The Breaching of Sand Barriers at Perched, Temporary Open/Closed Estuaries — A Model Study

Abstract

The mouth dynamics of small temporary open estuaries play a key role in their overall functioning. Intermittent breaching of the sand barriers of these systems leads to large changes in the physico-chemical environment, which in turn triggers major biological responses. The breaching process can also cause significant morphological changes because the strong breach outflows can scour large quantities of accumulated sediments from an estuary. Simple laboratory experiments are reported that aim to understand what determines the size of a breach in the sand barrier. The experiments were specifically designed to test the influence of storage volumes on the breaching process. They suggest a remarkably simple result that the breach width scales on the 1/3 power of the total volume of water that flows through the breach. This scaling is shown to be consistent with breaching at actual estuaries (or coastal lagoons) where storage volumes are six orders of magnitude higher than the models. Furthermore, a review of data from earth dam failures also reveals a broad consistency with the scaling deduced from these model tests.