WSP06933

• File Number: 8272.500
• Description: Colorado River Basin Salinity Control - Colo Dept of Public Health - WQCC and WQCD
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 11/1/1989
• Author: WQCD
• Title: Colorado Nonpoint Assessment Report - November 1989
• Water Supply Pro - Doc Type: Report/Study

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The Lower portions of the Big Thompson and Little Thompson Rivers carry

significant levels of sediment. Salinity and phosphorus concentrations are.

'also very high in these streams. Irrigated croplands in this portion of the

basin account for these problems. Soft, easily eroded, Cretaceous soils such

.,:" as the Pierre Shale underlie the Little Thompson watershed and contribute to

sediment and salinity problem!!. The Little Thompson watershed was prioritized

as the State's first choice for installation of best management practices

under the Rural Clean Water Program to reduce sediment and salinity levels.

This project never received funding, and the problems described herein still

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iJ reamin. Between the Little Thompson River and St. Vrain, Creek, near Terry

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Lake, there is a critical soil erosion area possibly contributing sediments to

both drainages.

The South Platte River, from the Big Thompson River to the Weld-Morgan County

iine, increases in sediment and salinity but decrea~es in nutrients levels.

The nutrients added to the river from upstream urban sources are removed

through diversion of water for irrigation of agricultural land. Between the

major irrigation canals from Brighton to Kersey, the Platte River is

replenished by flow from the St. Vrain, Big Thompson, and Poudre rivers,

groundwater, and irrigation tail water. Reports from the West Greeley and

Southeast Weld Soil Conservation districts describe erosion, and agricultural

activities along this stretch of the South Platte which may contribute to the,

increase of sediment and salinity.

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