Risk analysis for flow duration curve based seasonal discharge management programs

A non-seasonal discharge standard may be too stringent and not cost-effective for a season of large flow, if the variation of seasonal streamflow of a river is significant. Seasonal discharge programs established based on streamflow variation were therefore explored in this work. A design procedure using the flow duration curve method, two total-mass-load based discharge programs, linear programming, and Monte-Carlo analysis is proposed for determining and analyzing the pertinent seasonal division of a two-season discharge management program. The flow duration curve method was used to compute the design low flow. The maximal total waste load and uniform treatment programs were the two total-mass-load based programs analysed. Linear programming models were established to determine the optimal division of seasons based on the objective of maximally allowable total waste load. Monte-Carlo simulation with QUAL2E-UNCAS was implemented to assess the risk of violation of water quality of seasonal programs. The proposed procedure is demonstrated in a case study of the Tung-Kang River basin in Taiwan.