Study On The High Efficient Sediment-carrying Water Volume In The Lower Yellow River After The Construction Of Xiaolangdi Reservoir

The Yellow River is famous in the world for the high frequency of disaster and the difficulty to be controlled. The main reasons are insufficient water and excessive sediment, which lead to a large quantity of sedimentation, the raise of the bed level year by year, and the decrease of the flood-conveying capacity. Along with the economical development in the Yellow River basin in recent years, the problem of the Yellow River becomes more protruding. To harness and explore the Yellow River, we must make full use of the limited water recourse to best meet the water-consuming requirement as well as to improve the serious sedimentation in the lower Yellow River. Thus, the high efficient sediment-carrying water volume in the lower Yellow River after the construction of Xiaolangdi reservoir is emphatically studied in this dissertation.By analyzing and summarizing the characteristic of water-sand and sediment-carrying in the lower Yellcw River, new concepts and methods to calculate the sediment-carrying water volume are stated. The sediment-can-yuig water volume and unit sediment-carrying water volume in the lower Yellow River are then calculated. Finally, the high efficient sediment-carrying water volume in the lower Yellow River after the construction of Xiaolangdi reservoir is studied by using the sediment mathematic model. The main conclusions are as follows,(1) Based on previous research and commenced on the analyzing of sediment-carrying mechanism, the function of transporting sediment of every part in whole water volume is studied according to the real sediment-carrying process in channel. Apart from the net water volume, the new concept of sediment-carrying water volume and its calculating methods base on the sediment-carrying efficiency, such as the sediment-carrying volume, the sediment concentration and scouring-depositing ratio, are put forward.(2) According to the field data of sediment and water volume in the lower Yellow River from 1950 to 2000, the characteristic of water-sand and sediment-carrying in lower Yellow River in different periods and their influential factors are analyzed. In the flood seasons of 1950-1959, 1960-1973, 1974-1985, 1986-2000 and 1950-2000, when the scouring-depositing ratio in the whole lower Yellow River is 0, the critical discharges at Xiaolangdi station are 3110, 3499, 3701, 3902 and 3349m3/s respectively, and the corresponding critical sediment concentrations at Xiaolangdi station are 30.13, 27.72, 18.72, 15.18 and 23.98kg/m3. When the scouring-depositing ratio is 20%, the critical discharges at Xiaolangdi station are 2038, 2178, 2356, 2499 and 2224m3/s respectively, the corresponding critical sediment concentrations at Xiaolangdi station are 49.19, 43.70, 34.96, 30.17 and 41.06 kg/m3.(3) According to their concepts and calculating methods, the sediment-carrying water volume and unit sediment-carrying water volume in the lower Yellow River from 1950 to 2000 are calculated, meanwhile, their characteristic is analyzed. Moreover, the relations between them andtheir influential factors, such as volume of runoff and sediment, discharge, sediment concentration, sedimentation, etc., are investigated and an equation reflecting the relation between the unitsediment-carrying water volume and sediment concentration, is established, q'=k Sm. In theflood seasons of 1950-1959,1960-1973, 1974-1985,1986-2000 and 1950-2000, the high efficient unit sediment-carrying water volumes of the lower Yellow River are 17.25, 19.40, 24.18, 27.99 and 20.63 m3/t respectively, the corresponding high efficient sand-transport water volumes are 183.76, 196.16,211.72, 224.18 and 200.22 10V.(4) Based on the real happened water-sand series in the lower Yellow River from 1974 to 1979, the optimized water-sediment combinations are studied by the sediment mathematic model. The optimization results show that adjusting the water-sand processes by Xiaolangdi reservoir can decrease deposit obviously and save water greatly. To transport the same amount of sediment in the flood season, up to 40% of water could be saved th...