Study On The LID Mechanism Of A Northwest Campus By SWMM And GIS Technology

As one of the seven geographical regions,the northwest region of China has a complex natural terrain and rich mineral resources.However,with the acceleration of the urbanization process and the continuous expansion of the city scale,the original natural landscape has gradually been replaced by impermeable surfaces such as road squares and other buildings in recent years.In addition,the unreasonable design of municipal pipe network has resulted in increasing surface runoff and causing serious urban waterlogging.As a new decentralized small-scale rainwater treatment measure,Low Impact Development?LID?can effectively relieve frequent urban waterlogging through retention and storage.According to the regional topographic and rainfall data,a storm-flood management model for a campus in northwest China was constructed on SWMM and GIS technology platform in this paper.Based on the measured rainfall data,sensitivity analysis,calibration and verification of model parameters were analyzed and calibrated.At the same time,the calibrated model was analyzed the variation rules of surface runoff process,node overflow and pipe section overloading in the study area under different development scenarios and design rainfall in different recurrence periods,and evaluated the effect of LID on waterlogging control.The main conclusions are as follows:?1?Based on the ArcGIS platform,the study area was generalized into 227 subcatchment areas,241 pipelines and 249 nodes?including 3 discharge outlets?,and the SWMM model of the study area was obtained by inpPINS software.?2?A modified Morris screening method was used to analyze the sensitivity of SWMM model parameters in the study area,and it was found that Des-imperv was showed high sensitive to the runoff volume and runoff peak under different rainfall intensity.Especially,it is higher sensitive to runoff peak.?3?The calibrated SWMM model was used to verify the discharge runoff process on May 6,2019?moderate rain?and October 15,2019?moderate rain?,the simulation results are in good agreement with the measured data.The E_NS values of the two rainfalls are 0.92 and0.806,both of which are greater than 0.75,indicating that the model based on the measured data rate is consistent with the law of production and sink flow in the study area.It has good stability and applicability,and its model parameters can be used to simulate the runoff process of the study area under different rainfall scenarios.?4?Under the conventional development scenario,the static water accumulation algorithm was used to simulate the overloading of rainwater pipe network nodes.It is found that the typical pipeline section 1-Y175 to 1-Y176 with a large slope and a low-lying section,and the pipeline section 1-Y239 to 1-Y250 near the discharge port,their overload depth of the pipe section was maintained within the range of 3.32-6.9m under the design rainfall during the high recurrence periodand,and the full flow state was maintained within 2 hours after the end of the rainfall.A long time overload depth will inevitably cause impact and corrosion on the inner wall of the full-flow pipeline,which may lead to a series of problems such as pipe network leakage and cross-contamination.In addition,when conducting Kriging Gaussian model interpolation analysis and waterlogging risk rating assessment,the area and proportion of high-risk areas increases with the increase of recurrence period.Especially under the long-term design rainfall,the proportion of high-risk area is above 60%.Compared with the conventional development scenario,the runoff control effect of the study area was evaluated for the designed rainfall in different recurrence periods after Green roof and Permeable pavement were added,and it was found that the runoff coefficients were reduced by 74.2%,68.1%,67.1%,66.9%,66.0%,59.1%,55.9%,and 52.3%,the decline of which is getting smaller and smaller as the return period increases.This indicates that LID has a good effect on the control of medium and small intensity rainfall with short recurrence period,but the effect of LID measures will reduce with the increase in recurrence interval.The annual daily rainfall data of Lanzhou city in 2018 were used to simulate the annual runoff control rate of each drainage area before and after the implementation of LID measures.The results showed that the total annual runoff control rate of the drainage area corresponding to No.57 and No.171 outlets had reached respectively 85.12%and 87.95%,and satisfied the control index requirements of 85%???90%stipulated in the sponge city technical construction guide.This result can provide reference for the determination of local runoff control target.