On the location in flow plan of erosion–deposition zones in sine–generated meandering streams

Abstract

This paper concerns the location in flow plan of the laterally adjacent erosion–deposition zones (“deeps” and “hills”) in sine–generated meandering streams. The aim of the paper is to gain insight into how the location of the aforementioned erosion–deposition zones is affected by stream sinuosity, as well as other geometric and flow–related parameters. For this purpose, a series of movable bed runs is carried out in a sine–generated channel having an intermediate value of the deflection angle θ0, namely 70°. This value extends the range of θ0–values investigated by previous authors, who tended to focus mainly on the limiting cases of “small” and “large” values of θ0 (θ0 ≤ 30° and θ0 ≥ 100°). The runs started from a flat bed, which subsequently was allowed to develop until the equilibrium state, or a near–equilibrium state was achieved. The bed topography maps showing the bed surface at the end of the present runs were analyed together with those from previous authors' runs. It is found that, all other conditions remaining the same, the L/2–long erosion–deposition zone which in streams having small θ0 extends from any apex–section ai to the next consecutive apex–section αi+1, gradually moves upstream as θ0 increases from 0 to 126°—so that in the limiting case of large θ0, this erosion–deposition zone extends from the crossover–section Oi to the crossover–section O i+1 (O i and O i+1 being the upstream– and downstream–crossover sections of the meander loop whose apex–section is αi). For any specified θ0, the location of the L/2–long erosion–deposition zones appears to be affected mainly by meander wavelength relative to flow width, and perhaps also by the flow friction factor. A quantity characterizing the different distributions in flow plan of the erosion–deposition zones is introduced, and its mathematical form is investigated.