Statistical approach to sediment sampling accuracy

A variety of hydraulic and ecological processes in rivers depend in part on the grain size distribution of the riverbed. For this reason it is importa nt to accurately sample the bed to determine the grain size distribution. T o describe the accuracy of riverbed sediment samples, techniques based on t he multinomial distribution are presented. These techniques allow confidenc e intervals to be calculated for grid, areal, and volume samples. Additiona lly, sample sizes can be estimated to achieve a desired accuracy for the th ree sample types. A transformation is necessary when considering areal and volume samples. This is because neither of these two sample types is well c onditioned for statistical analysis. The transformation is based on the res ults of a previously performed grid sample. The transformation then estimat es either an areal or volume sample size that is necessary to match the acc uracy of the grid sample. This procedure is useful when obtaining a hybrid distribution from grid and areal samples. Having areal and grid sample resu lts of known accuracy allows confidence intervals to be placed on the final hybrid distribution. A series of laboratory experiments is used to illustr ate the various techniques. Comparisons are also made with techniques prese nted in the literature.