| Flood disaster is one of the most frequent and most destructive natural disasters in the world today.For thousands of years,flood disasters have always threatened the survival and development of the Chinese nation.Therefore,people have always attached great importance to the prevention and control of flood disasters.Since our country enter the 21st centey,the role of non-engineering measures for flood control and reduction has been recognized by people in the process of preventing and controlling flood disasters.Among them,the risk assessment of flood disaster can fully grasp the situation of regional flood disaster,and it is the prerequisite and preparation for scientific formulation of flood control and disaster reduction measures.The application of long time scale flood series data to flood risk assessment can extend the time scale of flood risk assessment and improve the accuracy of risk assessment for rare flood disaster.The Hanjiang River is a tributary of the Yangtze River with the highest frequency of flood disasters.Hanbin District of Ankang city,located in the low-lying areas of the Ankang basin,is the political,economic,cultural and transportation information center,and the old town of Hanbin District,witch built on the South Bank of the Hanjiang River,is a place where flood disasters occur more frequently since ancient times owing to the low terrain,concentrated and high intensity precipitation.In history,the old town of Hanbin District has been relocated for many times due to the influence of the flood disaster.In recent years,the project group has studied and investigated the flood evolution of the major flood events in the Holocene epoch of the Upper Hanjiang River.And their results can extend the flood sequence of Ankang section on the upper reaches of the Hanjiang River to a ten thousand year scale,improve the accuracy of the design flood,provide reliable data for the risk assessment of flood disaster and then provide the basis for the government of Ankang City to implement the flood control and disaster reduction work.On account of the analysis about the change characteristics of the flood disaster in the upper reaches of Hanjiang River,the paper takes Ankang section of the Upper Hanjiang River as the research area.Based on the hydrological data from the Ankang hydrological station,the historical survey flood data and the research results of the paleoflood,the paper calculate the flood frequency of the river section,analyze the inundation of 4 typical flood frequencies(0.01%,0.1%,1%and 10%)based on HEC-RAS model,build the risk assessment model,and evaluate the flood risk of the study area.Finally,the paper compare and analyze the results of two cases.The following conclusions are drawn:(1)The analysis of the characteristics about flood disasters in the upper reaches of Hanjiang River shows that,in terms of time,flood disasters in the upper reaches of the Hanjiang River in the historical period can be divided into three stages(221aBC?618aAD619aAD?1368aAD,1369aAD?2015aAD).Among them,the Eastern Han Dynasty and the Northern Song Dynasty were the period of high frequency of flood disaster in the former two stages respectively.At the same time,there are three circles of flood disasters in the upper reaches of Hanjiang River,2?3a,6?8a 16?18a,respectively.And the main circle is 17a.In terms of space,the frequency of flood disasters has obvious spatial difference,and the frequency of flood disaster in Hanbin Distric is the highest.The frequent flood disasters seriously threaten the lives and property of the people in the region.So it is necessary to analyze and assess the flood risk based on the flood sequence of different time scales in Ankang section.(2)The paper calculates the relationship between flood peak flow and frequency in Ankang section.The flood-peak discharge of a-100-year flood recurrence is 31230 m3/s and 31770m3/s respectively,the flood-peak discharge of a-1000-year flood recurrence is 42680 m3/s and 45200 m3/s respectively,and the flood-peak discharge of a-10000-year flood recurrence is 53810 m3/s and 58800 m3/s respectively based on the short time scale and long time scale of the flood sequence.The results show that,the flood peak flow,that calculated by the extension of the data series based on the limited measured flood and historical flood data,is obviously smaller than that of the data calculated by the data added to the ancient flood.So it is necessary to analyze and assess the flood risk based on the flood sequence of different time scales in Ankang section.(3)Based on historical flood and measured flood sequence,the high risk area of flood disaster in Ankang section is mainly concentrated in the old urban area with low topography,dense river network and well-developed economy.As the flood recurrence period increased from 10 years to 10000 years,the high risk area of flood disaster also expanded from the old urban area to the south of the new urban area and the proportion of the high risk area is increasing,which increased from 8.91%to 31.13%,with higher extent of increasing.(4)Based on paleoflood,historical flood and measured flood sequence,the high risk area of flood disaster in Ankang section is mainly concentrated in Ankang city and some village,including Bai village,Shuangjing village,Zhangwan village,etc,which distributed on both sides of the main stream and tributaries of the Hanjiang River.With the increase of flood recurrence period,the proportion of high risk area is also increasing,which increased from 4.89%to 32.19%,with a greater increase than before.(5)Through the comparison and analysis of the results of the flood risk assessment under the two cases,the distribution location of flood high risk area is basically same under two time scale flood sequences and the high risk area of flood disaster in Ankang section is mainly concentrated in Ankang city and some village distributed on both sides of the main stream and tributaries of the Hanjiang River.With the increase of flood recurrence period,the direction of high risk area is consistent based on two time scale flood sequences,the scope of high risk area is continuously extended from the old town on the South Bank of Hanjiang River to the new urban area,and the proportion of the total inundated area in the high risk areas based on the two time scale flood sequence has increased 22.22%and 27.3%,respectively.Under the same recurrence period,the high risk area of flood disaster based on long time scale flood sequence is larger.(6)Based on the results of flood risk assessment in Ankang section the corresponding engineering measures and non engineering measures for reducing the risk of flood disaster in the study area are put forward.The paper applies palaeo flood hydrology data to flood risk assessment firstly.It has a good reference value and improves the accuracy of risk assessment for flood disaster in Ankang section of the upper reaches of Hanjiang River,and provides a new way of thinking for flood risk assessment.The research results are of great practical value for strengthening disaster prediction,establishing and implementing flood emergency plan,minimizing flood loss and promoting healthy,stable and sustainable development of economy and society. |
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