Present Elevated Situation of the Lower Yellow River and

Preliminary Discussion on Its Regulation

Xie Jianheng

(Wuhan University of Hydraulic and Electric Engineering)

Abstract   The sediment load entering the Lower Yellow River is so larger than that transported to the deep sea that the siltation of the river channel and esturay is unavoidable. Increasing the sediment-carrying capacity of the river channel can only delay the channel siltation but, after all, it can not change the situation from aggradation to degradation. Therefore, the principle to control the river bed aggradation is not mainly to increase the sediment-carrying capacity, but is to decrease the incoming sediment load, increase the deposited area  and reduce the influence of estuarine deposition on the upstream affects of back water.

Key words   Elevated river, incoming sediment load, erosion datum, dredging, warping.

Types and Mechanism for Formation of Sediment Disasters

Jing Ke   Li Fengxin

(Institute of Geography, Chinese Academy of Sciences)

Abstract  The sediment formed by the actions of water flow and gravity has the dual characters resulting in disasters and to serving as a precious resource. In light of the processes and features of disaster, sediment disasters may be divided into direct and indirect types. Landslide, collapse and debris flow are the direct type, and flood disaster caused by sediment transport and deposition is the indirect. Analyzing the cases of the Lower Yellow River, it is found that the prerequisites for indirect sediment disasters are severe soil erosion and serious sediment yield in the upper and middle basin of the river, intense sediment transport in gullies and trunks, restriction of sediment accumulation and inharmony in the relation between oncoming water flow and sediment load.

Key words  sediment disaster types, mechanism of sediment disaster formation.

Abstract   Based on particle size data of suspended sediment at three anchored (25h) stations and ten hydrographic stations in a longitudinal profile   during spring and neap tides in low freshwater season(in Nov.1994), the paper discussed the changes of the size distribution region of suspended sediment and the tidal cycle by means of statistics and calculations of different size fractions and median diameters as well as particle size parameters of suspended sediment, and indicated that the distribution is mainly influenced by the factors of sediment sources, resuspension   of bottom sediment by tidal scour and flocculated settling of suspended sediment. Of which, the action of the second factor during spring tide is more remarkable than that during the neap tide, while the action of the third factor during the neap tide is more pronounced than that during the spring tide.

Key words  Jiaojiang River estuary, turbidity maximum,particle size of  suspended sediment, response.

Abstract  Obvious differences of transport mechanism exist between the uniform and non-uniform sediment. In this paper, some transport mechanisms of non-uniform sediment are discussed and a formula used to compute thethreshold velocity for each grain size of the non-uniform sediment is established in consideration of their expose and shelter actions, and alteration of the size distribution, etc. Coefficients in the formula are determined based on the experiments and field data. The computed results fully reflect the characteristics of threshold motion of non-uniform sediment: the fine particles are more difficult to be moved for non-uniform sediment than those with the same grain size of uniform sediment, while the coarse particles are of the contrary.

Key words  Non-uniform sediment, threshold velocity, relative degree of expose and shelter actions.

Abstract   Based on results of physical model, this article deals with  water and sediment transportation capacities of three crossing forms and measures of preventing from siltation, and puts forward the non-silting velocity formula in culvert. The results of computation are confirmed by those of the model.

Key words  Crossing underground culvert, non-silting velocity, measures of preventing from siltation

Bai Shilu  Yu Ronghai

Abstract   Based on the similarity theory of river model and the ratio of drag force τ of flow on river bed to the movability index of bed material, The distortion ratio e of distorted model for alluvial river is determined by the density of model sand,which can be expressed as λ_ρ=e² . The relationship between  e=λ_L/λ_h and λ_p`=is given for the model design of alluvial rivers.

        Special treatment technique in model design also are presented in this paper, which has the high applicability to the design of river models.

Abstract   Based on the model experiments of flow pattern, transversal distribution of flow velocity, river bed evolution and flood peak stage, etc., in the upstream and  downstream reaches of a rubber dam at a meandering reach of an artificial channelized river, the following conclusions have been drawn.

     After the rubber dam built, the dam foundation brought a slight changes of the flow patterns for the peak discharge with different flood recurrences, and made velocity as well as discharge in cross section upstream of the rubber dam more well-distributed than those before the dam foundation built.

    After the rubber dam built, both the strength of hydraulic scour at concave bank and the intensity of bed material sweep caused by spiral current at upstream of the rubber dam were restricted. So the height of the convex bed close to the dam was lower than the original bed height with increasing flood peak discharge.

     The dam foundation made the flood peak stage raised in a certain distance upstream from the dam at different flood recurrences. The raised stage and the backwater length would increase with increasing flood peak discharge.

     When the flood discharge from tributary on the concave bank affluxed into the main river, the raising of flood level by dam foundation would be mitigated in  a certain extent.

Key words   Rubber dam, flow pattern, river bed evolution, flood peak stage, velocity distribution.

Li Silong  

(Beijing University)

Cai Qiangguo   Wu Shuan

Abstract   From runoff plots at Zhangjiakou,Hebei Province, Wubujingou and Wufendigou gullies, Inner Mongolia Autonomous Region in the semi-arid region,soil loss data were collected to analyse the effect on some equations including runoff(Q),rainfall intensity(I₃₀) or slope (S), The results indicate that the equations Q_s=kQ^mSⁿ and Q_s=kQ^m are reasonable for description of soil loss (Q_s),but care must be taken when I₃₀ is used  to replace Q in the above equations.

Key words   Rainfall intensity,runoff,soil loss, slope.

Zhang Keli

(Department of Geography, Beijing Normal University)

Abstract  Runoff experiments were conducted on the loess slope to  determine the hydrodynamic characteristics of the rills.Hydraulic geometry of rills on the loess slope could be found by a set of power relations relating the mean width of cross-section,mean velocity,mean depth of flow in the rill.The exponents are 0.26,0.48 and 0.26 respectively.Roughness coefficients are closely related to Reynolds number,but the tendencies are quite different.The roughness coefficients are inverse proportional to Reynolds number on gentle slopes, and on the contrary,they are direct proportional to Reynolds number on steeper slopes.

Feng Jinliang   Zhang Wen

(Institute of Geography, Hebei Academy of Sciences)

Abstract   The geometric patterns of the stream networks in a draiange  basin can be viewed as a fractal with fractal dimension. The Haihe and Luanhe draiange basin is located in the North China. It is a fan-shaped draiange basin.The area of drainage basin is about 319,029 km²,and the mean annual precipitation is about 542.9 mm. It consists of the Haihe River water system and the Luanhe River water system. The fractal dimension of the Haihe and the Luanhe river networks is 1.49. Besides, the drainage is divided into some sub-districts, the river network fractal dimension of every sub-district has been counted, and then the composition principle of two fractal sets has been discussed, the fractal dimension obeys the principle of choosing maximum value. In the end, the relations of fractal dimension and geographical environment factors are also discussed.

Key words    Haihe and Luanhe draiange basin, fractal of river networks,box  counting dimension, composition principle of dimension, runoff modulus.

Li Zuoyong    Deng Xinmin  

(Chengdu Institute of Meteorology)

Hou Yuguang

(Chengdu University of Science and Technology)

Abstract   A prediction model of the yearly average sediment concentration in a watershed is developed using the projection pursuit regressive technology. The results of the PPR prediction model developed by using area-mean rainfall and annual runoff suggest that the qualified rates of fitting and predicting are 100% and 75% respectively. The study proves that it is practicable to predictthe transportation law of sediment by means of the projection pursuit regression.

Key words   Watershed, amount of sediment, projection pursuit regression, prediction.

Huang Caian   Mei Xiaowen

(Yangzhou University)

Abstract   There are two formulae for mean suspended-sediment concentration in vertical which may be confused in practical use. In this paper, the relationship between the two formulae have been discussed. Results show that the   area-mean concentration is always greater than the discharge-mean concentration; the more non-uniform of the distributions of suspended-sediment and velocity, the   more differential of the two formulae. When the suspension index z≤0.3, the   difference will be not more than 10%. Finally, the preliminary apply of the twoformulae has been studied.

Key words  Suspended sediment, suspension index, area-mean concentration, discharge-mean concentration.