PROGRESS IN GEOGRAPHY ›› 2009, Vol. 28 ›› Issue (4): 567-574.doi: 10.11820/dlkxjz.2009.04.012

• Original Articles • Previous Articles     Next Articles

Progress in the Research of Hydrodynamic Characteristics of Sediment-laden Overland Flow

LUO Rongting1|ZHANG Guanghui1,2|CAO Ying1   

  1. 1.School of Geography|Beijing Normal University|Beijing 100875|China;
    2. State Key Laboratory of Earth Surface Processes and Resource Ecology|Beijing Normal University|Beijing 100875|China

  • Online:2009-07-25 Published:2009-07-25


Overland flow is the main cause for slope erosion, which has unique hydrodynamic characteristics. This paper made a systematic and thorough discussion on the flow pattern, frictional resistance, mean flow velocity measurement and runoff energy of sediment-laden overland flow, sediment concentration as well as the impacts of the above. Reynolds number (Re) and Froude number (Fr) are used to express flow pattern. The branch point of Re exists in the definition of “laminar flow”, and raindrop splash is the main reason for its specificity. Fr of overland flow free of sediment on bare soil is generally considered to be >1. Different flow pattern results are also obtained in the meager literature of sediment-laden flow. However, most scholars believed that sediment-laden flow belonged to tranquil flow. There are different values of Darcy-Weisbach Friction Coefficient (f) in different experiments on hillslopes, and the factors that affect f are Re, water depth, Fr and sediment concentration. On the study of sediment-laden flow, f is closely related to Re, but the tendencies are quite different. In addition, f is inversely proportional to Fr, and on the contrary, it is directly proportional to sediment concentration. Many measurements of surface flow velocity have their respective advantages and disadvantages. Exact instrument is characterized by high price, required routine maintenance and harsh work conditions, which is usually used to measure overland flow free of sediment. So, exact instrument is not suitable for sediment-laden flow temporarily. The accuracy of flow measurement with tracers is not high, but the process of tracers diffusing would be slower through the effect of sediment concentration. As a result,  using tracers to measure the velocity of sediment-laden flow is still applicable. Formulas for velocity of overland flow are usually simulated by a power function of discharge and slope gradient, and there are a negative relationship existing between flow velocity and sediment concentration. Runoff energy is synthesis of hydrodynamic characteristics of sediment-laden flow on hillslopes. Most scholars use different formulas of water potential energy to express runoff energy. Generally speaking, the runoff energy consumption of shallow flow on slope increases as sediment concentration increasing. On the basis of reviewing recent research at home and abroad, deficiencies from experimental device and skill and experimental content are also discussed. The main problems of experimental device and skill include low-precision of velocimeter and poor comparability of data. Besides, results of every hydrodynamic parameter acquired by experiment are almost about its average values of the whole hillslopes, and most experiment has been done under the condition of overland flow free of sediment on gentle slope. Finally, the corresponding suggestions are put forward to provide a theoretical basis for slope erosion mechanism and slope erosion model perfection.

Key words: flow pattern, flow velocity, frictional resistance, overland flow, runoff energy, sediment concentration