Study of runoff generating processes in mountainous catchment

Abstract

Employing saturation runoff and interflow processes the presented research is focused on study of runoff formation processes in headwater catchments using statistical multiple regression approach and a water balance approach by dividing the landscape into variable saturated areas. For selected episodes the rainfall-runoff relationship was analyzed in four experimental catchments with more than ten years of continuously recorded hydro-meteorological data. Three of the sites, subjected to monsoonal climate, are located in Ethiopia; the fourth catchment is located in temperate climate region in the Czech Republic. The experimental sites not only differ in climate but also in size, topographic relief and land use.Despite the different characteristics between the catchments, the response is very similar. Each catchment reaches a threshold point where runoff response can be predicted by a linear relationship with rainfall depth. After the rainfall threshold is satisfied the preferential flow pathways become interconnected and the runoff contributing area remains the same independent of the amount of rainfall or its intensity. Up to the threshold value the runoff strongly depends on the initial saturation conditions. With much longer observational time series, it may be possible to identify additional parameters and conceptualize the hydrological behaviour below the threshold. After approximately 500 mm of cumulative seasonal rainfall has fallen since the beginning of the season all the three Ethiopian catchments exhibit consistent hydrological behaviour. In case of the Uhlířská catchment in the Czech Republic, the rainfall total in the range of approximately 60-70 mm is the threshold for significant runoff formation in both the subsurface hillslope stormflow and consequent streamflow.The outcome of applying the framework is a confirmation of the hypothesis (Jakeman and Hornberger, 1993) that, after allowing for antecedent conditions, the response of a catchment is predominantly linear. It may be added that the response is linear over a range of climatological regimes and catchment scales.It is believed that similar conceptual hydrological water balance methods based on comparison and focused on similarities in catchment behaviour can provide needed insight into the water transport process in heterogeneous soils dominated by preferential flow where current approaches fail.

Employing saturation runoff and interflow processes the presented research is focused on study of runoff formation processes in headwater catchments using statistical multiple regression approach and a water balance approach by dividing the landscape into variable saturated areas. For selected episodes the rainfall-runoff relationship was analyzed in four experimental catchments with more than ten years of continuously recorded hydro-meteorological data. Three of the sites, subjected to monsoonal climate, are located in Ethiopia; the fourth catchment is located in temperate climate region in the Czech Republic. The experimental sites not only differ in climate but also in size, topographic relief and land use.Despite the different characteristics between the catchments, the response is very similar. Each catchment reaches a threshold point where runoff response can be predicted by a linear relationship with rainfall depth. After the rainfall threshold is satisfied the preferential flow pathways become interconnected and the runoff contributing area remains the same independent of the amount of rainfall or its intensity. Up to the threshold value the runoff strongly depends on the initial saturation conditions. With much longer observational time series, it may be possible to identify additional parameters and conceptualize the hydrological behaviour below the threshold. After approximately 500 mm of cumulative seasonal rainfall has fallen since the beginning of the season all the three Ethiopian catchments exhibit consistent hydrological behaviour. In case of the Uhlířská catchment in the Czech Republic, the rainfall total in the range of approximately 60-70 mm is the threshold for significant runoff formation in both the subsurface hillslope stormflow and consequent streamflow.The outcome of applying the framework is a confirmation of the hypothesis (Jakeman and Hornberger, 1993) that, after allowing for antecedent conditions, the response of a catchment is predominantly linear. It may be added that the response is linear over a range of climatological regimes and catchment scales.It is believed that similar conceptual hydrological water balance methods based on comparison and focused on similarities in catchment behaviour can provide needed insight into the water transport process in heterogeneous soils dominated by preferential flow where current approaches fail.