WATERSHED RESPONSES TO FOREST PRACTICES STUDIED
28 September 2000 - DOE/Pacific Northwest National Laboratory

Researchers at the Department of Energy's Pacific Northwest National Laboratory have expanded the capabilities of a watershed model to make it possible to explore economic and environmental trade-offs of various land-use activities. The research is sponsored by the National Council of the paper industry for Air and Stream Improvement, or NCASI, and the U.S. Forest Service.

Called the Geographic Information System-based Modeling System for Watershed Analysis, GISWA could provide information on how alternative practices can be used to help avoid altering a watershed's natural processes. Forest roads have received attention recently for their potential effects on watersheds and wildlife habitat. The Clinton Administration ordered a moratorium in February 1999 on road construction in some national forests.

"With the new enhancements, this model could be a valuable tool for planning new forest roads for the least effects to a watershed and its wildlife habitat," said Mark Wigmosta, a senior research engineer at Pacific Northwest. "The watershed analysis model is designed to make the link between cause and effect."

GISWA simulates hydrologic conditions at thousands of locations within a single watershed to provide a detailed representation of water movement. This includes flow below the ground's surface, called subsurface flow, which may be redistributed when trees are harvested or roads are built. Forest roads often cut into hillsides, which can divert subsurface flow into culverts. The culverts then can route greater amounts of water at a faster rate into streams if a direct connection exists between the culvert outlet and the stream.

"As a result, changing stream flow can erode channel banks, transport more sediment and alter the stream channels," Wigmosta said. "All of these factors have the potential to affect fish habitat."

GISWA is an updated version of a watershed model Wigmosta developed during his DOE-funded postgraduate work at the University of Washington in the early 1990s. The original model, called Distributed Hydrology-Soil-Vegetation Model, showed how climate change could effect hydrology and water resources.

In 1998, Pacific Northwest researchers integrated their version of the distributed watershed model with a version from the University of Washington. Then they incorporated a GIS-based modeling system and data on logging road networks and stream channels. In 1999, Pacific Northwest researchers began developing graphical user interfaces and preparing a user's manual. NCASI is expected to test the latest version in the next year then evaluate it for potential use by the forest industry.

http://www.pnl.gov

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