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Accelerated Erosion and Sea Level Rise: The Case for Adaptive Policies
| Lisa Granquist Northeastern University (PhD candidate, Law & Public Policy), Woods Hole Oceanographic Institution (Guest student) |
What happens when a shoreline experiences 50 years of erosion in a matter of months? Or 50 years of sea level rise in 2 days due to increase in tide range? Do policies designed to respond to decadal processes adequately and fairly address situations of accelerated erosion and sea level rise? Are there more aggressive actions that might be suitable to save existing structures and property without negative environmental impacts?
There are two categories of cases: Type I cases are those with a history of stability with period(s) of accelerated erosion or sea level rise returning to stability and Type II cases, those with accelerated cycles of erosion or sea level rise returning to historical cycles of accretion. In these cases of short and mid-term cyclic processes, adaptive policies that allow more aggressive actions might be suitable to save existing structures, since the impacts on the shore processes will be mitigated over the decadal timeframe as higher water levels (i.e. increased tide range, wave heights) and resultant shore erosion processes will diminish.
Type I cases presented are Pleasant Bay in Cape Cod and Siasconset Beach on Nantucket Island, both in Massachusetts. Type II case presented is Plum Island, Massachusetts. The current one-size-fits-all policy responses resulted in decreased property values and property loss and have not necessarily provided environmental benefits. In many cases dwellings simply collapsed or needed to be removed as a result of accelerated processes. There is no doubt that in some instances structures should never have been built in these sensitive areas. However, where the decadal processes would return the shoreline to or close to pre-existing conditions, planning and implementation strategies designed for different time scales could reduce property loss and subsequent litigation while fully protecting resource values.
In Type I cases, the accelerated events have clear beginning, middle, and end stages. For example, around Pleasant Bay and its enclosing barrier spit, Nauset Beach, changes in tides have been identified and shoals have been stable in the past. Recently-formed tidal inlets on Nauset Beach have temporarily increased the tide range by up to 0.3 m. Historical analyses show that this inlet will migrate south or close. At Plum Island, a Type II case, shifting off-shore bars, not instantaneous sea level rise, caused the accelerated erosion events. Specific locations experienced rapid isolated short-term increases in erosion rate. There is evidence that the trend will return to its historical rate.
Adaptive policies to address these short and mid-term accelerated conditions are needed. Proposed solutions might include zoning variances and wetland resource area responses that temporarily allow more aggressive protection methods than in other settings where the decadal processes are dominant.