Sediment Modelling of a Catchment to Determine Medium-Term Erosional Trends

Abstract

This study was part of a project designed to simulate the long-term landform equilibrium of a rehabilitated mine site. The project utilized event Fine Suspended Sediment (FSS) fluxes in a receiving stream following a rainfall event as an indicator of landform stability. The aim of this study was to use HEC-HMS to determine sediment and discharge quantity upstream to determine how it affects the downstream development of the catchment landform, in terms of sediment changes and geomorphology. Thus, the study focused on hydrology and sediment modelling of the upper catchment with HEC-HMS (Hydrologic Engineering Centre-Hydrologic Modelling System) to determine the daily discharge and sediment output at the catchment outlet. HEC-HMS was used to calibrate the stream discharge and FSS quantities at the catchment outlet to observed continuous discharge and FSS values. The calibration of the HEC-HMS model was carried out for two water years and then the same model parameters were used to validate the model for a third water year. The catchment discharge and FSS were calibrated and validated for continuous rainfall events against observed discharge and FSS data at the catchment outlet. The model was then run for a projected rainfall of 50 years. The denudation rate predicted by the model was 0.0245 mm per year, which falls in the range previously determined for the region. The simulated sediment output was compared to the rainfall trends over the years. As a result, the sediment spikes following a rainfall-runoff event gradually decreased over time. Reducing FSS spikes indicates that the landform gradually attains stability. This modelling study can be used for long-term simulations to determine erosion equilibrium over the years and to quantify sediment yield in catchments for projected time periods.