Sediment transport in rivers - report on experimental and theoretical investigations

Sediment transport in rivers - report on experimental and theoretical investigations

De Vriend, H.J.
Koch, F.G.

TU Delft

TOW

1987-11-01

I: Flow of water in a curved open channel with a fixed plane bed II: Flow of water in a curved open channel with a fixed uneven bed III: Accuracy of measurements in a curved open channel In this report the flow of water in a curved open channel, which consists of a38 m long straight section followed by a 90° bend with a radius of 50 m (see Figure 1), has been investigated. The channel cross-section was rectangular with a horizontal concrete bed, a width of 6 m, and a depth of flow of 0.25 m, and measurements were executed at two discharges: 0.610m3 /s and0.305 m3/s (average velocities of about 0.4 m/s and 0.2 m/s respectively). During these experiments the following phenomena were investigated: a. the vertical distribution of the horizontal velocity components (main flow and helical flow) ; b. the horizontal distribution of the total depth-averaged velocity; and c, the horizontal distribution of the water surface elevation. The experimental results have been compared with the results of a mathematical model of flow in curved open channels, developed at the Laboratory of Fluid Mechanics of the Delft University of Technology.The vertical distributions of the main velocity turned out to be highly similar throughout the flow field, the distribution being well described by the logarithmic profile. The helical velocities derived from the measured data were too inaccurate to compare them more than roughly with their theoretical distributions. The point in a cross-section where the observed depth-averaged velocity reaches its maximum lies near the inner wall in the first part of the curve and moving downstream it gradually shifts towards the outer wall. This phenomenon is attributed to the advective influence of the helical flow. As this influence is not accounted for in the present mathematical model, this model does not predict the phenomenon. The water surface configuration agreed reasonably well with the computed configuration.

sediment transport
river flow
river morphology
bed stability

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