| There are many rivers and lakes in the plain water network area of the Taihu Lake Basin,and both natural and social resources are abundant.It is one of the areas with the highest degree of urbanization in China.However,with rapid urbanization,the number of rivers and lakes in the region has decreased,and the impervious surface has increased significantly.In addition to the increase in extreme precipitation events in the region,water problems such as frequent flooding disasters in the river basin have occurred,which has seriously affected the safety of people’s lives and property and the regional sustainable development.In response to the frequent occurrence of floods and waterlogging disasters in the study area,in recent years,the construction of flood control projects has been continuously strengthened,and the drainage pattern has changed accordingly,bringing new challenges to regional flood control.Therefore,there is an urgent need to explore the research on the changes of storm floods of different magnitudes in the return period under the background of rapid urbanization,so as to provide a more reasonable reference for flood prevention and disaster reduction in the Taihu Basin under the new situation.This article takes the plain water network area of the Taihu Lake Basin(Su-Xi-Chang area)as an example,and comprehensively uses multidisciplinary analysis methods such as geography,hydrology and hydraulics to "extreme precipitation and characteristic water level changes in the context of urbanization-rainstorm,flood recurrence period Change-the impact of urbanization on the flood process of different magnitudes of recurrence period " as the main line,analyzed the changes of storm floods of different magnitude of recurrence periods in rapid urbanization areas,and explored the impact of different human activities on the flood process of different recurrence periods Degree,main research content and results are as follows:(1)Characteristics of spatiotemporal changes of extreme precipitation and water levelThe maximum precipitation day,maximum 5 day rainfall and heavy rain days were selected as the extreme precipitation index.The annual maximum water level,average water level and minimum water level were selected as the characteristic water level.The statistical method was used to analyze the spatiotemporal changes of extreme precipitation and characteristic water level in the study area.The results are as follows:(1)The spatial distribution of annual precipitation,precipitation during the flood season and extreme precipitation index in the Taihu Plain water network area are characterized by higher southeast and northwest,and lower middle area.Through inspection,they all showed an insignificant upward trend.Moreover,the coefficient of variation of precipitation in the flood season is large,and there are many extreme weather in summer.There is a high possibility of extreme precipitation weather in the extreme value center with short duration and long duration.(2)The spatial distribution of characteristic water levels in the water network area of the Taihu Plain shows an increasing trend from southeast to northwest.Using the M-K trend test,it is found that the characteristic water levels all show a significant upward trend,and the overall water level in this area has increased.(2)Changes in the recurrence period of storm floods of different magnitudesFirstly,the highest water level sequence is revised through the current analysis to ensure the consistency of the hydrological sequence.Using the P-III frequency curve to calculate the frequency of storm floods in the past years,and using the Kriging interpolation technique,combined with the contour map method to construct the relationship between time-recurrence period-storm flood,quantitative analysis of the change law of the storm flood recurrence period.The results show that:(1)The extreme precipitation in each typical magnitude recurrence period in the Taihu Plain area from 1960 s to 2010 s showed an increasing trend,and the frequency of extreme precipitation increased.(2)The water level of the small-scale flood recurrence period(once in 5 and 10 years)shows a rising trend of fluctuation,and the frequency of flooding increases;the larger-scale flood recurrence period(once in 50 years)shows a significant difference between urban and suburban stations.Under the recurrence period of the same magnitude floods,the water level of urban sites showed a trend of rising from 1960 s to 1990 s and decreasing from 1990 s to 2010 s.For example,the flood level of Changzhou Station in the 1990 s increased by 10 cm compared with1960,and the flood frequency increased by 36%.By 2010,it fell to 5.9 m,and the flood frequency decreased by 12%.However,the water level of the suburban sites showed an overall upward trend during the study period.For example,the water level of Pingwang Station in the 2010 s increased by 10 cm compared with 1960,and the flood frequency increased by 28%.(3)For smaller magnitude floods,the underlying surface changes such as land use changes and river network water system attenuation have a greater impact,resulting in higher flood levels and increased flood frequency;while larger magnitude floods are affected by gate pumps,etc.Water conservancy projects have a greater impact,and a large number of flood prevention projects can reduce the flood level.The flood level in suburban areas has increased to a certain extent and the frequency has increased.(3)Simulation analysis of storm flood process of different magnitudes under urbanizationBy constructing the MIKE11 hydraulic model in the Changzhou water network area,and combining different design scenarios,the impact of urbanization on the flood process of different magnitude recurrence periods was explored.he results show that:(1)The impact of urbanization on the flood process of different magnitudes of recurrence is as follows: urbanization has a small impact on a small-scale rainstorm flood in 10 years,which is mainly manifested by the decrease of the water level in the central urban area and the rise of the water level in the suburbs.The peak water level varies from 2 cm to 13 cm.For large-scale rainstorm events,the impact of urbanization on the flood process is more significant.The peak of the water level in the central urban area dropped by 27 cm,the peak current time was advanced by 2 h,and the high water level lasted shorter.The water level outside the surrounding and suburban areas increased significantly.The change range of the peak water level ranges from 13 cm to 31 cm,the change range is large,and the peak present time and the high water level duration both change significantly.(2)The process of storms and floods of different magnitudes in different urbanization areas is as follows: For low magnitude floods(once every 10 years),the peak water level of floods in highly urbanized areas is obviously controlled,generally controlled at 4.2-4.4m.The peak water level of low-urbanization areas varies greatly,generally ranging from 3.6 to 4.6m,which is higher than that of highly-urbanization areas as a whole.In addition,for high-level floods(once in 50 years),the average peak water level of floods in highly urbanized areas is lower than that in low-level urbanized areas,generally 4.9-5.3 m. |
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