Compound flooding from lake seiche and river flow in a freshwater coastal river

Abstract

Compound impacts on water level caused by seiche and high flow in freshwater coastal rivers can result in extreme flood risks. A seiche is an oscillation in the lake caused by strong wind or rapid change of atmospheric pressure. Seiching and high flow can be statistically dependent, therefore a copula-based joint distribution is used to investigate their compound effects on flooding in a freshwater coastal river. A hydrodynamic model is used to predict inundation areas for developing flood probability maps. This two-fold approach allows the development of a joint probability-based flood map resulting from seiche and high flow. The methodology is applied to the Buffalo River (Buffalo, New York), draining into Lake Erie, which is subject to significant seiching. Results show that seiches can have an impact on flooding and the compounding effects of seiche and high flow can increase the inundation area. The study also shows that the present Federal Emergency Management Agency (FEMA) 100-year flood scenario for the study site is equivalent to compound 100-year high flow and 10-year seiche, and the 100-year high flow and corresponding most probable water level (slightly larger than the long-term average lake level) is approximately 7 times more likely to occur than the FEMA scenario. The analysis framework can provide insight into the compounding effects of seiche and high flow on inundation, and on the probability of occurrence of such events for overall flood engineering in a freshwater coastal river.