OCEAN DRIVEN FLOODING OF A COASTAL LAKE

Abstract

Analysis of Lake Conjola flooding in April 2006, provided in this paper, attributes it to waves pumping water over a 300 m long beach berm and into Lake Conjola. This overwash, generated by the medium wave height swell occurring during this flooding, was able to lift the lake levels near the entrance, persistently over several tidal cycles, to well above the ocean water levels. The wave pump model was used to model this flooding. Lake Conjola water storage and dynamics were modelled by using a two-node continuity based model that a change in storage in time is driven by the net inflow to a node and these nodes and the ocean are linked by log-law. The extents of these two nodes were established from previous water surface measurements. While the qualitative flood behavior was reproduced by this remarkably simple model, the peak flood level was not satisfactorily predicted when using literature values for model turning parameters. One reason for this mismatch was that the waves pumped against a head including critical flow on the beach berm. Based on recent images of Lake Conjola wave overwash events, it may be concluded that pumping against critical flow is too harsh. Removing this from the model has halved the gap between the measurements and predictions. However, more research is definitely required to establish what components should be included in the hydraulic head pumped against.