中文摘要：

古洪水水文学是全球变化科学领域的新兴学科。通过对渭河上游天水段基岩峡谷的详细考察,对在杜家坪村附近发现的全新世古洪水滞流沉积剖面进行了深入研究。沉积学观察和分析结果表明这些沉积物为洪水悬移质泥沙沉积形成,因而其主要成分为粉沙,分选良好。其磁化率值很低,表明它们是全新世晚期的沉积物,还没有受到风化成壤作用的改造。通过与其下游宝鸡峡全新世古洪水沉积剖面的地层学和考古年代学对比,确定其发生的时代在3200-3000aBP之间,即全新世大暖期结束之时。利用古洪水水文学方法,求出该组古洪水沉积层所记录的特大洪水的洪峰流量介于23460-25480m^3/s之间。同时,通过进一步分析验证,表明对于古洪水洪峰流量计算结果是可靠的。本研究获得了渭河万年尺度特大洪水的水文学数据,延长了洪水水文数据序列,在工程水文领域有重要应用性价值,对于揭示全球变化的水文响应具有重要的科学意义。

英文摘要：

Palaeoflood hydrological studies were carried out at the upper reach gorges of the Weihe River. Palaeoflood slackwater deposits were found at the DJP site in the Tianshui gorges of the mainstream of the river. Analysis of the grain-size distribution indicates that these SWD consist of silts and clayey silts, sourced from the suspended sediment load of the floodwater. The low magnetic susceptibility indicates they are fresh deposits without weathering and pedogenic alteration. Stratigraphic correlation with the SWD discovered downstream at the Guchuanzhen site of the Weihe River shows that these extreme floods occurred between 3200-3000 a BP at the end of the mid-Holocene climatic optimum. The reconstructed peak discharges of the palaeofloods range from 23,460 m^3/s to 25,480 m^3/s which are much larger than gauged floods. These results were further tested and proved to be reliable with reconstruction of the modern floods at the same reach. This research is of great importance for hydrological engneering and flood mitigation. And it is also very important for the establishment of the relationships between extreme flood events and global climate change.