汉江上游郧西段全新世古洪水事件研究

古洪水水文学是全球变化科学领域的前沿课题.通过对汉江上游的深入调查研究,在郧西段基岩峡谷发现全新世古洪水滞流沉积地层.通过沉积学观察研究,采样分析和与2010年汉江洪水滞流沉积物的粒度、磁化率特征对比,判定为典型的全新世洪水滞流沉积物(SWD).通过全新世地层对比和光释光(OSL)测年,确定其记录了全新世时期3200-2800 a BP的特大古洪水事件.在确定了古洪水洪峰水位和相关参数的基础上,采用比降法水文模型推算出该期洪水洪峰流量在48830～51710m3/s之间.同时在该断面观测了汉江上游1983年、2005年和2010年洪水洪痕水位,采用相同水文参数和模型,恢复了其洪峰流量,与白河水文站实测流量比较,误差在1.99％～4.21％之间,说明我们对于古洪水水文参数选择与洪峰流量计算结果是合理的.从而将古洪水数据加入洪水频率序列中,建立了万年尺度洪水流量与频率关系.该研究成果为汉江上游水资源水能源开发利用和防洪减灾等,提供了重要的水文资料.

The Holocene Palaeoflood Events in the Yunxi Reach in the Upper Reaches of Hanjiang River

Through field investigation in the upper reaches of Hanjiang River,palaeoflood slackwater deposits(SWD)were found in the bedrock gorges in the Yunxi reach.Based on field observation,laboratory analysis including grain-size distribution and magnetic susceptibility,and comparison with modern flood deposits,this SWD is identified as the most typical Holocene palaeoflood deposits in the Hanjiang River basin.By using stratigraphic correlation and OSL dating method,the palaeoflood events were dated to 3200-2800 aBP at the turn from the middle to late Holocene.According to the palaeoflood peak stages and hydraulic parameters,the peak discharges of the palaeoflood were reconstructed to 48830-51710 m3/s by using the slope-area method.At the same time,the flood peak discharges of 1983,2005 and 2010 extraordinary floods were reconstructed with the same method and hydraulic parameters in the same cross-section.The error between the reconstructed and gauged discharges is 1.99%-4.21%.This shows that the reconstructed palaeoflood peak discharges are reliable.The flood peak discharge-frequency relationship at 10000-year time scale is established by a combination of the data of gauged flood,historical flood and palaeoflood hydrology.