Research On The Effect Of The Rain Garden On Rainfall Detention And Ecological Purification In The Southern Hilly Area Of Ji'nan

With the development of social economy and urbanization process,the shortage of water resources and the serious water pollution coexist with floods in Ji'nan.It is one of the effective ways to solve the problem by storing,retaining and utilizing some of the rainwater resources,and it plays an important role in improving the water ecological environment construction in Ji'nan,reducing the pressure of municipal flood and drainage pressure,and balancing the balance of water resources in Ji'nan region.The paper selectes the low impact development measure-rain garden as the main object,and the orthogonal test was carried out according to the specific experimental conditions and purposes.Firstly it is to determine the different levels,different factors under different structures of the rain garden,and then it is to carry out the preliminary experiment,the mid-term test and the post test analysis.The paper studys on the rain garden on runoff detention and purifying effect,and ascertains primary sorting of the influence of different levels and factors on the detention and purification effect,the significance of every factor to the results.The structure of the detention and purification effect rainwater garden is ascertained by using the comprehensive evaluation method-the TOPSIS method.At last by improving the TOPSIS method,it confirms the structure of the detention and purification effect rain garden with the specific functional requirements.The main results obtained in this paper are as follows,The rain garden have obvious effect on runoff detention,and the detention rate of each scheme is between 34.65%-82.83%.The integrated allocation scheme of the best rain garden detention effect is as follows:vegetation selection is purple loosestrife,selection of ingredients for planting soil layer is 50%garden soil+30%decaying leaf soil+20%river sand,the choice of artificial fillers is 30cm quartz sand+20cm coal ash,the particle size of artificial fillers is the small one.The comprehensive allocation scheme of the best rain garden purification effect is as follows:vegetation selection is the wolf tail grass,selection of ingredients for planting isoil layer is 40%garden soil+30%decaying leaf soil+30%river sand,the choice of artificial fillers is 30cm quartz sand+20cm zeolite,the particle size of artificial fillers is the small one.Using regional rainfall runoff simulation software-the storm management model(SWMM model),it studys on the application of rain garden in typical area of hilly area,analyzes different states and different area ratios of rain garden design to control the rainfall runoff and non-point source pollution.And it also determines the specific effects of different measures.The main results obtained in this paper are as follows:The larger area of rain garden design is accounted for on the runoff peak,peak flow lag effect.In addition,within the simulation range,the layout area of each doubling,the runoff coefficient shows the same reduction ratio.Compared with the single rain garden layout,in the LID+rain garden state,the peak concentration and the total pollutant reduction effect is obviously improved,and the peak concentration and total amount of pollutants decrease with the increase of rainfall return period.The research provides technical support for the design and application of rain garden and the implementation of specific measures for the construction of "sponge city".