Bathymetric Data Collection during high-flow event in the Green River near Tukwila, Washington on 20160121

Field Data: The second ADCP data collection effort for this project was done on January 21, 2016 represented with these bathymetric point locations on the Green River near Tukwila, WA. The stream surface in the vicinity of the project area was relatively flat and water clarity was fair. Stream stage (water-level elevation) was 6.83 ft. higher relative to the July 2015 ADCP data collection effort. The upstream and downstream extent of the fishing site was identified by the Muckleshoot’s fisheries biologist Martin Fox to correspond with the tribes’ traditional fishing location. Reverse flow was first observed immediately along the right bank at the upstream end of the fishing site where the channel width slightly increases. This area of reverse flow was observed for approximately four meters (0.004 km) downstream where uniform flow returned across the stream channel. Due to the relatively high stage during the January 2016 data collection, a rubberized inflatable boat (R.I.B.) with a 15 horse-power outboard motor was used to collect the ADCP data. The transects measured on this date are not exactly the same as those measured in July 2015 due to the swift water conditions. As a result, multiple overlapping transects were measured to ensure high resolution XYZ point data that would be comparable to the July 2015 data. Transects measured here included a “zig-zag” transect that traverses multiple times between the upper and lower and near right and left bank extent, two parallel longitudinal transects in the immediate vicinity of the fishing site, one longitudinal transect along the left bank, and four parallel latitudinal transects covering the upper and lower extent of the fishing site. Processed Data: USGS provided the mean surface water elevation(or mean stage) collected at real-time streamgaging 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_20160121.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, as explained in a comment within the attached spreadsheet.

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