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Watershed & Watersheds: Turbidity Threshold Sampling

^ Main Topic | Caspar Creek Watershed Study | Fine Sediment in Pools Kings River Turbidity Threshold Sampling Study | CALFED |

Grass Valley Creek Hydrologic Data:

Study Information

The Trinity River Task Force (established in 1984) initiated several studies and inventories in the Grass Valley Creek, California watershed. Federal, state and local agencies and the public have participated in the effort to conduct analyses for watershed management. In water year 1998, Redwood Sciences Laboratory operated a trial sediment sampling station to test Turbidity Threshold Sampling in a stream with a coarse sediment load and to develop an overhead boom and turbidimeter housing for a high-energy environment. The station was dismantled after one winter of operation.

Turbidity Threshold Sampling

Location Information

"Grass Valley Creek flows west from Shoemaker Bally (a bally is a mountain) on the Trinity/Shasta County divide and empties into the Trinity River 7 miles (11 km) below Lewiston Dam. The Grass Valley Creek watershed encompasses approximately 36 square miles (23,000 acres or 93 km²) of rugged mountainous terrain that varies in elevation from 6,000 feet (1,830 m) near Shoemaker Bally to 1,600 feet (488 m) at the mouth of Grass Valley Creek. Nearly 80% of the slopes in the area exceed 50%. Annual precipitation ranges from 30 to 45 inches (75 to 115 cm) at lower elevations and from 60 to 75 inches (150 to 190 cm) in the upper reaches of the watershed."

Excerpt from: Bedrossian, T.L. 1991. Timber Harvesting in Granitic Terrain, Grass Valley Creek, Trinity County, California. California Geology. November.Unpublished.

The Grass Valley Creek station is located in Trinity County, off of State Highway 299 near the town of Lewiston, California.

Data Available

Data available upon request.

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Related Information and Publications

Grass Valley Creek Photo Gallery

Manual depth-integrated sediment samples are collected using a crane and D-49 sampler from a bridge upstream from the station.

The boom can be manually positioned so that the sediment sampler intake and turbidity probe remain submerged at the proper depth. The angle of hinged arm increases with higher flows positioning the sampling equipment higher in the water column. When the boom is struck by large debris, it is lifted out of the water allowing the debris to pass underneath the boom.

The boom is raised and lowered by an electric drill and winch. Cables between two trees (not shown) support a block that the winch cable passes through. The base of the boom pivots allowing the entire boom to swivel to the upstream bank for servicing.

The boom is raised and pivoted towards the upstream bank to clean the turbidity probe.

In this experiment, three pumping samplers are connected in series and controlled by a data logger allowing a sample to be collected every 15-minutes for entire storm event.

Two OBS-3 turbidity probes were installed for redundancy in event that fouling or instrument malfunction occurred. The three pumping sampler intake tubes are shown at the bottom of the photo attached to a hinged fin.

Last updated on October 25, 2000, by Rand Eads

Research is being conducted by:

Cumulative Effects of Forest Mgmt on Hillslope Processes, Fishery Resources, and Downstream Environments (RWU-4351)

Last Modified: Aug 28, 2008 06:46:54 AM