Geologic Publications for Mount Rainier
Assessment, restoration, and management of the North Puyallup Trail, Mount Rainier National Park
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Taylor R. Kenyon
M.S. Earth and Space Sciences Applied Geosciences (MESSAGe) Thesis
University of Washington
The N Puyallup Trail, on Klapatche Ridge in Mount Rainier National Park, was originally the end of the Westside Road. The N Puyallup Trail has developed issues of surface erosion and landsliding since the area east of Klapatche Point was converted to wilderness area in 1988 (Owens, 2006). The wilderness designation limits the park's ability to provide cyclic maintenance using motorized equipment. As a result many features on the trail are damaged by infilling of soils, erosive damage from the lack of surface water management, and landslides (Owens, 2006). These conditions have resulted in damage to the trail surface and the production of harmful sediment inputs into the N Puyallup River, home to the endangered bull trout (ECOS, 2015).
A major task for this project was to determine and catalogue features on the site worthy of priority status for restoration or repair. The ultimate goal of the investigation was to recommend repairs that would protect the road surface while also minimizing the production of fine sediment and landslides that reach the N Puyallup River. In doing so, this project helps safeguard both the historic trail and the sensitive river ecosystem downslope from further harm.
My results indicate that the most significant concern is unmanaged surface water on the trail. These flows have led to surface erosion to the trail surface and fill slope, deposition of sediments onto the trail surface, and shallow landslides. In many cases issues of drainage occur in combinations at a single point. This can be seen as deposition of alluvial materials coming from multiple channels, excess water incising the trail surface and being pirated down the road grade, and incision leading to a point where the flow path is occasionally directed off the fill slope causing erosion and mass wasting.
Debris flows are the most common form of mass wasting on the trail, and most of these have surface water piracy as either triggers or at least contributing to their instability. All debris flows on site are sourced from the fill slope of the trail. Most debris flows on site transport material into pre-existing channel convergences, but some have scoured new paths downslope that are now being occupied by pirated surface water flows. Rockfall occurs across the length of the trail on several headwalls with slopes greater than 45 degrees, and appears to be independent from drainage problems on site. Points posing the greatest threats to the trail include upslope headwalls producing both dry rockfall and shallow slides. Colluvial hollows left by debris flows show headward retreat, narrowing the width of the trail and oversteepening slopes. The steepest sections of ridge have rockfall accumulating near the fill slopes, narrowing the trail further and loading the already at-risk slopes.
All points mapped for this investigation were at risk of damaging the trail surface, affecting the water quality of the N Puyallup River via fine sediment inputs, or harming the overall quality of the river habitat via landslides. The combinations of surface erosion and mass wasting types were the deciding factor as to what designs are recommended at each point. The list of repairs includes culvert restoration, waterbar installation, segments of ditch clearing, spillways for drainages, soil bioengineering to add root stability, buttressing of colluvial slopes, and gabion reinforcement.
The top priority is the cleaning or replacement of culverts. Culverts in my designs are used to handle areas that need to pass high or constant discharge, and their flow paths are built to drain into stable channel networks. I have recommended that they be replaced by high volume relief drainages to allow them to be maintained without the assistance of machinery. Waterbars should be used to provide erosion-resistant flow paths, allowing us to direct water toward more stable outlet locationsalong the fill slope. These will be installed in multiples, enabling the new drainage to handle various flow levels and be able to withstand at least one slope failure. Using waterbars helps reduce the problems of water piracy and direct surface water away from the crowns and scarps of mass wasting features.
Soil bioengineering is a low-cost, easily-installed approach for reinforcement of unstable soils along the site, encouraging a progression toward a naturally stable state (Polster, 2002). I have recommended the use of wattle fences to reinforce the headwalls of colluvial hollows, and live staking on oversteepened fill slopes. I also recommend the use of live staking as buttressing measures intended to reduce effective slope and act as a colluvial storage system. Rockfall should also be unloaded where it is piled near stone walls, near steep slopes, or narrows access to the trail.
After repairs are completed efforts should made to establish annual or bi-annual monitoring and maintenance procedures to ensure that the trail progresses toward a stable state, remaining accessible to visitors and environmentally friendly. Maintenance actions will also be partly dependent on the monitoring process, as some features will not need maintenance unless they fail. This will help determine when maintenance is required and where it should be focused. Regular maintenance procedures should be performed every 2 or 3 years because the chosen designs should make most of the structures somewhat self-cleaning and fail-safe.
Investigation should be performed for any components of the site that I was not able to. The features that I think will need better investigation are of the condition of each of the stone walls, and the natural channels that contact the trail from upslope. For walls investigation should note the slope of the front face and the integrity of walls to see if their condition is deteriorating. Channels contacting the trail from upslope should be investigated to assess the discharge and flow paths of each, allowing for continued monitoring. These channels exist at some of the most unstable points on the trail and have and are generally the primary source of surface water at those points. Increases in discharge or changes in flow path on the trail could necessitate that changes be made to the local drainage networks and other reinforcements.
If all these plans are followed the N Puyallup Trail should remain stable and even become a higher quality experience for park visitors.
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In Text Citation:
Kenyon (2016) or (Kenyon, 2016)
Kenyon, T.R., 2016, Assessment, restoration, and management of the North Puyallup Trail, Mount Rainier National Park: M.S. Earth and Space Sciences Applied Geosciences (MESSAGe) Thesis, University of Washington, 50 p..