Optimized design of storm surge barrier and seawall defenses for Macao under extreme typhoons and sea-level rise

For low-lying coastal metropolises all over the world, coastal infrastructure is particularly vulnerable to typhoon-induced storm surges, which can be significantly intensified by accelerating sea-level rise. The efficacy of hard engineering defenses in such dynamically changing conditions needs thorough evaluation. This study employs a high-resolution coupled model to evaluate and optimize hard engineering defenses and propose an economic yet effective design criterion, taking the Macao Peninsula as a key example. The modeling framework rests on a novel blended Holland-ERA5 wind field and an unstructured computational mesh refined to 10 m resolution along the Macao coastline. Concretely, the analysis demonstrates that the government’s existing plan for an inner harbor seawall is insufficient, whereas a storm surge barrier at the harbor entrance is necessary when considering future sea-level rise. Meanwhile, the minimum crest height of the barrier can be lower than the height of a peak storm tide. For instance, a barrier crest height of just 2.40 m above mean sea level can effectively prevent inundation during Typhoon Hato, which had a peak storm tide of 3.78 m. The difference stems from the short duration of the surge peak and the limited overflow volume, revealing a design criterion that the barrier height can be decoupled from absolute peak water levels by exploiting the buffering capacity of the sheltered basin. This study also identifies key vulnerabilities along the urban shoreline where no overflow can be tolerated, and prescribes staged crest elevations for both the supplementary seawalls and the barrier itself under present-day and future sea-level conditions. Without these integrated defenses, the extent of Hato-intensity inundation would expand by 13% by mid-century and 84% by the end of the century under a high-emission trajectory. By establishing a transferable methodology that links dynamic surge processes to cost-efficient defense elevations, this work provides both an applicable design criterion and a high-resolution modeling framework that can be adapted to other tidally choked urban estuaries worldwide.