Model-based carrying capacity investigation and its application to total maximum daily load (TMDL) establishment for river water quality management: A case study in Taiwan

The carrying capacity of a river was explored through combining use of HEC-RAS and Qual2K and the obtained results were applied to establishing the total maximum daily load (TMDL) system for water quality management, considering three water quality protection (i.e., long-, mid- and short-term) targets and two wastewater reduction strategies (i.e., individual- and group-reductions). Group-reduction control strategy was regarded as a better pollution control measure, in which more pollution reduction in high volume wastewater discharges resulted in a better improvement of river water quality. While many studies statistically investigated the conceptual framework of carrying capacity under the premises of mass balance between pollution sources and sinks, this study quantified the carrying capacity and established a TMDL system based on the respective water quality criteria using water quality modelling. [Display omitted] •Qual2K and HEC-RAS were used for carrying capacity and TMDL calculation.•Carrying capacity was estimated based on the respective water quality criterion.•The downstream carrying capacity becomes smaller because pollution accumulates.•Control of the high volume discharge contributes to significant pollution reduction.