An examination of extreme floods, effects on land-use change and seasonality in the lower St. Johns River Basin, Florida using HSPF and statistical methods

As population growth and urbanization are steadily rising, the need for dependable flood estimation techniques is crucial. This study evaluates extreme flood events in select sub-basins of the Lower St. Johns River in Florida, USA. The study considers the effect of urbanization on the natural hydrologic processes and flood magnitudes in the watershed. Additionally, the effects of varying seasonality into the hydrologic modeling procedure are also investigated. This research focuses on determining the 10-, 25-, 50-, and 100-year return frequency flood flows in Julington Creek, Ortega River, and Pablo Creek of the Lower St. Johns River Basin in Florida, USA. The major findings of this research indicate that by implementing a range of flood estimation methods one can better describe the inherent uncertainty with traditional estimates. Also, the research showed that varying seasonality in the hydrologic modeling procedure does not result in vast differences in the resulting flood estimates. However, various land-use scenarios may produce simulated flood flows of greater magnitude—especially when a more urbanized land-use scenario is modeled.