WHAT IS IT?
Riprap is a heavy stone facing (armor) on a shorebank used to protect it and the adjacent upland against wave scour. Riprap depends on the soil beneath it for support and should be built only on stable shores or bank slopes.
ENVIRONMENTAL CONSIDERATIONS
Stabilizing shore banks with shrub and tree vegetation provides excellent habitat for fish and wildlife species. It also provides a vegetated buffer strip along the lake capable of taking up pollutants and nutrients (such as phosphorus). The application of riprap requires the use of an approved GEO-TEC filter fabric as an underlayment prior to the placement of the riprap.
WHAT IS RIPRAP COMPOSED OF?
Riprap is composed of three sections: the armor or stone layer, the filter layer, and the toe protection. Typical armor is composed of rough, angular rock. The second component, the underlying filter layer, supports the stone against settlement, allows groundwater to drain through the structure, and prevents the soil beneath from being washed through the armor layer by waves or groundwater seepage.
In certain cases, overtopping of the top of the riprap slope may be a factor which needs to be considered. The top of the slope can be protected by including a stone overtopping apron in the design.
STONE SIZE
To assure that a riprap shoreline will remain stable, you must specify the size of the stone to be used. Stone selection is a factor of both personal preference of aesthetic design, as well as erosion control from wave activity. Larger stone may be placed where main channel wave action is greatest, and a thickness depending on the height and slope of the bank. Including a mixture of smaller stone sizes will ensure the small voids in the rock mix are filled.
