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Chapter 5 - Test results
5.2 Preliminary tests
Two series of preliminary tests (A1 and A2) were performed. Both of them had an initial bed slope
of 0.5 %. For these preliminary tests, the sediment feeding rate was maintained at a constant value.
The order of magnitude of the transport rate was estimated with SMART &JÄGGI’s (1983) formula
(§ 3.4.2/4) and adjusted at the beginning of each discharge by observing the straight inlet reach
(maintain the longitudinal bed slope at the initially built in value). The first series of measurements
was taken without macro-roughness (A1), the second one with ribs placed every 2° (about 23 cm).
5.2.1 Tests without macro-roughness
1) Test procedure
The test series was started with a low discharge (20 l/s) and increased progressively by steps of
10 l/s. At discharges between 120 and 140 l/s the bed started eroding. Then the discharge was
progressively increased to 170 and 212.5 l/s (maximum possible discharge of the pumps). These
two discharges were maintained until the scour hole stabilized. The following table gives an overview
of the discharges (Q), the bed load supply (Q s ), the runtimes and whether the bed topography
was measured () after the experiment or not (-). The bed topography was manually
measured (see 4.4.6 b) at the following positions: in the inlet reach at 2.90 and 5.90 m, in the bend
at 10°, 40°, 70° and 90° and in the bend at 4.40 m. The final bed topography after the tests is given
in Appendix 3.1.
Q [L/S]
Q S . [G/MIN]
DURATION
[H:MIN]
TOPOGRAPHY MEASURED
Initial topography - -
120 - 0:45
130 100 2:00
140 800 2:50
150 1'500 0:50 –
170 4'400 3:30
212.5 5'000 1:40
Table 5.4:
Overview of the preliminary tests without macro-roughness
The Froude numbers ranged between 0.75 (Q = 120 l/s) and 0.76 (Q = 212.5 l/s).
page 102 / November 9, 2002
Wall roughness effects on flow and scouring