HR: 08:45h
AN: H11F-04 INVITED     [Abstracts]
TI: Restoration Planning in a Severely Disturbed Catchment: the Lower Merced River, California
AU: * Downs, P W
EM: downs@stillwatersci.com
AF: Stillwater Sciences, 2855 Telegraph Ave., #400, Berkeley, CA 94705 United States
AB: The Merced River, as it exits the Sierra Nevada foothills, was formerly part of an anastomosing alluvial complex up to 7 km in width, with a bankfull flow of 286 m³s^-1 and a sediment supply of 10,000 - 19,000 ta^-1. Since the 19th century, the 11-km `dredger tailings reach' has been subject to significant ecosystem alteration as a consequence of dams and flow regulation, flow diversion, gold mining, floodplain conversion, and loss of riparian vegetation. These stressors have markedly reduced the quality and extent of habitat for native vegetation, fish, invertebrates, birds, and mammals. Restoring the ecological integrity of the reach is challenging because the stressors are long-lived and do not allow for assisted recovery. Instead the emphasis is on reconstructing the channel-floodplain and providing periodic sediment augmentation to create a channel morphology that is functional rather than historically-inspired. The restored system is intended to support the accumulation of spawning gravels and an increased channel complexity and floodplain connectivity to benefit native riparian habitats. Functional channel design requires knowledge both of hydrosystem dynamics and habitat factors constraining the populations of multiple target biological species. To support the catchment context, baseline data has been collected at several spatial scales, including at the Merced River Ranch, the first proposed restoration site encompassing 1.3 km of the larger reach. Site-level surveys have included volume and texture of dredger tailings, the potential for methylmercury release, and a native tree-growth experiment. These are complemented by reach-scale baseline surveys of fish, birds, invertebrates, geomorphic dynamics, and analysis of reach hydrology, hydraulics, and sediment transport. Upstream processes are either effectively disconnected or can be summarized as outputs from the dam. Locally modifying fluxes of water, sediment and organic matter should improve aquatic and riparian habitats suitable to support viable populations of native plants and animals despite continued constraints on natural processes. Regionally, this should increase the abundance, distribution and resilience of species that have been long compromised by habitat loss and degradation in California's Central Valley. Baseline data collection was designed to allow other restoration schemes in the dredger tailings reach to be implemented without significant additional effort, and some data may be transferable to other dredge-mined rivers. Monitoring and evaluation of the implemented restoration elements based on conceptual models of ecosystem operation should help maximize learning about restoration best-practice. The project stems from an earlier investigation identifying the regional requirements for river corridor restoration in the lower Merced River.
DE: 1719 Hydrology
SC: Hydrology [H]
MN: Fall Meeting 2005