Dynamics of suspended sediment flux on the rivers bandon and owenabue, ireland

Abstract

Monitoring, analysis and modelling of suspended sediment transport in riverine systems has received much attention in recent decades. Quantitive analysis techniques have been applied to allow river basin managers to assess suspended sediment transport and its importance in transporting a range of pollutants including excess metals and nutrients, which negatively impact on aquatic systems. In this paper, an analysis of the suspended sediment fl ux (SSF) dynamics is presented for the small and medium sized catchments of the River Owenabue and the River Bandon, respectively. The results contribute to the fi lling of a research gap in an Irish context where SSF analyses at this scale have not previously been presented. River fl ow rate and turbidity data were collected on both rivers for one full year. Turbidity was found to be an excellent surrogate for suspended sediment concentration on both rivers with r 2 values greater than 0.87 found. The annual SSFs passing the gauging stations for the River Bandon and River Owenabue were found to be 6012 and 2635 tonnes, respectively. SSF analysis reveals that 85% and 92%, respectively, of the total annual fl ux was transported on the Rivers Bandon and Owenabue during the high fl ow storm-based events. SSFs were investigated at the seasonal, intra- and inter-event scales – the largest 10 SSF events were identifi ed and analysed. Seasonally, most of the fl ux is delivered in the winter months from October to March. At the intra-event scale, it was found that events of similar fl ow magnitude do not necessarily transport similar fl ux levels. Total fl uxes were found to decrease for sequential events as a result of sediment exhaustion. At the inter-event scale, hysteresis is observed and analysed for the identifi ed events with clockwise hysteretic loops dominating implying that suspended sediment transport is generally supply limited, and that the primary sources of sediment are located near or within the river.