Composite T-Head Groins for Erosion Control

Beach restoration with periodic renourishment has proven to be an effective solution in some locations. However, considering project size, location, erosion rates and the availability of a suitable sand source, some erosion problems may be more cost effectively addressed with erosion control structures. Additionally, depletion of sand resources for nourishment has resulted in an increased level of interest in structural erosion control alternatives. The most difficult aspect of erosion control structure design is avoiding downdrift impacts. Conceptually, an optimum solution might consist of a low maintenance erosion control structure, which interacts with the littoral system to perch a stabilized beach and maintain longshore sediment transport. Such a design has been applied since 1997 at four locations along the southwest coast of Florida. The composite T-groin design developed by Humiston and Moore Engineers uses the combined function of a nearshore breakwater and a low profile shore-perpendicular groin. Sheetpile are utilized in the core of the structure to establish a barrier to control sand losses through the breakwater segment, with a precise crest elevation to allow a desired level of overtopping. This establishes the shape of the salient formation. Weir sections are included in the design to limit the extent of the salient formation and promote lateral sand bypassing in the lee of the breakwater, or T-head, segment. Two permanent installations have been completed and monitored for over three years in southwest Florida. One of the most important documented findings of the monitoring collected thus far is that the design allows for sand bypassing to eliminate adverse downdrift impacts. Additionally, post storm surveys have shown that storm waves overtopping the low profile structures redistribute sand from the salients to adjacent beaches. This appears to be beneficial to adjacent beaches by increasing the sand supply under conditions which are otherwise conducive to erosion.