation area for the Study Reach. The calculated water surface
elevations in Arroyo del Valle are high enough that water could potentially flow into Lakes A and/or B (see
Attachment C for elevation profiles along each lake).
Figure 12. 100-year flood inundation along Study Reach based on baseline HEC-RAS modeling results
4.2.1 Realigned Channel and Floodplain
BC performed additional steady-state hydraulic simulations using the proposed (reclaimed) conditions
geometric model described in Section 3.3.1, which included the realigned/restored Arroyo del Valle corridor
from Stations 108+98 to 175+65. The calculated water surface elevations indicate that the newly
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constructed corridor would contain flows associated with all four flood scenarios (10-, 50-, 100-, and 500-
year recurrence) (see Figure 13).
Figure 13. Example cross-section at Station 144+00 showing flood flows contained within restored corridor
BC examined the results for the 100-year (i.e.,7,000 cfs) flood more closely to evaluate potential flooding
impacts in the vicinity of the restored corridor. Figure 14 shows a comparison of the baseline and proposed-
conditions flood profiles, along with the channel invert and the top elevation of the restored corridor.
Figure 14. Comparison of 100-year profiles for baseline and proposed conditions along restored corridor
400 500 600 700
370
380
390
400
Station (ft)
Ele
vation
(ft)
Legend
WS 500YR
WS 100YR
WS 50YR
WS 10YR
Ground
Ineff
Bank Sta
340
350
360
370
380
390
400
410
420
10000 12000 14000 16000 18000 20000
ELE
VAT
ION
(F
T)
STREAM STATION (FT)
Top of Restored Corridor
Proposed 100-year W.S.
Baseline 100-year W.S.
Proposed Invert
Baseline Invert
RESTORED CORRIDOR
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The results shown in Figure 14 indicate that the modifications to the channel along the restored corridor
raise 100-year water surface elevations above the baseline conditions. Table 6 compares baseline and
proposed conditions along the restored corridor.
Table 6. Comparison of Hydraulic Parameters along the Restored Corridor
BC performed additional steady-state hydraulic simulations to evaluate the potential flood impacts of an in-
channel diversion as described in Section 3.3.2. BC executed 10 simulations with incrementally increased
obstruction heights ranging from 1 foot to 10 feet. For comparison, Figure 17 shows plots of water surface
elevations for the reach upstream of the obstruction.
Baseline 100-year
Proposed 100-year
Inundation Areas
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Figure 17. Water surface increases resulting from incremental adjustments to obstruction height
The water surface increases associated with an in-channel obstruction diminish rapidly upstream, largely
due to the relatively steep channel slope, approximately 1 percent between the obstruction and Vallecitos
Road. Figure 18 shows the upstream water surface increases associated with a 10-foot in-channel
obstruction. The results show that for the 10-foot obstruction the water surface increase at Vallecitos Road
(approximately 1,100 feet upstream) is less than 0.5 foot.
Figure 18. Water surface increases resulting from a 10-foot in-channel obstruction at Station 245+00
425
430
435
440
445
450
455
460
24000 24500 25000 25500 26000
ELE
VATIO
N (
FT)
STREAM STATION (FT)
10-FT Obstruction
9-FT Obstruction
8-FT Obstruction
7-FT Obstruction
6-FT Obstruction
5-FT Obstruction
4-FT Obstruction
3-FT Obstruction
2-FT Obstruction
1-FT Obstruction
No Obstruction
Channel Invert
OBSTRUCTION(HEIGHT VARIES)
WATER SURFACE PROFILESVALLECITOS
ROAD BRIDGE
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
24000 24500 25000 25500 26000 26500 27000
WATE
R S
UR
FAC
E I
NC
RE
AS
E (
FT)
STREAM STATION (FT)
IN-C
HA
NN
EL
OB
ST
RU
CT
ION
VALLECITOSROAD BRIDGE
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BC performed additional inundation mapping using the water surface profile from the simulation with a 10-
foot obstruction at Station 245+00 (see Figure 19). The mapping results indicate if an in-channel diversion
with a structure as high as 10 feet was to obstruct flow during a 100-year event, there would be some
additional inundated areas in the immediate vicinity around the diversion and Lake A. Figure 19 shows
potential flooding on Vineyard Avenue and flooding in close proximity to a small residential structure near the
intersection of Vineyard Avenue and Vallecitos Road. Installation of a diversion structure as high as 10-feet
would require raising of adjacent grades to avoid these potential impacts. Note that the additional inundated
areas do not extend upstream of Vallecitos Avenue.
Figure 19. Potential flood inundation increase (red) resulting from a 10-foot in-channel obstruction
Baseline 100-year
10-FT Obstruction
Inundation Areas
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Section 5: Conclusions BC developed a HEC-RAS hydraulic model of the Arroyo del Valle channel and floodplain. The model covers
5.4 miles from approximately 1,000 feet downstream of Bernal Avenue to roughly 3,000 feet upstream of
Vallecitos Avenue. BC used the model to evaluate potential channel stability and flooding impacts related to
the proposed/reclaimed conditions at the Eliot Facility, including the realignment and restoration of the
Arroyo del Valle corridor along Lake B and addition of an in-channel diversion structure near Vallecitos
Avenue. The following bullets summarize BC’s findings:
• Average annual sediment loads within the restored reach will be roughly equivalent to the annual
sediment loads in upstream reaches, and those loads are similar to the estimated loads for the baseline
condition. In other words, the restored corridor will maintain sediment continuity, and therefore it is not
likely to experience channel instabilities due to substantial aggradation or degradation.
• Calculated water surface elevations for baseline conditions are higher than the ground elevations
separating the channel from Lakes A and B in at least two locations, indicating that floodwaters could
potentially enter into the lakes during a 100-year flood event (see Attachment C for details).
• Water surface elevations along the restored corridor are on average approximately 1.6 feet higher than
under baseline conditions; however, the proposed geometry for the restored corridor has sufficient
depth to contain the 100-year, as well as the 500-year flood flows.
• The 100-year water surface elevation increase at the upstream end of the restored corridor is
approximately 1.6 feet; however, this increase diminishes rapidly upstream and will not result in
additional inundated areas if the modified corridor is tied into high ground.
• Water surface increases along the restored corridor are due to a combination of a narrower floodplain
width and a higher Manning’s roughness.
• An in-channel diversion with an obstruction as high as 10 feet at the upstream end of Lake A would
increase water surface elevations in the vicinity immediately upstream of the diversion; however, those
increases diminish rapidly and are negligible beyond Vallecitos Avenue.
• An in-channel diversion with an obstruction as high as 10 feet at the upstream end of Lake A could also
increase the area inundated by a 100-year flood event unless adjacent grades are raised. In particular,
the 100-year flood could potentially inundate a small portion of Vineyard Avenue, and comes close to
impacting a nearby residential structure.
Eliot Facility Reclamation Plan Amendment Hydraulic Modeling of Arroyo del Valle
26
Use of contents on this sheet is subject to the limitations specified at the beginning of this document. CEMEX AdVHS TM01 20140212.docx
References San Francisco Estuary Institute (SFEI), February 2013. Alameda Creek Watershed Historical Ecology Study.
Alameda County Community Development Agency (ACCDA), June 2013. Letter from James Gifford to Ron Wilson titled “Completeness Review of Application to Amend Surface Mining Permit and Reclamation Plan No. 23.”
Ayres Associates, December 2001. Zone 7 Water Agency Geomorphic and Sediment Transport Evaluation: Prepared for Zone 7 Water Agency and West Yost and Associates.
California Department of Water Resources, April 1968. The Resources Agency, Department of Water Resources Bulletin No. 119-29 Feasibility of Serving The South Bay Contractors from The State Water Project. http://archive.org/stream/feasibilityofsersouthbay11929calirich/feasibilityofsersouthbay11929calirich_djvu.txt
California Department of Water Resources, 2001. South Bay Aqueduct (Bethany Reservoir and Lake Del Valle) 4/01. http://www.water.ca.gov/pubs/swp/south_bay_aqueduct__lake_del_valle_and_bethany_reservoir_/south-bay-aque.pdf
E-mail correspondence from Colleen Winey to Nathan Foged, August 16, 2013. “RE: CEMEX Eliot Facility Rec Plan -- Data needs for Arroyo del Valle hydraulic study.” Attachment: “Z7 Diversion Criteria.docx” [Draft Design Criteria for the Arroyo Del Valle Diversion Structure.]
EMKO Environmental, 2013. Hydrology and Water Quality Analysis Report, Lake A And Lake B Expansion, CEMEX Eliot Quarry – SMP-23, Pleasanton, California. Prepared by: EMKO Environmental, Inc. 551 Lakecrest Drive, El Dorado Hills, California 95762,dated June 7, 2013.
Federal Emergency Management Agency (FEMA), 2009. Flood Insurance Study for Alameda County, California and Incorporated Areas. Effective August 3, 2009. Flood Insurance Study Number 06001CV001A.
Kamman Hydrology & Environmental Engineering, Inc. (Kamman), 2009. Phase 2 Technical Report, Sycamore Grove Recovery Program, Sycamore Grove Park, Livermore, California. Prepared for Livermore Area Recreation and Park District 4444 East Avenue, Livermore, California 94550 and the Zone 7 Water Agency 100 North Canyons Parkway, Livermore, California 94551. Edited by Kamman Hydrology & Engineering, Inc., 7 Mt. Lassen Drive, Suite B250, San Rafael, California 94903.
Lane, E. W., 1955. “The Importance of Fluvial Morphology in Hydraulic Engineering.” Proceedings, American Society of Civil Engineers, No. 745, July 1955.
LSA Associates, 2013. “Results of Biological Surveys, CEMEX Eliot Quarry, Alameda County, California.” Letter to Ron Wilson, CEMEX, 5180 Golden Foothills Parkway, El Dorado Hills, California 95762 from Malcolm J. Sproul, LSA Associates, Inc., 157 Park Place Point, Richmond, California, 94801.
Raines, Melton & Carella, Inc. (RMC), 2006. Zone 7 Stream Management Master Plan. Appendix C
Spinardi Associates (Spinardi), June 2013. Reclamation Plan Amendment, CEMEX SMP-23, 1544 Stanley Boulevard, Pleasanton, California 94566, Unincorporated Alameda County, Submitted to: Alameda County Community Development Agency Neighborhood Preservation and Sustainability Department, 224 W. Winton Ave, Suite 205, Hayward, California 94544, Prepared by: Spinardi Associates, 265 Sea View Avenue, Piedmont, California 94610
USGS. Flow data obtained from United States Geological Survey stream gaging station on Arroyo del Valle (USGS #11176500 ARROYO VALLE NR LIVERMORE CA) and (USGS #11176600 ARROYO VALLE A PLEASANTON CA) http://waterdata.usgs.gov/nwis/dv/?site_no=11176500&agency_cd=USGS&referred_module=sw http://waterdata.usgs.gov/nwis/dv/?site_no=11176600&agency_cd=USGS&referred_module=sw
Wolman, M.G., and J.P. Miller. 1960. “Magnitude and Frequency of Forces in Geomorphic Processes.” Journal of Geology; v. 68, pp. 54–74.
Eliot Facility Reclamation Plan Amendment Hydraulic Modeling of Arroyo del Valle
A-1
Use of contents on this sheet is subject to the limitations specified at the beginning of this document. CEMEX AdVHS TM01 20140212.docx
Attachment A: Maps
Map 1: Site and Study Reach
Map 2: Tributary Drainages
Map 3: FEMA Flood Hazards
Map 4: HEC-RAS Model Cross-sections
Map 5: 100-Year Flood Inundation
STAN
LEY B
LVD
ISABEL AVE
VALLE
CITOS RDLIV
ERMO
REPL
EASA
NTON
RUBY HILL
SHAD
OWCL
IFFS
BORI
SLA
KE
CONC
ANNO
N BL
VD
STUD
Y REA
CHBO
UNDA
RY(DO
WNST
REAM
)
STUD
Y REA
CHBO
UNDA
RY(UP
STRE
AM)SYCA
MORE
GROV
E PAR
K
ELIOT
FACIL
ITY SI
TEAN
D ARR
OYO D
EL VA
LLE
STUDY
REAC
HTe
chnic
al Me
moran
dum
No. 1
- Atta
chme
nt A
Hydra
ulic M
odeli
ng of
Arroy
o del
Valle
Eliot
Facil
ity Re
clama
tion P
lanSu
rface
Mini
ng Pe
rmit 2
3 (“S
MP-23
”)
MAP 1
BC Pr
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Numb
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4718
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Hydra
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MP-23
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Numb
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4718
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. 1 - A
ttach
ment
AHy
drauli
c Mod
eling
of Ar
royo d
el Va
lleEli
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Surfa
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L E G
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HA: Z
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photo
graphy
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IP dat
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Nation
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Data S
erver:
http://v
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map.g
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STAN
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0+00
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Tech
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. 1 - A
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AHy
drauli
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eling
of Ar
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lleEli
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Recla
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Surfa
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MAP 4
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Numb
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based
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IP dat
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Nation
al Map
Data S
erver:
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ational
map.g
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wer/.
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LEY B
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CITOS RDLIV
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REPL
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NTON
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Tech
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. 1 - A
ttach
ment
AHy
drauli
c Mod
eling
of Ar
royo d
el Va
lleEli
ot Fa
cility
Recla
matio
n Plan
Surfa
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Perm
it 23 (
“SMP
-23”)
MAP 5
BC Pr
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Data S
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ational
map.g
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Eliot Facility Reclamation Plan Amendment Hydraulic Modeling of Arroyo del Valle
B-1
Use of contents on this sheet is subject to the limitations specified at the beginning of this document. CEMEX AdVHS TM01 20140212.docx
Attachment B: Detailed Modeling Output
10-Year Water Surface Profiles
50-Year Water Surface Profiles
100-Year Water Surface Profiles
500-Year Water Surface Profiles
10-Year Tabulated Hydraulic Parameters
50-Year Tabulated Hydraulic Parameters
100-Year Tabulated Hydraulic Parameters
500-Year Tabulated Hydraulic Parameters
0 5000 10000 15000 20000 25000
Stream Station (ft)
320
340
360
380
400
420
440
460
480
Ele
vati
on
(ft
)
L E G E N D
Proposed Water Surface
Baseline Water Surface
Proposed Channel Invert
Baseline Channel Invert
Vertical Scale: 1 inch = 20 feet, Horizontal Scale: 1 inch = 2,000 feet
Isa
be
l A
ven
ue
Be
rna
l A
ven
ue
Va
lleci
tos R
oa
d
Eliot Facility Reclamation Plan Amendment HEC-RAS Hydraulic Profiles
10-year Water Surface
Hydraulic Modeling of Arroyo del Valle
TM01 | Attachment B\\BCSEA06\projects\CEMEX\144718 Arroyo del Valle Hydraulic Study\300 Analysis\HEC-RAS\AdVHS Hydraulic Profile 10YR.grf
Restored Corridor
0 5000 10000 15000 20000 25000
Stream Station (ft)
320
340
360
380
400
420
440
460
480
Ele
vati
on
(ft
)
L E G E N D
Proposed Water Surface
Baseline Water Surface
Proposed Channel Invert
Baseline Channel Invert
Vertical Scale: 1 inch = 20 feet, Horizontal Scale: 1 inch = 2,000 feet
Isa
be
l A
ven
ue
Be
rna
l A
ven
ue
Va
lleci
tos R
oa
d
Eliot Facility Reclamation Plan Amendment HEC-RAS Hydraulic Profiles
50-year Water Surface
Hydraulic Modeling of Arroyo del Valle
TM01 | Attachment B\\BCSEA06\projects\CEMEX\144718 Arroyo del Valle Hydraulic Study\300 Analysis\HEC-RAS\AdVHS Hydraulic Profile 50YR.grf
Restored Corridor
0 5000 10000 15000 20000 25000
Stream Station (ft)
320
340
360
380
400
420
440
460
480
Ele
vati
on
(ft
)
L E G E N D
Proposed Water Surface
Baseline Water Surface
10-FT Obstruction W.S.
Proposed Channel Invert
Baseline Channel Invert
Vertical Scale: 1 inch = 20 feet, Horizontal Scale: 1 inch = 2,000 feet
Isa
be
l A
ven
ue
Be
rna
l A
ven
ue
Va
lleci
tos R
oa
d
Eliot Facility Reclamation Plan Amendment HEC-RAS Hydraulic Profiles
100-year Water Surface
Hydraulic Modeling of Arroyo del Valle
TM01 | Attachment B\\BCSEA06\projects\CEMEX\144718 Arroyo del Valle Hydraulic Study\300 Analysis\HEC-RAS\AdVHS Hydraulic Profile 100YR.grf
Restored Corridor
Ob
stru
cti
on
0 5000 10000 15000 20000 25000
Stream Station (ft)
320
340
360
380
400
420
440
460
480
Ele
vati
on
(ft
)
L E G E N D
Proposed Water Surface
Baseline Water Surface
Proposed Channel Invert
Baseline Channel Invert
Vertical Scale: 1 inch = 20 feet, Horizontal Scale: 1 inch = 2,000 feet
Isa
be
l A
ven
ue
Be
rna
l A
ven
ue
Va
lleci
tos R
oa
d
Eliot Facility Reclamation Plan Amendment HEC-RAS Hydraulic Profiles
500-year Water Surface
Hydraulic Modeling of Arroyo del Valle
TM01 | Attachment B\\BCSEA06\projects\CEMEX\144718 Arroyo del Valle Hydraulic Study\300 Analysis\HEC-RAS\AdVHS Hydraulic Profile 500YR.grf
Restored Corridor
Eliot Facility Reclamation Plan Amendment HEC-RAS Output Page 1 of 32