Changing pattern of runoff coefficients in urban underlying surfaces under simulated rainfall conditions
YAN Chao, HU Haibo, XU Xiaomei, CHENG Hao, XU Hongjiao
1. Co-Innovation Center for Sustainable Forestry in Southern China, Nanjing Forestry University, 210037, Nanjing, China; 2. Jiangsu Province Key Laboratory of Soil and Water Conservation and Ecological Restoration, 210037, Nanjing, China
Abstract：[Background] The rapid development of cities leads to frequent occurrence of urban waterlogging, and thus the impact of urban underlying surface on urban runoff generation should be studied. Studies on the impact of underlying surface on runoff generation mechanisms are necessary in alleviating urban waterlogging.[Methods] Non-permeable surface of asphalt concrete and cement concrete, as well as permeable surfaces of coarse-grained permeable concrete, fine-grained permeable concrete, permeable bricks, grass-planting bricks, and grass were selected as the research objects. The three aspects of underlying surface characteristics, rainfall intensity, and rainfall duration were compared to analyze its impact mechanism. Standard runoff plots were set up, the rainfall simulation method was used to carry out precipitation of different rainfall intensities of 30, 60, 80 and 100 mm/h respectively. The runoff conditions were monitored, and the effects of different rainfall intensities and different rainfall durations on runoff coefficients were observed and compared.[Results] 1) Under the same rainfall intensity, the runoff coefficient of the impervious surface is greater than that of the permeable ones. Among them, the grassland has a prominent rainwater regulation and storage function, and the runoff coefficient is 0.27-0.41. 2) The variation of rainfall intensity significantly affects the runoffs of permeable pavements in a city, which is mainly reflectin in the variation of runoff coefficient. The runoff coefficient of urban permeable pavement is generally small when the rainfall intensity is small; while the runoff coefficient of urban permeable pavement tends increasing quickly when the rainfall intensity increases. The runoff coefficients of other permeable pavements reach over 0.6 or except for grassland and grass-planting bricks. Runoff reduces by 30% compared with impervious pavements. 3) The increase of the runoff coefficient of the permeable surface gradually is slow down as the rainfall duration increases, and the slowdown of it mainly occurs 60 min after the rainfall. 4) Compared with the impervious surface, the runoff coefficient of the urban permeable surface in a rainfall is more obvious. Regardless the underlying surface is grass, grass-planting bricks, permeable bricks, fine-grained concrete or coarse-grained concrete, the runoff coefficient increases fast in the first 20 minutes, and then the growth trend slows down; but the variation in runoff coefficient is still more obvious with the increase of rainfall duration.[Conclusions] To sum up, in preventing urban waterlogging, the ability of permeable pavement to reduce runoff is much higher than that of non-permeable pavement. Therefore, various types of permeable pavements are preferred in the construction of ecological cities and sponge cities. i.e., increasing urban grassland coverage, increasing the rate of urban permeable paving, preferential use of permeable concrete for roads, thus strengthening the drainage efficiency of permeable pavement, and reducing urban runoff from the root cause.
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2022, Vol. 20 
