New Analysis Shows Coastal Communities Can Benefit from Early Planning of Inland Retreat

Tourists and locals enjoying a sunny Vero Beach day in Florida on Hutchinson Island. (Photo by Ryan Tishken)

"Our study shows that considering relevant uncertainties and multiple objectives causes strategies that appeared to pass the benefit-cost ratio threshold to fail," said recent Dartmouth Engineering PhD graduate Prabhat Hegde Th'26, first-author on the study published in Earth's Future. 

In order to consider the option of a retreat, both communities and the US Army Corps of Engineers need this type of quantitative analysis to inform their decisions and to know when to start planning. "You really can't wait to introduce such analyses to know what makes the most sense, because if you wait you might have very little time to prevent poor outcomes," said Hegde. "Especially when you have to get everyone on board, having 20 years to plan versus 10 years makes the effort look very different. So even just the consideration of retreat now can be very helpful."

The paper uses Hutchinson Island, Florida as a case study, because there are multiple previous studies that can serve as a baseline. The research team—including Dartmouth Engineering professors Vikrant Vaze and Klaus Keller, and former research scientist Adam Pollack—addressed how uncertainty affects decision-making and how to balance competing goals such as maximizing the opportunities for beach tourism and recreation while minimizing investment costs and storm damages.

Figure 1 from the study illustrates the framing of the decision analysis using uncertainties, policy levers, system relationships, and performance metrics.

Currently, when a coastal town carries the risk of continued flooding and erosion, it will often ask the US Army Corps to come in and do a study. "But the only thing the typical Army Corps study considers is how frequently to add sand to the beach," explained Hegde. "Should it be more or less than 10 times over the next 50 years? It uses a simple mathematical formula required by law for all its projects to determine a frequency that meets a certain benefit-cost ratio. It neglects many potentially important uncertainties."

The study aims to provide a method that better captures the complexity of the problem, including important trade-offs involved, so that coastal communities can make better decisions about how best to secure their own future, and when.

The more time for such planning the better, the researchers point out, because a well-managed retreat is complex. "Where do people move to? Are there laws and policies that need to change? How do you maintain a sense of community?" said Hegde.

Timing is key. He added, "The bottom line is that managing risks proactively and acting early can provide many benefits."

This research was conducted as part of the adaptation strategy design focus area within the Megalopolitan Coastal Transformation Hub (MACH) project, which was supported by the National Science Foundation (NSF) through awards ICER-2103754 and No. 1750587, as well as by Thayer school of Engineering at Dartmouth, and Dartmouth College. Led by a team at Rutgers University, MACH is a consortium of 13 institutions whose mission is to conduct the scientific research needed to develop effective, evidence-based responses to coastal climate change risks. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author) and do not necessarily reflect the views of the NSF.