Study On Coupling Modelling And Control Measures Of Urban And Rural Nonpoint Source Pollution In Dianchi Lake Basin

China has made progress in water pollution prevention and control in recent years;however,the situation of water pollution in key river basins is still serious.The daily changes of water pollution emissions brought by nonpoint source pollution are not taken into consideration by the watershed water quality management system,which is based on the annual load target control.The existing watershed nonpoint source pollution load calculation methods just combine the urban and rural nonpoint source pollution load roughly,and cannot simulate the temporal and spatial characteristics of nonpoint source emissions to provide effective and reliable technical support for watershed water quality management.This study established a comprehensive watershed nonpoint source pollution load simulation system based on the coupling of urban nonpoint source pollution load simulation model SWMM and the rural nonpoint source model IMPULSE-extend.Dianchi Lake Basin were chosen as the study area to carry out nonpoint source pollution load simulation and identify daily load emission characteristics.The emission reduction potential of nonpoint source pollution load reduction strategies was quantitatively calculated and key issues of nonpoint source pollution control were put forward.The rural nonpoint source model IMPULSE-extend was developed by adding the modules of calculating nonpoint source pollution loads for unenclosed agricultural watersheds,river nodes and interactive agricultural grids to the model IMPULSE.An agricultural watershed and a drainage zone in the central city zone in Dianchi Lake basin were selected to calibrate the parameters in the simulation system.The calibration results of IMPULSE-extend model showed that Nash coefficients of simulated runoff,SS,TN,TP and COD were 0.77,0.78,0.80,0.67 and 0.32.The Nash coefficients of validation results were 0.46,0.20,0.39,0.63 and 0.66,respectively.The calibration and validation Nash coefficients of SWMM model for hydrological parameters were 0.78 and 0.40.Nash coefficients of SS,TN,TP and COD in water quality calibration results were 0.52,0.33,0.27 and 0.42,respectively.Based on the parameter identification and validation results,the daily nonpoint source water pollution emission load of 25 rivers discharging intoDianchi river basin in 2010 was simulated.The total annual nonpoint source SS,TN,TP and COD load in 2010 discharging into Caohai were 12714.6 tons,136.3tons,101.2 tons and 3314.7 tons.The load discharging into the Waihai were99782.2 tons,2002.7 tons,702.6 tons and 23888.8 tons,respectively.In this study,the upper reaches of the Panlongjiang River Basin were chosen as the research area for nonpoint source pollution control strategy analysis.Daily loads of 7 kinds of nonpoint source pollution control strategies were simulated.The results showed that the conversion of cropland to forest and terraced fields performed well on both total and daily maximum water pollutant loads reduction.The reduction rates of terraced fields in SS,TN and COD pollution load were 7.7%,15.3% and 5.8%,respectively.Slow release fertilizer reduced TN total and daily maximum load by 7.8% and 12.6%,respectively.Roof rainwater collection device performed the best in reducing nonpoint source TP pollution load.The total load and the maximum daily load reduction of TP reached 8.3% and 7.3%,respectively.