ABSTRACT: The project proposes to reduce the flood risk to the city of West Sacramento which is located between the Sacramento River and Yolo Bypass at the confluence of the Sacramento and American Rivers. The non-federal sponsors are the California Natural Resources Agency Central Valley Flood Protection Board (CVFPB) and the West Sacramento Area Flood Control Agency (WSAFCA).
The study area includes the Sacramento River watershed, which covers approximately 27,000 square miles in central and northern California. The city of West Sacramento is essentially surrounded by the river or floodways: the Sacramento River to the east, Sacramento Weir and Bypass to the north and the Sacramento River Deep Water Ship Channel and Yolo Bypass to the west. To the south is the existing, non-Federal South Cross levee. Approximately 50 miles of levee surround and provide various degree of flood risk reduction for West Sacramento. The existing levee system was designed and built many years ago, before modern construction methods were employed. These levees were constructed close to the river to increase velocities in order to flush out historic hydraulic mining debris. This debris is essentially gone now and the high velocities associated with flood flows are eroding the levees that comprise the flood risk management for the study area.
The consequences of flooding in the study area would be catastrophic. Cold flood waters would rapidly inundate a highly urbanized area with minimal warning or evacuation time. The study area is also at the crossroads of two major highway systems, which would be impassable should a major flood occur. The effects of flooding within the study area would be felt not only at the local level, but at the regional, state and national levels as well.
The planning objectives are to reduce risk to life and property in the study area, reduce impacts to critical infrastructure, encourage wise use of the floodplain and educate the public about the residual risk of flooding. The strategy to reduce flood risk in the study area focused on reducing the greatest risk drivers first. Because the performance of the existing levees in the study area is so poor, improving the levees in the study area will achieve the most risk reduction. These highest risk factors involved the risk of a geotechnical levee failure from levee through and underseepage or stability problems. The next highest risk was from erosion of the levees during high flow events. Following this, the next risk is from high flow events exceeding the flood carrying capacity of the levee system.
The recommendation of the District Engineer of the Sacramento District, U.S. Army Corps of Engineers, is that the NED Plan (Alternative 5) is the Recommended Plan and that it be authorized for implementation as a federal project. The Recommended Plan consists of construction of levee work to address seepage, slope stability, and erosion concerns identified for the various reaches. It includes levee improvement for flood risk reduction to the existing Sacramento River Deep Water Ship Channel levees. The Recommended Plan includes construction of a setback levee at Southport, along the Sacramento River. This setback levee, the Southport Setback Levee, is being pursued by the State and WSAFCA as proposed sponsor construction under Section 408. The project was issued Biological Opinions from the resource agencies for potential impacts to the federally listed salmonids, steelhead, green sturgeon, Delta smelt, valley elderberry longhorn beetle, and giant garter snake.
The total estimated first cost of the Recommended Plan is $1,420,759,000 (October 2015 price levels). The Federal share of the first cost is $ 923,493,000. The non-federal share of the first cost is $497,266,000 and estimated average annual operations, maintenance, repair, rehabilitation and replacement (OMRR&R) costs of $106,000. Based on the current 3.125 percent discount rate and a 50-year period of analysis, the total equivalent average annual costs of the project are estimated to be $77,277,000. The equivalent average annual benefits are estimated to be $210,570,000 with net average annual benefits of $133,393,000. The benefit-cost ratio is approximately 2.7 to 1.
The Southport Setback Levee is eligible for consideration of credit per approval by the ASA (CW). As such, this proposed Section 408 work was not considered to be in place as part of the future without-project condition, enabling analysis of this portion of the study area for flood risk reduction and determination of Federal interest. For the same reason, a second Section 408 feature is similarly included in the Recommended Plan; this one was built by the sponsor and was also determined to be eligible for credit by the ASA (CW).
REPORT DOCUMENTATION: Pertinent documentation on the project, the results of the Civil Works Review Board (CWRB), and subsequent Washington-level review actions, are listed below (items not linked will be provided when available):
- CWRB Agenda
- Project Map/Placemat
- Project Summary
- CWRB Briefing Slides
- CWRB Lessons Learned
- CWRB Meeting Record
- State & Agency Review Comment Letters
- Documentation of Review Findings
- Signed Chief of Engineers Report
- Advance Copy to Congressional Committees
- ASA(CW) Memo to OMB
- OMB Response
- ASA(CW) Transmittal to Congress
- Signed Record of Decision (ROD)