汉江上游晏家棚段全新世古洪水研究

通过对汉江上游详尽的野外考察,在湖北郧县晏家棚河段全新世黄土—古土壤地层中发现3层典型古洪水滞流沉积物。在沉积学的基础上,使用OSL技术断代,确定3期特大洪水事件分别在1 000~900 a BP,1 800~1 600 a BP和3 200~2 800 a BP期间发生。采用"古洪水SWD尖灭点高程法"确定这3期古洪水事件的洪峰水位介于176.20~176.73 m。运用Arc GIS耦合HEC-RAS水力模型,推求这3期古洪水事件的洪峰流量介于53 770~55 950 m3/s,并从多种角度验证了该模型计算结果的科学性和合理性。将此结果与实测洪水和历史洪水资料接续,构成万年尺度洪水水文数据序列,得到汉江上游晏家棚河段万年一遇和千年一遇洪水的流量分别为59 100和45 200m3/s。采用HEC-RAS模型对研究河段进行古洪水模拟,方法科学,结果可靠。将该河段洪水水文数据序列有效地延长到万年尺度,极大地提高了设计洪水的可靠性。

Holocene Palaeoflood Studies of the Yanjiapeng Reach in the Upper Hanjiang River,China

Three bedsets of typical palaeoflood slackwater deposits (SWDs) were identified in the Holocene loess-soil sequence at Yanjiapeng (YJP) sites along the banks of Yunxian County in the upper Hanjiang River during the detailed investigations. They were studied by field observations and laboratory analysis. These extreme flood events were dated to 1 000~900 a BP, 1 800~1 600 a BP and 3 200~2 800 a BP with the Optically Stimulated Luminescence (OSL) dating in combination with the previously studies in the Hanjiang River. The palaeostages of these flood episodes were 176.20~176.73 m estimated with the elevations of the end-point of these SWDs. HEC-RAS model within an ArcGIS environment showed that the palaeoflood peak discharges ranged from 53 770 to 55 950 m³/s. The hydraulic parameters and the results were tested from different aspects. The results indicated that the palaeoflood peak discharges reconstructed by the HEC-RAS model were reliable and accurate. Besides, flood data series are extended to a 10 000year time scale established by a combination data of the gauged flood, historical flood and palaeoflood in the upper Hanjiang River, which provided the values of 59 100 m³/s and 45 200 m³/s for the 10 000 a and 1 000 a floods, respectively. This paper establishes a new way in hydrological reconstruction of upper Hanjiang River and is considerably significant in water resource management, flood mitigation and hydrological engineering.