Jingjiang River Research Articles

Flood routing models in confluent and dividing channels

By introducing a water depth connecting formula, the hydraulic equations in the dividing channel system were coupled and the relation of discharge distribution between the branches of the dividing channels can be yielded. In this manner, a numerical model for the confluent channels was established to study the variation of backwater effects with the parameters in the channel junction. The meeting of flood peaks in the mainstream and tributary can be analyzed with this model. The flood peak meeting is found to be a major factor for the extremely high water level in the mainstream during the 1998 Yangtze River flood. Subsequently the variations of discharge distribution and water level with channel parameters between each branch in this system were studied as well. As a result, flood evolution caused by Jingjiang River shortcut and sediment deposition in the entrance of dividing channels of the Yangtze River may be qualitatively elucidated. It is suggested to be an effective measure for flood mitigation to enhance regulation capability of reservoirs available upstream of the tributaries and harness branch entrance channels.

Regulating Effect of Dongting Lake and Impacts on Runoff in the Jingjiang Reaches of the Yangtze River

The Dongting Lake has a high efficiency in regulating runoff of the Jingjiang Reaches of the Yangtze River. Based on the analysis of long term hydrological data, after the regulation of runoff, the annual average runoff amount, runoff amount of flood season and ratio of runoff amount of flood season to dry season decreased by 26.3%, 32.9% and 32.4%, respectively. Annual average runoff amount and runoff amount of flood season decreased along the river. All these are quite unique in the main stream of the Yangtze River. The maximum discharge amplitude Q k is 0.892 in the lower Reaches of the Jingjiang River which is the smallest among the main stream of the Yangtze River.

Particle Model for Simulating Flow over Large Areas

On the basis of traditional particle-in-cell methods, a particle model has been developed to simulate flow over large areas. Under the assumption that the fluid medium is an assembly of many small independent fluid particles, the momentum equation for a particle is derived for shallow-flow conditions. In the formulation used, only two forces are involved. One is the hydrostatic force arising from the accumulation of different numbers or particles at different locations. The other is a friction force that varies inversely with flow depth and quadratically with particle velocity and bed roughness. The velocity and spatial positions of all particles are averaged at fixed grid points to obtain the overall flow behavior. The particle model is demonstrated through an application to a documented 1954 flood in the Jingjiang River flood diversion area in Hubei, China. The flood lasted 300 h, with the total discharge volume being 4 billion m³. Good agreement between computed and observed water levels was obtained. Convergence of the method is demonstrated by repeatedly doubling the number of particles employed in the computation until there is little change between simulations.

The Hydraulic Geometry of Chenglingji Outlet, Dongting Lake

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.

Characteristics of runoff and sediment and regularity of alluviation and siltation in east and south Dongting Lake

通过实地调查并对1957年以来水文、泥沙观测资料做系统分析和计算,探讨东、南洞庭湖出、入湖水量、沙量的年际和年内变化特征,以及长江下荆江段裁弯对湖区径流和泥沙的影响。提出了湖区泥沙汛淤枯冲的变化规律及水位升降与湖区泥沙冲淤的关系;论证了丰、平、枯年湖区淤积严重,面积日益缩小对径流的调节作用正在减弱。;1.The inflow of East and South Dongting Lake mainly comes from West Dongting Lake and the Xiang-jiang River, making up about 78.3% of the total inflow.However.the hydrological regime is affected to a larger extent by the inflows of the Ouchi.Songzi and Taiping mouthes of the Changjiang River rather than by the Xiang, Zi, Yuan and Li rivers.The lake regulating function between flood and drought years is weak, since the correlation coefficient between inflow and outflow is 0.98.2.In flood season the inflow and outflow in the lake are concetrated in the period from May to Oct.Because the lake is charged by the inflow of the Xiang and Zi rivers before flood water of the Changjiang River comes, the regulating effect for flood of the Changjiang River is getting reduced.3.The suspended sediments of the lake mainly come from the three inlets.Their accumulation is dominant in the silt-abundant years, producing about 67 000 000 tons of sediments per year and 2.09 cm thick in average.4.The sediments of the lake are characterized by siltation during flood seasons and alluviation during drought seasons.Generally, the fomier occurs during the period of Jan.-Apr.and Nov.-Dec.and the latter between June and Sep..The maximum intensity values appear in Apr.and July to Aug., respectively.The total amount of yearly alluviation is much less than that of yearly siltation, so the lake is always in the serious silting situation whenever in flood year, average year or drought year.5.the curve cut-off on the part of the Jingjiang River obviously shows a decrease in the inflows from three inlets.Among these, the Ouchikou has a decrease of more than 60%.It also makes the sediment discharge decrease to some extent.The Ouchikou has a decrease of more than 50%, the Chenglingji about 40%, and the net sediment discharge only 16%.6.The lake is mainly in the silting status in case of high-water level.The alluviation intensity is much less than the silting intensity at any water level.The alluviation and siltation can be distinguished from the variation of water level.