Snake River (Middle) – Succor Creek Subbasin | Idaho Department of Environmental Quality

Data	Details
Hydrologic Unit Code	17050103
Size	2,002 square miles (1,281,280 acres)
Water Bodies with EPA-Approved TMDLs (Category 4a)	Birch Creek, Castle Creek, Hardtrigger Creek, Jump Creek, McBride Creek, Pickett Creek, Sage Creek, Sinker Creek, Snake River, South Fork Castle Creek and tributaries, Upper and Lower Succor Creeks, Vinson Wash
Beneficial Uses Affected	Cold water aquatic life, salmonid spawning, primary contact recreation, drinking water supply
Major Land Uses	Rangeland, irrigated agriculture
Date Approved by EPA	December 2003 EPA Partial Approval Letter January 2004 EPA Approval Letter
Date Addendum Approved by EPA	December 2007 EPA Approval Letter
Date Tributaries Sediment Addendum Approved by EPA	October 2013 EPA Approval Letter

Subbasin Characteristics

The Mid Snake River/Succor Creek subbasin is a 2,002-square-mile semiarid watershed in the Snake River basin. To the north of the Snake River, the terrain is primarily a gently rolling basaltic plain occasionally studded by gently sloped buttes. To the south lies a dissected lowland plateau of valleys, canyons, and mesas that increases in elevation as they rise to meet the Owyhee Mountains. The tributaries to the Snake River are primarily low-volume rangeland streams that run through sagebrush steppe country.

2003 Subbasin Assessment and TMDL

This document addresses the water bodies in the Middle Snake-Succor Creek subbasin in Idaho that have been placed on the §303(d) list of impaired water bodies. Within the subbasin, 23 segments were identified on the §303(d) list and were assessed to determine if TMDLs were warranted. TMDLs were established for 6 of these segments.

The subbasin is an arid watershed characterized by hot summer temperatures. The tributaries to the Snake River are generally low volume streams that have a combination of high ambient temperatures, poor shading, low flow volume, flow alteration, and naturally warm springs that often leads to exceedances of the temperature standard. Even with maximum potential shade, some of the streams in the subbasin cannot meet the cold water temperature standard. These streams were evaluated to determine the best achievable temperature based on the maximum potential shade.

Nutrient loading to the Snake River comes from the upstream segment of the Snake River, drains, tributaries, and point sources. The primary nutrient impairing beneficial uses is phosphorus. A total phosphorus target of 0.07 milligrams per liter has been set for the Mid Snake River, based upon the work done in the draft Snake River-Hells Canyon TMDL.

Instream channel erosion is the primary source of sediment loading in Castle Creek, Sinker Creek, and Succor Creek. Land management practices contribute to unstable banks and this resultant instability leads to sediment delivery to the stream channel. A bank stability target of 80% was selected as a surrogate target to achieve 28% depth fines in the creek.

2003 TMDL: Streams and Pollutants for Which TMDLs Were Developed

Stream	Pollutants
Snake River (Swan Falls to Oregon line)	Nutrients, dissolved oxygen
Castle Creek	Sediment
Jump Creek (Mule Creek to Snake River)	Sediment
Sinker Creek	Sediment, temperature
Succor Creek (Headwaters to Oregon line)	Sediment, temperature
Succor Creek (Oregon line to Snake River)	Sediment, bacteria

2007 Addendum

The addendum addresses water quality in Succor, Castle, and North and South Fork Castle Creeks:

South Fork Castle Creek appears on the §303(d) list of impaired water bodies for bacteria. However, bacteria levels have been found to be well below the standard, so DEQ is proposing to remove South Fork Castle Creek from the state’s §303(d) list for bacteria and a TMDL for bacteria in South Fork Castle Creek was not developed.
Succor Creek, Castle Creek, and North Fork Castle Creek were placed on the 303(d) list by EPA for temperature. Data collected in 2002–2004 on these creeks verify temperature exceedances of the cold water aquatic life and Rainbow Trout salmonid spawning criteria. As a result, TMDLs to improve temperature by reaching potential natural vegetation conditions have been developed for these water bodies and several of their tributaries.

2007 Addendum: Streams and Pollutants for Which TMDLs were Developed

Stream	Pollutants
Succor Creek and tributaries	Temperature
Castle Creek, North Fork Castle Creek and Alder Creek, South Fork Castle Creek, Juniper Creek, Clover Creek	Temperature

2013 Addendum

This document addresses five water bodies (seven assessment units) in the Mid Snake-Succor Creek subbasin that have been placed in Category 5 of Idaho’s Integrated Report. It quantifies sedimentation/siltation pollutant sources and allocates responsibility for load reductions needed for Birch Creek, Hardtrigger Creek, McBride Creek, Pickett Creek, and Vinson Wash AUs to meet water quality standards. The impaired beneficial use in the subbasin is cold water aquatic life. Sedimentation/siltation pollution sources include natural background contributions, livestock, wild horses, wildlife, roads, cultivated agriculture, and irrigation projects.

The identified pollutants in this subbasin are exclusively nonpoint source in nature. Tributaries are generally low-volume, rangeland streams that have a combination of geographic and geologic features, land uses, low-flow volume, and flow alteration that can lead to exceeding the Idaho water quality standard for sediment that is necessary to support the cold water aquatic life beneficial use. Irrigated agriculture is the likely primary source of sediment loading in Birch Creek and Vinson Wash. Therefore, the target was established as 20 milligrams per liter as a rolling 4-month average sediment concentration throughout the critical irrigation season (April 1–September 30). Instream channel erosion is the likely primary source of sediment loading in Hardtrigger, McBride, and Pickett Creeks. As a result, 80% bank stability was selected as a target to fully support the cold water aquatic life beneficial use in these creeks.

2013 Addendum: Streams and Pollutants for Which TMDLs Were Developed

Stream	Pollutants
Birch Creek (upstream of Castle Creek Road to Snake River)	Sediment
Hardtrigger Creek (headwaters to Snake River)	Sediment
McBride Creek (headwaters to Oregon Line)	Sediment
Pickett Creek (Bates Creek confluence to Browns Creek confluence)	Sediment
Vinson Wash (Polson Creek to Snake River)	Sediment

Subbasin Document(s)

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