Assessing Nantucket’s Relationship with Coastal Erosion

Sponsor:	Nantucket Civic League
Sponsor Liaison:	Peter A. Morrison, Charles Stott
Student Team:	Sara Beauchesne, Ivan Eroshenko, Madison Govaert, Michael Keable
Abstract:	Erosion on Nantucket is an increasing threat to public and private property. In addition to observations in the field, we interviewed and surveyed stakeholders to identify erosion mitigation measures applicable to Nantucket in general and Madaket in particular. We recommend the town consider implementing a sand motion study, creating artificial reefs, dredging/beach nourishment, stabilizing dunes (by planting grasses, erecting fencing, and limiting beach access points), and installing shoal modules. Policies that restrict beach driving and establish property setbacks may also be effective. Finally, future success will require much greater coordination of erosion control efforts between the town, local organizations (such as the Civic League), and property owners.
Link:	Report: Assessing Nantucket’s Relationship with Coastal Erosion Final IQP Presentation: Assessing Nantucket’s Relationship with Coastal Erosion Presentation Survey: Madaket Survey Results Final

Executive Summary

Coastal erosion is a major concern among coastal communities in the United States. In 2000, a report for the Federal Emergency Management Agency (FEMA) estimated that there were 350,000 structures within 500 feet of the U.S. shoreline (outside the major coastal cities), and that 25% (87,000 structures) would be lost to erosion over the next 60 years. Each year, approximately 1,500 homes are lost to erosion at the cost to homeowners of more than $530 million (Heinze Center 2000). Given predictions about the increased frequency and intensity of storms due to climate change, it is likely that erosion costs and losses will escalate in the future. As an island 30 miles off the coast of Massachusetts, Nantucket suffers from some of the highest rates of erosion in the state, ranging from 2-25 feet/year (CZM). The Nantucket shoreline has retreated hundreds of feet since the 1950s, especially along the south coast of the island and in particular locations, such as Madaket. Dozens of houses have been lost over the years, and many more are at risk in the future. Many property owners have taken steps to try to limit the damages from erosion, such as installing sandbags and groins. These efforts have been controversial, however, because they are often ineffective and cause unintended consequences, such as fouling fishing gear or creating excessive scouring on neighboring properties.

Given the ongoing and growing concerns, the Nantucket Civic League chose our team to characterize coastal erosion and its physical manifestations locally, trace the communitywide consequences of coastal erosion (physical, social, and institutional), distinguish the perspectives of various stakeholders on coastal erosion and potential actions for mitigating its effects, and delineate alternative mitigation strategies for public consideration and debate. Our team has focused on Madaket as a case study for the management of coastal erosion in other communities on the island.

The overarching goal of our project was to assist the Civic League in developing strategies and materials to help communities on Nantucket manage coastal erosion. The project objectives were to:

1. Evaluate best practices in the management of coastal erosion, and identify lessons learned from their application in selected communities in the U.S.

2. Assess the policies and plans currently in place on the island to mitigate the adverse effects of coastal erosion.

3. Develop a case study on the erosion problem and potential mitigation strategies in Madaket.

In order to accomplish these objectives and provide the Nantucket Civic League with appropriate guidance, we interviewed coastal erosion experts, town officials, local property owners, community activists, and other stakeholders. We reviewed existing policies and plans and conducted site observations. Lastly, we have developed a survey for the residents of Madaket to assess their understanding of erosion and the strategies they would like to see implemented to manage it.

It became evident that the issue of erosion impacts the island in broad ways. Several different organizations and committees are involved in protecting public and private properties and infrastructure from the threat of erosion. The topic of erosion on Nantucket is also very divisive. Some people believe ‘erosion happens’ and there is little that can or should be done, but many others are keen to explore innovative ways to stave off and limit losses. After compiling the information obtained in our interviews and survey results, we have developed a list of technologies, policies, and organizational tactics in order of priority that Madaket and the town can adapt to mitigate the effects of erosion. The goal in the end, is for the town to learn from this Madaket “case study”, and apply the recommendation across the island.

In order to implement some of our recommended strategies, such as artificial reefs, beach dredging, and Joe Farrell’s project, further research of the sand movement around the island must be conducted prior to executing the strategies laid out below.

In ranked order:

Rebuild Dunes

In general, the United States has shifted from the use of hard structures to control coastal erosion to the use of soft structures (National Research Council, 2014). Many states and local governments on the east coast are encouraging communities to protect and re-establish saltwater marshes and dune systems since they protect against storm surge, flooding and coastal erosion.

We recommend that Nantucket explore opportunities to protect and encourage the development of more extensive dune systems. Dunes can be maintained by erecting sand fences and planting dune grasses and other vegetation. Stabilizing existing dunes and encouraging dune growth and development are environmentally friendly solutions that have been shown to reduce coastal erosion in several areas on Nantucket. The structures are relatively easy and inexpensive to install, but may require periodic maintenance. They can also be damaged by beach driving and destroyed by severe storms.

To coincide with the efforts already being conducted by the town, individual private homeowners should apply for funds from the United States Department of Agriculture (USDA) for implementing dune fencing with dune grasses in front of their properties. In addition, the Madaket Conservation Association should facilitate group efforts to plant beach grasses and install dune fencing in areas that are vulnerable to coastal erosion in Madaket. The more vegetation incorporated into the dune systems, the more stabilized they will be. Finally, clearly marked beach access points in Madaket should be installed to reduce the number of people traversing the dunes and, ultimately, mitigating the rebuilding effort.

Guidance for Homeowners and “Erosion” Committee

Based on the interviews and survey results, the conclusion drawn is that homeowners want the town to take more action in regards to mitigating coastal erosion. Despite the town’s initiatives to be more proactive by implementing the Hazard Mitigation Plan and establishing the Coastal Resilience Advisory Committee (CRAC). Which works directly with Coastal Resilience Coordinator, Vincent Murphy, on drafting the island’s Coastal Resilience Plan. Although these plans are in place, more action must be taken to mitigate coastal erosion. In addition, better guidance must be disseminated to private homeowners from the government and large conservation associations.

After publication of Coastal Resilience Plan, the Coastal Resilience Advisory Committee, in collaboration with Vince Murphy, should refocus their roles. In the future, the committee should take on the role of an “erosion czar”, overseeing the implementation of the erosion control efforts suggested as well as organizing a plan for future erosion efforts. The committee should also assess the long term vulnerability of the Millie’s Bridge.

We also propose the committee to work with the town and large conservation organizations to provide a better guidance for homeowners by establishing a new web-portal or add new features to CRAC’s current website. The website should include descriptions of the past, current, and future efforts completed or planned by both public and private entities to mitigate erosion. Ideally, the posted solutions would be inexpensive, innovative, and effective so that homeowners could learn from them and potentially apply the solutions to their properties. The Civic League and other smaller homeowner associations may use this solution to keep homeowners abreast of the most updated information on the website. Potentially, a system like this could help in organizing group efforts of homeowners in certain areas and neighborhoods.

In the short term, the inexpensive updating of the CRAC’s website to include more pertinent information on erosion will be an asset to the residents of the island. Over the long term, establishing effective communication and collaboration between several committees will, over time, foster a communal effort to improve the current situation of coastal erosion. If all stakeholders are involved in a solution, the solution will be well received and, hopefully, cost effective.

Restrictions on Beach Driving

One of the popular policy-based strategies to mitigate coastal erosion effects is ban on beach driving in areas that are especially vulnerable to coastal erosion. As mentioned in section 4.3.2, driving too close to dune systems can uproot the vegetation and destroy the embryonic dunes, which collapses the dune system. The difficulty in implementing this recommendation is that beach driving is a big economic driver for Nantucket, because tourists have to purchase permits that allow them to legally drive on certain beaches. Sales of beach driving permits yield approximately 6% of annual town budget (V. Murphy, personal communication, October 24th, 2019).

A majority of Madaket residents support reducing the number of beach driving areas prone to coastal erosion and the recommendation to do so would protect the dune systems.

Reinstating Nantucket Conservation District

Reinstating the Nantucket Conservation District (NCD) could assist in channeling funding from the USDA to homeowners’ non-profit group projects such as beach grass planting and culvert building. This strategy should encourage homeowners to undertake group effort projects rather than individual projects in addition to providing organizational aid for these projects outside of town-owned property. However, this initiative would also require electing a board of members to oversee the responsibilities of NCD.

It is a recommendation to reinstate Nantucket Conservation District and hold elections for the board of NCD members so that homeowners may have another option for information, demonstration, organization, and funding for their group non-profit projects.

Overlay Amendments (Setback laws, building restrictions, etc.)

Set-back ordinances are property laws governing lines and boundaries. A set-back law establishes a minimum distance from a property line that a building can be built. The distances are generally regulated by zoning laws. The zoning overlay laws cannot, unfortunately, protect any existing structures. In culmination establishing set-back laws is a good option for mitigating coastal erosion in the long term. To further support our conclusion, 90% of responses from the survey are in favor of the town implementing set-back laws to restrict structure building in these vulnerable areas (Figure 36).

With overwhelming support from the citizens, it is recommended that the town adjust the current overlay and/or introduce a set-back law to prohibit additional development on land within a certain distance (i.e. 100 ft) from the mean high water mark (HWM).

Farrell’s Shoal Modules

Joseph Farrell’s multi step project is worth implementing. The project consists of three stages: 1) collecting data on wave action and sand transport during a nor’easter in Madaket, 2) sinking temporary shoal modules off the beach in front of endangered houses and 3) replace the shoal modules with 100 to 140 feet of concrete units. The shoals could create artificial reefs and provide new habitats for sea creatures. The modules will be submerged deep enough so that they will not interfere with boat navigation. The project is currently on hold with permits needed to begin the second phase. As with implementing artificial reefs to sink temporary shoal modules

properly, there should be more data gathered on sand movement. Based on survey responses, this project has garnered the support and attention of several homeowners in Madaket (Coastal Recovery).

It is recommended that the town to conduct a sand study on the island to identify the most efficient place for Farrell’s shoal modules to be installed. Then, it is recommend that the residents of south shore and the town proceed with implementing the temporary shoal modules off the shore and observing the results. If the results prove the temporary shoal modules to be efficient, it is recommended that Farrell proceed further into the phases of his project.

Stilting

Stilting houses is an additional way to mitigate the effects of coastal erosion. Elevating a house will protect it from flooding and storm damage. As stated in section 4.3.2, some homes in Madaket has started to implement this strategy. Outer Banks, NC is an example of a similar location with many stilted houses. Stilting houses, in some cases, can even be partially funded by FEMA.

Based on the federal funding available to lower the costs of this solution, it is recommended private homeowners in Madaket explore the option of stilting their houses and request funds from FEMA. The stilting may currently only be a few feet (three feet to five feet) in order to stay in compliance with home height restrictions of twenty five feet. It is also recommended that a an edit to local building codes be drafted to state that the height of the home begins at the first level mark and not at ground level.

Artificial Reefs in Madaket Harbor

Artificial reefs can make a positive impact in reducing the rate of erosion in certain coastal areas. As mentioned previously in section 4.3.1, artificial reefs, if implemented correctly, can reduce wave energy, thus reducing erosion impact on the coastline. Artificial reefs can also provide a new habitat for shellfish and are environmentally friendly. However, to implement artificial reefs properly and avoid any negative coastal impact more data should be gathered on sand movement around the island. Prior to implementation in the harbor and applicable areas, positive results from the Sesachacha project first need to be observed.

Following positive results from both the sand study that verifies an adequate ecosystem, as well as applications of it in Nantucket, it is recommend that artificial reefs be placed in Madaket Harbor. Though the area of Madaket Harbor does not necessarily receive high rates of erosion, it is a very crucial area, not just for Madaket, but for the whole island. Therefore, planning proactively could prove quite successful.

Beach Renourishment through Dredging

Proven to be successful in places such as Cape May, New Jersey, despite the various aspects such as determining material compatibility, long permitting process, high cost of implementation, and potential danger to the environment, beach renourishment through dredging can make a positive impact on reducing coastal erosion rates in Madaket. Dredging on Madaket’s south shore would only be successful following specific findings in the proposed sand study. For example, if the sand study finds the ecosystem in Madaket Harbor to be too fragile, then dredging from father offshore may be the best solution.

It is recommended that the town to dredge material from Madaket harbor and deposit the material on the southern shore of Madaket as long as the dredged material and receiving material are compatible. Before beginning a dredging operation, local shell fishing needs to be considered in order to not disturb these areas.