THE WESTSIDE ROAD: PHYSICAL FLOOD PROTECTION IN MOUNT RAINIER NATIONAL PARK, WA

The Westside Road in Mount Rainier National Park (MORA) provides access to six major trailheads & fourteen hiking destinations. Over the last 40 years the 20 km road has sustained severe damage from almost annual flooding and debris flows. While these processes are not considered out of the ordinary for the glacier fed rivers flowing off Mount Rainier recent climatic changes are suspected to be driving an increase in the frequency of extreme events. Relocating the road is precluded by its proximity to wilderness areas that would require an act of Congress in order to move it; this & limited budgets have compelled park managers to seek a solution that will allow the road to remain accessible to the 50,000 annual visitors that have historically traveled the Westside Road. To address the Westside Road Problem a three tier hazard evaluation model has been developed that involves: (1) hazard assessment, (2) mitigation strategies, & (3) implementation/construction. The efforts of GIP research since 2013 have resulted in the development of an experimental protection strategy that is designed to extend the life of the Westside Road & reduce annual maintenance costs. Traditional construction techniques utilize rock & loose sediment as material for park roads. In MORA, the rivers are capable of transporting material of far greater size relative to the material composing the road. During a flood event where the water rises and intercepts the road, the fill material is entrained by the river and erosion ensues. The mobile sediment is deposited downstream negatively impacting aquatic habitat & threatening park infrastructure.

During the summer of 2016, construction began to install flood protection structures that utilize wood & rock. The Large Woody Structure (LWS) is designed to mimic naturally formed log jams & was designed based on standard engineering principles. After the installation of the LWS is complete, a second phase construction will take place using phyto-engineering concepts & involves the planting of pioneer species such as the Sitka Willow in order to revive the riparian gallery forest along Tahoma Creek's edge. To date, this project is unique in MORA as it is the first to combine rock, wood, & live plants in an effort to create low-cost, effective solutions to reducing the damages that result from geologic events.