Characteristics of the Yihe River Paleo-valley in the Last Glacial Maximum in Tangtou–Liudaokou Reach

The Tangtou–Liudaokou reach of the Yihe River is selected as the research object. The authors carried out electrical sounding and drilling work along Chuanliujie–Xiejiazhuang cross section. Drilling data of Liuhang rubber dam, Jiefang Road Yihe Bridge, Taoran Road Yihe Bridge and Luocheng Road Yihe Bridge were selected. Based on electrical sounding and drilling results and drilling data, five pieces of stratigraphical cross sections for the location of the incised valley were drawn. After that,14C and OSL samples of Chuanliujie cross section, Xiejiazhuang cross section, Liuhang cross section, Benghe River Bridge south shore and riverbed near Taoran Road Bridge were collected. The samples above were tested at the BETA Analytic Radiocarbon Dating Laboratory, AMS 14C Laboratory in Peking University and OSL Laboratory in Nanjing Normal University by14C and OSL methods. Twenty-six results were obtained and the conclusions are as follows: The incised valley about –70 m below Chuanliujie drill hole, about –69.53 m below the area around Liuhang rubber dam drill hole, –55.09 m below the area around Jiefang Road Yihe River Bridge drill hole, –50.36 m below the area around Taoran Road Yihe River Bridge drill hole and –56.35 m below the area around Luocheng Yihe River Bridge drill hole constitute the incised valley at the last glacial maximum period. The lithological characteristics at the bottom of Yihe River channel are complicated. Local deep cut was developed at Jiefang Road Yihe River Bridge and Taoran Road Yihe River Bridge because of fractural structure, lithology and branch inflows. Yihe River incised valley's breadth depth ratio is large, the channel is wide and shallow, and hence it belongs to the braided river.