COASTAL DUNE FIELD CREATION TO MANAGE BARRIER ISLAND SEDIMENT LOSS AND PROVIDE INFRASTRUCTURE DAMAGE PROTECTION FROM FLOODING AND OVERWASH PROCESSES

A series of anchored sand dunes were created in a run-off channel on Santa Rosa Island, Okaloosa County, Florida (N30° 23'14” W086° 49'22”). The installation site is approximately 155 feet by 135 feet and lies at the north end of the run-off channel immediately adjacent to the lowest elevation bounded by the road bed. The design uses 10 anchored dunes of two geometric shapes that create a tortuous path for floodwater to follow. This artificial meandering path attenuates the energy of the flowing water and allows sediment to drop out of transport in the lower energy accommodation spaces of the anchored dune field.

This project attempts to create a series of anchored dunes that will retard the water flow in the run-off channel as it floods towards the road. The concept of anchored dunes uses burial of a permeable structure at the core of the dune. Once buried, the anchored dune resembles a normal dune in that there is no visible evidence of the buried structure. Only when the burial sand is removed by erosive means would the structure be visible.

In this experiment, heavy gage wire baskets lined with geotextile fabric are filled and buried to create the core of the dune structure. Individual 3'X3'X3' baskets are connected in a 5 unit string to create a 3'X15' rectangular units. The geotextile material allows groundwater to flow through the buried baskets. The 3'X15'basket units are connected and stacked together so that several units combine to make a core structure that is 6' high (relative to the bottom elevation). The entire structure is buried with enough sand to create a 3' thick dune face. Because the tops of the baskets are not closed, vegetation planted on the dune faces will be able to extend their root systems into the basket sediment.

Several advantages are provided by this design. The long fetch of impounded flood water is eliminated. Sand eroded from the beach will have several low energy accommodation spaces for deposition. Road shoulder erosion should be minimized. Sediment in the baskets will not have to be replaced. Vegetation rooted into the basket sediment will have an improved rate of survival. The permeable buried structure allows natural hydrological conditions to exist within the dune field.