伊河龙门峡段全新世古洪水和历史洪水水文学重建

对伊洛河流域进行水文学和沉积学野外调查,在伊河龙门峡（LMX）地点发现典型的全新世黄土—古土壤剖面,根据野外沉积特征和磁化率、粒度分析判定该剖面夹有五层洪水滞流沉积层（SWD）。通过OSL测年和地层对比,确定该地层记录了四期五次特大洪水事件,分别发生在3100~3000 a BP、1800~1700 a BP、770~610 a BP和420~340 a BP,并结合史料等初步判断其中包含了AD 223和1761年历史洪水的沉积记录。这些古洪水事件与全新世气候恶化、转折和气候事件有明确的对应关系。采用古洪水水文学方法恢复洪峰水位,并采用比降—面积法计算出古洪水和历史洪水事件的洪峰流量介于14100~15800 m³/s。同时,根据实测获得1958年7月17日伊河龙门大洪水的洪峰水位和流量数据,采用相同参数和方法恢复其洪峰流量,误差仅有-3.6%,表明在该河段古洪水水文学重建所选参数和计算结果是可靠的。这些研究成果既证明季风气候区河流水文系统对全新世气候异常事件响应敏感,又为伊洛河流域水利、交通和防洪工程建设提供基础数据,具有重要的科学意义和实践价值。

Hydrological reconstruction of Holocene palaeofloods and historical floods in the Longmen Gorge of the Yihe River

In this study, palaeoflood hydrological and sedimentary investigations were carried out in the Yiluohe River basin. Typical loess-soil stratigraphy of the Holocene period was identified at the Longmenxia (LMX) site in the Yihe River basin. Based on the analysis of sedimentary characteristics, magnetic susceptibility and particle-size distribution, the five flood slackwater deposits were identified and interbedded into the loess-soil stratigraphy. By the stratigraphic correlation and the optically stimulated luminescence method (OSL), the four episodes of flooding events occurred at 3100-3000 a BP, 1800-1700 a BP, 770-610 a BP and 420-340 a BP, respectively, namely at the end of the mid-Holocene Climatic Optimum and the beginning of the late Holocene, the dynasties of Eastern Han to Western Jin, Song-Yuan and the Ming-Qing, respectively. These flooding events might include the AD223 and 1761 flooding events and they well corresponded to the phase of the Holocene monsoonal shift, climatic abrupt change and climatic decline. The flooding peak stages were estimated with the elevations and the depositional depths of the SWD. According to the flood peak stages and hydraulic parameters, the peak discharges were reconstructed at 14100-15800 m³/s with the slope-area method. The reconstructed peak discharges of the flooding events are much more than those of the gauged modern floods at the Longmenxia gauge station in the middle reach of the Yihe River.