Bathymetric Data Collected for Pre-levee Repair in the Green River near Tukwila, Washington on 20150730

Field Data: The first ADCP data collection effort for this project was done on July 30th, 2015 represented with these bathymetric point locations on the Green River near Tukwilla, WA. Stream surface conditions in the vicinity of the project area were relatively flat and water clarity was good. The upstream and downstream extent of the fishing site was identified by the Muckleshoot’s fisheries biologist Martin Fox to correspond with a traditional fishing location. The upstream extent of the surveyed stream reach was defined by a slight riprap bank geometry change causing a seam in the stream flow. The seam is an observable line on the water surface separating two different flow regimes. Looking downstream and to the right of this seam, a zone of reverse flow was observed off the right bank of the fishing site. The lower extent of the surveyed stream reach was defined where uniform stream flow again occurred across the channel width. The uppermost surveyed cross section was collected one meter above the riprap bank geometry change. Each successive cross section was one meter downstream from the previous one and are labeled as minor cross sections. The U.S. Army Corps of Engineers identiied two major cross section locations and were incorporated into the meter interval sequence of cross sections. GPS data points were collected along major and minor cross sections for this bathymetry dataset. Processed Data: USGS provided the mean surface water elevation (or mean stage) collected at real-time streamgageing station No. 12113344 approximately 11 river miles upstream of the project surveyed site. The mean stage was estimated over the time period of ADCP data collection for this dataset and was used as the reference elevation for calculating the bed-elevation point data. Latitude, longitude and water depth were exported from the ADCP instrument using VMT (The Velocity Mapping Toolbox), a processing and visualization suite for moving-vessel ADCP measurements (Parsons, D.R., et al., 2013). These data are presented in the accompanying spreadsheet (GreenRiverBathymetry_20150730.csv) where the bed-elevation of the river bottom was calculated by subtracting the measured depth from the mean stage. An offset was applied to each measurement point in both the July and January datasets to correct for an error discovered during data post-processing.

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