Puget Sound DEM - 2002 We are about to update the DEM of the Puget Sound area. Updating the terrestrial component involves: When this data is merged with bathymetry, an interpolation scheme will be devised to assign elevations to river mouths, which are sometimes left as no-data quite a ways upstream on the 10m DEMs.

After the 10-meter DEM is complete, a 30-meter DEM will be built. The bathymetric elevation will be determined by averaging the nine component cells. Terrestrial elevations will be given a value that lies between the mean of nine cells and the minimum of nine component cells. The mixing of these two values will be proportional to the maximum of the flowaccumulation value in the nine-cell neighborhood. Thus, 30m cells that contain streams will be assigned an elevation close to the minimum of the nine component elevations, while 30m cells that contain no large flows will be assigned elevations close to the mean of the component cells. This algorithm will provide some drainage enforcement without being too heavy-handed about it.