Effects Of Low Impact Development Measures On Rainwater Utilization And Runoff Regulation

With the rapid development of urbanization,impervious areas in urbanized region increased rapidly and urban water cycle was greatly changed.The modification of urban surface morphology changed the natural runoff generation mechanism,resulting in decreasing infiltration,shortening the concentration time,increasing the peak flow and surface runoff,bringing forward the occurrence of peak flow and increasing the risk of urban waterlogging disaster.It is necessary to recover urban hydrological system to natural water cycle mode by applying the new urban development pattern of low impact development(LID).LID-based urban development can not only effectively use rainwater resources to mitigate the problem of urban water shortage,but also reduce runoff at source to alleviate urban waterlogging disaster.Taking the Xianlin Campus of Nanjing University as the study area,this study was carried out based on investigating the change process of land use,rainfall characteristics and waterlogging occurring situation in the study area.Firstly,the hydrological effects of land use change are analyzed,especially focusing on the impacts of underlying surface change on surface runoff generation.Secondly,in order to alleviate the negative impact of urbanization on urban hydrological system,the feasibility of applying LID measures in the study area is explored,and typical LID measures for rainwater utilization and runoff control are evaluated quantitatively according to the characteristics of LID measures on improving the utilization efficiency of rainwater resources and controlling runoff at source.Finally,the low impact development pattern of the study area is designed to achieve the goal of zero growth of surface runoff.The main conclusions are as follows:1.With the continuous construction of the study area,runoff is more likely to be produced.Annual runoff before the year of 2000 has little change due to the study area was under undeveloped situation.There was a substantial increase in runoff in 2010 when the first stage construction was completed in the study area.2.The requiring storing capacity for per square meters of the roof area is 0.0398 m3.The retention of concave green land is related to its concave depth.Rainwater at rainfall frequency 50%and 10%can be retained in concave green land when the concave depth is 13.51 mm and 35.53 mm,respectively.Comparing with setting up rain barrels,it is more suitable for applying of concave green land in the study area.3.LID measures of green roof,permeable paving,rain tank and concave green land are effective in surface runoff reduction based on hydrological simulation using SCS-CN model.The runoff reduced by green roof is related to precipitation.The runoff reduced by permeable paving and rain tank is related to precipitation and effective storage depth which has remarkable negative correlation with runoff.The runoff reduced by concave green land is related to rainfall amount and concave depth,and the reduction effect is better when rainfall is smaller and concave depth is deeper.4.Runoff control in the study area can be achieved by using the total annual runoff control target rate of 80%,85%,90%,corresponding to the design daily rainfall are 29.0 mm,35.4 mm and 45.9 mm.5.To achieve an annual runoff control rate of 80%,corresponding to the design daily rainfall 29 mm,it needs to implement LID measures of green roof,permeable paving and concave green land in the study area covering areas of 0.165 km2,0.581 km2 and 0.447 km2 respectively,and the concave depth of concave green land should be 0.2 m to achieve the goal of zero growth of runoff.