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Chapter 5 - Test results
with and without macro-roughness which will be discussed later (§ 5.2.2). For these two highest
discharges, a second scour hole can be observed at the end of the bend.
Fig. 5.1 shows that it is difficult to determine weather the first or second scour will be more
important: In the present case, the maximum scour depth appears in the first scour hole for a discharge
of 170 l/s and in the second scour hole for the highest discharge (212.5 l/s).
c) Point bars
Appendix 3.1 and 3.2 show that there are important deposition zones at the inner bank at high discharges.
The point bar is located almost at the position of maximum scour depth. Since the measured
cross-sections for the preliminary tests were not as dense as for the final tests, the point bar
seems to appear exactly at the location of the scour holes. But the main tests will show, that the
upstream point bar is located downstream the first scour hole and upstream the second scour hole
(see § 6.2.1).
d) Grain size distribution
Figure 5.2 shows the channel bed at 45° after the test run with macro-roughness. It can be stated
that the coarse grains are accumulated near the outer wall and that the fine sediments are deposed
on the point bar at the inner side. The same phenomenon is observed both, with and without
macro-roughness.
Figure 5.2: Grain sorting, view across the outer side wall at 45° (test with macro-roughness - A2)
page 104 / November 9, 2002
Wall roughness effects on flow and scouring