FLOURESCENT SAND TRACING IN COASTAL ENVIRONMENTS

Clients: U.S. Army Corps of Engineers, U.S. Coast Guard

The study of coastal sediment transport is complex. Attempts to quantify sand movement through traditional means such as direct observation, coastal surveying and area photo analysis are not always sufficient. An alternative method that we have successfully applied involves the use of beach sand that has been coated with fluorescent dye. Following release, sand samples can be collected over time and viewed under a "black" light to determine the extent of fluorescent sand content. Subsequent mapping of the dyed sand allows an interpretation of sand movement direction and transport rate.

Site of Flourescent Tracer Study, Crescent Bay, Laguna Beach

AREAS OF APPLICATION

Study of Shoaling - San Diego Harbor

  • Release of two dyed sands (red and green) at two possible source locations to determine shoaling mechanism

  • Sediment collection (both above- and below-water) over a two month period indicated the presence of only one dyed sand color in the shoal, thereby definitively establishing the source

COASTAL PROCESSES IN A POCKET BEACH - CRESCENT BAY, LAGUNA BEACH, CA

  • Allowed a determination of sand movement within this confined cove over a period of one year

  • Following release of the tracer sand, winter storm erosion transported the beach sand offshore

  • Once the sand returned to the beach in the spring, dyed sand was found on the beach, rather than up- or down-coast

  • The study provided evidence that the sand within Crescent Bay remained within the cove and was not lost or replenished by sand moving alongshore seaward of the rock headlands that bound the bay