Abstract:

Based on the research on palaeoflood hydrology in the upper reaches of Hanjiang River, the palaeoflood events recorded by slackwater deposits in upper layers of 6 loess-soil profiles were found to occur during the Eastern Han Dynasty. In this paper, the flood time of the palaeoflood events during the study period was examined textually by the historical literature analysis, and the flood simulaton was made using the HEC-RAS model. The study results showed that the palaeoflood during the Eastern Han Dynasty might be an extraordinary flood event that occurred in September (lunar month), the second year of the Jian'an period (197) in terms of the influence scope, degree, intensity, and the deposit rule of the floodmarks. Then selecting reasonable channel sections and roughness coefficient, and setting the river boundary conditions and initial conditions, we used the HEC-RAS model to conduct the flood simulation of the palaeoflood events. The errors between the simulated and the calculated flood stages were -0.18%~0.25%. Moreover, the errors of the simulated flood stages in 1983 were 0.25% less than those of the floodmark stages in 1983 found near the profiles. The flood simulation results showed that the selected channel sections and hydrological parameters were accurate and reliable, indicating that the palaeoflood events during the Eastern Han Dynasty might be an extraordinary flood event. The study results not only prolonged the flood sequences, but also provided the important hydrological data for the hydropower project construction, water resource management and the flood control and disaster mitigation in the upper reaches of the Hanjiang River.

Key words: the palaeoflood events, sedimentary record, Eastern Han Dynasty, the upper reaches of Hanjiang River, textual research