Abstract:

[Objectives] With the socioeconomic development, conflicts among the population, water resources, and the environment have become increasingly prominent. Conducting research on water quality and quantity in rivers that flow through urban areas and serve functions such as water supply and irrigation, and implementing rational scheduling, is of significance for ensuring a healthy aquatic ecosystem and enhancing the well-being of local residents. [Methods] The Nansu River Basin was selected as the research area. A one-dimensional hydrodynamic-water environment coupled MIKE11 model was constructed, utilizing chemical oxygen demand (COD) and ammonia nitrogen (NH₃-N) as key indicators. The external boundary conditions for the hydrodynamic module were defined by upstream inflow and downstream outflow, with observed hydrological data serving as model inputs. For the water environment module, the boundary conditions were established based on the water environmental characteristics at the river boundaries and pollutant discharge data entering the river. [Results] The water environmental capacity (WEC) refers to the maximum permissible pollutant load that a water body can assimilate per unit time under specified water domain boundaries, hydrological conditions, regulated sewage discharge modes, and predefined water quality targets. The monthly average WEC for COD and NH₃-N showed a consistent pattern, with the highest capacity observed during the high-flow season, followed by the normal-flow season, and the lowest during the low-flow season. Water quality in the Nansu River deteriorated rapidly during the early flood season. To improve water quality, seven scheduling schemes were proposed by addressing two key aspects: controlling pollutant inflow from tributaries and increasing mainstream flow. [Conclusions] Improving water quality requires intervention in two primary areas: controlling pollutant inflow from tributaries and increasing the flow of the main stream. Based on the actual conditions of the basin and a comparison of seven regulation schemes, the Oupugou tributary is identified as the primary source of pollution affecting the mainstream. While both approaches—pollutant inflow control and mainstream flow increase—can achieve water quality improvement, the effect of pollution control is more significant than that of flow regulation. According to the comparative analysis of the scheduling schemes, the optimal scheme for improving water quality is to close the sluice gates of the Oupugou tributary to prevent pollutant inflow, and to moderately regulate water flow to further improve water quality.

Key words: water resources scheduling, water quality and quantity coupling model, MIKE11, water environmental capacity, ecological scheduling, Nansu River