Hapua are complex and dynamic systems, and are especially vulnerable due of their location at the end of river catchments. The Hurunui River hapua is currently under pressure from the intensification of irrigation and agriculture, and a number of dam proposals in its catchment. The purpose of this research was to investigate the current conditions in the Hurunui River hapua, how they respond to the observed range of contemporary catchment and coastal processes, and to examine of the longer-term behaviour and vulnerability of the hapua. This information was then used to make predictions on how the hapua could be impacted if dams were to be built in the catchment, or if significant changes in the catchment occur.

A multidisciplinary approach was used to investigate the short-term baseline conditions, and the long-term geomorphology of the Hurunui River hapua. Water characteristics were investigated over a falling tide, in different areas of the hapua, and in different energy conditions. The short-term behaviour of the hapua was investigated using hourly images from a time-lapse camera. The long-term vulnerability over decadal time scales was analysed using aerial photographs.

This study showed that the flow of the river, the shape of the hapua, and the position of the outlet has a major control over the characteristics of the water. The surface area, the position of the barrier, and the width of the barrier of the Hurunui River hapua have been variable historically.

From this research, it is predicted that the greatest impact on the Hurunui hapua would result if there is a dam related change the shape and outlet of the hapua to a state that reduces water residence time and decreases water quality. It is also predicted that if the outlet is maintained at the northern end of the hapua, and no ponded areas are present, that there would be the least problems with water quality.

The findings of this research have improved the understanding of the water characteristics and processes of the Hurunui River hapua, and how they respond to change.