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Chapter 6 - Analysis of the test results
Analyzing the thalweg over the whole channel (Table 6.2, Figure 6.6 and Appendix 8) it can be
observed that without macro-roughness, the erosion of the bed (thalweg) starts at about 10°,
reaches its maximum in the first scour hole at approximately 30° 1 and reduces again up to a position
between 50° and 60°.
From 70° downwards, the erosion gets deeper again to reach its maximum (second scour)
between the end of the bend (90°) and 1 m after the bend. Towards the end of the channel the
thalweg comes up again (at about 2 m, sometimes 3 m after the bend). Between the two maximum
scour locations, the thalweg remains clearly below the initial bed level.
1400
Mean, min. and max. water− and bedlevels in the channel B01 Q=210
without macro-roughness >
1300
1200
1100
point bars
Level [mm]
1000
900
Thalweg
1400
1300
1200
Mean, min. and max. water− 800 and bedlevels in the channel B04 Q=210
Inlet reach
700
600
Bend
Water level (min,max,average)
Bed level (min,max,average)
Initial mean bed level
Outlet reach
−40 −20 0 20 40 60 80 100 120
Angle [°]
Level [mm]
1100
1000
900
< rib-spacing 1°
800
700
600
Water level (min,max,average)
Bed level (min,max,average)
Initial mean bed level
−40 −20 0 20 40 60 80 100 120
Angle [°]
Figure 6.6: Longitudinal plot over the whole channel; average / min. / max. bed and water levels for
S 0 =0.50%, Q=210 l/s, without ribs (on top) and with a rib spacing of 1° (bottom)
Adding vertical ribs along the outer side wall (Table 6.2, Appendix 8), the erosion still starts at 10°,
but the location of the maximum scour shifts more and more in the downstream direction with an
1. Sometimes the maximum scour is extended over the following 20° (between 30 and 50°).
page 120 / November 9, 2002
Wall roughness effects on flow and scouring