Author(s): Annandale; George W.
Linked Author(s):
Keywords: Turbulence production; Sediment transport capacity; Bed load; Total load; Suspended load; Criterion
Abstract: A criterion based on quantification of the vertical distribution of turbulence production in turbulent flowing water is proposed to identify the true nature of sediment transport equations. Generally the sediment transport capacity of flowing water increases with increasing turbulence production. The turbulence production in the near-bed region resembles the bed load sediment transport capacity, whereas the magnitude of the total turbulence production in the water column resembles the relative magnitude of total load sediment transport capacity. Changes in suspended sediment load transport capacity follows changes in turbulence production in the water column above the near-bed region. The turbulence production in the near-bed region increases with increasing bed roughness, and the bed load sediment transport capacity will therefore also increase. This is shown to be the case for the Meyer-Peter Muller (1948) sediment transport equation, which is used to estimate the bed load sediment transport capacity of flowing water. It is concluded that the Meyer-Peter Muller equation truly represent the sediment transport characteristics of bed load. No change in the total turbulence production of flowing water occurs when the bed roughness increases but other flow variables like bed slope, channel geometry and discharge remain unchanged. Therefore, if total load sediment transport capacity equations are used it is anticipated that no change will occur in the estimated total sediment load transport capacity when bed roughness is increased and the other flow variables remain unchanged. This was found to be the case for the Engelund and Hansen (1967) total load sediment transport equation. It is concluded that the Engelund and Hansen equation adequately represents total load sediment transport capacity characteristics. Two other total load sediment transport equations that were investigated do not show the same characteristic. The Ackers and White (1973) and the Yang (1973) total load sediment transport equations follow a decreasing trend with increasing bed roughness. It indicates that these two sediment transport equations represent trends in suspended sediment load characteristics rather than total load sediment transport characteristics. The amount of sediment that can be transported in suspension is a function of the turbulence production in the water column above the near-bed region. The turbulence production in this part of the water column decreases when the bed roughness increases, and the other flow variables remain unchanged. The decreasing trend in estimated sediment transport capacity when using these two equations for increasing bed roughness therefore more closely resembles suspended load sediment transport capacity rather than total load sediment transport capacity.
Year: 2007