Waikato River Hydrodynamic and Sediment Transport Modelling
Implications of a subsiding river bed
The first phase of the project, examined the hydrodynamic changes resulting from a 12 cm subsidence in the riverbed associated with mining activities. The second phase of the project looked at the effects on sediment transport in the river resulting from the change in the hydrodynamics. The study predicted changes in the current velocity, including expected impacts on the sediment dynamics. The modelling showed that there would be a decrease in river flow velocities as a result of the subsidence of the riverbed. Sediment transport numerical model studies were then undertaken to assess the time scale for infilling of the deepened area. The results of the sediment transport study suggested that the sediment fluxes and infilling rates after subsidence were of the same order as the subsidence induced depression volumes. Thus it was concluded that the river would remain essentially in equilibrium, especially since the subsidence would occur gradually over a span of years. For an assumed worst case of an instantaneous subsidence of 12 cm, the infilling would take on the order of 1-2 years and would not have a significant impact on river dynamics.
