| Data | Details |
|---|---|
| Hydrologic Unit Codes | 17050101 |
| Size | 2,133 square miles (1,365,120 acres) |
| Water Bodies with EPA-Approved TMDLs (Category 4a) | C.J. Strike Reservoir, Cold Springs Creek, Dry Creek, Little Canyon Creek, Snake River |
| Beneficial Uses Affected | Cold water aquatic life, primary contact recreation, domestic water supply |
| Major Land Uses | Rangeland, agriculture |
| Date Approved by EPA | June 2006 EPA Approval Letter |
Subbasin Characteristics
The 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.
2006 Subbasin Assessment and TMDL
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 that is contributing to excessive aquatic plant growth.
Instream 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 C.J. Strike Reservoir subbasin have extended periods of zero flow following spring runoff. 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.
2006 TMDL: Streams and Pollutants for Which TMDLs Were Developed
| Stream | Pollutants |
|---|---|
| C.J. Strike Reservoir | Nutrients, dissolved oxygen |
| Cold Springs Creek | Sediment |
| Little Canyon Creek | Sediment |
Subbasin Document(s)
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