Storm Surge & Critical Infrastructure on Nantucket

Sponsor:	Nantucket Emergency Management
Sponsor Liaisons:	Dave Fronzuto, Peter Morrison
Student Team:	Brian Bach, Cece Cotter, Matt Lepine, Sean Regan
Abstract:	Storm surge, produced by increasingly frequent severe storms, threatens the daily operations of downtown Nantucket. This project identifies and analyzes ways the Town might protect Nantucket’s downtown critical infrastructure from storm surge and offers recommendations for mitigating future adverse impacts. In collaboration with Dave Fronzuto and the Nantucket Emergency Management Agency, we assessed the risks caused by storm surge for each piece of infrastructure within the downtown area and developed a prioritized list of infrastructure to be modified. We compiled a database of relevant information for each infrastructure element in our study area, along with a GIS layer to facilitate data retrieval.
Link:	Report: Storm Surge & Critical Infrastructure on Nantucket Presentation PowerPoint: Storm Surge & Infrastructure Final Presentation

Executive Summary

High winds and excessive precipitation cause tremendous damage in severe storms, but “the greatest threat to life comes from the water in the form of storm surge” (Hurricane Storm Surge), as it has the potential to severely damage critical infrastructure and fatally disrupt the lives of nearby inhabitants in coastal areas. Storm surge is best defined as the “abnormal rise in water level, over and above the regular astronomical tide, caused by a severe storm” (Storm Surge and Coastal Inundation). Projections of future sea level indicate that ocean levels will likely rise, intensifying the associated problems.

Nantucket’s tourist-based economy and ever growing population heightens the need for action. “There are two primary reasons for the dramatic increase in natural disaster-related losses: an increase in the people and property in harm’s way, and an increase in the frequency or severity of the hazard events” (U.S. Army Corps of Engineers, Water Resources Science, Engineering, and Planning: Coastal Risk Reduction; Water Science and Technology Board; Ocean Studies Board; Division on Earth and Life Studies; National Research Council, 2014). These two primary factors call for actions to be taken to mitigate the threats of potential natural disaster-related losses looming in Nantucket’s future.

In particular, it is important that the Town embark on a long-range effort to protect its most critical pieces of infrastructure, which pose the greatest threat to the community’s viability if damaged.  Damage to a community’s critical infrastructure threatens the public health, environment, and economy.

This project identifies and evaluates potential ways to protect Nantucket’s critical downtown infrastructure from storm surge and offers recommendations for mitigating future adverse impacts. Our project had four main objectives:

1. Evaluate past and current practices, along with recognized best practices, for protecting critical infrastructure to determine what approaches have proven to be most successful;
2. Identify and characterize critical infrastructure in the defined downtown study area;
3. Evaluate the advantages and disadvantages of alternative planning, protective, and mitigation strategies for different infrastructural elements; and
4. Formulate and prioritize and recommendations for the future.

We began by reviewing the research on these topics to understand storm surge and its effects on communities, and protection measures that have been used in the past. To better understand the specific Nantucket context, we interviewed several knowledgeable local experts to gain an understanding of how the problems associated with storm surge are presently dealt with on the Island.

To identify and characterize critical Town infrastructure, we first defined our study area based on FEMA flood maps. FEMA has defined several types of “zones,” including the 100-year flood, or base flood, zone that shows those areas that face a one-percent annual risk of flooding equal to or exceeding a defined height (the so-called “once in a century” height). We used this area as a baseline for defining the boundary of downtown infrastructure that falls within the 100-year flood zone lower than 10 feet above sea level. Based on further discussions with the Emergency Management Coordinator, Dave Fronzuto, we defined our area of interest. Next, we focused on identifying elements of critical infrastructure essential to the day-to-day operations of the Town and its residents situated within that area of interest.

Our next step entailed developing data-gathering checklists referencing three categories of infrastructure: utilities, built, and transportation. We used this typology as a guide when collecting data in the field, drawing upon findings from the literature review and information from consultations with our sponsors, advisors, and other experts noted previously. Key data we acquired for each piece of infrastructure includes the base floor elevation, which is the height that often determines when water can enter a building and begin to do interior damage, and the height of critical components, such as electrical connections.

Drawing upon these data, we performed a risk assessment for each individual piece of infrastructure. This assessment weighed the measured likelihood of damage by a 100-year storm surge versus the resulting consequences were that infrastructure to be rendered inoperable.  Our assessment identified 7 high-risk, 11 medium-risk, 6 low-risk, and 2 very low-risk elements of infrastructure within our study area.

Based on our research, we identified three main ways to protect critical infrastructure: floodproofing, elevation, and relocation. For each piece of infrastructure, we have highlighted which of these three options is most effective. Elevation proves to be the most effective option for much of the infrastructure in our area of interest.

We have prioritized all identified pieces of infrastructure according to which are most crucial for immediate repair, based on both the degree of risk and how critical the infrastructure is. Of particular note, both the Sea Street Pump Station and the Candle Street Substation are each at high risk and merit top priority for future work. Any proposed mitigation tactics have the potential to take several years to complete, so it is imperative that all aspects of the Town’s planning take this into consideration.

To facilitate data retrieval in the future, we prepared a reference database, which we have made available in both digital and printed binder formats. This database furnishes the checklists, summaries, risk assessment, and recommendations for each individual element of critical infrastructure. Additionally, we have created a complementary Geographic Information System (GIS) database of pertinent infrastructure information, including its name, sector, value, ground elevation, critical elevation, risk value, and FEMA flood zone, along with the page number referencing the further information available in the database. The GIS layer incorporates currently existing layers used by Nantucket GIS, for seamless incorporation as a useful tool.