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

More research is needed to determine accelerated erosion rates near coastal structures

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)

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 • Unsustainable demand on taxpayer resources • Public underwriting of private risk • Incentivizes high-risk development & rebuilding

ECOLOGICAL IMPACTS • Accelerated erosion rates on beaches near structures • Sediment starvation • 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

• Historical shoreline transect data mapped on ArcGIS v10.1

• Measured differences of transect sets by year of data collection.

• Calculated erosion rates for transect sets and rate and percentage changes over time.

• Superimposed graph sections on Google Earth projection of coast.

• Shoreline data source: Mass Office of Coastal Zone Management Historic Shoreline Change Project

• Coastal structures and repair cost data source: Unpublished datasets from Mass Office of Coastal Zone Management, used with permission.

Method for

Erosion Rates

Challenges: • Accuracies of

shoreline measurements

• 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