Wairewa/Lake Forsyth outflow channel modelling

Abstract

A 1:50 scale model was constructed to simulate canal outflows from Wairewa/Lake Forsyth. A terrestrial survey was carried out at the canal opening to provide baseline topographic data. A depth sounding and side scan sonar survey was also carried out to provide data on nearshore bathymetry at the canal opening. These data were used to derive a high-resolution digital elevation model (DEM) of the area. Profiles taken from the DEM were derived, rescaled and used to cut metal guides to represent beach topography. These were placed in the model tank and a beach was shaped of fine, quartz sand to represent the area of the canal opening. The design depth of the watertight model was 0.26 m. Canal outflows were simulated using flow through a polystyrene channel with a rectangular cross-section. A thin-plate wave generator was built to allow for the simulation of waves. The model was initially designed to simulate sediment transport by longshore drift from southwesterly swells but was later adapted to also simulate south-southeasterly 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