Case Studies

Case studies of CEFF implementation are on-going throughout the state.  Updates on ongoing studies are often provided at the quarterly meetings of the Eflows Technical Working Group (a sub-group of the California Water Quality Monitoring Council).  As case studies are completed, reports and information will be provided below.

 

Lower Cosumnes River

The Cosumnes River is the largest undammed river on the west side of the Sierra Nevada. Located between the American and Mokelumne River watersheds, the Cosumnes River flows from the Sierra Nevada mountains 80 miles westward to the San Francisco-Bay Delta via its confluence with the Mokelumne River in the Central Valley. The lower Cosumnes River in the Central Valley supports a Chinook salmon run, hundreds of species of migratory birds, diverse groundwater-dependent ecosystems, as well as the largest remaining Central Valley riparian forest. In addition, the lower watershed supports thousands of acres of productive agricultural land and several local communities.

Under the auspices of the Sustainable Groundwater Management Act (SGMA), work is currently underway to address groundwater basin aquifer sustainability, characterize surface-groundwater interactions, understand the related groundwater-dependent ecosystems, and measure groundwater recharge and use. However, additional knowledge of surface water hydrology is needed in order to inform the development of instream flow targets supportive of anadromous fish, riparian habitat, and other ecological objectives.  To address this knowledge gap, the California Environmental Flows Framework (CEFF) was applied to determine ecological flow criteria based on a functional flows approach.  A technical report summarizing results from sections A and B of CEFF, an assessment of flow alteration (section C step 9), and a literature review of past studies on groundwater recharge and surface-groundwater interactions is provided below.  Results from this case study were also incorporated into a published paper on incorporating functional flows in groundwater-influenced streams.

San Juan Hydrologic Unit

The San Juan Hydrologic Unit in South Orange County (OC), California includes several major streams including San Juan Creek, Trabuco Creek, Oso Creek, Aliso Creek, among others.   Flow alteration and stream erosion have been identified as the highest priority water quality conditions for the region by local watershed managers and stakeholders. Flow alteration is a pervasive issue across South OC due to the effects of historical farming and ranching and more current rapid urbanization over the past 50 to 70 years. Flashier hydrology has led to channel erosion issues, and many streams have shifted from a historically intermittent-ephemeral system to a more perennial system due to augmented baseflows from irrigation overspray.  In some areas, these augmented flows now support sensitive species and habitats that were not historically present.  Despite the widespread hydrologic alteration, streams in South OC currently support a combination of willow and riparian scrub communities, as well as federally listed bird species, such as the least Bell’s vireo (Vireo bellii pusillus), and fish species of special concern, such as the arroyo chub (Gila orcuttii).

To remedy historic hydrology alteration and to support habitat restoration, key implementation strategies have been identified through the South OC Watershed Management Area (WMA) Water Quality Improvement Plan including management of unnatural flows and restoration of 23,000 lineal feet (4.35 mi) of degraded stream habitat.  However, reduction of in-stream flows through flow management actions, drought, and water conservation, pose a potential threat to novel habitat and sensitive species that currently depend on these “non-reference” flowsThis study aims to prioritize areas for flow management and restoration and to recommend management actions or targets.  Determining environmental flow needs will shed light on how to manage water to promote streamflow enhancement and environmental restoration while balancing the needs of the communities of south Orange County.  The California Environmental Flows Framework (CEFF) was applied to prioritize where to focus flow management efforts and to determine ecological flow needs that consider altered channel morphology and the flow needs of species of management concern.  A peer-reviewed manuscript summarizing the CEFF application at a priority reach in south OC illustrates how CEFF was applied in a highly modified, urban watershed.  Additional information on the larger study can be found on the project website.