Laboratory Measurement of Sediment by Turbidity

A low cost light transmission instrument is used to measure the concentration of suspended sediment in river water samples. Problems which have confronted previous workers such as the fast reduction of instrument sensitivity with grain size of sediment are investigated and the method shown to be viable. Good performance with acceptable accuracies and very short measuring times are shown to apply for samples in the concentration range 100 mg/L to 2000 mg/L. Sand sized particles are not measured with the laboratory instrument, although clay and silt sized particles are measured satisfactorily. A method is described of correcting the results for particles which are not measured, applicable to rivers which carry only small proportions of suspended sand. The method is described and tested for laboratory application only, but the findings of the Calibration section may be applied also to field instruments which work on the turbidity principle.