Merced River Corridor Restoration Plan, Phase IV: Dredger Tailings Reach, Merced County, CA
Client: California Bay-Delta Authority Ecosystem Restoration Program

 

Reports

Channel and Floodplain Surveys

Hydraulic Model

Sediment Transport Model

Volume and Texture Analysis

Mercury Assessment

Conceptual Restoration Design

Baseline Monitoring

Revegetation Experiment

Design Rationale

75% Design and Specification

Environmental Documentation

Plan and Cost Estimate

Post Implementation Monitoring

Groundwater Monitoring

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The Merced River Corridor Restoration Plan - Phase IV Project (CALFED ERP-02-P12-D) evaluated strategies for channel and floodplain restoration in the Dredger Tailings Reach (DTR) of the Merced River (RM 45-52) within the context of the contemporary flow regime. The overarching goal of the project was to bolster ecologic integrity at the Merced River Ranch (MRR) through restoring fundamental geomorphic and floodplain processes, the latter achieved by scaling channel and floodplains to the regulated flow regime of the Merced River.

Stillwater Sciences, working with the California Department of Fish and Game (CDFG) and various subcontractors (URS Corp., KSN Inc., River Partners, Frontier Geosciences, Slotten and Ayers [UC Davis], Point Reyes Bird Observatory, Geomatrix, Inc., and McBain&Trush), developed restoration plans for the MRR (RM 50-51), a property purchased by CDFG in 1998 as a source of coarse sediment for future river restoration projects and as a floodplain restoration site. Historical gold dredger mining operations in the reach, and alterations to the natural hydrograph by upstream dams has resulted in the loss and degradation of habitat for native species. The reach is the primary spawning area in the Merced River for fall-run Chinook salmon (Oncorhynchus tshawytscha), an important management species for CDFG, and potentially steelhead (O. mykiss), which is listed as threatened under the Federal Endangered Species Act.  

 

The removal of tailings from the floodplain has the potential to yield multiple restoration opportunities and ecosystem benefits, but the detailed impacts of such restoration activities are largely unknown. As such, a suite of studies were undertaken to support restoration planning at this site, with a view towards providing transferable scientific information to reduce uncertainty in future restoration designs on the Merced River and potentially in other rivers in the Central Valley.

To support the catchment context, baseline data was collected at several spatial scales. At the MRR, studies have included analysis of the volume and texture of dredger tailings, an evaluation of the potential for methylmercury release from tailings, and a native tree-growth experiment under controlled conditions. Reach-scale investigations along the Dredger Tailings Reach included baseline surveys of the abundance and diversity of fish, birds, and invertebrates, and two years of monitoring channel form and sediment transport dynamics. Detailed cross-section and long profile surveys were used to construct reach-scale hydraulic and sediment transport models to interpret the prevailing flow regime.

Under of Phase IV of this project, restoration strategies were developed for the MRR based on current understanding of contemporary geomorphic and riparian vegetation design principles with the aim of using the channel-floodplain portion of the MRR as a pilot project for the similar areas in the DTR or elsewhere in the Central Valley. Design drawings were developed to the 75% completion stage, along with plans for gravel infusion and augmentation, implementation, and post-project monitoring and evaluation. Draft permit applications and cost estimates will be prepared as a pre-cursor towards implementation funding.

Two summary documents were produced: one detailing the scientific insights offered by the project (currently under review), and the other a pamphlet for public distribution outlining the proposed restoration.

 

Updated: 02/12/2007