Greytown's flood hazard: creating it and learning to live with it

Abstract

The overall objective of this thesis is to investigate the flood hazard presented by the Waiohine River to the Borough of Greytown. To meet this objective, three specific aims were defined: 1. To analyse the physical variables that determine the Waiohine River's flood hazard. 2. To analyse the human use of the Waiohine River's flood prone areas over time, and establish whether this has changed the potentiality of the flood hazard. 3. To measure the present risk to Greytown from the Waiohine River's flood hazard. The thesis is structured in two parts: Part One, the natural hazard, and Part Two, elements at risk, vulnerability and risk. Part One, the natural hazard, examines the physical determinates of flooding, including the Waiohine Catchment characteristics, its flood hydrology, and form and process variables such as sediment transport and channel meander quantification. Part One is concluded with a historical and modelled flood hazard map of the Waiohine floodplain. Part Two, elements at risk, vulnerability and risk, identifies what is at risk, how it came to be at risk and how vulnerable each element is to flooding. The principle component of Part Two is a flood risk assessment which provides an inventory of all flood prone assets, or elements at risk, and assesses their vulnerability to various flood frequencies and magnitudes. Risk is then quantified, where possible, in dollar terms and an average annual damage cost estimated. Finally three groups of recommendations are made: 1. River management recommendations. 2. Land use recommendations. 3. Floodplain management plan recommendations. It was concluded that a potential flood loss to Greytown of nearly a quarter of a million dollars exists annually, and that the thesis provides the necessary information, data and analyses for the development of a floodplain management plan and strategies aimed at a reduction in this risk.