Yellowstone National ParkPage 174 of 225
Midshipmen Design a Fix for an Eroding Bluff at Lake Yellowstone Hotel
Yellowstone Lake behaves like a coast. Winds raise waves, ice can move sediment along the shore, and higher lake levels lead to bluff retreat. The NPS and Naval Academy had engineering students look at the bluff in front of the Lake Yellowstone Hotel. The result, an engineering capstone project completed in 2018–2019, is described by NPS and Naval Academy staff.
The Lake Yellowstone Hotel from the water (NPS photo/Jim Peaco).
A partnership for coasts
Since 2014 the National Park Service (NPS) and the U.S. Naval Academy have worked together on ocean engineering projects. The Park Service finds capstone projects in park units for midshipmen to complete their Ocean Engineering Capstone Design course. Early sites were Fort Raleigh in North Carolina (2014), Cumberland Island in Georgia (2015) and Fort Sumter and Fort Moultrie in South Carolina (2017). A 2013 request for help with shoreline erosion on Yellowstone Lake led to this project.
The arrangement benefits both sides. Parks get a feasibility-style report to move design along. When it can, the park houses three to five students and at least one instructor for two to three days, while the Academy pays for their travel. Fieldwork happens in the fall, draft reports are reviewed in the spring, and the final product is a design report, an oral presentation and a poster shown each April at the Academy in Annapolis.
An inland sea
Yellowstone Lake sits 7,733 feet (2,357 meters) above sea level and is the largest lake above 7,000 feet in North America. It covers 132 square miles (341 square kilometers), reaches 427 feet (130 meters) at its deepest, and has 141 miles (227 kilometers) of shoreline. It formed through glacial processes and rhyolitic lava flows that filled the 631,000-year-old Yellowstone Caldera. Its shoreline processes are like those in the 88 NPS ocean and coastal park units. Lake level rises and falls, meter-thick winter ice moves loose sediment, spring rain works on the bluffs from above, and sustained wind builds large waves and wind set-up.
At the Lake Yellowstone Hotel, erosion of the bluff in front undercuts a viewing platform and threatens the parking area and the road. NPS policy lets natural coastal processes continue, but allows changes when they threaten historic resources or park infrastructure.
Erosion in the glacial till along the base of the bluff is plain from the first look at the site.
What the team found
A team of five midshipmen under their professor visited the site from September 12 to 14, 2018, hosted by the park’s geologist and hydrologist. They concentrated on a 1,200-foot (366-meter) bluff along the hotel’s parking lot. Waves were cutting holes in the glacial till where it meets the beach, and rain was digging gullies at the top. Visitors who scramble down to the lake had also worn a social trail that made things worse.
The team laid out nine transects about 130 feet (40 meters) apart, measuring elevation from the bluff top toward the shore, and threw a sonobuoy by hand about 50 feet offshore to record depth. They built a three-dimensional model from the data, divided the problem into three, and set constraints: no harm to the environment or the park’s beauty, upkeep within the park’s means, and safe passage to the shore. Back in Maryland in spring 2019 they analyzed rainfall, drainage, lake levels, wind and waves, and chose among designs using weighted decision matrices.
The designs
| Problem | Design |
|---|---|
| Runoff eroding the top of the bluff | A swale with a pipe and culvert, lined with local vegetation, to redirect surface water |
| Waves undercutting the base | A stone revetment of sloping boulders and sand, matched to the natural boulders on the shore, topped with a compacted sand walkway |
| No safe path to the lake | A log stairway from the parking lot down to the walkway, using natural logs |
The swale design would run beside the road between the hotel and the shore and redirect runoff that would otherwise erode the top of the bluff.
Profile view of the rock revetment designed to protect the base of the bluff from wave run-up.
The complete design: swale, buried culvert, walking path, log stairs and revetment.
The team also gave the park a cost analysis of each preferred design. The park can use the designs in early feasibility studies; they will be weighed against other options such as moving the parking lot and road away from the bluff, and a full environmental review would come before any construction. The students, meanwhile, got a taste of open-ended, on-site engineering work rather than exams and labs, and the Park Service says further projects are under discussion.
Sources
- National Park Service, Yellowstone National Park & United States Naval Academy Partnership: Student Designs for Improved Shoreline Access at Lake Yellowstone Hotel; rewritten in hubnx's own words.