Watershed Restoration for Baseflow Augmentation

Verna M. Jigour (2008-11) PhD Dissertation(1) Abstract

 

California’s water problems lie not just in the amount of precipitation but in its timing. The temporal disposition of precipitation is strongly influenced by the vegetation of the watersheds it falls on, but for at least the last five decades that relationship has been largely misunderstood in water resources management. Ponce (1989) succinctly defined the goal as “baseflow augmentation”, focusing there on streambank storage, while pointing to the potential for management of uplands and rangelands to contribute.

This dissertation expands on the efficacy of potential upland/rangeland management strategies to augment baseflow, focusing on the existing nonnative grasslands, including hardwood rangelands, that cover expansive areas of California’s semi-arid watersheds. Extensive review of little-known scientific and policy literature dating back to the early 20th century demonstrates that a body of knowledge supports the essential watershed functions conferred by native vegetation types, their deep rooting systems, and the soil ecosystems they engender—the soil profile as a natural detention reservoir. Framed within the context of the evolving biosphere per Budyko (1986), biospheric feedbacks on regional and local climate are included in this systems evaluation.

The synthesis considers the impacts of aboriginal burning, along with subsequent land management, on the watershed functions of vast areas of the state, proposing vegetative restoration of lands currently clothed in shallow-rooted, nonnative annual grasses to restore those vital functions and augment baseflow; replacing the existing high albedo landscapes that likely feed back into the regional climate system by reducing precipitation, with mosaics of native cover types.

Analyses performed on a GIS database I developed of historical California steelhead streams and watersheds south of San Francisco Bay provide correlations among steelhead status, land-cover types, stewardship status and counties. Most significant are estimates of the potential new detention storage with watershed restoration. Estimated additional storage possible on Salinas River subwatersheds not obstructed by dams surpasses the total storage capacity of the two largest reservoirs on that drainage. Potential detention storage in uplands of the upper Pájaro River watershed could significantly reduce downstream flooding.

This concept holds even greater potential for the watersheds feeding the troubled San Francisco Bay-Delta ecosystem.

 

(1)  Union Institute & University Graduate College – submitted in partial fulfillment of the requirements for the degree Doctor of Philosophy in Interdisciplinary Studies: Arts & Sciences: Conservation Ecology; approved by doctoral committee 2008, finalized 2011