Abstract:Using data collected at the Mero catchment during three hydrological years (2005/06-2007/08), an analysis of rainfall-runoff relationships was performed at annual, seasonal, monthly, and event scales. At annual scale, the catchment showed low runoff coefficients (23-35%), due to high water storage capacity soils as well as high runoff inter-annual variability. Rainfall variability was the main responsible for the differences in the inter-annual runoff. At seasonal and monthly scales, there was no simple relationship between rainfall and runoff. Seasonal dynamics of rainfall and potential evapotranspiration in conjunction with different rainfall distribution during the study years could be the key factors explaining the complex relationship between rainfall and runoff at monthly and seasonal scale. At the event scale, the results revealed that the hydrological response was highly dependent on initial conditions and, to a lesser extent, on rainfall amount. The shapes of the different hydrographs, regardless of the magnitude, presented similar characteristics: a moderate rise and a prolonged recession, suggesting that subsurface flow was the dominant process in direct runoff. Moreover, all rainfall-runoff events had a higher proportion of baseflow than of direct runoff. A cluster-type analysis discriminated three types of events differentiated mainly by rainfall amount and antecedent rainfall conditions. The study highlights the role of the antecedent rainfall and the need for caution in extrapolating relationships between rainfall amount and hydrological response of the catchment.
Abstract. This paper examines sediment and metal (Al, Fe, Mn, Cu, and Zn) exportation at different timescales (annual, seasonal and event) during a 3-year period (2005)(2006)(2007)(2008) in the Mero River headwater, a rural catchment under humid temperate climate. Interannual differences were found both in annual loads and their distributions throughout the year. At annual scale, sediment and particulate metal loads followed the same trend as streamflow, while dissolved metals showed different patterns. Runoff events contributed to 63 % of the total sediment load, whereas particulate and dissolved loads in events accounted for between 38-61 and 27-49 %, respectively. Runoff events were characterized by high variability in sediment and metal loads, a few events representing a high percentage of the metal exported. Sediment loads were related to maximum and initial discharge. Particulate metal loads were highly correlated with sediment loads, runoff being the hydrological variable that best explains the load of these metals. Dissolved metal loads displayed different patterns. Dissolved Al, showed a great correlation with runoff, while dissolved Mn with maximum discharge.
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