末次盛冰期长江南京段河槽特征及古流量

Characteristics and Runoff Volume of the Yangtze River's Paleovalley at Nanjing Reach in the Last Glacial Maximum

根据南京长江大桥、三桥、四桥的地质钻孔资料,绘制南京段长江古河槽地质剖面示意图。对拟建南京长江四桥附近的四个钻孔进行了采样分析,从钻孔沉积物样品的14C年代及阶地形成时间,可以判断,南京段约-60m^-90m的深槽为末次盛冰期时的长江河槽。钻孔揭示,南京段长江古河槽狭窄陡峭,呈V型,在南京长江大桥附近形成局部深切。根据长江三桥、长江大桥附近古深槽断面形态及底部沉积物颗粒级配,选用沙莫夫公式、河海大学公式等,计算了末次盛冰期时河槽底部的泥沙起动流速及断面平均流速。根据流量—流速—过水断面之间的关系式,计算得出末次盛冰期时长江的流量约为12000~16000m3/s。

Three cross-sections of paleovalley depositional sequences were established with references of hundreds of bore data and documents of the No.3, No.1 and No.4 Nanjing Yangtze River bridges. Through analyzing age results of ^14C from samples of four drilling cores near the No.4 Nanjing Yangtze River Bridge （to be built）, we can find that the time range of paleovalley is dated LGM at a depth of-60--90 m near Nanjing. It is also indicated that the deep incised-valley channel was narrow and the fiver flew swiftly. The ancient Yangtze River deep channel presented partially and deeply incised features near the No.1 Nanjing Yangtze River Bridge. According to previous publications, much research has been done on the main paleochannel of the Yangtze River, but few results have been achieved on discharge estimation. In this paper, the incipient velocity and average velocity of the LGM was calculated with Vc = 4.60d^1/3h^1/6,Vc=1.281g（13.15h/d95）√gd,V≈6.5u＊｜h/d90｜^1/6,etc.,in terms of the fiver shape, sedimentary grain size and sequences near the No.3 and No.1 Nanjing Yangtze River bridges. Moreover, the discharge in Nanjing reach of the Yangtze River during the LGM has been estimated to be around 12000-16000 m^3/s according to the relationship of discharge, velocity of flow and cross-section.