Date of Graduation
Master of Science in Environmental Management (MSEM)
College of Arts and Sciences
Valley Water is the primary water wholesaler and flood control agency in Santa Clara County, providing services to 1.9 million residents. The operation and maintenance of infrastructure for water supply and flood control often require work within legally protected natural resources such as riparian ecosystems. Riparian ecosystems are dynamic and diverse ecosystems that provide our society with valuable services such as wildlife habitat, water quality, and recreation. However, the threat of human development on native ecosystems has led to the degradation and loss of 85-98% of riparian ecosystems nationwide. Today, federal, state, and regional laws mitigate further impacts to riparian ecosystems and require compensatory mitigation when impacts to jurisdictional areas cannot be avoided. Reference sites can improve the outcomes of mitigation and restoration projects by providing regionally appropriate models of near-pristine ecosystems that allow for the development of ecologically based standards for evaluating the success of projects. This study provides a methodology for reference site selection and field assessment to determine regionally appropriate reference conditions for riparian ecosystems. The methodology of this study includes a literature review and a comparative analysis of existing riparian condition assessment methods. To determine suitability of a riparian ecosystem to serve as a high quality- reference site, this study evaluated criteria such as land use, invasive species cover, distance to roads, and history of past fire. Results confirm that reference sites should not be chosen from areas classified as urban or agriculture land use, because of the negative impacts those land uses have on hydrology, geomorphology, and vegetation. Riparian areas classified as rangeland maybe be used if they have not been overgrazed, and riparian areas classified as protected land use may serve as the highest quality reference ecosystems. Reference ecosystems should also have less than 15% invasive tree and shrub cover; less than 30% invasive herb cover; be further than 50 meters than a road; and to ensure the ecosystem has not been disturbed, not burned in a fire for four years. A combination of two assessment methods, the California Native Plant Society’s Vegetation Rapid Assessment and the California Rapid Assessment Method for wetland and riparian areas, provide the best method to measure parameters important for determining reference conditions and compensatory mitigation permit conditions such as vegetation, water quality, and habitat quality. By using this methodology for selecting reference sites and using field-assessment methods to define physical reference conditions, managers at Valley Water and agencies and nonprofits throughout California can gain a well-rounded understanding of reference conditions in their region. These regionally specific reference conditions will benefit restoration and mitigation project success, and help regulatory agencies apply regionally appropriate success criteria.
Mallen, Claire, "Assessing Methods for Determining Reference Conditions for Riparian Restoration in Santa Clara County" (2020). Master's Theses. 1448.