Coastal Erosion and Sea Level Rise
One of the most visual reminders of any major hurricane, flood, or storm event in Rhode
Island is a sudden, dramatic change in the shape of the state’s beaches. A visitor to
the shore will see that the coastline has retreated—sometimes literally
overnight—and large amounts of sand have vanished. As shoreline is lost, the risk of
damage to coastal properties increases.
Faced with the challenge of preventing and reducing losses due to coastal erosion,
decision-makers must answer some basic questions: What is at risk? What level of risk is
acceptable? What solutions are feasible, considering the financial resources available? An
understanding of erosion in the highly dynamic coastal environment is also essential to
the development of sound coastal hazard management policy.
Understanding Coastal Erosion
The majority of Rhode Island's ocean and Narragansett Bay coasts are
susceptible to erosion. The amount of erosion from storms - which are the biggest
causes of change on the shoreline - is directly related to their number, intensity and
duration.
Although they are susceptible to erosion, beaches form the first
line of defense against ocean waves, providing a buffer between the waves and coastal
properties. When beaches are cut back during storms - especially the more severe
storms that occur in fall and winter - they progressively lose this buffering ability,
making further coastal erosion more likely. (It is important to recognize, however,
that natural erosion and sedimentation - redepositing of sand - can vary among locations
and from year to year, depending on such factors as nearshore currents, ocean swells, and
the availability of sediment.)
As the beach erodes, vulnerable properties are placed at even
greater risk. A home constructed in the V-zone, or velocity zone, is likely to be
destroyed as the beach erodes and the barrier or headland is washed over by high water in
a storm.
Sea-Level Rise
Human beings have become active agents of change in the earth’s atmosphere and
oceans. As the rate of sea-level rise accelerates in response to greenhouse warming, we
may see an increase in coastal erosion. While sea level has risen and fallen in the past,
these changes occurred over hundreds to thousands of years. We are now facing rapid
sea-level changes on a scale of decades.
Higher sea levels could affect the coastal zone in a variety of ways, including greater
shoreline retreat, increased coastal erosion, property destruction, and saltwater
intrusion into bays, rivers, and underground water resources.
In addition, a general elevation in the water table could result from sea-level rise.
This could lead to the failure of both septic systems and other drainage systems, such as
storm drains, which need to be located at a certain elevation above the water table. This
problem could be seen in over 58 percent of Rhode Island’s coastal areas. Elevation
of the water table would also affect the river drainage systems of Rhode Island by slowing
down runoff and increasing the risk of flooding.
Reducing the Risk
Coastal erosion and sea-level rise have the potential to affect the majority of the
population, as well as the economy and use of natural resources in the Ocean State.
One past approach to reducing damage from coastal erosion has been the use of
engineered coastal protection measures. However, because the coastal system is so complex,
these techniques are not effective in most locations, and have caused additional problems,
such as changes in sediment supply along the shore.
To reduce coastal erosion, additional building or public infrastructure in hazardous
areas must be avoided. Beach replenishment (replacing sand in eroded areas) and other
"soft" structural methods should be used instead of other protection methods,
such as revetments, that were unsuccessful in the past.
A 100-year storm is one that, in a given year, has a 1-percent chance of
striking. While this may sound unlikely, we have seen such a storm in recent memory: the
great hurricane of 1938.
The coastal V-zone is an area defined for insurance purposes and categorized by
elevation above sea level and, to a lesser extent, distance from the shore. All locations
in the V-zone are considered to be "subject to battering waves."
