sir2016-5029_Hi_Res_Extents: Flood-Inundation Maps for the Coast Fork Willamette River from Creswell, Oregon to Goshen, Oregon

The Digital Elevation Model (DEM) utilized for this Willamette FIS submittal was produced by
combining multiple overlapping topographic surveys for the Middle Fork and Coast Fork of the
Willamette River. The DEM was created from four sources: LIDAR of the Springfield area that
was flown in 2008, LIDAR of Silk Creek that was flown in 2011, LIDAR of Fall Creek that was
flown in 2012, and photogrammetry of the Middle Fork and Coast Fork of the Willamette River
that was flown in 2004. In areas where no high-resolution elevation data were available, USGS
National Elevation Dataset (NED) data were used to supplement the DEM. This feature
represents the areas that higher quality information is presented. The horizontal datum of the
DEM is NAD 1983 State Plane-Oregon South HARN with units of International Feet (NAD83).
The vertical datum of the elevation model is NAVD 1988 with units of international feet (NAVD-88).
The higher resolution elevation data means that there is more confidence in the flooded area
polygon and water depth for a particular water surface elevation.