Investigation of first flushes in a medium-sized mediterranean catchment

The objective of this study is to investigate the significance and characteristic of first flushes in medium-sized agricultural catchments. Therefore, an analysis of the load distribution in the Vène River on the French mediterranean coast was done for first flood events in September 2003 and 2004. It considered total suspended solids (TSS), volatile suspended solids (VSS), total phosphorus (TP), soluble reactive phosphorus (SRP), total nitrogen (TN), organic nitrogen (org-N), nitrate and nitrite–nitrogen (NOx–N) and ammonium–nitrogen (NH4–N). Nutrient export was evaluated in terms of normalized cumulative loads (NCL) and three rating indices. Most important first flushes could be detected for ammonium (FF25 = 0.79) followed by TSS (FF25 = 0.72) and VSS (FF25 = 0.70). In situations, where first flushes can be important for downstream water bodies, a new concept for nutrient discharges should be considered taking into account the ambient pollution of the whole system.