HISTORICAL ANALYSIS OF THE CHANGE IN PERCENT FINES DURING BEACH NOURISHMENT

The loss of sand from Florida’s beaches and coastal systems is a serious problem that affects not only the coastal system but also the economic livelihood of Florida’s coastal communities. Identifying offshore sand resources in compliance with regulatory requirements for future beach nourishment projects is critical in order to sustain Florida’s beaches.

It is well understood that some portion of in-situ fines are lost during the dredging and beach placement process. Presently, regulations are necessarily enforced on the in-situ dredge material as a conservative assumption of the fine content of the material that is placed on the beach or nearshore. This assumption is understandable given the scarcity of data on fines loss, but it has the negative effect of limiting or completely eliminating many offshore sediment sources or opportunities to beneficially use material with higher in-situ fines contents. Understanding the change in fines content provides an opportunity to better manage valuable sand resources, while not endangering the environment.

This study quantified the change in the percent of fine-grained sediment between the in-situ sand source and placement on the beach during hydraulic dredging. Approximately 70 beach nourishment projects in Florida were reviewed; historic and recent data collected from borrow area and beach placement sites indicate that methods exist to provide justification for a fundamental shift in the current approach of sand source management.

This data set shows that 69% of the projects experienced a loss of more than 50% fines, while 90% of the projects experienced some level of reduction in fines during the dredging process. This suggests that it can be reasonably assumed that similar projects would see a change in fines during beach nourishment, with a 50% loss of fines being a conservative estimate. Permitting sediment sources with a higher fines content for beach nourishment and for beneficial placement will reduce the need for expansion of offshore dredge material disposal sites and upland dredge material management areas, increase the sediment available for beneficial use, allow more sediment sources to be used, warrant re-evaluation of existing sediment sources for a greater sediment yield, and offer additional Regional Sediment Management (RSM) opportunities.