Wetlands provide invaluable ecosystem services to moderate the effects of flooding. In the United States, Sect. 404 of the Clean Waters Act requires that mitigation of impacted wetlands from issued Environmental Resource Permits (ERPs) occur in the same watershed. This study investigated spatial patterns of impacted wetlands and compulsory mitigation (e.g., preservation and/or purchase of mitigation bank credits) in three watersheds of the lower St. Johns River basin, Florida, from ERPs submitted in 2006–2019. Each watershed was stratified by the Federal Emergency Management Administration’s (FEMA) designated 100-year floodplain, 500-year floodplain, and outside the floodplain. Flood hazards (e.g., projected 2030 Sea Level Rise, seasonal nuisance high tides, and storm surge) were compared among the three floodplain categories with ERP data, age and value of residential structures, FEMA field assessment following Hurricane Irma in 2017, and a composite flood hazard score. Results indicated that wetland loss occurred primarily in the 100- and 500-year floodplains, and wetlands were at greatest risk from projected 2030 SLR and nuisance high tides. These ERPs planned to preserve upland and wetlands by purchasing credits from banks located in areas with low risk of flooding. Older houses were typically in areas with greater flood hazard exposure, with higher home values. This study demonstrated that a watershed evaluation of flood exposure should be considered for future development, regardless of floodplain category. Given the significant social and economic costs from flood damage, community planners should prioritize protection of wetlands and open spaces in areas most vulnerable to flood hazards.

湿地提供了宝贵的生态系统服务，以减轻洪水的影响。在美国，Sect。《清洁水域法》第 404 条要求在同一流域内缓解已颁发的环境资源许可证 (ERP) 中受影响的湿地。本研究根据 2006-2019 年提交的 ERP 调查了佛罗里达州圣约翰斯河流域下游三个流域中受影响湿地和强制缓解（例如，保护和/或购买缓解银行信贷）的空间模式。每个流域都由联邦紧急事务管理局 (FEMA) 指定为 100 年泛滥平原、500 年泛滥平原和泛滥平原外分层。洪水灾害（例如，预计的 2030 年海平面上升、季节性滋扰性高潮和风暴潮）在三个洪泛区类别中与 ERP 数据进行了比较，住宅结构的年龄和价值、2017 年飓风艾尔玛之后的 FEMA 现场评估以及综合洪水灾害评分。结果表明，湿地损失主要发生在 100 年和 500 年泛滥平原，湿地受预计的 2030 年 SLR 和滋扰性高潮的威胁最大。这些 ERP 计划通过从位于洪水风险低的地区的银行购买信贷来保护高地和湿地。较旧的房屋通常位于洪水灾害风险更大的地区，房屋价值更高。该研究表明，无论洪泛区类别如何，未来的开发都应考虑对洪水风险进行流域评估。鉴于洪水造成的巨大社会和经济成本，