黄河上游洮河流域全新世古洪水水文学研究

通过对黄河上游洮河流域详细的野外考察，在临洮段下堡村（XBC）发现保存有全新世古洪水滞流沉积物的地层剖面并对该剖面进行系统采样，综合野外观测和室内理化数据分析确定为古洪水滞流沉积物。结合全新世地层对比、文化遗物分析和释光测年，确定这期古洪水事件发生在300~480 a BP左右，相当于我国"明清小冰期"气候转折阶段。利用ArcGIS耦合HEC-RAS模型，在获取河道水文参数条件下，恢复其洪峰流量介于4 865~6 700 m³·s^-1。保持水文参数不变，对河道糙率系数进行灵敏度测试，给定糙率±25%的变幅，结果误差在-9.12%~6.57%之间。依据2012年洪痕高程，采用HEC-RAS模型恢复其洪峰流量，与实测结果相比较误差仅为-2.9%，说明利用该模型得出的结果是比较可靠的。该研究成果有效延长了黄河上游洪水数据序列，这对于该流域内防洪减灾、水利工程建设和水资源开发利用等具有重要的参考价值。

Hydrological studies of the Holocene palaeoflood in the Taohe River Basin of the upper Yellow River

Recent palaeoflood study has been very common in the middle and lower reaches of the Yellow River region, but few studies in the upper reaches of the Yellow River. In the paper, palaeoflood hydrological studies were carried out in the lower reaches of the Taohe River which is the second largest tributary of the upper reaches of the Yellow River. A set of palaeoflood slackwater deposits of the Holocene period were identified by using sedimentological criteria at the XBC site in Lintao County. They were interbedded in the riverbanks at XBC profile, and they were about 73 cm in thickness. Observation(color, structure and texture)and experiment analysis (magnetic susceptibility, loss-on-ignition and particle-size distribution)of the profile indicate that it recorded three episodes of palaeoflood events. These palaeoflood events were identified to occur in 300-480 a BP in the initial stage of "Ming and Qing Dynasties Little Ice Age", by using the Optically Stimulated Luminescence (OSL)dating method and checked by some anthropogenic remains. During this period from warm to cold, climate change was more severe. By using the HEC-RAS model, the palaeoflood peak discharges were estimated to be 4 865-6 700 m³·s^-1. We selected eleven cross-sections about 700 m along the river reach. At the same time, based on the same hydrological parameters, the roughness coefficient of the channel was tested for sensitivity with a given range of ±25%, the variance of the result is between -9.12% and 6.57%. This paper restores the 2012 flood peak discharge by the HEC-RAS model, and compared with the measured results, the error is only -2.9%. This shows that the reconstruction of the palaeoflood peak discharges by the HEC-RAS model is reliable. The result has important reference value for flood control and disaster reduction, water conservancy construction and water resources development and utilization in the basin. The findings also provide a reliable basis for flood frequency-peak discharge relationship estimation in the upper reaches of the Yellow River in future.