Channel centerline for the Tillamook, Trask, Wilson, Kilchis, and Miami Rivers, Oregon in 1939
Description
The Tillamook Bay subbasins and Nehalem River basins encompass 1,369 and 2,207 respective square
kilometers of northwestern Oregon and drain to the Pacific Ocean. The Tillamook, Trask, Wilson, Kilchis,
and Miami Rivers flow into Tillamook Bay near the towns of Tillamook and Garibaldi. The Wilson and
Trask River basins cover the largest areas (500 and 451 square kilometers, respectively) whereas the
Tillamook and Kilchis Rivers encompass similar sized areas (156 and 169 square kilometers, respectively)
and the Miami River the smallest area (94 square kilometers). In cooperation with the U.S. Army Corps of
Engineers, the U.S. Geological Survey completed a reconnaissance-level assessment of channel condition
and bed-material transport relevant to the permitting of in-stream gravel extraction along the the major
alluvial portions of six river systems, including the lowermost 14.1 km of the Tillamook River, 16.3 km of
the Trask River, 15.2 km of the Wilson River, 7.8 km of the Kilchis River, 11.6 km of the Miami River,
and 31.4 km of the Nehalem River. To support these analyses, digital channel maps were produced to
depict channel and floodplain conditions in the Tillamook Bay sub-basins and Nehalem River basin from
different time periods. GIS layers defining the wetted channel and bar features and channel centerline in
the study area were developed for four time periods: 1939, 1967, 2005, and 2009. For this project, the
active channel was defined as area typically inundated during annual high flows, and includes the low-flow
channel as well as side channels, islands, and channel-flanking gravel bars. The wetted channel and bar
feature datasets were developed by digitizing from aerial photographs. Aerial photographs from 1939 and
1967 were scanned, rectified, and mosaicked for this project (See metadata for each photograph set for
more information on the rectification process and resolution of each dataset). Digital orthophotographs
from 2005 and 2009 are publicly available.