Study On Low Impact Development Rainwater System In Loess Region Based On Sponge City

Driven by the global warming environment and the accelerating urbanization process,urban waterlogging has become an important issue facing major cities,posing a huge threat to people’s lives and property.The reasonable utilization of rain and flood resources is a perfect choice for solving the problem of urban waterlogging.With the concept of sustainable development deeply rooted in people’s hearts,the sponge city was born.Due to the influence of its own geographical location,the loess region of China is in the contradiction of water shortage and urban waterlogging.In view of this contradiction,from the perspective of the sponge city,this article takes the Lanzhou Jiaotong University campus as the research object.First,based on the basic rainfall data in the study area,the Lanzhou rainstorm intensity formula is derived to determine the rainfall parameters of the later model.Then,a rain-flood runoff model is developed using the United States Storm Management Model(SWMM).Finally,the suitable LID measures are selected to simulate the effects of rainwater flood control in the study area under different LID measures at different recurrence periods.The main research conclusions of this article are as follows:(1)Based on the rainfall data of Lanzhou city in the past 20 years,according to the requirements of "Code for design of outdoor wastewater engineering"(GB50014—2006,(2016 edition))and "Technical Guidelines for the Preparation and Design of Rainstorm Types for Urban Rainstorm Intensity Formulas" The samples are selected by the annual maximum method to form statistical samples of different durations.Trends are adjusted by relying on Pearson III type distribution.According to the determined frequency distribution curve,the relationship between rainfall intensity(i),rainfall duration(t)and recurrence period(P),—the i-t-P data table is obtained.The calculation of the formula parameters uses the least squares method,and finally the Lanzhou heavy rain intensity formula is obtained.The accuracy of the formula after inspection has met the requirements of the specification.Aiming at the distribution of rainfall patterns in the study area,the Chicago rain pattern is selected as the design storm statistical model,and the calculated comprehensive rain peak position coefficient is 0.382.(2)Generalize the study area by artificial division,establish a storm runoff model in the study area,and set the basic parameters of the model by combining pipe network distribution data,field survey data,SWMM model manuals,and literature data.The calibration and verification of the model parameters are performed based on the two measured rainfall and discharge data in the study area.The Nash efficiency coefficients are greater than 0.7,the relative errors of the flood peak discharge are less than 10%,and the absolute errors of the peak time are relatively lower small,the simulation of the model is more consistent with the actual runoff process,and the accuracy of the model is higher.(3)According to the characteristics of the study area and the applicability of the LID measures,permeable paving and rainwater gardens are selected as the low-impact measures.There are three schemes in total.The first scheme is a separate arrangement of the rainwater garden,the second scheme is a separate arrangement of the permeable pavement,and the third scheme is a combined arrangement of the rainwater garden and the permeable pavement,which respectively simulate the runoff process of the study area at different recurrence periods under different schemes.(4)Taking the peak runoff,total runoff,peak time and runoff coefficient as the basic comparison parameters,the three schemes have a certain reduction effect on the peak runoff,total runoff and runoff coefficient in the study area,and the peak time appears delay.The third option is the best control effect when the rainwater garden and permeable pavement are combined.During the recurrence period 2a,5a,10 a,20a,50 a,the total runoff is reduced by 58.9%,56.6%,53.2%,53.2%,51.1% and 49.8%,the peak runoff is reduced by 57.0%,55.1%,52.5%,49.8%,48.7%,and the runoff coefficient is reduced by58.9%、56.6%、53.2%、51.1%、and 49.8%.When arranged separately,the rainwater garden runoff control effect is better than permeable paving.Both measures showed an upward trend in the control of total runoff and peak runoff,but the control rate showed a downward trend.This paper quantitatively studies the effects of low-impact development facilities on urban flood control,and compares and analyzes the reduction amount and reduction rate of each single LID facility and combined measures,with a view to providing suggestions and references for the construction of sponge cities in the loess region.