Snake River - Hells Canyon Subbasin - Idaho Department of Environmental Quality

Snake River - Hells Canyon Subbasin

Subbasin at a Glance

Hydrologic Unit Codes	17060101, 17050103, 17050115, 17050201
Size	2,500 square miles
§303(d) Listed Stream Segments^a	Six segments of the Snake River, encompassing river miles 409 to 272.5 and 247 to 188 (Oregon/Idaho border to Boise River inflow, Boise River inflow to Weiser River inflow, Weiser River inflow to Scott Creek inflow, Scott Creek to Brownlee Dam, Oxbow Reservoir, Hells Canyon Dam to Salmon River inflow)
Beneficial Uses Affected^b	Cold water aquatic life, primary contact recreation, domestic water supply, special resource water, salmonid spawning
Pollutants of Concern	Idaho's §303(d) list: Bacteria, dissolved oxygen, nutrients, pH, sediment, mercury, pesticides, temperature Oregon's §303(d) list: Mercury, temperature
Major Land Uses	Nez Perce Tribal use, agriculture, grazing, mining, recreation, urban
Date Approved by U.S. EPA	March 2004 September 2004

^aThe segments listed here are as listed on the Idaho §303(d) list. The Oregon §303(d) list divides the segments differently; however, the same total area (river mile 409 through 188) is covered by both lists. The Oregon §303(d) list includes the Hells Canyon Reservoir segment of the river (river mile 272.5 to 247).
^bThe uses listed here are only those as defined in Idaho's rules.

Overview

The scope of the this TMDL extends from where the Snake River intersects the Oregon/Idaho border near Adrian, Oregon, to immediately upstream of the inflow of the Salmon River. This includes the Hells Canyon Complex reservoirs: Brownlee, Oxbow, and Hells Canyon. The overall reach has been divided into five segments based on similar hydrology, pollutant delivery, and processing mechanisms; and operational, management, and implementation strategies. The five segments are:

Upstream Snake River (river mile 409 to 335, 74 miles total)
Brownlee Reservoir (river mile 335 to 285, 50 miles total)
Oxbow Reservoir (river mile 285 to 272.5, 12.5 miles total)
Hells Canyon Reservoir (river mile 272.5 to 247, 25.5 miles total)
Downstream Snake River (river mile 247 to 188, 59 miles total)

Within these segments, all designated beneficial uses and the following listed pollutants have been addressed by the TMDL: bacteria, nutrients, nuisance algae, dissolved oxygen, pesticides, pH, sediment, temperature, and total dissolved gas. The document recommends that the segment addressed by this TMDL be delisted for bacteria and pH. The mercury TMDL has been postponed to 2006 due to a lack of water column data.

Recognizing the complexity of the Snake River-Hells Canyon system, the TMDL adopts a phased approach to implementation that will identify interim milestones to determine the effectiveness of management measures or other action controls being implemented. It also includes a process for reviewing and revising management approaches.

The TMDL document includes two separate, state-specific implementation plans. Together, these documents represent the water quality management plan for the Snake River-Hells Canyon TMDL.

Stream and Pollutants for Which TMDLs Were Developed

Snake River (river mile 401 - 188): Nutrients/dissolved oxygen, pesticides, sediment, temperature, total dissolved gas

Subbasin Documents

Snake River - Hells Canyon Total Maximum Daily Load (TMDL)
(June 2004)
Snake River - Hells Canyon Total Maximum Daily Load (TMDL) Technical Appendices (July 2003)

Department of
Environmental Quality

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