David Ford Consulting Engineers, Inc. 2015 J Street, Suite 200 Sacramento, CA 95811 Ph. 916.447.8779 Fx. 916.447.8780 MEMORANDUM To: Brad Moore, PE, USACE From: Nathan Pingel, PE (Lic # CA 63242), and Mike Imgarten Date: September 30, 2011 Subject: Interim work product for the Central Valley Hydrology Study (CVHS): Identify HEC-RAS and HEC-ResSim model nodes corresponding to floods-of-record analysis points (part of Contract W91238-09-D-0004 TO 11, task 1: Develop a table of analysis point locations and corresponding model nodes) Situation The Central Valley Hydrology Study (CVHS) is an undertaking by the Sacramento District of the US Army Corps of Engineers (Corps) to develop estimates of the annual exceedence probability of flows and volumes for streams in the Sacramento and San Joaquin river basins. The CVHS is in support of an effort by the California Department of Water Resources (DWR) to update hydrologic data and complete floodplain mapping behind the Federal-state levees in the Central Valley. The September 2008 document Sacramento and San Joaquin river basins: Procedure for hydrologic analysis describes the analysis approaches and key tasks for completing the CVHS. Two different approaches are used, 1 for gaged watersheds the floods-of-record approach, and the other for ungaged watersheds. For the purposes of the CVHS, a gaged watershed is one in which: The streamgage record length is sufficient (preferably, at least 25 years of data). The data available from gage(s) are of adequate quality. 1 or more gages are located above the analysis point. Watersheds that do not meet the floods-of-record criteria require an alternative procedure for developing flow-frequency curves. Here, we focus only on gaged watersheds. Locations within watersheds where flow-frequency curves will be developed are referred to as analysis points. There are approximately 150 CVHS analysis points in gaged watersheds. Analysis points are placed at these locations: Start of a leveed reach. End of a leveed reach. Confluence of a major tributary to a study reach. 1
Where the change in local flow is greater than 10 percent of the total flow. (For this, contributing area was used to estimate the local flow criterion.) CVHS floods-of-record analysis points are defined throughout the Sacramento and San Joaquin river basins at locations were a flow change occurs. Therefore, cross sections and model nodes corresponding to the analysis points are defined just downstream of a flow change location in the CVHS HEC-RAS and HEC-ResSim models. To develop flow-frequency curves at the floods-of-record analysis points, both the at location and the total contributing flow are required. (Total contributing flow is also referred to in some CVHS documents as at latitude flow.) The total contributing flow is defined as the total contribution of runoff from the upstream watershed that would reasonably flow past a specified location. This total contributing flow serves as the basis of the volumefrequency analysis. Since the CVHS HEC-RAS and HEC-ResSim system models contain flow splits/diversions, the total contributing flow at an analysis point is the summation of the flow in the main reach and the diversion. Task We assigned HEC-RAS cross sections and HEC-ResSim model nodes to floodsof-record analysis point locations so that at location and total contributing flows can be determined. Actions To assign HEC-RAS cross sections and HEC-ResSim model nodes corresponding to the floods-of-record analysis points, we: 1. Identified all floods-of-record analysis points. 2. Imported a shapefile of the floods-of-record analysis points into the HEC- RAS and HEC-ResSim models. 3. Identified locations in the models appropriate for determining the at location flow at each analysis point by inspection. 4. Identified locations in the models appropriate for determining the total contributing flow at analysis point by inspection. Although not required for this task, we also created HEC-HMS system models of the Sacramento River and San Joaquin River basins to route flows throughout the respective basins where floods-of-record analysis points are located. Results We summarized our results in the Microsoft Excel spreadsheet AnalysisPointLocations.xlsx. It contains the following information: Analysis point name. River/stream on which the analysis point is located. A brief description that specifies the flow each analysis point represents. HEC-RAS cross sections and HEC-ResSim and HEC-HMS model nodes corresponding to each analysis point for both at location and total contributing conditions. (HEC-ResSim node names in the spreadsheet 2
correspond to the model submitted as part of the HEC-ResSim Data Quality Control (DQC) package dated April 27, 2011.) HEC-RAS, HEC-ResSim, and HEC-HMS output HEC-DSS pathnames for each analysis point for both at location and total contributing conditions. General notes describing any complexities near the analysis point. The spreadsheet AnalysisPointLocations.xlsx is located in the CVHS data repository at: http://tsunami:8080/svn/cvhs/transformdevelopement/task1 As noted in the last column of the spreadsheet, several analysis points are in hydraulically complex locations, such as near a weir. In those instances, we selected an alternative nearby HEC-RAS cross section to define the at location and/or total contributing flows. Table 1 summarizes our reasoning for selecting these alternative cross section(s) to represent the flow at these analysis points. For the analysis points presented in Table 2, the assignment of model nodes to the analysis points is not straightforward, or the analysis point is on a stream not included in 1 or more of the models. We propose to discuss our recommended assignment of model nodes to these analysis points at an upcoming CVHS team coordination meeting. 3
4 Table 1. Complexities in identifying HEC-RAS cross sections to represent flow at analysis points Complexity (1) Analysis point located in hydraulically complex area Analysis points located at a flood bypass (Fremont Weir) Total contributing flow not represented by parallel cross sections Analysis points affected by complexity (2) SAC-158, SAC-146, SAC- 119, SAC-63, SJR-216, EBY-15, EBY-6 SAC-83 SAC-90 Method for selecting cross section (3) When a cross section most near an analysis point was located where lateral weirs are configured to spill in the HEC-RAS model, we chose cross sections just downstream of the weirs to represent the at location flow for the analysis point. Since lateral weirs typically span several cross sections, the at location flows could differ at each cross section along the weir. Choosing a cross section just downstream of the weir to represent the flow at the analysis point provides a more consistent method of identifying the at location flow in the model. The analysis point SAC-83 is located on the Sacramento River at the Fremont Weir. SAC-83 represents the flow in the Sacramento River, plus the flow in the Sutter Bypass. Therefore, we chose a cross section in the Sacramento River upstream of the Fremont Weir and a cross section upstream of where the Feather River and Sutter Bypass parallel each other, as shown in Figure 1, to represent the flow at SAC-83. We chose the cross section in the Sutter Bypass well upstream of SAC-83 because the cross sections downstream of this location in the Sutter Bypass exchange flow with the Feather River during high flows via lateral weirs configured in the HEC-RAS model. Both the at location and total contributing flows are the same at SAC-83. [The next downstream analysis point, SAC-80, includes the contributing flow from the Feather River.] The total contributing flow at SAC-90 represents the flow in the Sacramento River at Knights Landing, plus the flow in the Sutter Bypass. Following the same methodology as with SAC-83 for defining cross sections to represent the total contributing flow, we chose a cross section in the Sacramento River near analysis point SAC-90 and a cross section in the Sutter Bypass well upstream of the analysis point. These cross sections are shown in Figure 1.
Table 2. Analysis point assignments we will discuss at an upcoming CVHS team coordination meeting. Analysis points (1) SSC-36 SAC-63 SAC-34, SAC-32, SAC-26, SAC-14, SAC-12, SSL-28, SSL-24, SSL-22, LSL-0, GSL-0 SJR-72, SJR-60, SJR-56, SJR-53, SJR-43, SJR-41, SJR-37, SJR-36, OLD-38, OLD-36 DJC-4 DRW-9 SJR-115 BCK-0, BCK-2, BCK-8, BCK-10, BCK-12, BCK-15 Comments (2) SSC-36 is located on the Sacramento River Deep Water Ship Channel (SRDWSC). The SRDWSC is tidally influenced and does not convey flow like other rivers and streams throughout the Sacramento River basin. SAC-63 is located on the Sacramento River just downstream of the Sacramento Weir. During periods of high flow, the flow reverses direction from the Sacramento River/American River confluence to the Sacramento Weir, and flows through the Sacramento Weir into the Sacramento Bypass. A cross section just downstream of the Sacramento Weir was selected to represent the at location flow. However, the appropriateness of an unregulated flow-frequency curve at this location should be considered. The analysis points in column 1 are located on the Sacramento River and the sloughs in the Sacramento-San Joaquin River Delta as shown in Figure 2. Since there are no additional flows entering the system models downstream of analysis point SAC-42, the unregulated flow-frequency curve developed at SAC-42 could be used to represent the flow at all analysis points downstream. The analysis points in column 1 are located on the San Joaquin River and Old River near the Sacramento-San Joaquin River Delta as shown in Figure 3. Figure 3 shows that SJR-41 is the most downstream analysis point in the San Joaquin River located within the HEC-RAS model extents (SJR-37 and SJR-36 are located downstream of the HEC-RAS model extents). The only flow entering the system between analysis points SJR-75 and SJR-41 is the flow from the Duck Creek watershed, which will be hydrologically routed to the San Joaquin River and input into the HEC-RAS model just upstream of SRJ-43. Therefore, the unregulated flow-frequency curve developed at SJR-75 could be used to represent the flow at all analysis points downstream of SJR-75, except for SJR-43 and SJR-41 where the flow from Duck Creek would be added to the flow at SJR-75. DJC-4 is located on Dutch John Cut, a diversion from Cole Slough to the Kings River. Neither Cole Slough nor Dutch John Cut are modeled in HEC-ResSim. The CVHS HEC-RAS model does not include the Kings River area. DRW-9 is located on Dry Creek in the Kings River watershed. There are no HEC-RAS or HEC-ResSim model reaches for this area and diverted flow to this analysis point is unknown. SJR-115 is located 1.5 mi to the east of the San Joaquin River just downstream of the San Joaquin River/Merced River confluence. SJR-115 is located at the upstream end of a National Hydrography Dataset (NHD) flowline and has a contributing area of 0.2 mi. This small stream is not modeled in HEC-RAS or HEC-ResSim. The analysis points in column 1 are located on Bear Creek below Comanche Reservoir. Flow-frequency curves were developed for these analysis points as part of the Lower San Joaquin Feasibility Study and may be adopted for CVHS. Thus, this assignment may not be necessary. And, at the present, none of the noted models include this reach. 5
SAC-90 SAC-83 Flow direction SAC-80 Figure 1. HEC-RAS cross sections (highlighted in blue) used to represent the total contributing flow at analysis points SAC-90, SAC-83, and SAC-80: SAC-90 and SAC- 83 represent the combined flow in the Sacramento River and the Sutter Bypass, while the total contributing flow at SAC-80 also includes flow from the Feather River. 6
Flow direction Figure 2. Analysis points downstream of SAC-42: These analysis points will have approximately the same unregulated flow-frequency curve as SAC-42. 7
Flow direction Figure 3. Analysis points downstream of SJR-75 (SJR-37 and SJR-36 are located downstream of the HEC-RAS model extents): These analysis points will have approximately the same unregulated flow-frequency curve as SJR-75, except for SJR-43 and SJR-41 where the additional flow from Duck Creek would be added. 8