Willapa Bay, WA (P270) Bathymetric Digital Elevation Model(30 meter resolution) Derived From Source Hydrographic SurveySoundings Collected by NOAA

Bathymetry for Willapa Bay was derived from eleven surveys containing 75,491soundings. Four older, less accurate, overlapping surveys were entirelyomitted before tinning. The overlap from two older, less accurate surveys wasomitted before tinning. The average separation between soundings was 69meters. Eight of the surveys dated from 1939 and three surveys, located in thenortheastern portion of the bay, dated from 1954. The total range of soundingdata was 2.1 meters to -30.8 meters at mean low water. Mean high water valuesbetween 2.1 and 2.7 meters were assigned to the shoreline. Four points were found that were not consistent with the surrounding data. These were removed prior to tinning. DEMgrid values outside the shoreline (on land) were assigned null values (-32676).Willapa Bay has eleven 7.5 minute DEMs and two one degree DEMs. The 1degree DEMs were generated from the higher resolution 7.5 minute DEMswhich covered the estuary. A Digital Elevation Model (DEM) contains aseries of elevations ordered from south to north with the order ofthe columns from west to east. The DEM is formatted as one ASCIIheader record (A- record), followed by a series of profile records(B- records) each of which include a short B-record header followedby a series of ASCII integer elevations (typically in units of 1centimeter) per each profile. The last physical record of the DEM isan 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.