ABSTRACT: The purpose of the American River Common Features (ARCF) project is to reduce the overall flood risk within the Sacramento metropolitan area, which is one of the most at risk areas for flooding in the United States due to its location at the confluence and within the floodplain of two major rivers. The non-federal sponsors are the California Natural Resources Agency Central Valley Flood Protection Board (CVFPB) and the Sacramento Area Flood Control Agency (SAFCA).
Both the American and Sacramento Rivers have large watersheds with very high potential runoff which has overwhelmed the existing flood management system in the past. 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. As the capital of California, the Sacramento metropolitan area is the center of State government and many essential statewide services are located here. The study area is also at the crossroads of four 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 Locally Preferred Plan (LPP) (Alternative 2) is the Recommended Plan and that it be authorized for implementation as a federal project. The Recommended Plan is similar to the NED plan in that it consists of construction of levee work to address seepage, slope stability, and erosion concerns identified for the various reaches. In lieu of the levee raises included in the NED, the Recommended Plan includes widening of the Sacramento Weir and Bypass by 1,500 feet to reduce the water surface elevation in the Sacramento River and allow more water to flow into the Bypass system. 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, vernal pool fairy shrimp, vernal pool tadpole shrimp, giant garter snake, and yellow-billed cuckoo. Appropriate mitigation for habitat impacts for these species are included in the Recommended Plan.
The Recommended Plan has a first cost of $1,596,650,000 (October 2015 Price Levels); an annual cost of $76,259,000 including operations, maintenance, repair, rehabilitation and replacement costs (OMRR&R); annual benefits of $344,696,000; net benefits of $268,437,000; and a benefit-to-cost ratio (BCR) of 4.5 at a discount rate of 3.125 percent, for a 50-year period of analysis and a ten-year construction period. The Federal portion of the estimated first cost is $895,123,000 and is based on the cost sharing percentages established by the NED Plan. The non-federal portion of the project is $701,526,000, which includes the non-federal share of the NED Plan costs, plus 100 percent of the additional costs for the LPP. The sponsors are also responsible for 100 percent of the OMRR&R costs, estimated to be about $500,000 annually.
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)