The Santa Maria River watershed supports a population of anadromous southern steelhead, a federally endangered species. Currently a self-sustaining population of rainbow trout (the resident life-history of Onchorynchus mykiss) is found in the upper watershed, and anadromous spawning of adult steelhead (the ocean-going life-history of O. mykiss) is observed during some wet years. In 2008, pursuant to Public Resources Code 10004, California Department of Fish and Game (CDFG) identified the Santa Maria River as a high priority river for instream flow analysis, in order to provide the scientific basis for a legally mandated flow recommendation to the State Water Resources Control Board. To assist CDFG in meeting its requirements, the Ocean Protection Council provided funding and contracted Stillwater Sciences to conduct the instream flow study.
Instream flow study
The Santa Maria River is dry most of the year. However, the Sisquoc River is perennial and supports a self-sustaining population of rainbow trout/steelhead. Historically, anadromous steelhead likely migrated upstream from the Pacific Ocean in wet years, during the limited time when flows connected the Sisquoc River to the Pacific Ocean via the Santa Maria River. This pattern may continue, but continuous flow opportunities to the Pacific appear to be increasingly rare. The degree to which groundwater extraction and flow regulation at Twitchell Dam may be further limiting the frequency and/or duration of this migration window is unknown. The goal of the instream flow study is to identify the frequency, duration, and magnitude of surface flows in the Santa Maria River and to determine flows that would be needed for steelhead to migrate between the Pacific Ocean and habitat in the upper Sisquoc River. The study will result in flow recommendations that more closely support the historical timing, frequency and duration of migration opportunities for anadromous steelhead.
Since understanding how the groundwater aquifer is managed and interacts with surface flows is crucial to determining what flows are necessary to provide a continuous wetted channel during steelhead migration, the study includes a series of groundwater related research, review and modeling by Kear Groundwater.
The study will also assess habitat conditions in the upper Sisquoc River and in the Santa Maria River estuary. In the upper Sisquoc River, quantitative habitat assessments and temperature monitoring will demonstrate the relative value of the watershed for steelhead spawning and rearing. In the estuary, where migrating juvenile steelhead may over-summer, breaching patterns and water quality conditions will be assessed to determine the suitability of the estuary for juvenile steelhead rearing.
Stakeholder outreach during the study, which is being led by Central Coast Salmon Enhancement, will provide opportunities for stakeholders to voice their concerns and have their questions answered. In addition, it ensures that the study uses the best available information and benefits from the knowledge of local stakeholders. Stakeholders are encouraged to contact Stephnie Wald with questions and comments, as well as data or information that may be helpful to the study. Materials from the November 15, 2010 public meeting in Santa Maria are available here.
Santa Maria River, Santa Barbara and San Luis Obispo Counties, California
California Ocean Protection Council and California Department of Fish and Game
Materials from November 15, 2010 meeting:
Materials from September 26, 2011 meeting:
Materials from February 29, 2012 meeting:
Presentation by Stillwater Sciences [18MB]
Presentation by California Department of Fish and Game
Presentation by State Water Resources Control Board
Habitat Suitability for Steelhead in the Upper Sisquoc River Watershed
Instream Flow Study Final Recommendations
The Santa Maria River valley is one of California’s most productive agricultural areas and depends on water releases from Twitchell Dam to recharge the groundwater supply.View the gallery