Representative point-integrated suspended sediment sampling in rivers

Point-integrated bottle sampling is the traditional method used to acquire the mean concentration of suspended sediment. Sample duration is assumed to average over enough variability to represent the mean suspended sediment concentration. No study has examined the effect on point-integrated sampling. Here, we analyze continuous hour-long measurements of suspended sediment and grain size fractions collected using a LISST-SL in the sand bedded portion of the Fraser River, BC. Mean concentrations for suspended sediment and grain size fractions were computed over increasing time periods and compared to a long duration mean concentration to determine when a sample became representative. A cumulative probability distribution was generated for multiple iterations of this process. All suspended sediment load and grain size fractions bear a low probability of accurately representing the actual mean concentration over standard bottle sample durations. A probability >90% of accurately representing the mean of volumetric concentration requires 9.5 minutes of sampling.