Description: For the purposes of research and monitoring in marine environments, elevation data is typically most useful when it is expressed relative to tidal rather than orthometric vertical datums. For example, the potential habitat depth of submerged aquatic vegetation is often expressed as a range relative to mean lower low water (MLLW), representing the specific light requirements of each species. This MLLW bathymetric model (elevation values in meters) of the southern Salish Sea is based on the USGS CoNED topobathymetric digital elevation models of Puget Sound (OCM Partners, 2022a) and the Strait of Juan de Fuca (OCM Partners, 2022b), converted from NAVD88 to MLLW using NOAA’s VDatum 4.6.1 transformation grids (Office of Coast Survey, 2023), and projected onto NAD 1983 HARN StatePlane Washington South FIPS 4602. For more information, contact Tyler Cowdrey, WA DNR, Nearshore Habitat Program at: tyler.cowdrey@dnr.wa.gov or nearshore@dnr.wa.gov. Suggested citation: Cowdrey, T. (2024). Washington State USGS CoNED MLLW Bathymetric DEM [Data Set]. Washington State Department of Natural Resources, Nearshore Habitat Program. [https://gis.dnr.wa.gov/image/rest/services/Aquatics/WA_bathymetry_CoNED_MLLW/ImageServer]. The values of MLLW in this model were generated using source and intermediate data products with significant interpolation and are intended for informational and research purposes only. This product has not been reviewed by a licensed surveyor and should not be used in place of professional surveys for the assessment of tideland parcel boundaries. This product should not be used for navigation. WA DNR makes no warranties about the accuracy of this product. Rough processing workflow: CoNED tiles were bulk downloaded in GeoTIFF format from NOAA Digital Coast (https://coast.noaa.gov/htdata/raster2/elevation/). VDatum 4.6.1 was used to generate NAVD88 to MLLW transformation grids at a resolution of ~0.0002 degrees in ITRF14, which were were then combined and projected onto NAD 1983 (2011) UTM 10N and resampled at 1 meter resolution (snapped to CoNED) using bilinear interpolation. The combined grid was then used to batch transform CoNED tiles from NAVD88 to MLLW using ArcPy maintaining extent, PCS, cell size and snap raster. The new CoNED MLLW tiles were mosaicked and projected onto NAD 1983 HARN StatePlane Washington South FIPS 4602 (SPWAS) as a continuous raster to prevent tile discontinuities. Finally, the continuous CoNED MLLW SPWAS raster was re-tiled, tiles were named by row and column, and pixel values above 10 meters of elevation were removed to improve the reliability of the final product for marine applications. References: OCM Partners. 2022a. 1887 - 2017 USGS CoNED Topobathy DEM (Compiled 2020): Puget Sound, WA. NOAA National Centers for Environmental Information. https://www.fisheries.noaa.gov/inport/item/59971. OCM Partners. 2022b. 1891 - 2016 USGS CoNED Topobathy DEM (Compiled 2021): Strait of Juan de Fuca, WA. NOAA National Centers for Environmental Information. https://www.fisheries.noaa.gov/inport/item/65169. Office of Coast Survey, N.O.A.A., U.S. Department of Commerce. 2023. Vertical Datum Transformation (VDatum 4.6.1). https://vdatum.noaa.gov/download.php
Copyright Text: USGS CoNED. NOAA VDatum. Processed by Tyler Cowdrey, WA State Department of Natural Resources (WA DNR), Nearshore Habitat Program, 2024.