| The flood disaster is one of the major natural disasters which always affect the production and people's livelihood in our country. In order to solve this problem and protect the production and people's livelihood, getting the long scale hydrological series is becoming more and more important. At present, many scholars have researched the Paleoflood of some rivers in our country, and reconstructed the ages and the peak discharges of floods in ten thousands scale. The Paleoflood study in some rivers have involved the largest historical flood, but the techniques of the Paleoflood study in the age determination are limiting, so that the age of the largest historical flood is just an extent, not an accurate value. However, there are accurate ages in historical flood records, but this records lack of the accurate peak discharges, so we need to make a combination about the study of the Paleoflood and the historical flood. Thus, the textual research of the largest historical flood has an important significance in the scientific studies, on the one hand, it can provide an accurate age to the largest historical flood by the geologic records, on the other hand, it can also solve the problem about the short series of the measured flood, and improve the accuracy of the hydrological computation.The upper reaches of Hanjiang River is located between the Qinling Mountain and the Bashan Mountain, it is an important dividing line about the natural environment of the North and the South of China, and the monsoon climate area of the temperate area and the subtropics, and it is also a sensitive area of the regional climate changes. The Hanjiang River located in the center of the two big Mountains, and the flood disasters are always happen frequently in that this special terrain. In the recent years, the largest historical flood in the geologic records has been found with the development of the study about the Paleoflood, but there are not an accurate age in the largest historical flood because of the limit in the techniques of the age determination. Thus, the textual research about the age of the largest historical flood in the geologic records need to make a combination with the historical documents. It has a great theoretic and practical significance in some respects, such as the water conservancy, hydropower projects, constructions in flood control and the rational plannings about using the water resources.On the basis of the research results about the slackwater deposits (SWD) in the upper reaches of Hanjiang River by our research group, this paper collated the frequency of the historical floods in this region, analyzed the change laws of the times, spaces, periodic characteristics, hierarchies, and the flood impacts by the Excel and Arc-GIS. This paper researched the age of the largest historical flood in the geologic records in the upper reaches of Hanjiang River during the Eastern Han Dynasty through analyzing the flood change laws and the characteristics about depositions of the flood marks. By this researches, the paper got some conclusions are following:(1) This paper collated the 7 profiles about the flood slack water deposits(SWD) of the largest historical flood in the upper reaches of Hanjiang River during the Eastern Han Dynasty, they are LJT profile, XTC-B profile, LJZ profile, TJZ profile, GXHK profile, QFC-B profile, and LWD-A profile. Then, I collated the flood records in historical documents about Qin Dynasty to Sui Dynasty, and found that the flood frequency about 13 times is the most in the Eastern Han Dynasty. This conclusion proved the result that the Eastern Han Dynasty is a floods-prone period.(2)This paper researched the characteristics about the flood disasters in the upper reaches of Hanjiang River during the Eastern Han Dynasty. In the rule of the years, as time passed, the flood disasters'frequency was increasing in the Eastern Han Dynasty. In the rule of seasons and months, flood disasters was concentrated obviously in the upper reaches of Hanjiang River during the Eastern Han Dynasty, and flood disasters happened intensively in autumn, and the it was the most in September. In the rule of spaces, the Hanzhong Basin was a high frequency center of the flood disasters, and the frequency of flood disasters was decreasing gradually from the West to the East in the upper reaches of Hanjiang River, the Ankang Basin and the Nanyang Basin were the local small high-frequency center. In the analyses of hierarchy, the mild and severe floods were most in the upper reaches of Hanjiang River during the Eastern Han Dynasty, and the severe floods were happened intensively in the late Eastern Han Dynasty and their damages had the trend of worsening. In the periodic characteristics, the frequency of flood disasters had three obvious periods in the upper reaches of Hanjiang River during the Eastern Han Dynasty, they were 3-4a,8-10a, and 16-18a, and this consequences correspond to the strength of the solar activity. In the impacts analyses, the flood disasters in the upper reaches of Hanjiang River during the Eastern Han Dynasty made a series of direct and indirect impacts on social economy and agricultural development.(3) This paper analyzed the 5 times severe flood disasters, found that the flood disasters involved places about the two floods in Sept.197 and Aug.219 were more widely. Then this paper analyzed the historical flood records about this two floods in some respects, such as the refugee problems, social unrest and agriculture cultivation. And this paper researched the characteristics about depositions of the flood marks. In the end, we got the age of the largest historical flood in the upper reaches of Hanjiang River during the Eastern Han Dynasty was Sept.197.(4) This paper sort and analyzed the peak discharges of the 7 profiles about the Eastern Han Dynasty, the peak discharge of the LJT profile was 47900m3/s, the peak discharge of the XTC-B profile was 63830 m3/s, the peak discharge of the.LJZ profile was 60800 m3/s, the peak discharge of the TJZ profile was 58000m3/s, the peak discharge of the GXHK profile was 64321m3/s, the peak discharge of the QFC-B profile was 65830m3/s, the peak discharge of the LWD-A profile was 65420m3/s. This paper found that the extent of peak discharges about the largest historical flood in the upper reaches of Hanjiang River during the Eastern Han Dynasty was 47900m3/s-65830m3/s.(5) This paper analyzed the reasons of the flood disasters frequently occurred in the upper reaches of Hanjiang River during the Eastern Han Dynasty from two aspects about the natural factors and the social factors, found that the main reasons were the special climate in the Eastern Han Dynasty and the special terrain conditions in the upper reaches of Hanjiang River.The textual research of the largest historical flood in the Eastern Han Dynasty solved the problem that the age determination of the Paleoflood is not accurate, and provided an accurate extent of the peak discharges for the largest historical flood. This research provided the data references and theoretical supports for us to make the scientific and effective countermeasures for reducing the flood disasters and constructing the water conservancy projects. |
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