Angora Creek Restoration SEZ

South Lake Tahoe, CA

El Dorado County DOT
Summer/Fall 2005 –Phase I, Summer/Fall 2006- Phase II

Hanford ARC contracted with the Department of Transportation in 2004 to construct this two phase project, beginning in June 2005. The project was designed by Graham Matthews Associates of Weaverville, Ca.

The aggressive project scope includes restoration of approximately 4 acres of alpine meadow, construction of 2,000 LF of new main stem channel and 600 LF of tributary channel, a new vehicle bridge, utility relocation, culvert removal, and backfill of the main stem gully. The existing gully was deeply incised and straightened, which caused the stream to abandon its floodplain, reducing the habitat value and turning the historic floodplain into a dry meadow. In addition, a large headcut in the gully was contributing approximately 300-500 cubic yards of sediment to Angora Creek each year, polluting Lake Tahoe.

Demolition included the removal of over 300 trees and stumps, many of which were used for log structures in the new stream channel. The log structures along with rock cut-off walls, rock weirs, rock toe protection and meadow sod placement were used to stabilize and create habitat in the new channel, and allow high flows to return to the floodplain. In addition to the new channel construction, approximately 260 linear feet of rootwad bank revetment was installed to stabilize a reach of existing channel.

Agencies overseeing the project included the Department of Transportation, Tahoe Regional Planning Agency, US Forest Service, California Tahoe Conservancy, and the Regional Water Quality Control Board, Lahontan Region. Maintaining water quality throughout the project was the greatest challenge; the project required excavation below the water table in numerous locations. Furthermore, requirements of working in a designated Stream Environment Zone (SEZ) are stringent, and include Low Ground Pressure (LGP, <4PSI) equipment requirements.

In order to meet these challenges, Hanford ARC employed a number of non-standard techniques, including the use of all tracked equipment, a soil conveyor system, and hand-installed vinyl sheet pile in the SEZ. The conveyor system, used in the 2005 construction season transported soil from the meadow excavation area, across the 40-foot gully of the existing channel, to a stockpile area for placement during the 2006 season. The soil was excavated and transported to the conveyor hopper with LGP excavators, tracked trucks, and tracked skid steer loaders.

Floodplain restoration involved removal of top soil, sod borrow, re-grading and cutting of the new design channel. Approximately 5,700 yards of soil were removed from the meadow and stockpiled on site. To accommodate the relocated channel and floodplain, a new precast, concrete arch culvert was installed on View Circle, a residential street crossing the meadow. Underground work to install the bridge included sewer and water line replacement.

An extensive dewatering system installed in 2005 and modified in 2006, including tanks, 2” pumps, 6” pumps, a weir tank, a 24” pipe bypass, filters, irrigation and dust control sprinkler systems, and French drains helped to manage water on the site. Using vinyl sheetpile, the stream was diverted to its new channel at the beginning of the 2006 construction season.

A narrow window for construction and tight regulatory constraints, along with new restoration techniques meant that the project was watched closely by many. Hanford ARC completed construction in 2006, and will be performing vegetation irrigation and maintenance through 2008.