A rough-turbulent Froude law physical hydraulic model of the Waiho alluvial fan head: A dissertation submitted in partial fulfilment of the requirements of the degree of Master of Engineering (Natural Resources) at Lincoln University

Abstract

Located at the head of the Waiho alluvial fan, Wetland, New Zealand is the township of Franz Josef Glacier. Aggradation of this region of the Waiho alluvial fan has been occurring for much of this century, and as a consequence, the Waiho River now presents a significant natural hazard for the Franz Josef Glacier community. Intrinsic to the process of aggradation occurring on the Waiho alluvial fan head, is the inability of the Waiho River to transport sediment, and more specifically bedload. A 1: 100 scale, rough-turbulent Froude law physical hydraulic model of the Waiho alluvial fan head is developed to gain some insight into the potential bedload transport capacity of three steady flows across this region of the fan. In addition, an assessment of the validity of the use of the Schoklitsch (1962), cited in Young and Davies (1990) and Bagnold (1980) bedload transport capacity equations for predicting sediment transport on the Waiho alluvial fan proximal region is undertaken. Although there are limited prototype validation data available, similarity between the model and its prototype is shown to be achievable at the design scale of 1: 100. In the context of this study as a preliminary to further research, it is therefore considered that the representation of the prototype is sufficient to allow scaling of the results obtained at the design scale, to the prototype situation. Difficulties experienced with uncontrolled variations in the sediment feed rates to the model limited the accuracy of the measured bedload transport capacities to a range of values. The range of potential bedload transport capacities that would be expected on the proximal region of the Waiho alluvial fan, for the four year return period, annual return period, and the 500 m³s⁻¹ flood flows are determined to be 2160 - 2270 kgs⁻¹ , 1870 - 2080 kgs⁻¹, and 790 - 930 kgs⁻¹ respectively. The form of both bedload transport capacity equations investigated is found to be incorrect for application to the Waiho alluvial fan proximal region modelled here. It is concluded that the use of the Schoklitsch (1962), cited in Young and Davies ( 1990), equation is not valid for the prediction of bedload transport capacities on the Waiho alluvial fan proximal region. The Bagnold (1980) equation demonstrated potential for its use for the prediction of bedload transport capacities on the Waiho alluvial fan proximal region. However, given the limited measured bedload transport capacities for comparison, further research is required to allow a more comprehensive validation of the Bagnold (1980) equation.