| Frequent extreme weather around the world has a huge impact on the city,which also affects the construction and development of the city.Among them,the problem of urban rainwater has been a serious threat to the city’s production,life,transportation and public safety.Countries around the world are seriously considering the issues on how to deal with the rainwater in the cities and on the realization of highly efficient utilization of the rainwater resource as reducing interference of it.The low impact development,best management practices,water sensitive cities,sustainable drainage systems and the rainwater storage plan,etc.are being used as the important methods of urban rainwater management which have been widely adopted abroad.In order to meet the rain problem,our country has proposed the construction idea of "Sponge City",which has been carried out nationwide with pilot construction and procured preferable effect."Naturally accumulating,permeating and purifying" is the basic principle,which is raised up by General Secretary,to construct the sponge city.Also,it is an important concept to make sure the sustainable development of sponge city.However,the construction of sponge city in our country mainly uses the foreign experiences for reference at present.It has made achievements,but at the same time because we ignored the specific condition difference between China and abroad,some problems occurred,which has aroused the introspection of the society and educational circles.In fact,it is not possible to rely solely on green infrastructure to solve all urban rain problems.Only the optimal combination of urban gray infrastructures and green infrastructures can achieve the best comprehensive benefit.Scientific analysis about the status of typical underlying surface of urban green space and developing basic research,to establish the appropriate response measures based on data analysis,and applied in design of urban green space is an important way of the rainwater optimization.The average annual rainfall in North Henan Province is not high and more concentrated,which causes the phenomena of alternating drought and deluge and great shortage of urban water resource.Urban greenbelt is the most important part to carry the rain water in the construction of sponge cities,whose typical underlying surface,in terms of construction,has a relatively higher flexibility.Therefore,how to develop the urban greenbelt’s rainfall penetration,storage and utilization function to the utmost extent under semiarid condition has very important theoretical significance and application value in conducting research of the typical underlying surface of the green space.This study selects Xinxiang City in Henan Province,one of the central cities in the north area of Henan Province,as the study area,and takes the typical underlying surface of urban greenbelt as the research object.Based on the study of rainwater process and taking the influence of soil and plants on rainwater as the key point of study,this paper designs the research project according to the research objective and works out the feasible research technical route.The study is carried out in a combination of research and experiment:the research part is mainly the soil sampling of green land in the study area and the research and classification of plant disposition pattern,at the same time,it also involves the questionnaire survey for the relevant designers;The experimental part mainly uses the testing data from scientific equipment,which is then taken into deeper analysis.It is supported by research and experimental data,and a feasible solution to the construction of underlying surfaces of typical greenbelt in Xinxiang is proposed on the basis of rain characteristics in the end.The study is comprised by 7 chapters,and main content is listed below:Chapter 1:This chapter introduces the thesis’ background and its significance as well as the typical representativeness and general situation by choosing Xinxiang as the research area.It discusses the underlying surface rainwater characteristics’ related concepts of urban green lands and defines the research category.A literature review was conducted in this paper,and it summarized the current situation and the progress of the research at home and abroad,which analyzed the achievements and shortcomings of these research results,and determined the specific research objectives,research contents and the research technology route.Chapter 2:The related theoretical basis has analyzed and combined with the study:the contents such as the spatial scale,pattern and process about the utilization of rainwater in the theory of green infrastructure can be used to guide the optimal design of rainwater on the underlying surface of the green field;The design theory of climatic sensibility requires the soil structure and plant allocation of the urban green space to make adaptive changes according to the climatic changes;Theory of ecological elasticity requires that green lands shall have certain elasticity,and accordingly the soil and plants shall also have certain rainwater elasticity.The theoretical frame has been established:analyze the self-formation of city greenlands from the point of rainwater and conduct a quantitive research about soil and plants’ capacity of rainwater;To comprehensively improve the elastic adaptability of green space from the perspective of rainwater optimization.Chapter 3:Physical properties of soil are critical to rain seepage and collection.The study on physical properties of soil in the research area facilitates the preliminary evaluation of seepage performance of soil and provides the selection of the further experimental materials and parameter setting with foundations.A total of 136 sets of data are obtained from 34 soil samples at 0-20 cm,20-40 cm,40-60 cm and 60-80 cm these four layers.And soil texture,moisture content,water suction and compactness condition are also analyzed and discussed.In the soil taxon in Xinxiang city,loam occupies the highest proportion.The texture is mainly silty loam.The vertical structure of the soil sample is complex,which also makes the infiltration process of rainwater very complex.There is some regular pattern of the soil moisture content of soil layer:The water in the surface layer can be dissipated easily,while rain cannot go deep into the inner layer.In addition,the groundwater level is comparatively low.So,the soil moisture content of the deep soil layer is comparatively low.Between interlayers,water suction also has some certain regularities:The first three layers of water suction gradually decline,but if it does not reach excessive moisture level,it is more suitable for the growth of plants when it goes deeper;Nevertheless,it rises again at 60 to 80cm,which affects the growth of deep-rooted plant somewhat.Distribution of Soil Compacting Degree:Compacting degree of green land soil is generally higher;compacting degree of surface layer is lower,and it rises gradually at 20 to 60cm;There appears extremely high compactness in some sample spots,which would greatly affect rainwater infiltration.The pertinence analysis among 7 indexes demonstrates that there exists complex pertinence among those indexes.Research results show:multi-index quantitative analysis of soil is the key premise to analyze the scientific construction of green sponge lands.Chapter 4:choosing three types of soil which were the most representative kinds and two types of modified mixed soil,then using the rainfall simulator and other kinds of experiment equipment to study the influence of rainfall intensity on soil infiltration and runoff as well as indexes such as the infiltration time,soil saturability,hydraulic conductivity,the biggest water-holding capacity and field capacity,and 34 d tracking and monitoring the changes of moisture content,moisture suction as well as compatibility of each type of soil during a certain period after raining.The results showed that the sandy soil has the highest infiltration capacity,the water is easy to be absorbed by the plants due to its small suction,and because of strong water conductivity capability,it is favorable for deep penetration of rainwater;The permeability of the clay is the worst,while the loam is in the middle,but the permeability of loam is still far lower than sand.The monitor showed that after the rain,the difference of the capability of sand to absorb water and the degree of compacting is smaller.This is better for the growth of the plants while the water-holding capacity in the field is low;While the clay is just of totally different trait,it has the lowest infiltration capacity with big water retaining force,which makes it difficult for plants to absorb the water.And it has poor water conductivity which would greatly hamper the water from infiltrating,but it has an advantage of high water retaining capacity;The indexes such as infiltration rate,saturated hydraulic conductivity,field water holding capacity,and compaction of the improved soil are superior to those of the former.The soil of urban green space needs to meet the greater infiltration requirements and therefore,it is necessary to make reasonable improvement on the soil.The mulch should be good effects on rainwater retention,moisture keeping and high-quality landscape.It is suggested that the ground-surface mulch,besides soil and plants,can be the third main type of underlying surface.Chapter 5:The results of the study which researched the hold back capacity of 7 kinds of grass plants and 3 kinds of hedge plants’ hold back capacity of rain in different rainfall intensity show that:with the rising leaf area index of the plants,its hold back capacity for the rain has increasing trend.The plant canopy instrument has been used to monitor the leaf area indices of the main garden plants in the research area from March to October,and the data showed that the leaf area indices of different species of plants vary greatly;the monthly variation differences of the leaf area indices of the same plant are also quite large;and most plants reach the maximal value of its leaf area index during months from June to August.Taking the urban green space of Xinxiang City as the research object,the main plant allocation pattern of road green space and other green space was summarized.The typical configuration mode using composite page area index was calculated,the results showed that land-cover plants should be paid attention to increasing coverage and adopting the higher leaf area index of species;The collocation gradation of tarbor and bush plants and the planting area of the plants with higher LAI(leaf area index)are two main influence factors.Increasing the total plant coverage,improving the gradation collocation and choosing the plants with higher single LAI should be noticed in the design to achieve the best result of rainwater interception.Chapter 6:The standard and rainwater-optimized design model are put forward from aspects of the soil,plants and covering,based on the research of Xinxiang City,considering city green lands’ present situation and planning and sponge city project,with reference to this research snd other existing results.It discussed and suggested some specific measures on the optimization strategy of rainfall in the typical underlying surface of Xinxiang City’s stocked green area and incremental green area.Chapter 7:This chapter summarized the research results,analyzed the deficiencies and put forward the research prospect. |
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