A GIS and TIR procedure to detect and map wall-base channels in Western Washington

Wall-base channels are groundwater fed streams whose origins are on a river terrace, flow over the floodplain and are not directly influenced by the stage of the river. They are important to juvenile coho salmon (Oncorhynchus kisutch) for refuge from high flows and for rearing habitat. Unfortunately, wall-base channels are poorly represented on resource management maps and therefore not well protected from anthropogenic disturbance. To address this problem a three-step procedure was developed to locate, detect, and map wall-base channels. First, a geographic information system (GIS) using digital elevation models (DEM) and digital hydrography was used to automatically locate river floodplains and terraces, the geomorphic structures responsible for the creation and maintenance of wall-base channels. Geographic information system procedures were empirically developed for the South Fork Stillaguamish River, Washington, and tested on the Clearwater River, Washington, where the location of wall-base channels were known. Second, the relative thermal stability of wall-base channels was used to remotely detect them with an aerial mounted thermal infra-red (TIR) scanner. A test flight over the Clearwater River, under less than optimal conditions, achieved detection of 81% of the wall-base channels. Third, the wall-base channels were mapped from selected frames of the TIR video. Frames were used to digitize wall-base channel images into the GIS. Comparison of digital wall-base channel-river confluence positions with pre-existing Washington State Department of Natural Resources digital hydrography showed a spatial accuracy of ±32 m. It was concluded that application of the protocol will assist in wall-base channel protection and proper consideration of the channels in watershed-wide fisheries management plans.1998 Academic Press Limited