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Parameters of the experiments
4.2 Parameters of the experiments
4.2.1 General test parameters
The following paragraph gives an overview over the general test parameters. The chosen indicative
1 geometric scale is of 1:30.
a) Channel geometry
The bend radius at the centerline is 6.00 m. The channel is composed of a 2 m long inlet box, a
7.50 m long entry reach, followed by a 90° bend with a radius of 6.00 m at the centerline, a 6.00 m
long exit reach and finally a 1.5 m long outlet box. The cross-section is rectangular (1.00 m wide
and 1.00 m high). The ratio bend radius at the centerline to channel width ( R c ⁄ B ) is 6.0 (see also
§ 4.1.1).
Before a test serie, the bed was levelled to fit the desired initial longitudinal bed slope; in every
cross-section the bed was horizontal (perpendicular to the centerline of the channel). During the
test, the sediment supply was adjusted to keep the longitudinal bed slope in the straight inlet reach
as constant as possible.
b) Flow conditions (discharge, bed slope)
The used discharges ranged between 70 and 210 l/s: 70 l/s were used for the initial armoring of
the bed (before the test started properly); 150, 180 and 210 l/s were used for the main tests. These
discharges correpond to propotype discharges of about 350, 750, 890 and 1040 m3/s at a model
scale of 1:30. The flow regime was maintained subcritical.
The bed slope in the inlet reach was maintained as constant as possible (as close to the initial bed
level), by adjusting the sediment supply.
c) Sediment transport
The tests were performed for a constant discharge at equilibrium conditions in the straight entry
reach. The sediment transport balance in the channel depends on the sediment supply, the transport
capacity and the equilibrium conditions. The quantity of sediments introduced in the channel
was variable to maintain the desired longitudinal bed slope in the entry reach (see also § 4.3)
except for the preliminary tests where it was maintained at a constant rate.
The ratio of water depth to mean sediment diameter is of about h m ⁄ d m ≈ 15 .
S 0
Since the slope and sediment density coefficient s are the same for the laboratory experiments
and a test reach in nature, the Shields parameter (eq. 3.42) will be proportional to R h ⁄ d . In order
to have the same transport characteristics, this ratio needs to be the same for the prototype and
1.The present study does not test a specific site. But if we consider prealpine rivers, the following
set of parameters is quite representative: width of the river = 30 m, with a radius of about 200 m
(e.g. the Emme River close to Wolhusen LU, Switzerland)
EPFL Ph.D thesis 2632 - Daniel S. Hersberger November 9, 2002 / page 77