Study On Rainstorm Waterlogging In Urban Community Scale Based On Rainstorm Scenario Simulation

In the context of global change and sea level rising,urban rainstorm waterlogging disasters occur frequently.Especially coastal cities in the southeast of China are significantly affected by typhoons and monsoons,and heavy rainfall often leads to urban rainstorm waterlogging.Rainstorm is the direct disaster factor of urban rainstorm waterlogging.The causes of rainstorm are different,and the characteristics of the rainstorm process and the spatiotemporal changes may be different.The characteristics of the urban rainstorm waterlogging may also be different.Therefore,it is of great significance to distinguish the disaster-causing factors of urban rainstorm waterlogging for revealing the characteristics of urban rainstorm waterlogging.This study took the Hecheng community in Ningbo as the study area,based on the meteorological data,typhoon data,pipe network data and geographic data.Firstly,the disaster-causing factors of urban rainstorm waterlogging were subdivided into two types of typhoon rainstorm and non-typhoon rainstorm from the perspective of the cause of rainstorms.And the time variation characteristics of typhoon and non-typhoon rainstorm were analyzed,and the typhoon and non-typhoon rainstorm scenarios were constructed.Then,the SWMM model was used to simulate urban rainstorm waterlogging under different scenarios.And the characteristics and differences of typhoon and non-typhoon urban rainstorm waterlogging were compared and analyzed.The main conclusions are as follows:(1)The time variation characteristics of typhoon and non-typhoon rainstorm: The interannual variation of precipitation and intensity both showed an upward trend in typhoon and non-typhoon rainstorm during 2014 to 2019.And the frequency showed a slight upward trend.Compared with non-typhoon rainstorm,the precipitation and intensity of typhoon rainstorm had a more obvious upward trend,and the interannual fluctuation was also greater and the fluctuation range was wider.Typhoon rainstorm was mainly concentrated in later flood season,with the highest frequency in September;non-typhoon rainstorm was mainly concentrated in plum rains season,with the highest frequency in June.The diurnal variation trends of precipitation and intensity were roughly the same in typhoon and non-typhoon rainstorm,and there were differences in the variation trends of rainstorm frequency.The high-value areas of typhoon rainstorm appeared from 23:00 to 4:00 and 8:00 to 15:00,and the high-value areas of non-typhoon rainstorm appeared from 2:00 to 11:00.The duration of typhoon rainstorm was affected by the typhoon path and intensity,the rainfall process was relatively short,the proportion of continuous rainstorm was high,and the rainstorm was more concentrated.Non-typhoon rainstorm had a low proportion of continuous rainstorm,but they could occur repeatedly during several days of continuous rainfall,and the rainfall process was relatively long.(2)Characteristics and differences of typhoon and non-typhoon rainstorm waterlogging: In terms of drainage river channels,the river level of typhoon rainstorm was mainly affected by the tide level.At high tide level,the river level was consistent with the tide level in different return periods,which all exceed the warning river level.The river flow was affected by the tidal level and typhoon rainstorm,and the flow increases with the return period.However,it was still mainly influenced by the tide level.At high tide level,the flow rate dropped to a negative value,causing backflow.In non-typhoon rainstorm waterlogging,the river level and flow were mainly affected by rainstorm,which increased with the increased of the return periods,but the river level did not exceed the warning river level.In terms of node and pipeline surcharge,the number of surcharged nodes,surcharged hours,hours above full normal flow and hours capacity limited during typhoon and nontyphoon rainstorm waterlogging all increased with the return period.Affected by the tide level,typhoon rainstorm waterlogging surcharge was more serious,the drainage conduit network load rate was higher,and node flooding was more likely to occur.The average flow was relatively small,and the drainage time was longer.In terms of node flooding,the number of flood nodes,flood hours,flood rate,and total flood volume in typhoon and non-typhoon rainstorm waterlogging increased with the return period.The total flood volume in typhoon rainstorm waterlogging was greater than that in non-typhoon rainstorm waterlogging,and the node flooding in typhoon rainstorm waterlogging was more serious.In terms of rainstorm waterlogging level,the number and grade of subcatchment areas where waterlogging occurred in the study area increased with the return period under the typhoon and non-typhoon rainstorm scenarios.And the accumulated water area was distributed from scattered to continuous.The area of accumulated water gradually expanded from Nanyanwu Street and Nanzhenan Street to the surrounding area.During the same return period,typhoon rainstorm waterlogging was more severe,the accumulated water lasted longer,and the depth of accumulated water was greater.(3)Causes of rainstorm waterlogging in study area: The occurrence of rainstorm waterlogging was related to rainfall,diameter and topography.Affected by the location,the study area was susceptible to typhoon and non-typhoon rainstorm.Urban rainstorm waterlogging increased with increasing precipitation.At the same time,storm surge brought by typhoon would affect drainage operation,increasing waterlogging.The drainage network in the study area was unreasonable.The diameter was generally small,the drainage conduit network load rate was high,the conduit surcharge and the node flooding were serious.The topography in some areas of the study area was low,and it was easy to gather water around and not easy to discharge.