Study On The Impacts Of Underlying Surface Change On The Waterlogging In The Downtown Area Of Wuhan

With the acceleration of urbanization in major cities in China,urban waterlogging disasters have become more and more serious.From 2010 to 2016,nearly 180 cities suffered from waterlogging disasters every year,"Every rain will flood" has become an urgent urban problem to be solved.In recent years,heavy rainfall in Wuhan has also caused frequent waterlogging in the whole city,resulting in huge economic and social losses.It is urgent to carry out waterlogging control in Wuhan as one of the first construction pilot of spongy cities in China.The mechanism of rainstorm flood control is complex and involves many factors,among which the change of urban underlying surface plays an important role in urban waterlogging.It is of great significance to study the influence of the underlying cushion on urban waterlogging to reduce the loss of urban disaster and to assist the construction of sponge city.In this paper,the urban waterlogging situation in Wuhan city is analyzed,and the GWR model is applied to study the correlation between the underlying surface characteristics and urban waterlogging,and the spatial differentiation of the influencing factors of rainstorm is studied.Then,the effects of underlying surface change and rainfall intensity change on urban runoff are studied.Finally,the effects of low impact development(LID)measures on urban waterlogging control are simulated and evaluated,and the following laws are found:(1)The influencing factors of urban waterlogging.The effects of drainage system,land use,landform and soil texture on the severity of waterlogging were studied.The relationship between rainwater system and waterlogging is most significant,and the densities of drainage outlet and drainage network are highly consistent with the distribution of waterlogging.Next is land use type,the proportion of impermeable surface area has the biggest influence on the waterlogging,while the permeable greenbelt and waterhave obvious regulating and storing effect on rainwater,and there is a negative correlation with the degree of waterlogging.The elevation and slope factor also affected the degree of waterlogging.The areas with large topographic fluctuation and unstable topography were more likely to experience water accumulation.Due to the high urbanization of the surface water impermeability,the impact on waterlogging is relatively weak.The results of GWR model show that different factors affect the severity of waterlogging in different spatial locations.The river plays its role of regulation and storage in the old urban area along the river,while the inland area far away from the river is more dependent on the drainage function of the drainage pump station.There is a negative correlation between the content of sand and the degree of waterlogging in the outer space of the central city,and the permeability of soil can still play a role in alleviating urban waterlogging.(2)Effect of underlying surface change on waterlogging In the case of relatively stable urban soil types and landforms,the effect of underlying surface change on urban rainstorm waterlogging is mainly reflected in the impact of land use change.From 2011 to 2015,natural resources such as vegetation and waterin downtown Wuhan were encroached upon and the area of urban construction land increased significantly.The surface storage capacity of rainwater is weakened,and the runoff coefficient is obviously increased.When the proportion of urban green space increases,the storage function of underlying surface will be obviously improved.Under the condition of rainfall intensity of 50mm,when the proportion of urban green land occupied increases from 25%to 35%,about 2.4%-20%of rainwater runoff could be controlled.With the continuous increase of the rainfall in different return periods,the runoff depth of rainwater,which is raining for an hour,increases gradually,while the runoff depth and runoff coefficient increase gradually,and the increase of rainwater runoff coefficient decreases gradually.The increase rate of runoff depth and runoff coefficient is the highest while return period equals five years.The higher the soil moisture in the early stage of rainfall,the worse the storage capacity of soil to rainwater,which led to the greater runoff depth and runoff coefficient of rainwater.The runoff production capacity of different land use conditions is different,but the difference between runoff depth and runoff coefficient of different land use schemes decreases with the increase of rainfall intensity.Through low-impact development measures,it is possible to control rain runoff at a low cost without changing landuse type and rainwater pipe network,thus greatly reducing the pressure of the urban drainage system.