ANALYSIS OF CHANNEL WIDTH CHANGE ON THE NISQUALLY AND WHITE RIVER WATERSHEDS WITHIN MOUNT RAINIER NATIONAL PARK
This study used open-source GIS software to quantify the change in active channel width using historical satellite imagery available through USGS EarthExplorer for the Nisqually and White River. The study area encompassed a 10 km stretch of the Nisqually and 15 km along the White River, each with a time series including five images spanning from 1955-2019. This included imaging from 2006 and 2009 to encompass a special interest in a historic flooding event that took place on November 6th and 7th of 2006 throughout MORA. This flood damaged park infrastructure and created limits to visitor access with repercussions that are still being addressed in the park to this day.
A GIS model was created to automate the process of extracting channel width measurements from active channel margins. The resulting widths were assessed to evaluate channel width over time and identify areas of significant change as a result of flooding or other environmental processes. Following the 2006 flood, we noted a 27% increase in the average channel width of the Nisqually and a 21% increase in the average channel width of the White River. Combining our results with field surveys and hydrologic records allowed us to confirm flooding events as drivers of the mapped channel width change in these areas. Using these river monitoring efforts in MORA can aid park management in making scientifically-backed decisions. This procedure can be applied in other river systems to analyze channel margin change and, when coupled with site specific data and context, can assist in understanding past and future hazards.