Quantifying ecosystem services can be challenging, particularly in the context of groundwater and surface water management—as human populations expand, droughts increase in severity and duration, and costs for water resources climb, determining the degree that freshwater ecosystem health will be traded for water security becomes increasingly contentious. Adding endangered species to the mix further muddies the waters, particularly when the basic natural history needs are poorly parameterized. In the Santa Clara River watershed of southern California, Steelhead face a variety of challenges as they complete their anadromous life cycle, including a spatially intermittent mainstem, substantial year-to-year variation in the timing and availability of contiguous flows, physical barriers to fish passage, as well as water diversion for human use. Unlike the rest of southern California, which relies on imported water, local rainfall (and subsequent natural and human-mediated infiltration to groundwater) provides the majority of water budget for the Santa Clara watershed. To address these issues, we have collected and analyzed long term migration data for steelhead, developed a hydrologic model for the complex surface-groundwater interactions, and applied potential operational scenarios to estimate effects to fish and water resources.
Results/Conclusions
Using a 20 year dataset of steelhead detection at the Freeman diversion facility, we present efforts and challenges to understanding the life history needs of migrating Steelhead. Low smolt abundance and rare detection of adult Steelhead, as well as a highly variable and fluctuating natural flow regime, require the use of surrogate measures (e.g., critical flow analyses) for migration success and additional uncertainty analyses to estimate potential impacts of flow diversion on Steelhead. Combining natural history data and critical flow analyses, we propose methodology to assess balanced instream flow budgets for fish migration and groundwater management.