Identifying a reliable method for estimating suspended sediment load in a temporary river system

Sampling strategies and methods used for estimating load can lead to large uncertainties in suspended sediment transport quantification, especially in rivers with high variability in streamflow. The aim of this paper is to evaluate suspended sediment load, using a number of direct estimation techniques, in order to find a suitable method for temporary river systems and to assess the uncertainty associated with load estimation, due to the specific method applied. One year of continuous measurement of flow, and discrete sampling (n=216) of suspended sediment concentrations, taken from 2010 to 2011 in the Celone River (SE, Italy), were used to estimate annual load. Averaging, ratio and regression estimator methods were applied to the entire dataset, and to subsets of data, to calculate the load. The results show a wide range of values, from 220 to 1123 t km-2 yr-1, with respect to the applied suspended sediment load estimation techniques. Averaging methods resulted biased. Sediment rating curves underestimated load, while, if the back-transformation bias correction was used, load was overestimated. The ratio methods generally overestimate load. Increased precision and accuracy was achieved through applying data stratification, based on flow regime and seasonality. After applying three different flow regime stratifications, the annual load ranged from 240 to 606 t km-2 yr-1 and, using seasonal stratification, from 258 to 974 t km-2 yr-1. It seems that ratio estimator methods, and the regression equations applied to the stratification on a flow regime basis, are more suitable for estimating load in temporary, flashy streams.