By Ted Grantham and Peter Moyle

This drought year, as in those past, California water regulators have given away to cities and farms some river flows critical to fish and wildlife. It’s a dicey tradeoff considering most of our native fishes are in trouble even without the drought.

There are, however, legal backstops to prevent harmful reductions in fish flows, even during a drought as severe as this one. They include the “beneficial use of water” section of the California constitution, state and federal endangered species acts, the public trust doctrine – and one rarely applied state regulation specifically aimed at preventing loss of fish through the operation of dams.

Adopted more than a century ago, Section 5937 of California Fish and Game Code explicitly requires dam owners to release enough flow “at all times” to keep fish “in good condition.”

To this day, however, many dam owners have not met this requirement and the state has not enforced the rule. This is perhaps not surprising given the vast number of dams in the state – more than 3,000 – as well as the high cost of changing dam operations and political resistance to allocating water for environmental purposes.

Citizen lawsuits have successfully applied Section 5937 on the San Joaquin River and a few other dammed waterways. [Listen to Peter Moyle’s story of how Putah Creek got its fish flows back (2 mins)] In other words, the rule has been implemented where conservationists’ influence in decision-making is greatest – not necessarily where fish protection is most needed.

If Section 5937 were more broadly applied to improve fish flows, which dams should get the focus of attention?

With that question in mind, the UC Davis Center for Watershed Sciences developed a systematic and science-based approach for evaluating and targeting dams for potential enforcement.

The newly published method screens dams for evidence of inadequate downstream flows for sustaining healthy fish populations. It provides a scientific basis for dam operators, natural resource managers and policymakers to perform water “triage” — setting management priorities for dams requiring the most urgent attention.

Screening of dams for potential Section 5937 enforcement. High-priority dams are identified by evidence of alteration to natural flow patterns and potential to affect sensitive native fish species. Source: BioScience

The system first screens dams subject to the fish flows law – those on relatively large rivers and streams with enough storage capacity to change the timing and magnitude of river flows.

Next, dams are filtered for evidence of alteration to natural flow patterns that could harm fish. This is because California’s native fish species are highly adapted to the natural seasonal variability of flows in rivers and streams.

For example, migratory salmon have evolved to return from the ocean to their natal rivers in the winter, when flows are high from rainfall. After spawning, their young either quickly move out to sea before the home stream gets too warm or grow throughout the summer if the water stays cool. Dams built for water supply storage and flood control can impede the migration and spawning if they capture too much of the winter flows needed for the salmon’s upstream journey or release too little water in the summer for juvenile salmon to migrate downstream or to survive instream.

To assess flow alteration, we compared flows at monitoring stations below dams with predictions of unimpaired flows – the difference indicating the degree dam operations have changed the rivers’ natural flow patterns. In the absence of downstream flow gauges, we examined the dam’s total storage volume relative to the river’s annual flow. (Studies show that dams large enough to capture most or all of the annual river flow are more likely to alter downstream flows.)

Finally, dams with evidence of altered downstream flows are screened for effects on native fish. The filter flags dams in watersheds known to support imperiled native fish sensitive to unnatural changes in flows, salmon, lampreys and splittail are among the kinds of fish highly tuned to California’s seasonal river flow patterns — fishes that would presumably benefit from water releases from dams during migration and spawning.

Using these multiple filters, we evaluated 753 dams on relatively large streams and rivers and identified 181 of them – 25 percent – as high-priority candidates for Section 5937 enforcement.

These dams span the state and represent a broad diversity in reservoir size; ownership (public, private, state agency); and function (flood control, water storage and diversions). All show evidence of downstream flow alteration and are within the range of imperiled fish populations.

One dam on the high-priority list is the Casitas on Coyote Creek, a tributary to the Ventura River. The endangered southern California steelhead trout historically spawned in the creek and still occur in the Ventura River. Currently, the Casitas Municipal Water District exports virtually all water stored behind the dam, leaving completely dry the three-mile reach of Coyote Creek between the dam and the Ventura River.

The 400-foot-high Pine Flat Dam on the Kings River in Fresno County also made it on the list because its operation has greatly changed the river’s natural flow regime, potentially to the detriment of the Kern brook lamprey, a threatened native fish species that lives below the dam.

Several Sacramento River dams, including Shasta, Keswick and Anderson Cottonwood, also are high-priority candidates because of the potential to alter river flows critical to sturgeon, lamprey and Central Valley Chinook salmon.

Identifying dams as “high priority” does not necessarily mean they are, in fact, out of compliance with Section 5937; that determination requires a closer, on-site investigation of dam operations and their effects on fish.

For example, our system flagged Dwinnell Dam on the Shasta River because of its large storage capacity relative to river inflows and its potential to harm coho salmon and other sensitive fish species. Indeed, since its construction in the 1930s, operators have diverted most of the Shasta’s flow for irrigation. The dam’s owner (Montague Water Conservation District), however, recently agreed, as the result of a lawsuit, to release significantly greater flows and to take other measures to protect fish down stream.

Our screening framework relies on relatively coarse indicators of how dams may be affecting the environment. This is because the vast majority of dams have no downstream monitoring of flows or fish population health.

Nonetheless, there is ample evidence that many large California dams likely fall short of providing adequate flows to keep fish in “good condition.” A recent study estimated that more than 80 percent of California’s native fish are at risk of extinction if present trends continue. The fate of these species depends on how we manage dams.

Strategic implementation of Section 5937 could provide reasonable protections of California’s dammed river and streams. A systematic and transparent system for monitoring, evaluating and mitigating the environmental effects of dam could help inform decisions by dam operators, fish and water managers and regulators alike. Our study is a first attempt at providing such a framework.

Ted Grantham is a research scientist with the U.S. Geological Survey and Peter Moyle is a professor of fish biology at UC Davis. Grantham conducted the dams study as a postdoctoral researcher with the university’s Center for Watershed Sciences.

Further reading

Börk KS, Krovoza JF, Katz JV, Moyle PB. 2012. The rebirth of Cal. Fish & Game Code 5937: water for fish. UC Davis Law Review 45: 809-913

Grantham TE, Viers JH, Moyle PB. 2014. Systematic screening of dams for environmental flow assessment and implementation. BioScience [EarlyView] Appendix 1: Hydrologic model description and performance evaluation; Appendix 2: Flow-sensitive fish species list for California; Appendix 3: High-priority candidate dams for assessing environmental flow needs for imperiled species conservation and recovery. Appendix 4: Ranking of candidate dams based on hydrologic, ecological and jurisdictional criteria

Grantham TE and Moyle PB. 2014. Assessing flows for fish below dams: a systematic approach to evaluate compliance of California’s dams with Fish and Game Code Section 5937. Center for Watershed Sciences Technical Reports (CWS-2014-01) :1-136

Grantham TE and Viers JH. 2014. 100 years of California’s water rights system: patters, trends and uncertainty. Environmental Research Letters 9: 084012

Kiernan J, Moyle PB, Crain PK. 2012. Restoring native fish assemblages to a regulated California stream using the natural flow regime concept. Ecological Applications 22: 1472-1482

Moyle PB, Katz JVE, Quiñones RM. 2011. Rapid decline of California’s native inland fishes: A status assessment. Biological Conservation 144: 2414-2423

Moyle, P.B., J. D. Kiernan, P. K. Crain, and R. M. Quiñones. 2013. Climate change vulnerability of native and alien freshwater fishes of California: a systematic assessment approach. PLoS One

Moyle PB, Marchetti MP, Baldridge J, Taylor TL. 1998. Fish health and diversity: justifying flows for a California stream. Fisheries 23: 6-15

Quiñones, R.M., Grantham, T.E., Harvey, B.N., Kiernan, J.D., Klasson, M., Wintzer, A.P., Moyle, P.B. Dam removal and anadromous salmonid (Oncorhynchus spp.) conservation in California. Reviews in Fish Biology [EarlyView] DOI 10.1007/s11160-014-9359-5