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LAPWAI/MISSION CREEK, LEWIS COUNTY, IDAHO - WATER QUALITY STATUS REPORT, 1986
Description:
Lapwai Creek, Idaho (17060306) was identified in the Agricultural Nonpoint Source Pollution Abatement Program as a first priority stream segment for reduction of agriculture related pollutants. A water quality study was conducted on the Mission/Lapwai drainage from February 25, 1985 to April 8, 1986. Objectives of the study were to determine baseline water quality in various reaches of Mission/Lapwai Creeks and to document the effects of storm event runoff on water quality. Current beneficial uses are as domestic and agricultural water supplies, for primary and secondary contact recreation, cold water biota, and anadromous fishery habitat. Water quality in these streams is most severely impacted by 2 periods, runoff and low flows. Periods of minimal discharge (less than 3 cfs) normally occur from early May to the following January. Most of the sediment load lost from the drainage was delivered during the storm events. 92% of the 1400 tons of sediment from Lapwai Creek was lost during the April 2, 1985 storm. An estimated 1800 to 7000 tons of suspended sediment were lost during the February 23, 1986 storm. The influx of nutrients were event related. The total sediment and nutrient loads reported herein are considered to be 10-20% of the loads annually lost from the Mission/Lapwai drainage. Factors that minimized the recorded loads were: 23% below normal precipitation; 25% below normal discharge at the Lapwai USGS station; and inadequate sampling data, particularly of peak flow events. Latham, R. 1986. Water Quality Status Report No. 65. Idaho Department of Health and Welfare, Division of Environment, Boise, ID. 46 pp.