Decades of erosion had carved out a 3-m (9.84-ft) drop along a 180-m (196.9-yd) stretch of the Red Deer River’s bank, which cuts through the park. The eroded section also is directly adjacent to a picnic and recreation area. As the park’s popularity and visitor traffic have grown, the sharp drop-off posed a safety concern that required the slope to be rebuilt.
The slope’s design needed to meet three criteria: The slope had to be safe, it had to blend in naturally with the rest of the park, and it had to survive a one-in-10-year flood event. “One of our main concerns was safety,” said Dick Vogelsang, capital-projects coordinator for the Alberta Environmental Protection’s Natural Resources Service, Vulcan, Alberta. “Yet you’ve got to have something that looks nice. A standard retaining wall of concrete and large rock would not have been very appealing.”
The park had several alternatives for solving the erosion problem. The first was to line the slope with riprap. This idea was discarded after assessing pricing and transportation logistics--the cost of transporting the riprap 150 km (93 miles) to the park made this alternative too expensive.
Erosion-control blankets also were considered. Although a river bank lined with erosion-control blankets would have been sufficiently durable and would have met the project’s aesthetic criterion, this idea was rejected because the project’s engineers feared the blankets might be washed away before they could become secured to the bank.