Sauter mean diameter determination for the fine fraction of suspended sediments using a LISST-25X diffractometer

The LISST-25X ability for measuring the Sauter mean diameter of the fine fraction of sediment samples, SMDf, is evaluated. A simple algorithm to determine the SMDf is proposed. The algorithm is based on the standard output variables from the LISST-25X diffractometer: Sauter mean diameter of the complete sample, SMDt; Sauter mean diameter of the coarse fraction, SMDg; total suspended sediment concentration, SSCt, and coarse suspended sediment concentration, SSCg. Validation is performed in the laboratory by contrasting algorithm results from complete sediment samples against LISST SMDt measurements made on the fine fraction of the samples. A second validation is performed by comparison between algorithm results and Malvern measurements on the same samples. The samples are from the Salado River (Argentina) and the Paraná River (Argentina). Their SMDt range from 10 μm to 70 μm.Results indicate that the algorithm determines the Sauter mean diameter of the fine fraction in a reliable way, with average differences of 1.4 μm (algorithm-LISST comparison) and 3.4 μm (algorithm-Malvern comparison). The observed differences are attributed to operational conditions rather than to algorithm limitations. A correlation between calculated SMDf and d50 of the fine fraction is also established, with a determination coefficient of R2 = 0.46.

► Evaluation of the LISST-25X ability for measuring the size of fine sediments.
► Algorithm to determine the Sauter mean diameter for the fine fraction.
► Algorithm based on the traditional output variables from the LISST-25X.
► Good correlation between algorithm results and measurements made on fine sediments.
► Algorithm limitations attributed to operational conditions in the laboratory.