Estimating the suspended sediment loads of rivers in the LOIS study area using infrequent samples

A central objective of the LOIS Community Research Programme is to provide estimates of the land ocean flux of suspended sediment from the LOIS study area. While high frequency (15-minute interval) suspended sediment concentration data are recorded within the programme at six tidal limit sites, infrequent (weekly-monthly) sampling undertaken by the Harmonized Monitoring (HM) Programme provides additional concentrati- on data for 23 tidal limit sites in the LOIS study area. In order that these infrequent data can be used to generate sediment flux estimates, the accuracy and precision of 22 load estimation procedures are assessed in the context of sampling frequency (weekly, fortnightly and monthly) and basin scales representative of the LOIS study area. Sampling frequency is demonstrated to exert a significant influence on the precision of the individual procedures, with precision being inversely related to sampling frequency. Accuracy is less clearly influenced by sampling frequency, although different procedures were identified as being the most accurate at the three sampling frequencies. Basin scale is shown to exert a significant influence upon accuracy and precision, with the performance of the load estimation procedures being inversely related to basin scale. For one interpolation procedure, an error correction procedure is developed, based on the strong relationship identified in this study between the error associated with individual flux estimates and the ratio of mean sampled discharge to the mean discharge obtained from the high frequency record. This relatively high resolution error correction method is applied to HM data from eight tidal limit sites in the LOIS area, and corrects the initial annual load estimates to provide values that are considered to be more representative of rivers from the LOIS study area.