Estimating nutrient and sediment flood loads in a small Mediterranean river

Various methods were evaluated for estimating the loads of total suspended sediments and particulate associated and dissolved nutrients during floods. The six selected methods were compared using field data from two carefully sampled floods at the outlet of a small Mediterranean catchment. Water samples were available during floods at short time intervals (i.e. from 1 to 6 h time steps) and discharge was measured every 5 min. In the first step, the load estimators were compared on the basis of available data. Despite a fine description of the species concentration, there were significant differences in load estimates between the six methods. In the second step the sampling sensitivity of the methods was compared. For the two floods, 3000 random sub-samples were generated from Monte Carlo simulations. The estimates derived from the random sub-samples were compared to the load estimated by using the entire record. The results show that bias and precision are affected by the sample size and the transport phase of the species. Generally speaking, two methods allow reliable load estimation as long as a detailed water flow and at least three to four samples per day are available.

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