Santa Clara River - Hydraulic Analysis Report
Introduction
Santa Clara River is located in the unincorporated areas of Ventura County, California. The
study was performed for 39.34 miles of the stream. The extent of the stream is from the
confluence with the Pacific Ocean to county boundary. The channel is a regular natural
channel. The entire study reach area is mostly agricultural except for downstream portion on
left over bank which is urban.
Structure Data
There are 9 bridge crossings and 1 inline weir along Santa Clara River in Ventura County.
Width of the bridge opening, low-chord and high-chord measurements were obtained from
the field reconnaissance. As-built plans provided by Ventura County were used to obtain
additional information. The structure information for all these structures was obtained from
as-built plans and general measurements during field reconnaissance. Further information on
the shape and type of the structures was obtained from photographs taken during field
reconnaissance.
Name of Crossing
New Hall Bridge
Torrey Road
Chambersburgh Road
S Mountain Road
Los Angeles Avenue
Ventura Blvd
Union Pacific RR
Victoria Avenue
Harbor Blvd
Data Source
Field Data
As-Builts from County
As-Builts and HEC-RAS model from
County
Hec-RAS model from County
Hec-RAS model from County
Hec-RAS model from County
HEC-2
Hec-RAS model from County
As-Builts from County
Terrain Data
LIDAR data was provided by Ventura County Watershed Protection District. The data was in
the form of mass points (each point was attributed with latitude, longitude and elevation),
with a horizontal datum of NAD 1983 with projection of “State Plane California V FIPS
0405 Feet” and the vertical datum is “NAVD 88”. Projected mass points were used to create a
Triangulated Irregular Network (TIN) for the areas surrounding the stream. 2-foot, 5-foot and
10-foot contours were generated from the TIN.
Imagery
Color imagery was purchased from Geo-Community for Ventura County, CA. The Imagery
was collected in 2005, as mentioned in the metadata.
Streamline and Flow Paths
 The streamline for the main stream was delineated using aerial imagery and 2-foot
contour data.
 Bank stations were first created with 20-feet offset on each side of the stream. These
stations were later adjusted in the hydraulic model based on 10-percent water surface
elevation and aerial imagery.
Santa Clara Hydraulic Analysis Report
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
Flowpath lines were created with a 50 feet offset on both sides of the stream in GeoRAS.
Cross Section Generation
A total of 21 TINs were used in a Digital Terrain Model (DTM) to cut 154 cross-sections in
Ventura County and 5 cross-sections in Los Angeles County.
Other GIS Layers
In addition to the River, Bank lines, Flowpaths, and Xscutlines layers, the following layers
have been generated in Geo-RAS for the hydraulic model:
Bridge
Lateral Structures
Levee
Ineffective Flow Areas
Landuse
Manning’s Roughness Coefficient (n) Calculations
Manning’s coefficient values were determined for each cross section using the Cowan (1956)
procedure outlined in “Guide for Selecting Manning’s Roughness Coefficients for Natural
Channels and Floodplains”(Authors: G.J. Arcement and V.R. Schneider, USGS Water supply
Paper 2339). Photographs taken during field reconnaissance were used in conjunction with
the aerial images to estimate Manning’s coefficients for the channel portion of the cross
section. For overbank areas, land-use classification data was developed from the aerial
imagery. Polygons were digitized for different landuses, which were attributed with the
corresponding Manning’s n values. Manning’s n ranged from 0.02 to 0.08 for the channel
and 0.016 to 0.11 for the overbanks. (See attached computation table)
HEC-RAS Project
 PLANS: The name of the project is Santa_Clara.prj
o
o
o
o
With Levee Plan (p01, g01, f01)
WO_Lev_and_Lateral_Str_Along_Gonzales_rd (p02, g02, f02)
Without Levee and Floodway Plan (p03, g02, f03)
SCR Overflow South of Gonzales Road (p04, g03, f04)
Discharge Point Locations
Hydraulic modeling was performed using 22 discharge change locations starting from the
mouth to the upstream point at Ventura/Los Angeles county boundary. Discharges at
Montalvo and County line were obtained from Ventura County, and the additional discharges
were calculated using the discharge transfer technique. A discharge flow change location
shapefile is provided for this stream. See the hydrology report for the discharge change table.
The table below provides the reduced discharges resulting from optimization of lateral
structures in Plan 02. These discharges were used in Plan 03.
22
23
RS
19944
18391
100Yr
224154
216950
10Yr
74152
74152
Santa Clara Hydraulic Analysis Report
50Yr
174679
174198
500Yr
331652
298889
fw_red
224154
216950
02/15/2008
2
24
25
26
27
16954
15610
13347
11659
213500
74152
199954
74152
197985
74152
195535
75062
195518
75062
28
11169
(231576) (75062)
29
10126
194922
75062
30
8849
194456
75062
31
2033
194456
75062
Discharges in parenthesis are actual discharges
173971
170321
169638
169846
169846
(176873)
169720
169660
169660
276005
230145
225852
220861
220625
(380364)
219055
217805
217805
213500
199954
197985
195535
195518
194922
194456
194456
Plan 1: With-Levee Plan
A natural run was performed using a hydraulic model with 10 structures and 22 discharge
change locations.
 Bank stations were modified in the hydraulic model by moving them to the 10-year
water surface elevation.
 Cross-sections were oriented perpendicular to the contours. In HEC-RAS, the
maximum limit for the number of points in a cross-section is 500. Hence the crosssections were filtered using the cross-section point filter option in HEC-RAS.
 Levees were digitized using topographic data, information from the County and
effective flood insurance maps.
 Lateral structures were placed on top of the levees to account for the overtopping
discharge and providing more accurate water surface elevations for the with-levee
scenario.
 Critical depth is used as the downstream starting condition because the Mean higherhigh water elevation at the mouth of Santa Clara River was 4.54 ft (NOAA Tide
station in Santa Barbara, CA, Station ID: 9411340), which was less than the 10percent annual chance critical water surface elevation at the most downstream crosssection.
 A multiple profile run was performed using 10%, 2%, 1% and 0.2% annual chance
discharges.
 Sub-critical flow regime was used for this plan.
Plan 2: Without Levee and Lateral Structure Along Gonzales Road




The geometry used for with-levee plan was used; however the levee option and lateral
structures from Plan 01 were removed.
Levees along the downstream portion of the river were replaced with ineffective flow
areas.
A multiple profile run was performed using 10%, 2%, 1% and 0.2% annual chance
discharges.
It was observed that the 1% annual chance flood was flowing into a different
watershed, along Gonzales Road, starting from approximately 3.3 miles from the
mouth.
Santa Clara Hydraulic Analysis Report
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


Lateral structures were placed along Gonzales road, starting from approximately 6300
ft east of the intersection of Patterson Drain and Gonzales Road. They extended
towards the mouth, to a point where, when optimized, no more overtopping occurs.
The 0.2% annual chance flood did not converge, but when checked, the flow
upstream of the lateral structure was equal to the sum of the flow exiting the lateral
structure and the downstream flow.
Flow in Santa Clara River will be reduced at all the cross-sections which cross the
lateral structures.
Plan 3: Without-Levee and Floodway Plan





The same geometry as Plan 02 was used here; however, the lateral structures were not
optimized. Instead, reduced discharges resulting from Plan 02 were used (see table in
the ‘Discharge Point Location’ section)
The 1% annual chance profile from the without-levee scenario was used to perform
the floodway analysis.
As a first attempt, the floodway run was performed with reduced discharges for the
1% annual chance profile and full discharge for the floodway profile. However, this
resulted in surcharges more than the allowable value of 1.00 ft.
Therefore, the final floodway run used reduced discharges for both the 100-year and
floodway profile.
Sub-critical flow regime was used for this plan.
Plan 4: SCR Overflow South of Gonzales Road




A separate geometry file was created for the area south of Gonzales Road.
The discharges for the overflow were obtained by subtracting the reduced discharges
from the actual discharges in Santa Clara River (see table below).
An approximate flood zone designation was selected for the area south of Gonzales
Road to represent the extent of flood hazard due to the overflow from Santa Clara
River.
A detailed hydraulic analysis was not performed because, not all the interactions
within the watershed are known.
RS
16139
14645
13676
12231
8989
100-yr
5183
12387
31352
36041
36058
Results / Mapping

The water surface elevations obtained from the “with levee” scenario will be used to
plot BFEs for the main stream.
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
The water surface elevations from the without-levee plan will be used to plot BFEs
for the overbanks.

The overflow area south of Gonzales Road will be designated as an approximate
Zone A.
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