How To Stop Shoreline Erosion

One Redi-Rock manufacturer in western Montana hasn’t been making waves this season—but that’s a good thing when the goal is to stop waves from damaging a shoreline. Diversified Materials & Construction of Missoula has installed more than 22,000 sq. ft. of shoreline retaining wall so far this season, much of it in pristine but  turbulent Flathead Lake near Glacier National Park.

Construction below the high water mark of this beautiful glacial lake is overseen by the Confederated Salish and Kootenai Tribes who have strict regulations for shoreline protection retaining walls. The Tribes’ Shoreline Protection Ordinance 64A states that concrete walls should be used as a last resort, with wood or rip rap walls recommended as they provide a more natural look. This spring, however, the tribe was presented with an innovative alternative to traditional shoreline protection walls—an alternative that has been turning heads.

Blaine Wright, a Flathead Lake resident, needed to replace the rotting wooden retaining wall on the shoreline of his residence and also install a way for swimmers to enter and exit the water. Wright was unhappy with the durability of wood retaining walls and wasn’t pleased with the look of a concrete retaining wall. He was impressed, though, with a brochure for Redi-Rock retaining walls on display in the building permit office. Wright called local Redi-Rock dealer Mark Thomas at Diversified Materials and Construction, who was confident that Redi-Rock’s line of Big Block retaining wall products could meet the tribe’s stringent standards.

Tribal regulations demand that wave speed, upon hitting a wall, be slowed in order to prevent erosion and sand transport. On a poured-in-place wall, waves actually accelerate upon impact, so contractors must insert gussets every eight feet or so to slow the water—a tedious and time consuming job. Preliminary testing on Redi-Rock retaining walls showed that Redi-Rock’s unique stone texturing causes waves to accelerate significantly less than a poured in place wall. However, texturing alone was not enough to slow the waves to meet the tribe’s standards.

So Diversified got creative. Mark Thomas brainstormed various options, and Redi-Rock’s protruding planter blocks eventually presented themselves as the perfect solution to slow wave action and provide safety exits.  Protruding planters, which are usually used for ornamental plants in above-ground walls, were manufactured with the planting area filled with concrete. Staggered across the walls every 16 to 20 ft, the planters slowed wave speeds to well below the tribe’s standards. Since protruding planters rise 18 inches each, they exceed the height requirement to be considered a step; Thomas is calling the safety exits “modified ladders.”