The Hydraulic Geometry of Chenglingji Outlet, Dongting Lake

Abstract

根据1951-1988年洞庭湖城陵研(七里山)站的水文测验资料,运用L.B.Leopold河床水力几何形态原理,建立洞庭湖出口──城陵矶水道的河相关系式,研究该水道水力几何形态的特点及变化研究表明,与河流水道相比,洞庭湖出口水道河宽指数b随流量的变化较小,而水深指数f及流速指数m随流量的变化较大,河床横断面具有窄深的特点主要原因在于洞庭湖对泥沙的分选沉积作用而使城陵矶水道水流挟沙力得以增强,而河流的冲刷作用却主要发生在河底近40年来,由于荆江三口分流水道的自然淤积和1967-1972年下荆江系统裁弯工程的影响,m值与m/f值均逐期增大,以及城陵矶水道输沙量显著减小,均促使该水道水流挟按力增大,河床冲刷增强,导致该水道横断面窄深的特点逐渐加强.;Based on the hydrologic data from Chenglingji (Qilishan) Hydrologic Station, Dongting Lake from 1951 to 1988, the formula of hydraulic geometry in the section of Chenglingji-Dongting Lake mouth-are constructed according to L.B. Leopold's principle on hydraulic geometry of stream channels. in addition, the characteristics and changes of hydraulic geometry of stream channels are also studied. As a result, the stream channel width exponent b of Chenglingji outlet changes little with the discharge, whereas the deepth exponent f and the velocity exponent m change greatly with the discharge. Moreover, the cross section of the Chenglinji outlet is getting narrow and deep. The main reason is that the deposition processes of the Dongting Lake leads to an increase in the sediment transport capacity of Cherglinji outlet, while the eroding processes take place in the channel bottom mainly. in the past 40 years, because of the natural depositions of flood diversion in 3 waterways of the Jingjiang River as well as the influences of the curve cutoff of the Low Jingjiang River in 1967-1972, the values of m and m/f are increasing with each passing way and the sediment transport rate is decreasing obviously in Chenglingji outlet. All of these make sediment transport capacity increase and the eroding processes of the stream channel strong, resulting a deep and narrow cross section of the outlet.