In summary

We propose an approach to water management that treats the environment as a priority rather than a constraint on operations.

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By Sarah Null

Sarah Null is the 2021–22 CalTrout Ecosystem Fellow at the PPIC Water Policy Center.

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Jeffrey Mount, Special to CalMatters

Jeffrey Mount, a geomorphologist, is a senior fellow at the PPIC Water Policy Center.

Two weeks ago, Gov. Gavin Newsom released his water supply strategy, which is designed to address California’s warming climate and increasing drought intensity. Central to this strategy is expanding storage to capture water during wet periods and to help urban and agricultural users make it through dry times.

But why stop there? What about storing water for the environment?

In our recent Public Policy Institute of California report, titled “Storing Water for the Environment: Operating Reservoirs to Improve Freshwater Ecosystems,” we explore how to do a better job of managing rivers that are affected by large dams and how to make restoring river health a primary objective of reservoir management.

Reservoirs are crucial for water management in California’s highly variable climate. The construction and operation of dams, however, has taken a toll on the environment. Dams change water quality and flow timing, and they block access to high-quality headwater habitat. This — along with many land-use changes and the introduction of invasive species — particularly harms salmon and steelhead, two of California’s most iconic and endangered fishes.

By law, dam operators are required to prevent or mitigate harm to river ecosystems and the native species that make use of them. The current approach to environmental management below dams relies on constraining water and hydropower operations, usually by requiring dam operators to meet minimum flow and water quality standards.

This constraint-based approach has neither improved the health of rivers and estuaries nor led to the recovery of native species populations. This approach is also notoriously complex, inflexible and hard to adjust, making it ill-suited to manage rapidly changing conditions. Moreover, these standards are the epicenter of water litigation.

We propose a change in course. Using a simple reservoir model, we demonstrate that ecosystem managers can achieve better environmental outcomes when they are granted a percentage of reservoir inflow along with a portion of storage capacity. Flexibly managed, this combination of inflow and storage leads to the most efficient use of environmental water.

We think our approach — which effectively grants assets to the environment that can be flexibly managed — is the better way to go. It treats the environment as the priority it is rather than a constraint.

Here’s why this is a better approach: Research has demonstrated the importance of varying the timing and amount of streamflows to meet specific ecosystem functions. Everything from fish, insects and amphibians, to birds and plants rely on this variability. All are adapted to the first freshet in the fall, the winter flood pulses, the slow decline in spring flows as snows recede, and the low flows of summer. And all are adapted to the wet and dry cycles that are part of California’s climate.

Storing water set aside for the environment in reservoirs allows ecosystem managers to vary flow releases to create the seasonal and year-to-year variability necessary for healthy rivers below dams. Done well, with good governance and investments in physical habitat, managing stored water also reduces uncertainties for both the environment and other water demands.

Several consequential regulatory and planning efforts in progress in the Central Valley would benefit from adopting this approach. These include:

  • An update of the water quality control plan for the Sacramento–San Joaquin Delta and its watershed;
  • Negotiations over voluntary agreements that seek to meet the objectives of the water quality control plan;
  • Efforts to develop a coordinated operating plan for the Central Valley Project and State Water Project that protects endangered species; and
  • Major investments of state funds in new storage and water for the environment.

All these efforts rely upon storing water in reservoirs to meet environmental requirements. And all will struggle to adapt to rapidly changing conditions as the climate warms and droughts intensify. We think reserving storage space and reservoir inflow for the environment is better than traditional regulatory approaches. And we recognize that this approach is novel — even risky — but we need to take some risks to manage growing threats to the health of our rivers and estuaries.


Jeffrey Mount previously has written about Gov. Gavin Newsom’s water framework, the Endangered Species Act and the Klamath Basin dam removal.

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