Ecohydrologic Analysis of a Riverine and Reservoir-Fringe System: A Case Study in Support of Reservoir Management Efforts
by Mark Rains, University of California at Davis

ABSTRACT
In the United States, there are more than 75,000 dams greater than six feet in height, and the reservoirs created by these dams cover approximately three percent of the land surface. Most reservoirs are managed exclusively for traditional purposes: municipal and irrigation water supply, hydroelectric power, flood control, and recreation. However, there is growing interest in managing reservoirs, at least in part, for the maintenance of plant and wildlife habitats. Most of the discussion surrounding this management objective is centered on the downstream effects of reservoir operations. Thus, decommissioning dams or otherwise restoring natural flow regimes has been the focus of many recent efforts. This approach, however, does not always clearly result in net ecosystem benefits since reservoir-fringes often support regionally-unique plant communities that serve as critical habitats for regionally-uncommon wildlife species. Decommissioning dams or otherwise altering reservoir operations may restore some channel and floodplain functions but may degrade or eliminate these regionally-unique, reservoir-fringe ecosystems.

In this project, we explore how reservoir operations affect riverine and reservoir-fringe ecosystems upstream of East Park Reservoir on the east front of the Coast Range, California. The overall objective of this project is to develop concepts and tools for the planning, implementation, and monitoring stages of regional reservoir management efforts. First, we use isotopic and chemical procedures to identify the seasonally-varying sources of shallow ground water. Shallow ground water is recharged primarily by stream water and regional ground water, with regional ground water by far the more prominent source in the dry season. Second, we use hydrometric procedures to identify the key boundary conditions governing shallow ground water. A ground-water backwater effect caused by the reservoir extends up valley under the delta and reduces the impacts of regional ground water pumping on the shallow ground water resources. Third, we use a linked ground-water and vegetation distribution model to simulate conditions under alternative reservoir operations. Simulated vegetation distributions on the delta differ markedly under alternative reservoir operations, though some of the regionally-unique plant communities persist even under the full drawdown scenario.


Seminar held February 3, 2003 at New Mexico Tech, at 3:15 pm, MSEC 103
Sponsored by Hydrology Program