Encounter Risk Of Rainstorm And Tide Level And Waterlogging Hazard Analysis In Zhong-Zhu Catchment Area

Under the influence of global climate change and increased human activities,heavy rain and waterlogging disasters occur frequently in China.The occurrence and damage degree of waterlogging disaster are affected by two disaster-causing factors,rainstorm in the waterlogging area and water level in the corresponding drainage area.When the rainstorm in the waterlogging area exceeds the designed value or the water level in the corresponding drainage area exceeds the designed value,the waterlogging phenomenon will occur.In order to reasonably determine the scale of drainage arrangements and drainage facilities in waterlogging areas,and to identify the characteristics of waterlogging disasters to provide guidance for disaster prevention and mitigation decisions,it is necessary to analyze waterlogging disaster from the perspectives of risk probability and disaster hazards.This study takes Zhong-Zhu catchment area,which across Zhongshan City and Zhuhai City in Guangdong Province,as the research object.The Annual Maximal Series sampling method and Peak Over Threshold sampling method are adopted to conduct risk probability analysis of rainstorm in waterlogging area and tide level in corresponding drainage area,and the risk law of rainstorm and tide level under different sampling methods is compared and analyzed.Meanwhile,in order to analyze the hazards of waterlogging disaster,the numerical model of waterlogging disaster is used to simulate the inundation scenario under different encounter conditions of rainstorms and tide level.The main content and conclusions are as follows:(1)The risk probability analysis results showed:(1)The encounter event was a small probability event when the annual maximum 24h rainstorm with return period exceeds 20 years occurred and the annual highest tide level with return period exceeds 5 years occurred at the same time.(2)If a certain return period is adopted as the waterlogging prevention standard for Zhong-Zhu catchment area,the actual probability of waterlogging occur is higher than the design frequency corresponding to waterlogging prevention standard,which reflects that the waterlogging disaster is formed under the combined action of two disaster factors of rainstorm and tide level.(3)At the same time,if Zhong-Zhu catchment area did not occur annual maximum 24h rainstorm with return period exceeds 100 years,it is very unlikely to encounter the annual highest tidal level with return period exceeds 5 years in corresponding drainage area.(4)By comparing the risk probabilities obtained by combining the 24h rainstorm in Zhong-Zhu catchment area with the tide level of tidal river and the tide level of sea area,it is found that the risk probability obtained by combining with the tidal level of tidal river are higher than results obtained by combining with tidal river of sea area.(5)By comparing the risk probabilities obtained by different sampling method,the results of risk probability obtained by the Annual Maximal Series sampling method are all less than results obtained by the Peak Over Threshold sampling method.(2)The results of waterlogging disaster numerical model show that:(1)In the case of annual highest tide level with 5 years'return period in corresponding drainage area separately encounter with annual maximum 24h rainstorm in waterlogging area with 5 years',10 years',20 years'and 50 years'return period,the maximum submerged water depth and submerged area increased with the increase of rainstorm return period,the maximum submerged depth is 0.93?1.35 m,and the submerged area is 36.23?57.48 km~2.(2)Among them,first appeared disaster area is also the main submerged area,located in Tanzhou area in the southern part of catchment area,the affected areas are mostly low-lying farmland,fishing ponds,etc.The Sanxiang area in the northern part of catchment area affected by the waterlogging in Tanzhou area in the south,the outflow of flood is impeded,and the central plain,which undertakes flood from mountainous areas on all sides,is severely submerged.The Zhuhai area in the eastern part of catchment area is dominated by urban areas.Under the circumstance that return period of rainstorm does not exceed 20 years,the main submerged area are located in the partial river section on the left bank of Guangchang River and the right bank of Qianshan River where Shaxin River diverting from,and there is no obvious waterlogging in the remaining location.With the increase of rainstorm return period,waterlogging gradually appeared on the both banks of the narrow river section of Dongguan River.(3)In the case of annual maximum 24h rainstorm in waterlogging area encounter with annual highest tidal level in corresponding drainage area,the sluices at the mouth of tidal river operate for a very short period of time,in most period,the water level in front of the sluice is higher than the river level inside the sluice,so the sluice is closed and logged water cannot be discharged;the waterlogging drainage of sluice at the mouth of sea area is more smooth,and the sluice can be kept open most of the time to discharge the flood into the corresponding drainage area.