Englebright

DOSECCs drilling project on Englebright Reservior in California represents an important advance in the collection of core samples for environmental assessment. This type of study will gain in societal significance as efforts are made to address environmental situations that have no easy solutions.

GLAD200 on Englebright reservior

This project was part of the Upper Yuba River Studies Program that is being conducted by the USGS with funding from CALFED. This was a multi-disciplinary investigation of the feasibility of introducing anadromous fish species to the Yuba River system upstream of Englebright Dam. Englebright Lake is a narrow, 14-km-long reservoir completed in 1941 for the primary purpose of trapping sediment derived from mining operations in the Yuba watershed.

Possible management scenarios include lowering or removing Englebright Dam, which could cause the release of stored sediments and associated contaminants, such as mercury used extensively in 19th-century hydraulic gold mining. Transport of released sediment to downstream areas could augment existing hazards including flooding and mercury bioaccumulation in sport fish.

GLAD200 setup at marina on Englebright Lake

To characterize the depositional history, extent, grain size, and chemistry of this sediment, a coring campaign was done with the DOSECC GLAD200 rig in Englebright Lake in May and June 2002. Thirty holes were drilled at 7 different locations along the longitudinal axis of the reservoir, recovering 20 complete sequences of post-reservoir deposition and progradation. The total length of sediment recovered was 379 m, with 83% average recovery.

Sediment accumulation varied in thickness and grain size: 6-8 m dominated by silt near the dam; 31 m of layered silt and sand in the middle of the reservoir, and 22 m of sand and gravel at the site farthest upstream. These cored thicknesses match those from an isopach map derived by differencing the present-day lakebed surface, and the pre-dam topography of the river valley.

Subsampling of the cores for grain-size analysis, mercury concentration, ¹³⁷Cs and ²¹⁰Pb geochronology, and sediment provenance studies is underway. The large sediment load of the Yuba River system provides a high-resolution record of fluvial transport and depositional events in an anthropogenically disturbed tributary of the Sacramento River.

See USGS Website for more details on the Project.

More on Englebright Reservoir, Smartville, California