Department of
Environmental Quality

Subbasin at a Glance

Overview

The King Hill-C.J. Strike Reservoir Subbasin lies mainly in the plains and low hills of the western Snake River plain in southern Idaho. The Snake River is the primary drainage in the subbasin, but due to the arid climate, most tributaries to the river are intermittent or dry. C.J. Strike Reservoir provides hydroelectric power to the people of southern Idaho.

Nutrient loading to the Snake River comes primarily from the upstream segment of the Snake River. Other smaller sources include several tributaries and the Glenns Ferry Wastewater Treatment Plant. The primary nutrient impairing beneficial uses in the river is phosphorus. A total phosphorus target was established for the Snake River between King Hill and C.J. Strike Reservoir. A nutrient TMDL was developed based on meeting this target.

As with nutrients, sediment loading to the Snake River comes primarily from the upstream segment of the Snake River. However, the Snake River between King Hill and C.J. Strike Reservoir does not currently exceed surrogate water column targets. Even with the lack of exceedances, a sediment TMDL was established for the Snake River between King Hill and C.J. Strike Reservoir. The intent of the TMDL is to help address a sediment bedload problem in the river, which is contributing to excessive aquatic plant growth.

In-stream channel erosion is the primary source of sediment loading in Little Canyon Creek and Cold Springs Creek. Land management practices contribute to unstable banks in many areas, and the resulting instability has led to sediment delivery to the stream channel. TMDLs were developed based on achieving 80% bank stability.

The Snake River arm of C.J. Strike Reservoir currently experiences dissolved oxygen sags in the metalimnion—the middle layer of a thermally stratified water body. These sags occur due to excess total phosphorus in the water column and increasing sediment oxygen demand. Both nutrient and dissolved oxygen TMDLs were established for the reservoir.

In most water years, many of the §303(d) listed stream segments in the King Hill-C.J. Strike Reservoir Subbasin have extended periods of zero-flow following spring run-off. Pollutant standards only apply when flows exceed 1.0 cubic foot per second. Therefore, TMDLs were not be prepared for the intermittent segments of Bennett, Ryegrass, Cold Springs, Alkali, Little Canyon, Browns, Sailor, and Deadman Creeks.

Streams and Pollutants for Which TMDLs Were Developed

Snake River

Sediment, nutrients

C.J. Strike Reservoir

Nutrients, dissolved oxygen

Cold Springs Creek

Sediment

Little Canyon Creek

Sediment

Subbasin Documents

• King Hill – C.J. Strike Reservoir Subbasin Assessment and Total Maximum Daily Load (March 2006)
• King Hill - C.J. Strike Reservoir Subbasin Assessment and TMDL (November 2007)
• C.J. Strike Reservoir Total Maximum Daily Load Dissolved Oxygen Implementation Plan (December 2008)