Coastal erosion is a natural process. Beaches typically erode in response to high energy winter waves, and then build up (accrete) again with the lapping summer waves. In unaltered conditions, longshore transport also carries sand from sources to sinks within the littoral cell.
However, historical development patterns quarantine sediment sources. Dredging navigation channels and disposing the sand offshore removes sediments from the natural transport system that feeds adjacent beaches. Installation of hardened shorelines prevents erosion of upland sand that would otherwise nourish beaches. Groins and jetties interrupt littoral drift. These alterations to natural coastal processes increase erosion rates at the shoreline. As Climatide’s Heather Goldstone also points out, sea level rise and increased storm intensity could really draw down our beaches. This is particularly true considering the limited sediment supply.
There is an interesting case study in Rhode Island of two communities considering all three approaches to coping with sea level rise and coastal erosion: armoring, reinforcing beaches, and retreat.
One of the alternatives we will be investigating for Narragansett is dredging sand from the mouth of the Narrow River, where it has accumulated from littoral drift, and placing it on a reinforced Town Beach. Regional Sediment Management (RSM), which attempts to close the loop of littoral drift and reuse sand from the same system, is a practice we favor at Woods Hole Group because it reduces costs, minimizes environmental impacts, and eliminates the uncertainty of having potentially incompatible grain sizes.