USGS Washington Water Science Center
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9722-D5G - Mapping Inactive Side Channels for Habitat Protection and Enhancement of Tributaries in the Mid-Columbia River Basin - Completed FY2008
Problem - The operators of privately owned hydroelectric dams in the Mid-Columbia River basin are required by licensing agreements to compensate for the unavoidable mortality of endangered salmonids (estimated to be 9 percent) through stream rehabilitation/enhancement (with a target compensation of 2 percent) and hatcheries (7 percent). Siting potential project areas for in-stream structures, side-channel reactivation, and hatchery acclimation channels by field work alone is problematic, as inactive side channels may be subtle features difficult to identify visually or may be hidden by riparian vegetation. A method to quickly identify side channels is needed so that field studies of other relevant factors, such as channel substrate, vegetation shading, and physical access, are most efficiently focused. Additionally, information on the relative height of these channels above the adjacent river surface elevation is needed as a first step in assessing project potential.
Objective - The objective of this proposed project is to identify, using high-accuracy, high-resolution elevation data, inactive side channels and their relative height above the adjacent river elevation. This information will subsequently be used by the Mid-Columbia Tributary Committee (Tributary Committee) to determine the best locations for detailed, on-the-ground analysis of the potential for successful protection or enhancement projects, such as in-stream structures, side-channel reconnections, or juvenile hatchery salmonid acclimation facilities.
Relevance and Benefits - This study will contribute to the USGS mission of "providing science for a changing world in response to present and anticipated needs to expand our understanding of environmental and natural resource issues" (Groat and others, 2000) by broadening the knowledge of stream morphology in the mid-Columbia Basin. It also will serve a broad coalition of governments, agencies, and tribes that comprise the Tributary Committee seeking to protect and enhance the natural ecological systems that support endangered and other aquatic species in rivers and streams tributary to the Columbia River.
Approach - LiDAR and digital color orthophotography have been used on the Dosewallips River on the heavily forested Olympic Peninsula in western Washington to identify inactive side channels. These methods will be adapted to the Mid-Columbia River basin.
The approach developed on the Dosewallips River was to use multiple lines of evidence gleaned from elevation models, slope models, and digital color orthophotography to digitize directly on a computer display the location of inactive side channels. This approach will need to be adapted to the floodplain geomorphology in the Mid-Columbia River basin and the broader, evolving objectives of the Tributary Committee.