The U.S. Geological Survey performed a bathymetric survey of Groundhog Reservoir using a man-operated boat-mounted multibeam echo sounder integrated with a global positioning system (GPS) and a terrestrial real-time kinematic (RTK) GPS in June 2011. The multi-beam echo sounder collected data at lake depths of approximately 3 feet and greater, whereas the terrestrial topographic survey was performed with the RTK GPS in shallow areas near the shore not navigable by boat to the elevation of the top of the dam plus about 2 to 3 additional feet. Bathymetric data from the multibeam echo sounder were collected June 27-29, 2011, and were compiled and stored using the hydrographic survey software, HYPACK 2010 from HYPACK, Inc. (HYPACK, Inc., 2010). The data were interpolated onto a 2-meter grid by computing the average of the data in each cell and positioning the mean at the cell center. The data were converted to elevation above the National Vertical Datum 1988 (Gesch and others, 2002) using reservoir stage. The bathymetry and GPS datasets were then imported into ESRI Arcmap so elevation contours could be determined. The data were used to create a Triangulate Irregular Network (TIN). This TIN was converted to a 2-meter raster dataset which was subsequently contoured. The contour lines were smoothed using a generalized 500 technique (ESRI, 2010). Some holes in the smoothed contour dataset were removed manually and some of the contours were manually adjusted to connect contours and fix any other issues. This created the final contour map.References:Environmental Systems Research Institute, Inc., 2010, ArcGIS—A complete integrated system: Redlands, Calif, ESRI. Accessed Oct. 17, 2011, from http://www.esri.com/software/arcgis/.Gesch, D., Oimoen, M., Greenlee, S., Nelson, C., Steuck, M., and Tyler, D., 2002, The National Elevation Dataset: Photogrammetric Engineering and Remote Sensing, v. 68, no. 1, p. 5-11.HYPACK, Inc., 2010, HYPACK® 10.0.5.31, Hydrographic survey software user manual: Middletown, Conn., HYPACK, Inc. [various paged], accessed Oct. 5, 2011, from http://www.hypack.com/new/Support/DocumentsManualsTechnicalArticlesetc/tabid/81/Default.aspxKohn, M.S., 2012, Bathymetry of Groundhog Reservoir, Dolores County, Colorado, 2011: U.S. Geological Survey Scientific Investigations Map 3202, scale 1:8,000 [https://pubs.usgs.gov/sim/3202/].U.S. Geological Survey, 2011, Colorado StreamStats: U.S. Geological Survey, accessed Oct. 17, 2011, from http://streamstatsags.cr.usgs.gov/co_ss/default.aspx?stabbr=co=1323879434710