Lake Lemon is a reservoir formed by Lake Lemon Dam on Beanblossom Creek approximately 10 miles northeast of Bloomington, Indiana. Originally, the lake was built to control water levels for Bloomington’s (and surrounding areas) drinking water supply. Today, Lake Lemon is mostly a recreational site. The constant wind and wave energy throughout the years had resulted in erosion along the entire shoreline. Compounded with the fluctuating water levels, the zone between well-established vegetated banks and the eroding toe of slope was expediting. The eroded bank consisted mostly of infertile subsoil and rock making re-vegetating the banks difficult. Any potential solution for the site would require all the following: create a wave break to dissipate the wind and wave energy, provide a specific plant community in the hostile growing environment and soils, allow for construction with very limited access, and require little to no long-term maintenance.
After the Lake Lemon Conservancy District (LLCD) received a LARE (Lake and River Enhancement) grant, they selected Donan Engineering to help administer the grant and address the shoreline erosion. Donan Engineering contacted D2 Land & Water Resource to evaluate the problems at Lake Lemon. After a site visit, D2 proposed the following design:
To combat the wave and wind energy, pre-fabricated 22 inch rock rolls filled with 4 to 6 inch riprap would be placed at the toe of slope. The rock rolls would provide the armor for boat and wind energy while creating an elevation for the introduction of vegetation. Upslope of the rock roll, a pre-vegetated 16 inch coir log with knotless brown polypropylene netting at a density of 9 lbs/ft3 would be installed. This type of coir log in terms of density and net type was selected for its proven performance history in waterway and shoreline bioengineering projects. The coir log would be pre-vegetated with native wetland species and provide a mechanism for controlled species introduction. The compressed coconut coir log, once pre-vegetated, can offer moisture and nutrients to the vegetation while establishing in its new location. This proposed cross section offered LLCD a low/no maintenance way to introduce these difficult plant species.
The results of this system were immediate. It provided a self-sustaining solution that allowed for sediment deposition behind the coir log for natural slope refilling, the rock toe allowed for energy dissipation and created an environment to allow the native species to establish. The site continues to be monitored, and even after nearly a decade in place, the system is still providing the erosion protection and habitat development.