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  California Water Science Center

2012 Georgiana Slough Non-Physical Barrier Study

Picture of bubbles reaching the surface along the BAFF alignment.

Picture of bubbles reaching the surface along the BAFF alignment.

The Sacramento-San Joaquin Delta (delta) is the hub of the California's water delivery system. Surface water supplies are in the north, demand in the south. Thus, water supply reliability in California critically depends on the amount of water that can be transferred from the north to the southern part of the state through the delta. Two thirds of Californians get their drinking water from the delta, roughly 27 million people, and half a million acres of farm land are irrigated annually using delta water. All told, the delta provides 60% of the water used in the state.

The delta is also an ecosystem. For the past four decades, environmental regulations designed to protect endangered species and downstream estuarine habitats have constrained water supplies south of the delta. Biological opinions designed to protect Chinook salmon, steelhead and delta smelt have been the principal drivers of water supply curtailments in recent years, and, thus, concerns over these organisms are also the principal drivers behind the Bay/Delta Conservation Plan (BDCP). If the BDCP is implemented as envisioned, it will provide the blueprint for spending upwards of 10-20 billion dollars on new water delivery infrastructure (Isolated Facility, Peripheral Canal, etc.) and roughly 6-10 billion dollars in habitat restoration over the next 20 years (tidal marsh restoration, levee setbacks, etc.).

For salmon, the subject of this proposal, the central conservation objective is to improve outmigrant survival through the delta. Recent acoustic telemetry studies have shown that overall salmon outmigrant survival through the delta is extremely poor – survival through the delta can be less than 20% depending on the river inflows and region of the delta (Perry, et.al. in press; Perry et.al., 2010; Holbrook, et.al. 2009). These survival rates are particularly alarming when compared to outmigrant survival in other highly disturbed systems, such as the Columbia River, where outmigrant survival is 50 percent (Williams, et.al., 2001). Salmon outmigrants in the Columbia basin traverse 600 km of reservoirs and 7 dams; whereas, the nominal distance travelled by salmon outmigrants that take the Sacramento River migratory pathway (e.g. from the City of Sacramento to Chipps Island) through the north delta is only about 100 km!

Salmon emigrate through the delta from three watersheds: (1) The Sacramento, (2) the San Joaquin and the Mokelumne River systems. The outmigrants from each of these regions are in jeopardy and thus each controls water project operations to varying degrees by location, time of year and water year type. The major exporters of water from the delta – the US Bureau of Reclamation (USBR), California Department of Water Resources (DWR) (East Bay Municipal water district in the case of the Mokelumne) - are required, as a condition of their permits to remove water from the delta, to conduct salmon outmigration studies to quantify the impacts of their operations and to develop management strategies that mitigate those impacts.

The current regulatory impetus for mechanistic fish-flow studies envisioned in this proposal is the National Marine Fisheries Service’s (NMFS) 2009 Biological and Conference Opinion for the Long-Term Operations of the Central Valley Project and State Water Project (BO) for Chinook salmon and other listed anadromous fish (NMFS 2009). Reasonable and Prudent Alternative Action IV.1.3 of the BO requires the California Department of Water Resources (DWR) to consider engineering solutions to reduce the diversion of juvenile salmonids from the Sacramento River into the interior and south Sacramento–San Joaquin Delta (Delta).

Project Chief: Jon R. Burau
Phone: 916-371-2582
Email: jrburau@usgs.gov

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