Rainfall, runoff and sediment transport relations in a mesoscale mountainous catchment: The River Isábena (Ebro basin)

Abstract

This paper examines the relations between rainfall, runoff and suspended sediment transport in the Isábena basin during a quasi-average hydrological year. The Isábena is a mesoscale river basin that drains a mountainous area comprising patches of highly erodible materials (badlands). The paper includes an analysis of the different hydrological and sedimentary responses of the catchment to a similar rainfall. Thirty-four floods were studied, with a very variable response observed. Runoff coefficients ranged from 0.32% to 33%. The sedimentary response was also highly variable, with maximum suspended sediment concentrations (SSC) oscillating between < 0.1 and 90 g l− 1 and flood sediment loads varying from 27 to 54,000 t per hydrological event. Most sediment load was concentrated in spring when competent floods occur frequently. Pearson correlation matrix and backward stepwise multiple regression indicate that the hydrological response of the catchment is strongly correlated with total precipitation, event duration, and rainfall of the previous days. Very low correlation was observed with rainfall intensity. The relation between rainfall and sediment transport followed the same trend. Sediment variables (e.g., total load and SSC) were significantly correlated with variables such as total rainfall and rainfall over the previous days, although the significance level was lower in comparison with the runoff related variables. There was again no correlation between sediment variables and rainfall intensity. On-going research in the area suggests that, apart from rainfall, factors such as sediment availability in the badlands and accumulation of sediment in the channels influences the river's sedimentary response. The non-linear hydrosedimentary response is reflected in the wide range of runoff coefficients and sediment loads that have been observed in response to similar amounts of precipitation.