Channel Capacity

Levee evaluations inform then-existing channel capacity values, as described in the Settlement, to safely convey flows in the Restoration Area. The San Joaquin Levee Evaluation Project is being implemented by DWR to conduct geotechnical evaluations of the flood control system integrity associated with levee seepage and stability on high-priority levees in the Restoration Area (Priority 1 and Priority 2 Levee Geotechnical Evaluations). To limit the risk of levee failure due to the release of Restoration Flows, channel capacities are limited to flow levels that would meet the U.S. Army Corps of Engineers (USACE) factors of safety for levee slope stability and underseepage. If data on the levees is not available to evaluate seepage and stability conditions, flows are limited to those that would remain “in-channel” until adequate data are available. From the initial geotechnical analysis findings, high flood hazards were identified for most levees in the Restoration Area. DWR has prioritized its geotechnical exploration based on current channel capacity limitations and anticipated Restoration Flow routing.

Priority 1 levee evaluations in Reach 2A, the lower portion of Reach 4A, and the middle Eastside Bypass are complete. The results showed that only one levee segment in these reaches — 2 miles of the right back of the Eastside Bypass below Sand Slough — cannot convey at least 2,500 cfs without exceeding USACE criteria. The 2-mile segment of levee was identified for improvements and DWR completed a Basis of Design report for this levee segment in 2017; 95% designs were completed in 2018 and completed in November 2020.

Geotechnical evaluations also continued on the Priority 2 levees, which include the Mariposa Bypass and Reach 4B2. Data was collected on these levee segments in 2016. Geotechnical evaluations on the levees were completed in 2018 and a Geotechnical Conditions Report will be released in 2019. The report will include remediation alternatives and cost estimates that will help the SJRRP determine the costs of improving these levees under the Reach 4B, Eastside Bypass, and Mariposa Bypass Channel and Structural Improvements Project.

Reclamation surveys a network of over 70 control points across the San Joaquin Valley in July and December of each year to monitor ongoing subsidence. Following are the bi-annual survey result tables, maps, and ArcGIS shapefiles. Section 8 of the original control network report, below, includes a description of the control points, locations, and photos. All elevations are in GEOID 03, NAVD 88, and the horizontal datum is NAD 1983, California Coordinate System of 1983, Zone 4, US survey feet. Free or minimally constrained adjustment elevations should be used as they better represent control point movement by removing adjustment distortion.

The California Department of Water Resources has also performed subsidence monitoring along the Lower San Joaquin Flood Control Project levees. This work was combined with Reclamation’s survey network into a subsidence monitoring methodology and status technical memorandum in 2014.

USGS San Joaquin Valley Subsidence Website – The United States Geologic Survey has done monitoring with InSAR and several extensometers.