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Environmental Stewardship and Statewide Resources Office
Levees and Environmental Engineering
Delta Risk Management Strategy
1416 9th Street, Room 1601
Sacramento, CA 95814
P.O. Box 942836
Sacramento, CA 94236-0001
Delta Risk Management Strategy
June 13, 2011 - The Department of Water Resources has released the Delta Risk Management Strategy Phase 2 Report and Executive SummaryThe Department of Water Resources has released the Delta Risk Management Strategy Phase 2 Report and Executive Summary (PDF: 605 KB). The Delta Risk Management Strategy (DRMS) Phase 2 report builds on the knowledge gained from the DRMS Phase 1 assessment to evaluate scenarios which could reduce the risks to our State economy. The methods include a selection of improvement strategies considered at the time of the study in 2009; however, today, there are more options in play. The information in the report provides insight to methods that may be used by the Department and others to manage risk.
The Department of Water Resources has released the Delta Risk Management Strategy Phase 1 Report and Executive Summary (PDF: 1.9MB). DRMS Phase 1 report findings will be used to help develop a set of strategies to manage levee failure risks in the Delta and to improve the management of state funding that supports levee maintenance and improvement.
Levees have protected 700,000 acres in the Sacramento-San Joaquin Delta since the 1860's. There is a dedicated workforce in place actively maintaining these critical structures. However, the Delta is subsiding and undergoing continuous changes making it necessary that maintenance be kept up. The Delta is located near the highly seismic San Francisco Bay Area. A major earthquake, in the region, could cause extensive damage to the various Delta assets, resulting in far reaching consequences.
- There are approximately 1,115 miles of levees protecting 700,000 acres of lowland in the Sacramento-San Joaquin Delta. In the Suisun Marsh, there are approximately 230 miles of levees protecting over 50,000 acres of marsh land.
- Only about a third of the Delta levees (385 miles) are Project Levees which were part of an authorized federal flood control project of the Sacramento and San Joaquin River systems and eligible for Corps of Engineers rehabilitation. However, the vast majority of Delta levees, over 730 miles, and all of the Suisun Marsh levees are non-project (local) levees.
- Local levees were constructed, enlarged, and maintained over the last 130 years by local reclamation districts. In general, the levee work by these districts was financed by the owners of the lands within the levees. In the last 30 years or so, the State of California has provided supplemental financing for levee maintenance and emergency response.
A major need for the State is to determine how to make the Delta sustainable in the future. The 2000 CALFED Record of Decision presented its Preferred Program Alternative that described actions, studies, and conditional decisions to help fix the Delta. Included in the Preferred Program Alternative for Stage 1 implementation was the completion of a Delta Risk Management Strategy (DRMS) that would look at sustainability of the Delta, and that would assess major risks to the Delta resources from floods, seepage, subsidence, and earthquakes. DRMS would also evaluate the consequences, and develop recommendations to manage the risk. Based on this need a Request for Qualifications was advertised and URS Corporation was the successful applicant to do the DRMS effort. The contractual definition of the DRMS work area is:
- Suisun Marsh east of the Benicia-Martinez Bridge on Interstate 680; and
- Sacramento-San Joaquin Delta as legally defined in Section 12220 of the California Water Code (CWC).
AB 1200 (CWC Section 139.2 et seq) requires that DWR evaluate the potential impacts on water supplies derived from the Delta based on 50-,100-, and 200-year projections for each of the following possible impacts: subsidence, earthquakes, floods, climate change & sea level rise, or a combination of the above. The DRMS work will provide the majority of this required information.
DWR produced a report based on the requirements of AB 1200. This AB 1200 report was submitted to the legislature in January 2008.
Many of the local levees in the Delta started out as 3 to 5-foot-high dikes of peat over a century ago. Modern engineering analyses and techniques were not available during the initial construction of the levees which generally rest on the original marsh soils. Over time, the weight of the levees compressed and displaced the soft, organic soils beneath them. In addition, the organic soils within the island interiors oxidized and were removed by wind over time, resulting in the land surface significantly subsiding. As a result, the levees have to be continually raised and broadened, which commonly initiates further settlement, embankment cracking, and loss of freeboard. This process will continue until the levees and their foundations stabilize, and many reaches have not yet stabilized to date. Delta levees today are now commonly 15 to 20 feet high, and often protect island interiors that are 10 to 15 feet below sea level. Permeable lenses in the levee and foundation, together with historic relics, such as abandoned pipes, and constant burrowing by various mammals also commonly result in seepage distress and internal erosion.
During the last century, there have been 162 Delta levee failures leading to island inundations. In many cases, the flooding of the islands has been extremely costly to both local residents and farmers, and to the State as a whole. Levee failures in the Suisun Marsh have also occurred with significant impacts to local and statewide interests. In February 1998, 11 exterior levee breaches in the Suisun Marsh resulted in the inundation of over 22,000 acres and threatened both the State Water Project and Central Valley Project facilities.
California has an immense interest in maintaining many of the Delta and Suisun Marsh levees, in part because the Delta is a source of drinking water for about two out of every three Californians. In addition, there are important critical environmental, agricultural, and recreational benefits in the region. There are also extensive infrastructure and capitol investments in the Delta, ranging from houses, businesses, and towns to State highways, rail lines, natural gas fields, gas and fuel pipelines, and drinking water pipelines (e.g. Mokelumne Aqueduct) and two deepwater ports.