A modified approach to determine mean sediment load and related discharge indices for suspended sediment transport

Discharge indices, viz., half-load discharge (Q1/2), and functional-equivalent discharge (Qfed), can be used to quantify the effectiveness of flow distribution in sediment transport through a river network. Q1/2 represents the flow below and above which half of the total long-term sediment load is transported, while Qfed indicates a uniform flow that replicates the total magnitude of the sediment load transported by the complete discharge distribution. In Magnitude Frequency Analysis (MFA), these indices are computed based on the estimate of mean sediment load (μS) transported through a river network. Conventionally, the analytical expression for μS was derived by assuming the discharges to be lognormally (LN) or Gamma (G) distributed. However, the assumption of discharge distribution is location specific and hence LN or G distributed discharge may not be valid for all catchments. Thus, it is necessary to assess the uncertainty in the estimate of μS and thereby the estimates of Q1/2 and Qfed when the discharge data do not follow either LN or G distribution. In this study, a modified approach is proposed to determine μS and related Q1/2 and Qfed for the general distribution of discharge datasets. The Proposed Approach (PA) includes the transformation of discharge data by applying the Box-Cox transformation followed by the estimation of μS, Q1/2, and Qfed. Furthermore, an analytical expression is derived for the solution of μS under the proposed framework. A simulation experiment is performed to establish the effectiveness of PA over the conventional (LN or G -based) approaches. Results indicated that PA provides reliable estimates of μS, Q1/2, and Qfed. The utility of the PA is demonstrated through its application to suspended sediment transport in four South Indian rivers.