The relationship between stage and discharge can be rather complex in compound channels due to the influence of numerous factors such as channel geometry, vegetation, or varying bed roughness. The latter aspect is of particular interest for sand rivers with bed forms, as the bed roughness changes with the bed form dimensions depending on flow depth and bed shear stress. However, the particular impact of the varying size of lower regime bed forms on the stage-discharge relation in compound channels has not yet been investigated in detail. This work addresses this issue by presenting results of a flume study using a cross-section of a half trapezoidal compound channel and two different floodplain roughness. The experiments were carried out with fixed and mobile main channel bed and the experimental data were used to derive stage-discharge curves highlighting the effect of main channel bed forms on the stage-discharge relationship in compound channels.
| Experimental flume | Model: |
|---|---|
| 30 m length | 20 m length |
| 2 m width | 1 m floodplain width |
| 0.8 m height | 0.2 m floodplain height |
| 0.0025 slope | 0.8 m channel bed width |
| 0.85 mm sand grain size |
The presence of bed forms revealed a high impact on the stage discharge relation in the tested compound channel model.
For example, bed forms reduced the conveyance capacity of the channel by 45% for bank full conditions. Whereas at the highest investigated water stages bed forms reduced the conveyance capacity by: