December 30, 2016
Firm Provides Sustainable, Cost-Effective Solutions to Save Steelhead Trout Spawning and Rearing Habitat
Based on its record of success implementing ecosystem restoration, natural channel design and biological stabilization techniques, Michael Baker International was contracted by the City of St. Helena, Calif., to restore the ecosystem of the Upper York Creek. This area is home to some of the highest-quality steelhead trout spawning and rearing habitats in the central Napa River Basin.
The project incorporates value engineering analysis – which is Michael Baker’s process to determine cost savings without sacrificing integrity of design – and design- and construction-phase services related to the removal of the 50-foot-by-140-foot earthen dam, re-establishing a natural fish passage channel, removing invasive plants, and revegetation of the riparian forest.
Upper York Creek existing spillway
The solutions Michael Baker experts propose minimize the potential for downstream habitat degradation caused by large sediment releases which historically have caused the mortality of fish and other aquatic organisms below the dam. The solutions also reduce the overall construction costs to fit within allotted funds. This is accomplished by decreasing the overall project footprint and length of channel reconstruction from approximately 1,200 feet to approximately 750 feet, while keeping the channel slope consistent with the upstream and downstream sections of the creek.
Other cost-savings opportunities include: changing the design approach toward channel profile modifications to reduce earthwork and the number of in-stream channel structures; performing additional sediment transport and channel stability analyses to eliminate channel armoring; and, to reduce revegetation, modifying the design approach toward corresponding earth-disturbing activities that require revegetation.
History of the Upper York Creek Dam and Reservoir
In the 1930s, the original Upper York Creek Dam was modified with the installation of a concrete spillway and a drop-inlet extension to the out-flow culvert. The dam height was raised 15 feet, and the sluice gates were removed. Because of these alterations, the dam no longer can operate as a managed water-storage facility and is not large enough to provide downstream flood control.
Debris just upstream of existing dam
The reservoir traps the annual supply of gravel and fine sediments produced by the watershed above the Upper York Creek Dam. Sediment accumulates in the reservoir at a rate of 1,000 to 5,000 cubic yards per year, depending on the magnitude of winter storm events. With total sediment storage potential of 28,000 cubic yards of material, the reservoir pool area fills up with sediment every 15 to 20 years.
More than 100 years of sediment trapping has altered the geomorphology of York Creek downstream of the Upper York Creek Dam and is thought to be a significant contributing factor to the six-to-eight feet of bed incision that has occurred in the Napa River over the last century. Regular maintenance of the dam is required, including annual debris removal from the drop-inlet and spillway to maintain storm water passage and periodic removal of accumulated sediment.
Innovating to Identify Solutions
Michael Baker will apply innovative technology to analyze sediment competence and capacity. RiverMorph software will ensure the proposed design will remain stable. Ground penetrating Light Detection and Ranging (LiDAR) technology (performed in a previous design phase) to locate existing bedrock beneath the sediment deposits upstream of the dam will help determine the location of the proposed channel.
Design tasks associated with the contract include: a supplemental field topographic survey; a geotechnical investigation, hydrology, hydraulics, sediment transport analysis, design evaluation and value engineering; a preliminary design report; plans for updated improvements; a soil disposal site evaluation and preliminary grading; channel improvement, specifications and cost estimates; and final improvements, structural and final basis design reports. Also included are creation of a Lower York Creek Monitoring and Management Program, a delineation of jurisdictional waters plan, the preparation/processing of regulatory agency applications and environmental compliance and Environmental Impact Report addendums.
Natural shade in channel within reference reach
Michael Baker also will assist the contractor with construction-phase services, providing in-field modifications to account for any unforeseen factors that weren’t visible during the design phase. This approach is typical for successful stream restoration projects delivered by Michael Baker.
“It’s an honor to be a part of Michael Baker’s team and the efforts to restore access to this vital habitat,” said David Mueller, a technical manager with Michael Baker’s Water Practice and manager of the dam project. “The firm’s commitment to the environment and the ways We Make a Difference
for this community are evident by our efforts to reduce the project’s construction costs through a streamlined, innovative design solution that provides the city with the expertise it needs within a cost structure it can afford.”
Mueller is managing the project, along with Kevin Gustorf, director of engineering services out of Michael Baker’s Rancho Cordova, Calif., office.