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Analysis of the grain sorting of the armoring layer
d in [mm]
UPSTREAM
UPSTREAM
DOWNSTREAM
DOWNSTREAM
SAMPLE TAKEN
OUTSIDE
INSIDE
OUTSIDE
INSIDE
AT OUTLET
ID
d m
d 90
d m
d 90
d m
d 90
d m
d 90
d m
d 90
E2b
E2c
E2d
13.1
16.4
15.8
19.2
20.4
19.5
6.7
5.7
5.1
9.3
6.9
5.5
12.6
14.4
15.0
16.0
18.5
19.4
5.3
7.9
3.8
6.1
12.7
4.2
-
-
-
-
-
-
E3b
E3c
E3d
15.9
15.9
16.9
20.0
19.8
20.5
6.3
6.1
5.7
7.6
7.7
7.3
14.3
15.7
15.0
19.3
19.9
18.6
5.9
5.8
7.7
7.6
6.9
10.4
-
-
-
-
-
-
E5b
E5c
E5d
16.6
16.3
15.8
20.8
20.3
19.7
8.9
6.0
5.8
10.9
7.2
7.0
11.8
14.3
15.7
17.0
18.7
20.1
7.6
5.6
5.7
10.3
6.7
6.5
-
-
-
-
-
-
Table 6.5:
d m and d 90 for the sediment samples of the armoring layer after the tests and at the outlet
Another interesting observation concerns the part of the channel being subject to the armoring
(Figure 6.21 and Appendix 10). Without macro-roughness, the armoring is limited to the outer
quarter of the channel cross-section. Adding vertical ribs, this zone is extended to 50% of the
cross-section. It is interesting that the tests without ribs and the one with the smallest rib spacing
(1°) behave the same way; the ones with a more optimal spacing of 2 and 4°, too. This phenomenon
can be explained by a flatter bed slope in radial direction and especially an almost horizontal
bed towards the outer side wall, facilitating the deposition of the coarse sediments.
Flow direction
Figure 6.21: Bed surface in the first scour hole (tests B1d and B2d) without (left) and with ribs (right)
EPFL Ph.D thesis 2632 - Daniel S. Hersberger November 9, 2002 / page 137