Author(s): James Ball; Lee Williams

Linked Author(s):

Keywords: Blockage; Flood; Hydraulics; Debris; Timing

Abstract: Estimation of floods remains a significant problem for managers of riverine systems. The occurrence of floods is the result of both climatic factors and catchment factors. One of the catchment factors that influences floods is the interaction between debris material and cross-drainage structures like culvert, bridges, etc. As the purpose of design flood estimation is the prediction of both flood magnitude and flood likelihood, there is a need to understand how blockage of cross-drainage structures influences the predicted flood levels and flows. Presented herein are the outcomes from a hydraulic modelling study into the impact of cross-drainage structure blockage on both the predicted flood level and the predicted flood flow. The study presented is based on predictions obtained from TUFLOW; TUFLOW is a 2-D model of flows in rivers and floodplains developed in Australia. Factors considered in the study were the timing of blockage, the magnitude of blockage, the peak flow of the flood hydrograph, and the catchment storage upstream of the cross-drainage structure. These factors were modified in a manner designed to enable a sensitivity analysis of cross-drainage blockage on flood predictions when compared to flood predictions obtained with no blockage present in the cross-drainage structure. Blockage results in a change to the flood profile and downstream discharge. This is dependent upon the relationship between the inflow magnitude and upstream storage volume. If the storage capacity is exceeded for the unblocked condition, the structure experiences over-topping. Therefore, any blockage will increase the upstream water level. A blockage will also reduce the time required to fill the storage capacity resulting in an increase in downstream discharge. The nature of this relationship is governed by the individuality of each structure. This study considers the results produced and highlights the need for further research.

DOI: https://doi.org/10.3850/IAHR-39WC25217119202256

Year: 2022