Snoqualmie Floodplain Dissolved Oxygen Study
Dissolved oxygen (DO) concentrations have frequently failed to meet Washington State water quality standards in many of the Snoqualmie River floodplain tributaries within the King County Agricultural Production District (APD), including Cherry and Ames Creeks. In 2006, WFC observed fish kills in Cherry Valley that occurred as a result of depleted DO (anoxic) conditions in the ditched floodplain tributaries. Substantial native fish kills were documented again in June 2008 in the Cherry Valley drainage ditches during a period of low dissolved oxygen conditions and low DO concentrations have been documented during events with varying temperature and flow conditions (WFC unpublished data, 2008). The cause of this impairment is not yet understood, and with funding from King County Conservation District, Wild Fish Conservancy is conducting a study is to investigate the mechanisms driving the depleted DO conditions and resultant fish kills.
Implications of the impaired conditions observed in the Cherry Valley drainage ditches extend throughout Snoqualmie Valley watershed as most of the lower mainstem tributaries flow across the Snoqualmie floodplain and several other tributaries have documented DO impairments. The Ames Creek drainage ditch system was selected as an additional study site to monitor and compare water quality, hydraulic, and hydrologic conditions. The objectives of this study are to: 1) characterize DO concentrations in the drainage networks, 2) identify possible mechanisms that influence DO, and 3) provide information about the possibility of low DO coinciding with high groundwater-to-surface water ratios during late spring following long periods of soil saturation. Study results will be used to direct future water quality improvement projects and help form a basis for continuing investigations. In addition, this study presents an unprecedented opportunity to document pre- and post- restoration conditions for the Cherry Valley Waterwheel Creek reconstruction and restoration project.
In partnership with Washington State Department of Ecology, WFC began initial data collection in the spring of 2011 to characterize water quality and hydrology of the Cherry Valley and Ames Creek drainage ditches. This project will continue through 2014 to provide a multi-year data set that includes comparison between dredged and un-dredged ditches, and pre- and post- restoration conditions. The results of this study should influence management of drainage ditches and fish habitat restoration scenarios. Identifying the mechanism behind the impaired DO conditions is paramount to protecting important salmon rearing and migration corridors in the Snoqualmie.