Geomorphic Mapping, Dosewallips River Completed

9722-BIX - High Resolution Geomorphic Mapping of the Dosewallips River Using Remotely Sensed Data: Method Development - Completed FY2004

Problem - The Port Gamble S’Klallam tribe in western Washington is making initial assessments of ways of protecting and enhancing aquatic habitat. As part of that work, and in response to recent listings of salmon under the federal Endangered Species Act, the tribe has asked the USGS to map current and potential aquatic habitat and other refugia such as pool/riffle systems and large woody debris (LWD) in the Dosewallips River. The Dosewallips is home to two listed species: Puget Sound chinook and Hood Canal summer chum. The Dosewallips River is on the east side of the Olympic Peninsula in Washington State and drains about 100 square miles into Dabob Bay, an arm of Hood Canal. The river is about 25 miles long and, because its headwaters are in the Olympic Mountains, has a steep gradient for most of its length, shallowing near the mouth at Dabob Bay. This project will be limited to the 12 miles below a waterfall that marks the upper extent of potential anadromous fish habitat.

Objectives - The objective of this study is to develop and evaluate methods to use LIDAR data and other remote sensing data to map abandoned and potential side channels, and other geomorphic features on selected reaches of the Dosewallips River.

Relevance and Benefits - This preliminary study of the feasibility of using remotely sensed elevation data and digital photography to characterize the geomorphology and aquatic habitat directly addresses three of the USGS-WRD priority issues (issue numbers are taken directly from OFR99-249 “Strategic Directions for the Water Resources Division, 1998-2008):

Issue 1: Effects of urbanization and suburbanization on water resources
The lower reaches of the Dosewallips River have seen the effects of development in that the channel has been isolated from the natural floodplain by levees and channel armoring. The historical floodplain will be assessed, allowing the tribe to subsequently quantify the amounts of habitat lost and evaluate the potential for restoration.

Issue 2: Effects of land use and population increases on water resources in the coastal zone
The logging of the Dosewallips basin had two detrimental effects on the river itself: first, the removal of LWD from the stream itself, and second, the removal of the LWD that would otherwise have eventually entered the stream. The consequence of these changes further altered the geomorphic evolution of the stream. Logjams that would normally raise the river level and provide it access to additional floodplain are gone, and many formerly active side channels are no longer occupied during low and medium flows. One objective is to identify abandoned side channels that may be reoccupied once historical levels of LWD are achieved.

Issue 3: Suitability of aquatic habitat for biota
This effort will identify current and future potential habitat for endangered species of anadromous fish.

Approach - The USGS and the Port Gamble S’Klallam tribe (PGST) will collaborate on the efforts. The tribe has mapped the river shoreline as depicted in the digital photography and performed limited field verification of existing LWD. The USGS will use LIDAR and orthorectified digital imagery (ODI) to map relative floodplain and terrace elevations, potential channel migration zones, abandoned historic channels, and other geomorphic characteristics identified in the ongoing method development. The analytical methodology as currently agreed upon for mapping are four or five (as time permits) approximately 1-mile long stream reaches representing different geomorphic and canopy conditions along the 15 miles of the lower Dosewallips River.