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Mean bed elevations of waterbodies on the Atchafalaya River floodplain

March 9, 2022

Waterbodies that exhibit persistent water and lack trees within the majority of its area are defined as open waterbodies by the National Hydrography Dataset (NHD, USGS, 2011). The data presented here were created to determine the volume of water for open waterbodies on the floodplain of the Atchafalaya River Basin. Open waterbodies and their surficial geometry were identified using a geographic information system (GIS) shapefile acquired from the NHD. The spatial coverage was clipped to areas within the Atchafalaya Basin Floodway System area of interest. Bed elevations of a representative set of channels were determined from bathymetric surveys conducted 2014-2017 during high river stages by the U.S. Geological Survey (USGS) personnel. A Lowrance HDS5 single-beam digital recording chart plotter was used to collect sound navigation and ranging (SONAR) bathymetry at a frequency of 10Hz. Horizontal position was recorded simultaneously from an GPS internal to the SONAR (plus or minus 2 meters). Most dredged canals and channels within, or to access an oil field were dredged to similar bed elevations so representative surveyed channel bed elevations were extended to similar channels types within a 4-kilometer distance. Mean bed elevations for the Henderson Lake Watershed Management Unit (WMU) were derived from Kelso and others, 2011. Inaccessible waterbody bed elevations were estimated based on GoogleEarth (2019) imagery from 2000 through 2019. Elevations derived from this imagery were based on exposure of the waterbody beds relative to laser imaging, detection, and ranging (lidar) elevations (USGS 2013), and/or similarity of aquatic vegetation relative to surveyed channels. The mean bottom elevations of waterbodies were calculated from channel or lake cross sections in meters North American vertical datum 1988 (NAVD88). Cross-sections were surveyed using SONAR. SONAR measured points along the channel banks were removed from the calculation of mean to avoid debris and bank slopes. The remaining points across the channel or lake bed were averaged to produce a mean elevation. Cross-section mean elevations were weighted by width of cross section and a weighted mean bottom elevation and calculated for each waterbody segment and added as a field value to the shapefile as MeanBotel. This work was partially funded through a cooperative agreement with the US Army Corps of Engineers. References: Kelso, W. E., Harlan, R., Kelley, D., and Pasco, T., 2011, Pre- and Post-Project Monitoring of Water Quality, Habitat, and Fish Communities in the Buffalo Cove and Henderson Lake, Units of the Atchafalaya River Basin: Task I. Final Report Submitted to JESCO Inc. Jennings, LA. U.S. Geological Survey (USGS), 2011, National Hydrography Dataset (NHD), accessed March 23, 2011 at: U.S. Geological Survey (USGS), 2013, 2010 U.S. Geological Survey Topographic LiDAR: Atchafalaya Basin, Louisiana, available at