Evaluation of floodplain restoration projects in the interior Columbia River basin using a combination of remote sensing and field data

Floodplain habitat restoration has become a common component of river restoration throughout the Pacific Northwest and is critical to the recovery of Pacific salmon ( Oncorhynchus spp.) and steelhead ( Oncorhynchus mykiss), yet little information exists on the physical or biological response to these habitat restoration efforts. Using an extensive post-treatment design and a combination of remote sensing and field surveys, we sampled 17 floodplain projects designed to benefit anadromous fish in the Columbia River Basin. We detected significant increases in side channel metrics (area, length, and the ratio of bankfull side-channel to main channel length), sinuosity, pool frequency, large wood, and the morphological quality index. On average, juvenile Chinook ( Oncorhynchus tshawytsch), coho ( Oncorhynchus kisutch), steelhead, and salmonid combined abundance was 1.17, 4.62, 1.62, and 1.65 times higher, respectively, in treatment reaches compared to control reaches, though these increases were only significant for steelhead and all salmonids combined. Our study demonstrated that a combination of remote sensing and field data can be used to monitor floodplain and instream habitat and detect fish response to floodplain restoration projects.