Study On Urban Rainwater Resources Utilization And Hydrological Ecological Effects In Loess Area

With the acceleration of urbanization,the type of underlying surface of the city has changed,the drainage capacity of the rainwater pipe network has been limited,resulting in a large amount of rainwater accumulating on the surface,which has led to a series of problems such as urban floods.It is important to study the utilization of rainwater resources to solve urban water resources problems.Affected by climate and geological factors,water shortage and flood disasters have become the bottleneck restricting the economic and social development of arid and semi-arid loess areas in Northwest China.Due to the special engineering geological properties such as collapsibility of loess,the utilization of rainwater resources in the city is quite different from that in other regions.Based on the research on the utilization of rainwater resources and its hydrological and ecological effects in the main urban area of Xi'an,the main conclusions are as follows:(1)Analysis of the utilization potential of rainwater resources in the main urban area of Xi'an,and the availability of rainwater resources is 1.42×10~8m~3,which is similar to the annual average urban public water consumption in Xi'an,indicating that Xi'an has great potential for rainwater utilization.(2)The SWMM model was established in the southeastern part of the main city of Xi'an,and the LID facilities were arranged.Seven LID development models were set to simulate the rainfall runoff process during the recurrence period of 1a,2a,5a,10a and20a,respectively.It is concluded that different LID development models can reduce the total runoff,peak flow and integrated runoff coefficients in the study area.The effect of rain and flood control on different LID development modes under the same return period is from large to small:combination 4(green roof&rain garden&permeable pavement)>combination 3(green roof&rain garden)>combination 2(rainwater garden&water-permeable pavement)>rainwater garden>combination 1(green roof&water-permeable pavement)>green roof>water-permeable pavement.Among them,combination 4 has the best rain control effect.Compared with un-LID facilities,in the case of 10a rainfall,the total runoff reduction rate was 59.08%,the peak flow reduction rate was 66.83%,and the integrated runoff coefficient reduction rate was 59.08%.(3)According to the characteristics of loess collapsibility and water shortage in the study area,it is proposed to consider the engineering measures such as foundation treatment and anti-seepage when implementing the utilization of rainwater resources,and at the same time regard the“storage”and“use”as important aspects of urban stormwater resource utilization.The volume of the reservoir constructed in the campus of Yanta Campus of Chang'an University was calculated by the rainfall estimation method,the water consumption calculation method and the economic volume calculation method,and the reasonable volume was 760m~3.(4)Through the calculation of roof evapotranspiration in the southeastern part of Xi'an main city,it is concluded that the annual evapotranspiration generated by the presence or absence of green roof is 328.13×10~4m~3 and 49.48×10~4m~3,respectively,which differed by about 6 times.It shows that the green roof has a strong evapotranspiration effect.