Grain size controls on turbidity-based suspended sediment estimation

Two different optical sensors were used to investigate the relationship between the grain size of suspended sediment and turbidity readings. Turbidity measurements are frequently used in practice to assess sediment transport in water bodies. If the influence of grain size on turbidity sensor readings is ignored or insufficiently addressed, the estimated sediment concentrations and, consequently, sediment amounts can be biased. This contribution presents laboratory results from an experiment on the dependence of turbidity readings on different grain size and concentration regimes. The importance of grain size is demonstrated using three wide grain-size range sediment suspensions and seven narrow grain-size sediment suspensions. Additionally, the findings were applied to a real-life example to illustrate how misleading “simplified” sediment rating curves can be when assessing sediment load.