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New horizons in water management: Sites Reservoir and Delta Conveyance set to strengthen California's water supply

Two major water infrastructure projects that will provide statewide benefits have recently passed important milestones in their decades-long planning and permitting saga.

Two major water infrastructure projects that will provide statewide benefits have recently passed important milestones in their decades-long planning and permitting saga. While there is little debate about the benefits the projects would bring, they both would have unavoidable environmental impacts and some level of opposition.

Sites Reservoir

Sites Reservoir is a proposed new reservoir that would be built in Glenn and Colusa Counties near Colusa, a city of about 6,000. Sites Reservoir is an off-stream reservoir, not formed by damming a river or stream. Instead, water is brought to the reservoir. This avoids impacts on migrating fish like salmon. The Sites Reservoir will cost about $5.2 Billion, have a surface area of almost 22 square miles, and be about 13 miles long. It will be able to hold 1.8 Million Acre Feet of water, making it more than twice as big as Diamond Valley Lake and 15 times bigger than Lake Perris.

Sites Reservoir is intended to capture excess stormwater and snowmelt from the upper Sacramento River system in wet years and store it for use in dry years. Water in Sites Reservoir will be available for agricultural, urban, and environmental uses. The project will be built and operated by the Sites Project Authority.

The project's final state and federal environmental studies were recently certified by the US Bureau of Reclamation and the Sites Project Authority. This clears the way for the issuance of water rights permits from the State Water Resources Control Board and the issuance of construction permits. Construction is anticipated to begin in 2023 and be completed in 2031.

Some are concerned that this project will divert more water from natural stream flows than is safe for fish populations and the habitat surrounding waterways. The Sites Project Authority has pledged not to do this, and it is anticipated that permit conditions will protect these important resources. The project has committed to release water to and through the Sacramento River Delta when needed for fish protection and to allow retention of colder water needed for salmon populations in upper regions of the Sacramento River watershed.

You can learn more about this project at

Delta Conveyance

Delta Conveyance is a proposed tunnel that would allow the movement of water from the upper Sacramento River Delta under the main part of the Delta to the California Aqueduct, which flows through Central California and into Southern California, where it supplements locally produced water for urban agricultural uses. It would be built and operated by the California Department of Water Resources.  

The project is important because the Sacramento River water cannot be pumped into the aqueduct from the primary pumping station in the lower Delta when the Delta Smelt, a federally protected species, is present, and because the Sacramento River channel through the Delta is maintained by a series of levees which are very likely to fail in a major earthquake in the Bay Area. The tunnel would allow water to be pumped under the Delta to the California Aqueduct whenever sufficient water is available. The Delta Smelt does not travel upstream to the point where water would be diverted into the tunnel, so the potential impact on the protected species can be averted. The tunnel intake will be upriver from the area of potential levee failure from earthquake or flooding. This will add a great deal of reliability to the State Water Project and the California Aqueduct.

In his 2019 State of the State Address, Governor Newsom said, “The status quo is not an option. We need to protect our water supply from earthquakes and rising sea levels, preserve Delta fisheries, and meet the needs of cities and farms. We must get this done – for the stability of our Agricultural sector, and the millions who depend on this water every day.” There is broad support for the project but also opposition from two primary perspectives. One is people who fear the project could increase Southern California’s take of water from the Sacramento River and Northern California in general. The other is an environmental concern that too much water will be taken from the Delta, and that will harm fish populations or riparian habitats and increase saltwater intrusion further into the Delta.  

These concerns have been addressed in the recently released Final Environmental Impact Report on the project. After hearings, the Department of Water Resources will consider adopting the Final Environmental Report, which would clear the way for final permitting and construction.

You can learn more about this project at

From my perspective, both of these projects are of vital importance to the resilience of California’s water supply. As our climate changes, we will see more precipitation in wet years and dryer, longer drought periods. Precipitation will tend to be more intense, and we will need to capture excess water for use in dry periods as well as to reduce flooding.