This DEM is a compilation of the best available elevation data to cover the area of interest.

Data includes

1) Bare earth LiDAR data downloaded from the DOGAMI LiDAR Viewer web map application:

https://gis.dogami.oregon.gov/maps/lidarviewer/

2) USACE Willamette River 2017 bathymetric LiDAR

3) USGS 2017 single beam hydrosurvey of the Willamette River

4) Various USACE bathymetric surveys of some Willamette Valley project reservoirs (as indicated below).

For the extent of each dataset included, polygons were produced from each DEM downloaded. The Raster Domain tool in ArcGIS was used to produce these polygonal footprints of each DEM. The geodatabase containing these polygons is called Raster_Domain_Polygons.gdb.

An ArcMap 10.7 project was produced to show each DEM included in each of the 15 basin DEMs and the order in which they were placed in the mosaic process. The ArcMap project is called Willamette_CWMS.mxd

After downloading the datasets, all data was reprojected to USA Contiguous Albers Equal Area Conic USGS version, US Feet with a three foot resolution. All elevations are in feet, NAVD88.

Care was taken to ensure the vertical units were all in US Feet. When vertical units were in meters, the DEMs were recalculated (Map Algerbra in ArcGIS) by multiplying the grid by 3.28084.

A modified Willamette Basin footprint that defined the required geospatial extent of data was profided by Jeff Ballantine (CENWP-ENC-HY).

This footprint was then intersected (Intersect tool in ArcGIS) with 15 different HUC8 basin boundaries. This also reduced the extend of the required data. The resulting polygon was buffered by 1000 feet to ensure overlap between final basin DEMs.

These basin footprints were then used to determine which of the LiDAR DEMs were required to fill each basin as completely as possible.

The individual DEMs were then mosaiced (Mosaic tool in ArcGIS) to combine the DEMs into a single DEM covering the individual basin. Great care was taken to order the DEMs in the mosaic process such that the most recent LiDAR data would overwrite the older data when overlap occurred.

In addition to the DOGAMI and WA DNR LiDAR DEMs, Willamette River 2017 LiDAR from USACE was also incorporated into the final basin DEMs when appropriate. There are two versions of this data: clipped and unclipped. Pryor to including this data, a USGS Willamette River single beam bathymetric survey was incorporated into the LiDAR. This was done following these steps:

1) A clipping polygon was produced by buffering of a shapefile of the river by 200 feet.

2) This clipping polgon was used to clip out (Extract by Mask tool in ArcGIS) the portion of the clipped version of the 2017 Willamette River LiDAR for the entire surveyed area.

3) The extracted 2017 Willamette River LiDAR grid was converted to points (Raster to Multipoint)

4) A Terrain was produced incorporating the Mass Points from the LiDAR, the USGS single beam bathymetric survey points, and the clipping polygon.

5) The new terrain was converted back to a raster DEM

Lastly, bathymetric surveys of USACE Willamette Valley project reservoirs were acquired where available.

Bathymetric data for the following projects was used as the last datasets mosaiced into the final DEMs:

Cottage Grove

Detroit

Dexter

Lookout Point

Fall Creek

Foster

Hills Creek

Next, each basin DEM resulting from the mosaicing process was clipped (Extract by Mask tool in ArcGIS) to the basin clipping polygon (1000 foot buffer of the basin, intersected with the original CWMS Willamette Basin DEM coverage area).

As a final check, hillshades were produced from each DEM to visually check for errors. The geodatabase containing these hillshades is called Willamette_CWMS_Final_DEM_Hillshades.gdb.

Lastly, each basin DEM was converted to a tiff image format.