Water Quality Monitoring Methods and Estimators for Efficient Estimation of Annual River Load

Abstract

Annual river load is the total mass entering receiving water bodies through a river. High-flow water quality monitoring has often been used in conjunction with periodic water quality monitoring to accurately and precisely estimate annual river loads. In this study, using daily water quality and discharge data from nine watersheds for a total of 25 years with seven water quality parameters, the load estimator that can provide accurate and precise load estimates was investigated based on two sampling strategies; monthly random sampling with high-flow sampling (eight samples per year) and discrete flow-proportional sampling with a sample size of 12. As a result, the bias-corrected regression estimator can provide accurate and precise load estimates for the former sampling strategy and the Horvitz-Thompson estimator can do so for the latter sampling strategy. The estimator by the rating curve method had a tendency to produce biased load estimates for the former sampling strategy and greater uncertainties for the latter compared to the other two estimators.