Marin Water is studying whether it can release less water from its reservoirs into Lagunitas Creek without harming aquatic species, allowing the district to hold onto more water this winter amid a historic drought. 

The flow reductions would occur from November to March, when the changes could affect spawning and the rearing of fish eggs. Hydrologists chose four stretches of the creek that are typical habitat and will complete a detailed topographic survey there, then use modeling to determine the conditions at a range of flows, from 20 to 10 cubic feet per second. 

The models show the water depth, velocity and temperature at thousands of points on the creek, and score them based on habitat suitability. If the study shows that a reduction in flows would have a minimal impact on the ecosystem, the water district will use it to apply for a petition to reduce its required releases during winter.

Any change would modify state water board order 95-17, which mandates a flow in Samuel P. Taylor State Park of 20 cubic feet per second during winters of dry years, and migration pulse flows of 35 cubic feet per second four times throughout the winter. Potential changes include reducing winter baseflows, cutting the number of migration pulses and delaying the winter releases. Marin Water releases about 10,000 acre-feet each year from its reservoirs, which hold up to 80,000 acre-feet. 

The watershed is home to three bellwether species that are endangered or threatened in California but hanging on in Marin: endangered coho salmon and California freshwater shrimp, and threatened steelhead trout.

Marin Water’s seven reservoirs are at 45 percent capacity, half of what is typical at this time of year. The water order has rules for normal and dry years, but nothing for a critically dry year—or two in a row.

“This is really uncharted territory, so there is a real need to better understand the relationship between instream flow, the releases from our reservoirs, and the habitat conditions for those three species, specifically the coho,” said Jonathan Koehler, the fisheries program manager for Marin Water.

The water district contracted the work to Environmental Science Associates in April and expects the study to conclude in September, allowing two months before winter for the State Water Resources Control Board to review a petition for a temporary urgency change order. The water board allowed Sonoma Water to temporarily limit its releases from Lake Sonoma and Lake Mendocino last month, reducing minimum creek flows in the lower Russian River from 85 to 35 cubic feet per second for the next 180 days.

Marin Water serves 191,000 people in the San Geronimo Valley and all of eastern Marin, except for Novato, which is served by the North Marin Water District. Marin is unique because it is not tapped into the California State Water Project, a massive and complex system for distributing water from the snowy Sierra Nevada to the Bay Area and Southern California. The federal Central Valley Project is also a major player.

Marin Water is giving monthly updates on the study to the Lagunitas Creek Technical Advisory Committee, the California Department of Fish and Wildlife, the National Marine Fisheries Service and the San Francisco Bay Regional Water Control Board. A change would come with ongoing monitoring and reporting rules.

Although the water district will only move forward if it can prove minimal or no impact, general manager Ben Horenstein said another dry year could force some tough decisions.

“It’s possible, if the severity of the drought continues, we could be faced with difficult issues of fish or people,” he said. “If this drought were to continue…no impacts isn’t necessarily a hard constraint.”

Director Monty Schmitt said that is why conservation is so important—not just for supply, but for wildlife, too. Habitat restoration is also critical because it enables the water that is released to have a greater impact, he said.

Water board order 95-17 is informed by studies from the 1980s, and the conditions in the watershed have changed. Millions of dollars have been spent on slowing and spreading streams, by softening channels and revegetating the banks. The coho population has slightly decreased in that time. 

Further down Lagunitas Creek, North Marin Water District indirectly pumps water out of the creek from its wells. General manager Drew McIntyre said the district would not be impacted by any changes in wintertime flow. North Marin is required to request more releases from Marin Water when the tributaries are dry and all of the water comes from the dams, so summertime flows are more of a concern he said.

In the San Francisco Bay Delta, water regulators have seen that when creek flows are reduced, saltwater contaminates the estuary. North Marin has issues with salinity intrusion at its wells, but Mr. McIntyre said varying creek flows have had little impact on salt levels in Point Reyes Station.

Marin Water is moving fast and in many directions this summer to prepare for a potential third dry winter. In addition to conservation measures and usage restrictions, the district is looking into transferring water across the Richmond-San Rafael Bridge. To do so, the district must locate someone who is willing to sell their water rights, build a pipeline, develop a wheeling agreement with an East Bay water agency and install a new pump station on the other side of the bridge. A consultant is searching for a willing seller, and staff is meeting with Caltrans to begin a structural analysis to support a pipeline on the bridge.

The district is also exploring a temporary desalination plant at its bayside yard in San Rafael. Another consultant was hired to conduct a feasibility analysis and request quotes from suppliers that can rapidly assemble mobile treatment systems. The volume that can be produced at a facility is not yet known.

Both of those options are complex, costly and have a high degree of uncertainty, operations director Paul Sellier wrote.