Turbidity-controlled sampling for suspended sediment load estimation

Automated data collection is essential to effectively measure suspended sediment loads in storm events, particularly in small basins. Continuous turbidity measurements can be used, along with discharge, in an automated system that makes real-time sampling decisions to facilitate sediment load estimation. The Turbidity Threshold Sampling method distributes sample collection over the range of rising and falling turbidity values and attempts to sample all significant turbidity episodes. A data logger activates a pumping sampler when specified turbidity conditions are met. The resulting set of samples can be used to accurately determine suspended sediment loads by establishing a relation between sediment concentration and turbidity for any sampled period with significant sediment transport. Relations between turbidity, concentration, and particle size are examined at five sites in northern California, USA. Despite the influence of particle size, turbidity is in all cases superior to flow as a surrogate for sediment concentration.