This Sierra river needs more water for salmon. San Francisco wants to give it gravel | Opinion

By Peter Drekmeier, Policy Director at Tuolumne River Trust

Nature designed the Tuolumne River to be a fast-moving, cold river. Dams and diversions have turned it into a slow-moving, warm stream. Its operators are trying to solve the problem with physical changes to help native fish. That won’t work if the river also doesn’t get some of its water back.

The Modesto and Turlock Irrigation Districts, along with the San Francisco Public Utilities Commission, recently announced a plan to invest $80 million to restore fish habitat in the river. Unfortunately, a critical issue remains: More water to make the habitat work. Without this, the Tuolumne River’s beleaguered salmon population will not recover.

Past attempts to restore Tuolumne fish populations without significantly increasing flow have all failed. Following a 1995 voluntary agreement, the Tuolumne diverters embarked on a plan to restore instream habitat. Their signature project involved filling a mining pit in the river with gravel to disrupt bass (a non-native predator of salmon) habitat. It failed. The districts’ own post-project report highlighted the resilience of bass populations in the Tuolumne River due to persistent low river flows.

There is no getting around that the core problem facing the Tuolumne River is the altered flow pattern, a river left with a fraction of its water. Less water means warm, slower-moving water. And warm water favors warm-water species like bass over native species. This is glaringly apparent during drier years when the river becomes clogged with non-native water hyacinth. Beneath the pariah vegetation, bass lurk in the shallows, awaiting their next meal of baby salmon.

The new habitat restoration program is essentially the proposed Tuolumne River Voluntary Agreement, which the diverters put forward as an alternative to the State Water Board’s Bay Delta Water Quality Control Plan. The state’s plan would require a range of 30%-50% of the River’s natural flow between February and June, starting at 40%. The idea behind the flow range is that if other measures (that don’t involve increasing flow) work, then the river might not need as much water. But if those measures fail, there will be a back-up plan. This approach encourages effective solutions, as opposed to the Tuolumne River Voluntary Agreement, which is more like a set of tasks to be checked off a list.

This proposed agreement is to sidestep a necessary rebalancing of the beneficial uses of the Tuolumne by its primary regulator, the State Water Resources Control Board. In a years-long process that is still under way, the Board is examining alternative agreements such as this one rather than exercise its authority and provide more flow to the river as a necessary use of the water. If the voluntary agreement is implemented and the measures fail, the Tuolumne River ecosystem will continue to degrade.

The main focus of the Tuolumne River Voluntary Agreement is to add spawning gravel to the river. However, research indicates that this isn’t what the river needs most. A study by the U.S. Fish and Wildlife Service found that while poor spawning habitat limits baby fish (fry) production, the river is already producing more fry than its rearing habitat can support. So just adding gravel would likely not lead to more adult fish.

To improve rearing habitat for baby fish we need to restore the river’s floodplains, as proposed by the districts. We also need to activate them with water, as dry floodplains do not serve an ecological function.

Proponents of the Tuolumne River Voluntary Agreement claim it’s based on science, but that “science” has been challenged by a number of natural resource agencies and fish biologists. A peer review commissioned by the National Marine Fisheries Service found major flaws in the fish models the voluntary agreement is based on.

The truth is, the Tuolumne River has been the subject of an unintended experiment for decades. The unasked question? Can native fish survive with only 20% of the river’s natural flow? The unequivocal answer is no. The Tuolumne salmon population is worse off than on any other Central Valley river.

Habitat restoration is important, but it must be coupled with higher flows. Non-flow measures cannot substitute for desirable water temperature, inundated floodplains and sufficient flow to transport juvenile salmon down the river and out to the Bay-Delta quickly so they are less likely to get eaten by bass.

Commitment to the restoration of the Tuolumne River requires a shift from traditional, single-focused solutions to a more integrated, science-based approach. Fortunately, there are very reasonable solutions that can help restore the Tuolumne while protecting our water supply and reducing flood risk in Modesto. For example, we need to capture potential floodwater and use it to recharge our groundwater basin, an initiative that could attract financial support from the SF Public Utilities Commission given its cost-effectiveness compared to developing new water supplies in the Bay Area.

We encourage the Tuolumne River diverters to take the next step toward a more sustainable community, economy and river ecosystem. Tuolumne River Trust stands ready to be part of a comprehensive solution.

Check out this Op-Ed at The Modesto Bee.