Publication Summary

The upper Yakima River watershed is an important water resource in the state of Washington. In 2002, the Washington State Department of Ecology (Ecology) set a total maximum daily load (TMDL) for suspended sediment, turbidity and organochlorine pesticides in the watershed. In 2006, Ecology, the Kittitas County Conservation District (KCCD), and the Kittitas County Water Purveyors (KCWP) collected samples for total suspended solids (TSS) and turbidity analyses from sites throughout the watershed. The resulting data was used to evaluate if TMDL targets were met as a result of the completion of implementation activities in the watershed.

The upper Yakima River watershed is an important water resource in the state of Washington. In 2002, the Washington State Department of Ecology (Ecology) set a total maximum daily load (TMDL) for suspended sediment, turbidity and organochlorine pesticides in the watershed. In 2006, Ecology, the Kittitas County Conservation District (KCCD), and the Kittitas County Water Purveyors (KCWP) collected samples for total suspended solids (TSS) and turbidity analyses from sites throughout the watershed. The resulting data was used to evaluate if TMDL targets were met as a result of the completion of implementation activities in the watershed.

This report describes the first five years of activities following implementation of the TMDL. It also evaluates the data collected by the Washington Department of Ecology, Kittitas County Conservation District, and Kittitas County Water Purveyors to determine if the 2006 TMDL targets are being met. The 90th percentile turbidity values of tributary and main-stem monitoring sites collected in 2006 are compared to 1999 values and to values collected at background monitoring stations in the watershed.

This report shows that implementation of the TMDL is successful so far. The analysis shows that TSS loading and turbidity values were lower in 2006 compared to 1999, but that assigned TMDL targets for turbidity were not met at all sites. TSS values were lower in 2006 compared to 1999, and were lower than the predicted loads required to meet interim turbidity targets. Turbidity targets were met on three out of four tributaries and at all main-stem sites. In order to maintain the success rate of water quality improvement, this study recommends continued implementation of suspended sediment-reducing activities and continued monitoring throughout the Upper Yakima River watershed.