pdf, 12 MiB - Infoscience - EPFL

Analysis of the final scour
e) Shape of the scour holes - development of the scour
Without macro-roughness the two scour holes have a completely different shape (Figure 6.8): the
first scour has an elongated elliptic shape with its deepest point at about 10 cm from the outer side
wall. This scour hole is located just upstream the maximum elevation of the first point bar.
The second scour looks like a drop, sticking to the outer side wall and “dropping” in downstream
direction. Its deepest point is at about the same distance from the side wall, located downstream
the highest point of the second point bar.
flow direction
Bed Topography Differences, Case B04, Q = 210 l/s
Bed Topography Differences, Case B03, Q = 210 l/s
Bed Topography Differences, Case B02, Q = 210 l/s
rib spacing 1°
7000
6000
5000
4000
Bed Topography Differences, Case B01, Q = 210 l/s
high velocities
1st scour or
reflection
point
rib spacing 2°
200
100
0
Y [mm]
3000
2000
1000
0
−1000
point bar
point bar
without macro-roughness
−2000
−2000 −1000 0 1000 2000 3000 4000 5000 6000 7000
X [mm]
rib spacing 4°
2nd scour or
reflection point
Figure 6.8: Shape of the scour holes and point bars with and without macro-roughness (S 0 = 0.50%,
Q = 210 l/s)
It is interesting to observe that almost no distinct scour holes can be found for a rib spacing of 4°
(about 40 cm). Increasing the rib density (2°) induces the creation of a first scour, which is still
quite small. This scour has the interesting property that it is located after the first point bar. This
becomes even more evident if additional ribs are placed in the channel (1°). This scour is even
EPFL Ph.D thesis 2632 - Daniel S. Hersberger November 9, 2002 / page 123
−100
−200
−300
−400