SEI water modelling forecast prompts California fish rescue

This summer, a local water agency in California took action to support a population of threatened native fish after SEI’s unique modelling tool predicted that the water it inhabited could become too warm for the fish to thrive.

The Central California Coast steelhead is a federally protected species that lives in the waters at the base of Anderson Dam, which is undergoing a seismic retrofit to improve its ability to withstand earthquakes and to comply with federal standards.

The dam, operated by the Santa Clara Valley Water District in San Jose, was ordered to be drawn down to 3% of its capacity late in 2020 by the Federal Energy Regulatory Commission to facilitate the construction.

Since then, SEI researchers, serving as technical advisors, have applied its flagship Water Evaluation And Planning System (WEAP) to model flow, temperature and habitat conditions for the threatened species in the Coyote Creek watershed.

As part of that work, SEI helped Valley Water identify reaches that could heat up above the suitable temperature range. The WEAP model projected average daily temperatures exceeding 24°C (about 75°F) in late June – above the preferred temperature range for the species.

“The estimates from WEAP give us a basis to predict when we should let the fish remain in place and when the conditions become less suitable for fish due to the Anderson Dam construction,” said Doug Chalmers, associate scientist at SEI.

The elevated temperatures occur as a result of the lack of local water storage available while the dam construction is underway, as well as the warmer water imported from the San Luis Reservoir.

WEAP helped local water managers account for a complex set of factors in the watershed to protect the critical fish population when operating reservoir releases.

Consequently, Valley Water, in consultation with the US Fish and Wildlife Service, National Marine Fisheries Service and California Department of Fish and Wildlife, enacted a plan to strategically capture and relocate portions of the fish populations to more suitable locations.

“The habitat directly downstream of Anderson Dam in Coyote Creek is some of the most ideal for steelhead, so it’s important to allow fish to stay there as long as conditions are suitable,” said Clayton Leal, Senior Water Resources Specialist at Valley Water. “However, if temperatures get too high, the conditions can become less than ideal, so it’s important to have a tool that can forecast stream temperature to make informed decisions for supporting vulnerable fish populations.”