Analysis Of The Present Situation And The Combination Of Different Sponges On Sponge City Construction In The Main Urban Area Of Xi'an

To provide a scientific basis and reference for the construction of sponge city at Xi'an existing-blocks.The article takes the main urban of Xi'an as an example,through the storm flood management model(SWMM)and others,the dependable rainfalls of the construction of sponge city were determined and the underlying surface permeability of the main urban in Xi'an was analyzed.The storage capacity and combination of different sponges were evaluated.At the same time,the related designed parameters of commonly used sponges and storage volume for the construction of Xi'an sponge city were determined.The results showed that:(1)Compared with 2000,the ratios of impervious areas in Xi 'an increased by11.29%,and bare lands,water,and vegetation decreased by 9.39%,9.39% and 9.39%respectively in 2015.The impervious areas of six districts in Xi 'an from large to small were: Lianhu(94.52%)> Beilin(94.22%)> Xincheng(88.49%)> Yanta(82.26%)>Weiyang(76.20%)> Baqiao(40.50%).(2)The renewal of park green space should be taken the first for the construction of sponge city at Xi'an existing-blocks.And then,a small amount of public facilities and residential lands would be renewed.So the corresponding requirements of the country would be reached.(3)The influence of collapsible loess should be noticed for the construction of Xi'an sponge city.It must be careful to use the rain infiltration facilities in southern and northern suburbs in Xi'an and the natural penetration way should be adopted preferentially.Other areas can take measures to strengthen the infiltration.(4)When the total annual runoff control rates(?)were 50%,80% and 85%,thecorresponding dependable rainfalls were 6.76 mm,17.43 mm and 21.22 mm,respectively.And the corresponding rainfall intensity were light rain level,moderate rain level and moderate rain level.When the dependable rainfall was 21.22 mm,the construction of sponge city can control rainfalls effectively for 87.14% of the whole year rainfall days.(5)The storage capacity of complex biological detention facility is very strong,and it should be constructed preferentially for the construction of sponge city.In the case of no clogging,the effect of the permeable pavement is also obvious in reducing the runoff.To avoid clogging of the permeable pavement,the seepage gap should be reserved and the permeability coefficient and porosity of the permeable layer should be increased.The storage capacity of planted ditch for rainwater is strong,and the effect is obvious in reducing runoff.So it should be used preferentially when the rainwater must be diverted.(6)The aquifers thickness of the sunken green space and biological retention facility are recommended to be 150 mm and 300 mm respectively.In order to ensure the biological retention facility on the efficiency of removing pollutants,its substrate thickness should not be less than 300 mm.The substrate thickness of permeable pavement should to be 200 mm,but in order to prevent clogging,the thickness of the substrate may be increased appropriately.(7)To meet the requirement of ? that construction of sponge city in Xi'an,the simplified calculation method of corresponding volume as followed:V=K×AV—volume(m3)A—area(ha)K is taken 30 to 64 for existing-blocks,K is taken 50 to 85 for new constructed city.