Moses Lake Sediment

Science Center Objects

Located in central Washington, Potholes Reservoir is a key feature of the Columbia Basin Project and serves as a vital source of irrigation water. Potholes Reservoir has traditionally been fed water through the East Low Canal, but due to operational changes over the years, the Bureau of Reclamation is looking for reliable alternatives to ensure an adequate portion of water supply to Potholes Reservoir. One alternative route being considered is Crab Creek, which flows into Moses Lake.

To help the Bureau of Reclamation address the concern about increased sediment loading to Moses Lake if flows are increased in Crab Creek, the USGS is providing data on past and current sediment loading to the lake to assess how changes in flow on Crab Creek may affect the rate of sedimentation in the lake.

9722-D8Q - Suspended Sediment Sampling on inflow and outflow to Moses Lake and Sediment Cores in Moses Lake - Completed FY2009

Problem - The Bureau of Reclamation (Reclamation) has recently completed the Potholes Reservoir Supplemental Feed Route Environmental Assessment that considers a proposal to route water via Banks Lake down Crab Creek and through Moses Lake to feed Potholes Reservoir (fig. 1). The current practice is to use the East Low Canal rather than Crab Creek to feed the reservoir, but this approach has made it difficult to ensure a full water supply to Potholes Reservoir. There is a concern about increased sediment loading to Moses Lake if flows are increased in Crab Creek. Data on current sediment loading to the lake are needed to assess how changes in flow on Crab Creek may affect the rate of sedimentation in Moses Lake.

Objective - The objectives for the sampling are to provide a history of loading to the lake over the last fifty or so years beginning when the first irrigation water from the Columbia Basin Irrigation Project began to flow in the early 1950's, an estimate of sediment loading to Moses Lake for a range of discharges in Crab Creek, and the relative amount of loading from Crab Creek compared to the other inflows to Moses Lake.

Relevance and Benefits - An important part of the USGS mission is to provide scientific information to manage the water resources of the Nation, and to enhance and protect our quality of life. This study is consistent with the national USGS mission and goals and water-resources issues identified in the USGS Washington District Science Plan 2004. Specifically, the study addresses the following "Water-Resource Related Issues": Water availability (issue 1), because it is addressing an issue related to efficient transport of water in a large irrigation project; and water quality (issue 5), because the data will be used to estimate the water-quality effect related to the proposed supplemental feed. The study is being conducted to assist a sister Department of the Interior bureau with their study of a water-resource management issue.

Approach - Several approaches are proposed to address these objectives. Sediment sampling at varying discharges will provide a sediment-transport curve that can be used to make estimates of sediment loading into Moses Lake. The sediment input estimated from/to Moses Lake for one year (within water years 2008 and 2009) will be compared to the annual sedimentation in Moses Lake estimated from examination of sediment cores taken throughout Moses Lake.

Suspended-sediment samples will be collected at the major surface inflows to Moses Lake the main outflow from the lake, and when flow is present, samples will be collected on Crab Creek just above the proposed input to the Supplemental Feed to characterize the sediment input of the Crab Creek headwaters. Stream discharge will be measured at the sites each time the suspended-sediment samples are collected. A suspended sediment transport curve will be constructed at each of the sites. Approximately four samples per site will be collected during a range of discharges during the fall, winter, and spring months of 2007 and 2008.

Lake cores will be taken in Moses Lake to identify the sedimentation rate over the last 50 years or so. If the Mt. St. Helens ash can be identified, it will be used as a dating tag for the core; otherwise, radiochemical methods will be used to date the core.