Flood mitigation: Regulatory and hydrologic effectiveness of multicomponent runoff detention at a Southwest Florida site

Abstract

This research investigates the capability of hydrological site design to mitigate inland flooding. Empirical data for a target watershed characterize interaction among three hydrologic components: stormwater detention ponds; seasonal wetlands; and soils/groundwater. Findings are (a) stormwater ponds' elevation change in response to precipitation events of a given magnitude varies sharply among storms, such that ponds' pre-event elevation and forecast precipitation are not reliable to predict ponds' ability to detain runoff sufficiently to avoid downstream flooding; (b) water table elevation is governed partly by long-term seasonal variation but also responds quickly to specific events, and powerfully affects the system's capacity to detain runoff; (c) water table elevation during wet weather periods common to Southwest Florida can be high enough to breach the soil surface for extended periods, severely reducing the capacity of the system to detain runoff; (d) in the target watershed of the Florida Gulf Coast University campus, depressed surface storage in seasonal wetlands compensates for reduced wet season capacity of ponds and soil storage. That mechanism explains why the campus has successfully mitigated flooding including from high-precipitation events most prone to produce flooding (intense rate, late wet season events), while some downstream communities with components designed to meet the regulatory minimum have experienced inundation.