Summary

Description

Bathymetry for the Columbia River was derived from forty-five surveys containing306,711 soundings. Nine older, overlapping, less accurate surveys wereomitted before tinning and the overlap from three older, less accurate surveyswas omitted. The average separation between soundings was 45 meters. Thesurveys used dated from 1935 to 1958. The range of soundings for the forty-fivesurveys was 3.0 meters to -59.1 meters at mean low water. Mean high watervalues between 0.1 and 2.0 meters were assigned to the shoreline. Forty-onepoints were found that were not consistent with the surrounding points.These were removed prior to tinning. DEM grid values outside theshoreline (on land) were assigned null values (-32676).The Columbia River has thirty-three 7.5 minute DEMs and four onedegree DEMs. The 1 degree DEMs were generated from the higherresolution 7.5 minute DEMs which covered the estuary. A DigitalElevation Model (DEM) contains a series of elevations ordered fromsouth to north with the order of the columns from west to east. TheDEM is formatted as one ASCII header record (A- record), followed bya series of profile records (B- records) each of which include ashort B-record header followed by a series of ASCII integerelevations (typically in units of 1 centimeter) per each profile.The last physical record of the DEM is an accuracy record(C-record).The 7.5-minute DEM (30- by 30-m data spacing) is cast on theUniversal Transverse Mercator (UTM) projection. It provides coveragein 7.5- by 7.5-minute blocks. Each product provides the samecoverage as a standard USGS 7.5-minute quadrangle but the DEMcontains over edge data. Coverage is available for many estuaries ofthe contiguous United States but is not complete.