Timing Managed Retreat for Robust Coastal Adaptation Strategies

Abstract

Many coastal communities rely on recurring beach nourishment to mitigate erosion risks. However, increasing hazards threaten the long‐term viability of this strategy. This raises the question: When to retreat, if at all? Past studies provide important insights but are typically silent on the timing of retreat, the effect of uncertainties, and the trade‐offs between objectives. Here, we address these gaps through a case study of Hutchinson Island in St. Lucie County, Florida. We analyze the effects of uncertainties and quantify trade‐offs between key objectives. We show that accounting for uncertainty changes the expected performance of adaptation strategies and alters the trade‐offs between key objectives. In our case study, only retreat‐triggering strategies satisfy a commonly used benefit‐cost ratio threshold by the U.S. Army Corps of Engineers. Our results suggest that initiating retreat a few decades earlier than recommendations from approaches employed by previous studies can improve robustness under uncertainty and better balance competing objectives.