Fill Site 6A was an approximately 2.5-acre area of contaminated fill soil and building debris located in the northeast corner of the Presidio of San Francisco, California. The emplacement of this fill and the associated 440 ft.-long storm drain installation by the U.S. Army resulted in the elimination of a creek corridor that is identified on historical maps of the site. The Presidio Trust decided to remove the fill from Fill Site 6A and to replace the storm drain with a creek corridor that would restore historic conditions at the site. The Thompson Reach restoration was one component of the Trust’s long term vision for ecological enhancement of Tennessee Hollow. Clearwater Hydrology (CH) was selected as part of the implementation team for planned stream restoration projects within the Tennessee Hollow Watershed.
CH prepared the restoration design for the daylighting of this historic channel, in conjunction with the broader fill site remediation. The design involved restoration of 500 feet of meandering channel with hydraulic and geomorphic characteristics appropriate to the current watershed flow regime and land use mix. Pertinent characteristics included soils, geology, bed gradient, peak flows, bankfull geometry, channel entrenchment, sinuosity and sediment load. Instream biotechnical stabilizing elements, including native material revetments, willow walls, log weirs and planted boulder revetments, were components of the design, as was a full complement of riparian and wetland vegetation (planted by PT botanists and field crews). The project also involved topographic restoration of the surrounding disturbed hillslopes, i.e. grading tie-ins linking the restored channel to the adjoining terrain. Excessive bank seepage and predominantly fine-grained soils were two site conditions that posed special challenges for the construction effort, which was concluded in the fall of 2005.
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