The Need for Benefit/Cost Analysis of Coastal Defense: There are many high-value residential properties along the southern shore of Connecticut which are periodically inundated by storm surges generated by tropical and winter storms. Although there is a reasonably high probability that properties nearest the shore or at relatively low elevations will be damaged in future storms, very little has been done to try to protect properties from that probable future damage either from storms or from sea level rise (SLR). Compared to the expected costs of future damage, and compared to the high present value of insurance premiums to cover those predictable costs, the costs of building a protective barrier (or other measures of coastal defense) are relatively low. There is a need to do an economic analysis of selected measures that would provide better community defense against future storms and sea level rise.

Objective of this Research: This proposed research will seek to determine the net present value and cost/benefit ratio of the expense of building a protective sea wall or requisite storm gate(s) (the cost) compared to the expected damage to be experienced in the absence of building such wall(s) or storm gate(s) (the benefits of a wall being equivalent to the costs averted by building a wall). The research will be conducted within the town boundaries of Guilford, CT, and will calculate the probability of storm surges of various heights and the associated damage to properties of each height (at each 0.1 meter above the NAVD88 reference elevation of zero (~mean sea level (MSL)).

Approach: The expected damage at each height is calculated by multiplying the probability of a storm surge at each level by the expected property damage based on expected storm damage at each height interval. Future probabilities of storm surges of various heights have been calculated for thirty years into the future based on the past 49 years of hourly sea levels (1970-2018) as measured at the NOAA tide gauge in Bridgeport, CT. Adjustment to future sea levels was made to account for expected sea level rise (SLR) (a minimum of 3 mm per year).

The Model: The objective of this study is to determine where (in Guilford, CT) to build sea wall(s) and/or storm gates and at what height. The study implements the observation that the optimal (most efficient) height of a sea wall or storm gate would be one that minimizes the total costs of building it. Total costs would be the sum of (1) the costs of building the wall/storm gate to each height, and (2) the expected costs of repairing the damage from a flood at each height of water.