The study examines the impacts of hard engineered coastal structures like seawalls on shoreline erosion rates and the economic costs in Massachusetts. It highlights unintended consequences, such as increased erosion and financial burdens on taxpayers, advocating for more research to inform coastal adaptation and resilience policies. Key findings suggest that retreat from the coast may be optimal in many areas due to unsustainable risks and costs associated with these structures.

1. Armoring the Massachusetts Coast: Increased Protection or Added Risk?
ABSTRACT Armoring the coast using structures like seawalls and revetments has been a traditional response to the natural changes in shoreline configuration. But hard engineered structures like seawalls can have unintended consequences on nearby beaches and properties. In addition to the environmental and property impacts of these structures, the enormous costs of construction and maintenance are proving financially unsustainable for taxpayers. With the increased risks to coastal property, infrastructure and livelihoods that are the inevitable results of rising sea levels and increased coastal storm activity and intensity, it is time to examine the effects of engineered hard protection structures. Political and societal impulses to armor the coast must be informed by the results of the study of the actual impacts of these structures. This study examines the change in shoreline erosion rates before and after the installation of hard engineered structures in two Massachusetts coastal communities and some of the economic costs involved. This initial look at the relationship between shoreline protection structures and accelerated erosion demonstrates that this topic is important for further research to support the decisions that will be made about the development and implementation of effective and equitable coastal adaptation and resilience policies.
Lisa Granquist, PhD candidate, Law & Public Policy, Northeastern University
Guest Student, Marine Policy Center, Woods Hole Oceanographic Institution
INTRODUCTION
Armoring the coast using structures like seawalls and revetments has been a traditional response to the natural changes in shoreline configuration. But hard engineered structures like seawalls can have unintended consequences on nearby beaches and properties.
CONCLUSION & POLICY IMPACTS
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More research is needed to determine accelerated erosion rates near coastal structures
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It is now possible to estimate increased costs of risks faced by properties with no structures (both waterfront and inland) near waterfront properties with structures with Kriesel et al. approach (hedonic pricing models)
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Retreat from the coast likely now optimal in many places
References
Selected references. Complete list available upon request.
1.
Kriesel, W. et al (several, 2000, 2003, 2007), An economic evaluation of beach erosion management alternatives; Measuring the cost of beach retreat
2.
Massachusetts Shoreline Change Project, 2011. Mass. Office of Coastal Zone Management, Boston, MA.
3.
Tol, Richard S.J., R. Klein, R. Nicholls, (2008). Towards Successful Adaptation to Sea-Level Rise along Europe's Coasts, Journal of Coastal Research, No. 242:432-442.
4.
Titus, J. G., R. A. Park, S. P. Leatherman, J. R. Weggel, M. S. Greene, P. W. Mausel, S. Brown, C. Gaunt, M. Trehan, and G. Yohe. 1991. “Greenhouse Effect and Sea Level Rise: The Cost of Holding Back the Sea.” Coastal Management 19 (2): 171–204.
ECONOMIC IMPACTS
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Unsustainable demand on taxpayer resources
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Public underwriting of private risk
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Incentivizes high-risk development & rebuilding
ECOLOGICAL IMPACTS
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Accelerated erosion rates on beaches near structures
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Sediment starvation
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Decreased benefits of ecosystem services
Accelerated erosion rates near coastal structures
Harlow’s Landing, Plymouth, MA, 172ft stone revetment, built c.1959
Economic Data
Erosion Rates Data & Results
ArcMap v10.1 analysis of erosion rates before and after c.1959 installation of revetment
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Historical shoreline transect data mapped on ArcGIS v10.1
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Measured differences of transect sets by year of data collection.
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Calculated erosion rates for transect sets and rate and percentage changes over time.
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Superimposed graph sections on Google Earth projection of coast.
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Shoreline data source: Mass Office of Coastal Zone Management Historic Shoreline Change Project
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Coastal structures and repair cost data source: Unpublished datasets from Mass Office of Coastal Zone Management, used with permission.
Method for Erosion Rates
Challenges:
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Accuracies of shoreline measurements
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Effects of accelerated Sea Level Rise?
One town’s problem, Scituate, MA
Scituate
Plymouth
South Shore structures
$33 million to repair existing structures (2009 estimates)
2009 estimates
2009 estimates
Erosion rate bars are not to scale