Bathymetry Digital Elevation Models for Eight Study Areas in Coastal Oregon and Washington, 2012

The research was conducted at nine tidal marshes in coastal estuaries spanning the Washington and Oregon coastlines from Padilla Bay in northern Washington to Bandon located at the mouth of the Coquille River in southern Oregon. We performed bathymetric surveys using a shallow-water echo-sounding system comprised of an acoustic profiler, Leica Viva RTK GPS, and laptop computer mounted on a shallow-draft, portable flat-bottom boat. The RTK GPS enabled high resolution elevations of the water surface. The rover positions were received from the Leica Smartnet system (www.lecia-geosystems.com) or base station and referenced to the same bench mark used in the elevation surveys. We mounted a variable frequency transducer on the front of the boat and connected it to the sounder; the sounder worked in areas of >10 cm of water. We recorded twenty depth readings and one GPS location each second along transects spaced 100 m apart perpendicular to the nearby salt marsh. We calibrated the system before use with a bar-check plate and adjusted the sound velocity for salinity and temperature differences. The bar-check plate was suspended below the transducer at a known depth that was verified against the transducer readings. We synthesized the bathymetry data to create a digital elevation model (DEM) of the nearshore regions at Port Susan, Skokomish, Nisqually, Grays Harbor, Willapa, and Bull Island using ArcGIS 10.2.1 Spatial Analyst with exponential ordinary kriging methods (5 x 5 m cell size). We removed portions of bathymetry data that overlapped with elevation surveys conducted on the tidal marsh. We present elevation data as local orthometric heights (NAVD88). At Padilla we mapped the nearshore area using the methodologies outlined in the project report as the dense eelgrass beds would have increased the error in acoustic measurements