STUDY ON OPTIMIZATION OF DRAINAGE SYSTEM CLOSURE UNDER WATER ENVIRONMENT CAPACITY CONTROL

The reconstruction of combined drainage network and the comprehensive treatment of black and odorous rivers in urban rivers have become hot issues. The determination of closure multiple is an important design parameter for water environment capacity treatment and pipe network reconstruction, but at present, the determination and research of closure multiple mainly rely on subjective experience, which is arbitrary and one-sided. In this study, the SWMM model (Storm Water Management Model) is used to establish the combined drainage network in the old urban area of W city center, and the model is calibrated and tested by using the actual rainfall and monitoring data. The overflow process of closure pipeline under different closure multiples is simulated. Results show that the SWMM model has certain applicability and feasibility for the variation process of overflow hydraulic and water quality of the drainage network in the study area. In terms of hydraulics, through simulation, the two rainfall events of Nash-Sutcliffe coefficient Ens are 0.83 and 0.85, respectively. For the water quality model, the Nash-Sutcliffe coefficients Ens of the export water quality indexes TSS, COD, TN and TP are 0.84, 0.82, 0.83 and 0.86, respectively. According to the result of n0=1, taking the increase of closure multiple n0 as an example, the annual overflow reduction rates are 15.52%, 25.67%, 31.80% and 34.95%, respectively. The annual closure growth rates are 8.48%, 16.35%, 22.15% and 27.65%, respectively. By reasonably determining the number of closure multiples n0, the economy and environment can be well balanced, which is conducive to the safe and healthy development of urban water environment system.