Physical modelling of a high energy coastal lake outflow, Canterbury, New Zealand

Abstract

A 1:50 scale laboratory physical model was constructed to simulate canal outflows from Wairewa/Lake Forsyth, Canterbury, New Zealand, in order to assess the propensity for canal blockage due to beach sediment transport. A terrestrial survey, depth soundings and side scan sonar surveys were carried out to establish baseline topographic data. These data were used to derive a high-resolution digital elevation model (DEM) of the area. Profiles derived from the DEM were used to cut metal guides to represent beach topography. These were placed in the model tank and a beach was shaped of fine, silica sand to represent the area of the canal opening. Canal outflows were simulated using flow through a polystyrene channel with a rectangular cross-section. A thin-plate wave generator was built for simulating waves. The model was initially designed to simulate sediment transport by longshore drift from south-westerly swells but was later adapted to also simulate south-south-easterly swells. Testing was carried out simulating the base conditions with and without the existing groyne configuration. The model simulated sediment movement well under these conditions. The effectiveness of five groyne scenarios in maintaining a permanent canal opening was tested. Swells from both the SW and the SSE were simulated.