Suisun Marsh Fish Screen Rehabilitation Project: Phase 1
Suisun Marsh, Solano County; Measure AA Region: North Bay
Vital Fish, Bird and Wildlife Habitat Program
The Suisun Marsh Fish Screen Rehabilitation Project: Phase 1 will develop and test repair designs to rehabilitate the Suisun Marsh Essential Fish Screens along Montezuma Slough to ensure resiliency for 5,369 acres of managed wetlands in Suisun Marsh of Solano County.
Suisun Marsh is largest brackish wetland on the Pacific coast. Its managed wetlands, primarily duck hunting areas owned by private landowners and the California Department of Fish and Wildlife (DFW), consist of diked lands that are managed to maximize waterfowl production by diverting water from adjacent sloughs at certain times of year and draining or pumping out water at other times of year. The ability to divert water from sloughs during low salinity periods into the managed wetlands is critical for improving habitats by flooding the wetlands, reducing soil salinities, and increasing germination and healthy growth of plants favored by waterfowl.
Levees, ditches, water control facilities, and drainage pumps are used to manipulate the timing, duration, and depth of flooding. If fish are pulled into the intakes (flood pipes), a process known as entrainment, the fish are either killed when they collide with water pumps or get trapped in the managed wetlands and stranded when the wetlands are later drained as part of the annual management cycle. To protect native fish populations from entrainment into managed wetlands, the US Fish and Wildlife Service, the National Marine Fisheries Service, and DFW have established a regulatory framework of diversion restrictions for unscreened diversions in Suisun Marsh. It reduces or prohibits diversions 7 months of the year (Nov 1-May 31). Restrictions coincide with critical flooding periods for wintering waterfowl habitat, spring salt leaching cycles, and wetland irrigations.
Essential Fish Screens (EFS) have been installed on intakes along Montezuma Slough in Suisun Marsh to prevent entrainment of fish. Suisun Marsh EFS were designed to comply with USFWS Delta smelt (0.2 feet/second) and the NMFS salmon (0.4 feet/second) requirements (Exhibit 2. EFS). With EFS installed, managers can apply water to the managed wetlands during sensitive biological periods for fish, i.e., when Central Valley populations of chinook salmon, most of which use Suisun Marsh during their migrations, and other fish species of concern such as Delta and longfin smelt, are present. To maximize habitat values of managed wetlands, water diversion infrastructure needs to be in optimal working order. After more than 20 years in a brackish, corrosive environment, the original EFS have exceeded their useful life and must be rehabilitated to extend their intended function.
Salinity in northern San Francisco Bay is determined by the interacting forces of sea level height and river inflow. With impending sea level rise due to climate change, as well as constant pressure from upstream water users to increase freshwater diversions and reduce river inflow to the Bay, salinities in Suisun Marsh are expected to increase. Therefore, properly operating EFS are essential for having the ability to divert low salinity water, when it is available, to maintain brackish habitat in the managed wetlands. This Project is the first of two Phases: Phase 1 will assess current condition of 14 existing EFS, develop a plan to rehabilitate the EFS and associated infrastructure, develop a design for EFS rehabilitation, and test the design in a pilot project on one EFS. Phase 1 also includes upgrading the solar systems that power pumps at six remote EFS sites that don’t have access to line power in order to improve efficiency and reliability (Exhibit 1, EFS Site Locations). The SRCD’s 1986 boom truck will also be rebuilt during Phase I in order to restore the capacity to regularly maintain the EFS. Phase 1 will establish a blueprint for rehabilitating the EFS including permitting and constructing a pilot project. Evaluation of Phase 1 will be shared in a summary report, and findings will guide Phase 2 which will rehabilitate the remaining 13 EFS to ensure reliability and increase resilience for Suisun Marsh managed wetlands. Staff recommends that funding for Phase 2 be considered after Phase 1 has provided the necessary findings.