Nov 26, 2018

Unimpaired flows: water solution or threat?

(Originally published in the Winter 2018 issue of California Waterfowl.)


Once again, it seems that every water issue revolves around fish, not waterfowl. The State Water Resources Control Board has decided that the answer to declining fish populations is a mandate that will result in losses of water supplies for agriculture and for wetland habitats.

The board wants to restrict storage and use of water from the Sacramento and San Joaquin rivers to a specified percentage of the “unimpaired flow” of the rivers. Unimpaired flows are the flows that would occur on the rivers and their tributaries in the absence of dams and other diversions of water.


The State Water Resources Control Board records and enforces water rights and regulates water quality. It comprises five members who are appointed by the governor and confirmed by the state Senate.

The State Board maintains a Bay Delta Plan that designates how much water must pass through the Sacramento-San Joaquin River Delta to provide a variety of environmental benefits, including flows for salmon, delta smelt and salinity control. The Plan adjusts water rights on the Sacramento and San Joaquin rivers and on the tributaries to those rivers and directly to the Delta.

The latest updates to the Bay Delta Plan have been in process for nearly 10 years. The proposed update on the San Joaquin River and its tributaries will require that between 30 and 50 percent of the water that would be in the river without any diversions or dams be left in the Merced, Tuolumne and Stanislaus rivers from February through June.

The State Board estimates this will increase actual instream flows in the Lower San Joaquin River and its tributaries by 26 percent. According to the State Board, a 40 percent unimpaired flow requirement would reduce the water supply for human uses by 14 percent. Because there is always some amount of instream flow in the rivers, the unimpaired flows requirements would not directly translate into full 30 to 50 percent cuts.

On the Sacramento River and its tributaries—the American, Yuba and Feather rivers—as well as the Cosumnes and Mokelumne rivers that flow directly into the Delta, the proposed requirement would be 55 percent unimpaired flows. The State Board estimates that this will result in approximately 20 percent cuts on average for human uses.


Although the State Board estimates that 14 to 20 percent of the water currently available for human uses will be cut, the distribution and timing of the cuts may result in some water users losing more than others. For instance, in the Sacramento Valley, a 20 percent reduction in water supply could result in fallowing of 100,000 acres of rice. If the distribution of water is weighted to favor tree crops, which cannot be fallowed, up to half the rice acreage in the valley may have to be fallowed. This could be catastrophic for both wintering waterfowl and California’s local breeding population (see article on page 30). Municipal and domestic uses will be favored over agriculture, and permanent crops will be favored over annual crops.

The water derived from the unimpaired flow requirements will flow through the Delta and past the Golden Gate out to the Pacific Ocean. Some amount may be exported to the Central Valley and Southern California by way of the Central Valley Project and the State Water Project, but the current export amounts will be cut as well. Unimpaired flow requirements will reduce the benefits associated with the “Twin Tunnels” project.

Unimpaired flow restrictions will affect reservoir operations. They may make it difficult, if not impossible, to fill proposed off-stream reservoirs such as Sites Reservoir or Los Vaqueros. Reservoirs usually fill during the spring runoff, but they will be required to release enough water to meet the unimpaired flow requirements.


The State Board’s main purpose in requiring unimpaired flows into the Delta is to provide flows for salmon and other threatened and endangered fish species. The theory is that flows are necessary to moderate water temperatures and restore fish habitat.

There is no question that native fish species in the Delta have been declining in population. Scientific research has identified flows as being an essential need for salmon and other fish species.

Other research, however, indicates that the timing of flows is critical, and the amount of nutrients contained in the water is also a determining factor in restoring habitat. (See Floodplain Fatties in Summer 2018 edition of California Waterfowl.) Flows of water alone are not sufficient to restore habitat. By building levees in the Delta and along the rivers, people have removed access for fish to the floodplains on which they once depended. Just adding flows to these sterile environments will not improve habitat.

Functional flows, timed to meet the greatest needs of the fish, such as flows of cold water onto spawning grounds, or flows through bypasses and winter rice fields, will provide greater benefits to fish species, while reducing cuts in water supplies.


Unimpaired flow requirements will reduce the amount of water available for wetlands. Two-thirds of wetland habitat are privately owned, primarily duck clubs, with the remaining third owned by the state as wildlife areas and the federal government as wildlife refuges.

Water for duck clubs is usually obtained through water rights. These water rights will be reduced by the unimpaired flow requirements, either 14 or 20 percent, according to the State Board’s estimates.

Water for wildlife areas and refuges is provided by the Central Valley Project under the Central Valley Project Improvement Act or CVPIA. Under the CVPIA, refuges and wildlife areas have the same priority as senior water rights holders for a portion of their supply, but the remainder depends on purchases from willing sellers and is already unreliable. Under the unimpaired flows plan, the remainder will probably no longer be available at all. Increased demand for water transfers to make up the loss of water to unimpaired flow requirements will price CVPIA water out of the market.


The state Department of Fish and Wildlife is working on an alternative: negotiating with water districts, water exporters, state and federal water management agencies, and environmentalist organizations to develop voluntary agreements, under which the parties will provide functional flows that are timed and calculated to meet the needs of fish at specific times of the year. These functional flows will provide suitable water supplies for the fish when needed, without sending water out to sea unnecessarily. If negotiations succeed, these voluntary agreements would be submitted to the State Board as a substitute to the unimpaired flow requirements.


The State Board has set Dec. 11 as the date when it will decide whether to adopt the unimpaired flow requirements for the San Joaquin River and its tributaries. The unimpaired flow requirements for the Sacramento River have not been scheduled yet, but are likely to be scheduled before Governor Jerry Brown leaves office in January. California Waterfowl has submitted comments on the San Joaquin River unimpaired flow requirements with the help of staff from the Grassland Water District.

Whether or not the State Board adopts the unimpaired flow requirements or accepts the voluntary agreements, many parties will sue to overturn whatever decision the board makes. Environmentalist organizations such as the Defenders of Wildlife and the Natural Resources Defense Council have indicated they will sue because they believe the unimpaired flow requirements are insufficient.

Water users will sue if the State Board adopts the unimpaired flow requirements on multiple grounds related to their loss of water rights.

CWA will post updates on this situation to our Current Issues website here. If you would like more information about California Waterfowl’s efforts in the Klamath Basin, contact Jeffrey Volberg at or 916-217-5117.