Eagle Creek Reservoir has had a long standing erosion control problem along the banks of the shoreline due to the annual fluctuating lake level of 5 feet. Erosion had been documented in a 1994 study compiled by Wabash Resources and Consulting for the Indianapolis Department of Parks & Recreation. Several property owners, south of Hobie Beach, which is on the south side of the 56th Street Bridge and the east side of the reservoir, decided to address the erosion issues at their docks. The erosion and deposition of sediments from the shoreline made utilizing their docks nearly impossible; therefore, the homeowners hired a contractor to dredge the areas surrounding the docks. This dredged material was then used to reconstruct the shoreline. Shortly after reconstruction, the shoreline erosion began all over again. Reconstructing a shoreline with dredged soils is difficult and not generally accepted as dredged soils are typically highly erodible.
In 1996, the homeowners contacted Jim Blazek to discuss strategies to stabilize the bank. Due to costs and concerns of permitting a section with riprap, the homeowners asked how they could minimize their burden as it was escalating beyond their means. Ignoring “the rules” that D2 Land & Water Resource had learned from overseas experts, the cross section included a coir log, which was plugged with plants on-site, coir mat & seeding on a 4:1 slope. What fundamental rules were ignored in this section? 1. Slope gradients at or below the normal pool water level were not 10:1 or less with a 5’ vegetative buffer zone for a 12” wave height to dissipate. 2. If the slope gradient at and below the normal pool water level is greater than 10:1, hard armor is to be used at the toe of slope in addition to the vegetative buffer. 3. The hard armor is to be placed at and below the normal pool with a transition to the vegetative components above.
After the failure of the previous system, a new cross section was installed in 1998. The new cross section included a rock roll hard armor at and below normal pool, a 12 inch diameter coir log, reconstructed on a 10:1 slope with geogrid reinforcement for a buffer zone, two secondary coir logs at the top of the slope to aid in a grade elevation change and 5:1 slope to the existing property grades. See the below cross section for the specific layout.
Although failure did occur with the original cross section, the failure was not due to the fault of any products, but rather, giving in to the requests of the homeowners to reduce costs and apply the system components outside of their limitations. In 1998, the cross section that was proposed included all the rules of a hard armor toe, vegetative system above normal pool, buffer zone, and decreasing the slope gradient. Since the installation of this system, erosion at this location has been stopped. This project proved that the bank stabilization rules in the Coir Log Design Guide are in place for very specific reasons and should never be ignored. A very valuable lesson learned from this particular project by all.
