GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 179-7
Presentation Time: 9:45 AM


KENYON, Taylor R.1, JOST, Robert P1 and BEASON, Scott R.2, (1)Mount Rainier National Park, Mount Rainier National Park, Mount Rainier National Park, L-117, L-201 Longmire Warehouse C/O NCR, Longmire, WA 98397, (2)Mount Rainier National Park, 55210 238th Ave E, Ashford, WA 98304

The dynamic alpine glacial environment of Mount Rainier National Park (MORA) has been a source of enchantment for millions of visitors over the last century, but also serves as a significant barrier to the preservation of infrastructure within the park. Climate trends over the last several decades have resulted in severe changes in river behavior, including massive increases in aggradation rates and observed flooding. The resulting damage has caused total loss of several roadways, destabilized trail networks, and a steady loss of access to much of the park. To combat these trends the park has recently begun to research and promote the use of methods which are new to the park Maintenance Division. The most recently employed methods include the use of targeted engineered log jams (ELJ’s), soil bioengineering practices, and rock barb flood mitigations. While these are all well accepted methods in many regions and professions, the extreme settings of MORA test them in ways they were not designed for. Our use of engineered log jams has been as a flood mitigation strategy focusing on small lengths of roadway under the threat of intense bank erosion from Tahoma Creek, a glacially sourced river carrying immense sediment loads and highly energetic waters. Normally these designs are intended to serve as adjustments to river planforms to reduce bank erosion, however our designs are placed to both protect from flooding events and the continuous erosion of a high-slope glacial river which has set its bank in direct proximity to a protected roadway. We’ve expanded the use of soil bioengineering strategies to stabilize slopes and create living structures well outside the normal riparian planting areas detailed by any manual we reviewed. The intention is to exploit favorable conditions to manually re-initiate the natural forest successional processes and begin re-foresting unstable hillslopes and trails. Rock barbs are a method designed as flood mitigations for low-slope and low-elevation rivers to mitigate continuous bank erosion, but have been used in MORA as protection for roadways from flood events on the White River. Each design is considered to be experimental in the settings we have installed them, and each has ongoing monitoring efforts attached to assess their viability as adaptive resource management practices for the NPS.