TECH TOOLS FOR UNDERSTANDING RIVERS AND FLOODPLAINS: MAPPING MIGRATION ON THE MIGHTY UPPER NISQUALLY RIVER

For roughly 364 days of the year, the Nisqually River on the border of Pierce and Lewis County, WA is a picturesque stream whose banks provide shady overlooks on which to view snow-capped Mount Rainier and the rugged Cascades. It is that other day of the year that the river shows it ‘teeth'. Floodwaters laden with sediment and debris derived from glaciers and landslides have change the river's path, creating new ‘river side vistas' and extensive gravel bars on the floodplain near Ashland, WA. It is that rare day that County regulators and emergency management officials want to know more about.

Homes sites with vistas, babbling brooks, and swimming holes are now at a premium. Often, regulators are faced with convincing arguments to allow development to occur adjacent to the river or on a bluff above. The Nisqually valley features, which include multiple river terraces of varying erodability, a history of large-scale channel avulsions, rapid channel changes, and disconnected levee-systems, make if difficult to interpret what the river will likely do in the future. An approach we used combined remote sensing technology and a new modeling process, a Relative Surface Model, to help regulators make better decisions on allowing riverside development and protecting existing infrastructure.

This case study will discuss some of the challenges of mapping gravel-bed rivers with high sediment and debris yields. It will also make recommendations of GIS/Remote Sensing tools to use. Finally we will display the Channel Centered: Relative SurfaceModel, created for the Nisqually River, which saw the brunt of the impact of the November 6th, 2007 storm event.