Influence Of Structure Change Of Underlying Surface On Comprehensive Runoff Coefficient Of Urban Construction Project

With the development of urbanization in China,the traditional development of construction projects has led to an increase in the area of hardening within the city,leading to the occurrence of urban flooding disasters as well as causing huge losses.The spread of hardening area makes the urban runoff coefficient continue to increase,and the total runoff volume and peak flow also increase greatly.Therefore,the use of pervious ground and green space in urban construction projects has become the top priority for urban soil and water conservation.However,in practical applications,the design of pervious paving and green spaces generally adopts an empirical estimation method.This article will analyze the structure of the underlying surface,explore the impact of changes on the hydrological effects of urban construction projects,and make an evaluation.In this paper,the residential communities and industrial projects in Beijing are taken as the research object.The scenario simulation method is used to simulate the underlying surface structure under different building densities and green land rates in accordance with the relevant regulations.The design rainfall at the frequency of 3 years is selected for the project area.The total amount of stonnwater runoff within the effluent and the comprehensive runoff coeff icient under the storage facility were calculated.The change trend of the structure of the underlying surface was analyzed.At the same time,combining the construction investment for the underlying surface in the project areas,the optimal underlying surface structure ratio under various scenarios was explored.The results show that the total amount of efflux runoff and the comprehensive runoff coefficient of the residential community and industrial project are positively related to the area of the hardened underlying surface in the area,negatively related to the area of the surface of the permeable submerged surface and the outdoor pavement.The minimum is obtained when all the floors are covered with water and all the green areas are sunken.Residential communities and industrial projects have different proportions of optimal underlying surface structure that can meet flood prevention and flood prevention requirements which minimum investment within the project areas in the combination of different building density and green land ratio,and whether or not there is a rainwater storage facility In the case of the best underlying surface structure ratio is also different.After analysis,the ratio of the underlying surface structure can be represented by the rate of sunken green and flooding pavement.In the residential community projects,if the project is in a built-up areas,the best ratio will be most easily achieved under various scenarios when the green area rate and the permeable paving rate are 50%and 70%respectively;if the project area is in a new development areas,It is easy to obtain the best ratio when the permeable paving rate is 100%.In industrial projects,the ratio of the best underlying surface can only be obtained when the project is in a built-up area and there are storage facilities.As the area of hardened area increases,not only does the rainwater storage tank need to be set,but also the concave green space needs to be adjusted and the required volume of the rainwater storage tank increases as the area of the hardened underlying surface increasing.The rate of concave green areas and permeable paving is also increased It has been verified that the optimal underlying surface structure ratio obtained from the research results meets the requirements of the project construction and it can be applied to the design of the actual underlying surface structure.This study provides a direct guide for designing the underlying surface structure while preparing the water impact assessment report.