Breaching Timescales and Peak Outflows for Perched, Temporary Open Estuaries

Abstract

Intermittent breaching of sand barriers at temporary open estuaries plays a key role in the functioning of these systems. In addition to their ecological impacts, breaching events can cause significant morphological changes because high breach outflows result in the scouring of significant amounts of accumulated sediments from an estuary. Estimation and modeling of these processes requires insight into the parameters that determine features of the breach such as its size and the timescales for the breach formation. The latter is particularly important for characterizing the outflow hydrograph and for estimating sediment transport effects. Simple laboratory experiments are reported that investigated the temporal evolution of the breach and the scaling of the breach formation time TF and peak outflow QP . The experiments were specifically designed to investigate the influence of the outflow volume S, the hydraulic head H, and the barrier breadth B. A scaling is suggested that gives a good description of the experimental data. The scaling is shown to be consistent with observed breach characteristics for actual estuaries (or coastal lagoons) and earth-dam failures where outflow volumes are several orders of magnitude larger than the models.