Belknap, William. 1994. Wall-base channels in western Washington: Location, detection, mapping and winter use by juvenile salmonid fishes. M.S.
Wall-base channels are groundwater-fed streams that originate on a river's floodplain or terraces. They typically have low gradients and relatively stable flow and temperature regimes. Most are located in the lower reaches of watersheds of meandering rivers on a wide floodplains bordered by abandoned terraces. Their physical characteristics and location in the watershed allow wall-base channels to provide important juvenile salmonid rearing habitat. Studies of two Pacific Northwest rivers have resulted in estimates that 20-25% of the coho salmon (Oncorhynchus kisutch) smolts in the drainage network overwinter in wall-base channels (Peterson and Reid 1984, Brown 1985). These studies suggest that wall-base channels could make significant contributions to salmonid production from large river basins (Jeff Cederholm, DNR, personal communication). Unfortunately, the extent and location of most wall-base channels are not well documented, so as a class of habitat they do not receive the regulatory protection warranted by their importance to salmonid fishes.
Geomorphic features, and vegetation which influence the location and size of wall-base channels are not well documented. The unfortunate consequence is that the normally small and obscure wall-base channels do not receive appropriate protection from land alterations to the lower floodplains of rivers, which are often subject to significant degradation by agriculture, residential and industrial development, and forest management.
The objectives of this thesis are to contribute toward the understanding of how to locate wall-base channels, and a better understanding of their function as winter juvenile salmonid habitat. Fundamental to location of each channel is knowledge of its existence. Chapter one presents a watershed-scale protocol for the detection and mapping of wall-base (and other) channels which are not on present maps. The protocol involves the use of a geographic information system to automate the location of geomorphic areas which have a high probability for the existence of wall-base channels, a remote sensing thermal infra-red scanner to detect them, and a procedure for mapping from the scanner images.
Chapter two explores the physical attributes of the individual channels which may affect their quality as fish habitat. While certain wall-base channels are important rearing areas for coho salmon fry (Peterson 1980, Brown 1987, Swales and Levings 1989), and pond morphometry can affect overwinter survival and growth (Peterson 1982a, Zarnowitz and Raedeke 1984), little is known about the variability of wall-base channel characteristics and their effect on such fish use. Chapter two presents the results of a study assessing fish use and condition in relation to certain physical factors of wall-base channels. Taken together this study provides a means of improving our inventory and furthering our knowledge about fish use of wall-base channels.