Managed Retreat

On the soft end of that spectrum are nature-based solutions which are engineered solutions designed to mimic or enhance natural processes, such as living shorelines and dune restoration. 

On the hard end are traditional engineered solutions such as revetments, seawalls, and bridges. 

The best solutions will be site specific and combine strategies, integrating green and gray designs for hybrid alternatives.

The selection of strategies will need to consider coastal processes and how a selected approach may affect downstream assets and infrastructure.

Managed retreat is the coordinated process of relocating infrastructure away from vulnerable coastal areas in response to episodic or chronic threats. It is important that the transition of communities inland is done voluntarily and equitably.  

However, it is worth noting that many road and road segments that have been prioritized for adaptation have been identified not only because of their exposure, but also because of their criticality to the transportation network so retreating or abandoning are not options. 

Herring Cove Beach North Parking Lot, Provincetown, MA (2018-2019) Sections of the north parking lot, asphalt revetment, and coastal areas near the south parking lot have sustained damage due to wave action. The final plan was developed by the Cape Cod National Seashore in consultation with agencies and the community, based upon coastal science and engineering practices to be responsive to shoreline change, projected sea level rise and visitor use. The purpose was to develop a long-term strategy for a one-time retreat including removing existing revetment and parking lot and replacing the parking lot 125 feet inland (west) and 15 feet higher in elevation. This strategy planned for expected sea level rise, continental subsidence, and major coastal flood events having a predicted 100-year occurrence. 

Breakwater Landing Beach, Brewster MA (2016) The town beach parking lot located at Breakwater Landing experienced repeated damage from coastal storms. Using managed retreat to address coastal erosion, the town decided to move the parking lot upland, away from the shoreline. The managed retreat also involved restoring the dune and planting hundreds of dune grass plugs, installing an erosion fence, and storm water bioretention system. 

In many coastal locations standard operating procedures have been established and developed internally to improve preparation for and response to coastal storms and flooding with the goal of maintaining service or restoring service as quickly as possible.

Most road and road segments fall into this category either because an alternative has not yet been determined or because it is the most viable option for the foreseeable future. However, this is an expensive and short-term option and most municipalities are looking to reduce and eventually eliminate ongoing maintenance requirements.

Cape Cod municipalities may not have sufficient alternative transportation modes and routes available in particularly sensitive locations to provide backup and continuity of service in responding to extreme weather events. Increasing redundancy to provide alternative modes or routes should be a priority. 

Coastal engineering protection solutions often combine soft and hard strategies for a hybrid solution.

Future infrastructure projects need to be planned and designed to withstand future climate conditions and extreme weather events. This is becoming easier as availability and confidence in climate data and projections improves. 

Dr. Bottero Road, Dennis, MA (2011-ongoing) To address coastal erosion of the beach, dune, and Dr. Bottero Road caused by coastal storms, the town of Dennis is considering various alternatives. One possible strategy is to nourish the beach and dune and construct two armored stone groin structures. This road provides the only access to Chapin Beach and the Aquacultural Research Center (ARC). This alternative improves coastal resilience, maximizes the beach width, and minimizes the groin length. In addition to protecting the roadway, the wider beach in this alternative will provide habitat for Piping Plovers and minimize the impacts to the offshore patches of salt marsh.  

Managed retreat may not be necessary for every low-lying road. In some cases, alternative strategies for resilience, such as “Protect” or “Accommodate,” as detailed in the Adaptation Strategies section, may be more appropriate for roads identified as having high criticality. After a full analysis of alternatives and feasibilities, if managed retreat is the recommended path forward for a low-lying road segment, it is necessary because the location of the transportation infrastructure is significantly threatened by ongoing flooding, and it has low criticality. Managed retreat is a strategy that is used when alternative strategies are not appropriate, cost-effective, or sufficient to address the risk. 

Some alternative strategies to retreating or relocating low-lying roads include:

• Maintain
• Increase redundancy
• Protect
• Accommodate

See the "Adaptation Strategies" section of this StoryMap for details on the above, and the "Fact Sheets" section for additional details on ways to manage flooding risk to low-lying roads.

If Cape Cod towns do not act to manage low-lying roads in ways that promote coastal resilience, then we can expect increased damage to infrastructure from sea level rise and storm surges that will be more difficult and expensive to repair. Inaction can also lead to increased negative impacts on the safety of residents and visitors, as well as the environment and natural resources.