pdf, 12 MiB - Infoscience - EPFL

Main tests
the plots gives the distance to a reference level fixed about 50 cm below the channel bottom
(to avoid negative values). The interpolation resolution in radial direction was of 10 mm.
• Appendix 8 shows the longitudinal equilibrium bed and water profiles (after the test). The
plots show the average, the minimum and maximum value (over the cross-section) of the
water and bed levels. The initial average bed level is also given to facilitate comparisons. The
values were computed every 1° in the bend and about every 10 cm (translated to degrees 1 )
in the straight inlet and outlet reach. Two vertical lines indicate the beginning and the end of
the bend (0° and 90°).
• Appendix 9 presents the grain size distributions of the armoring layer at the two maximum
scour locations at the inner and outer bank (surface samples). An additional grain size distribution
is given of a volume sample taken at the outlet at the end of the test.
• Appendix 10 gives a selection of pictures taken vertically every 15° between 10° and 85°.
They document the evolution of the grain size distribution of the armoring layer after each
test.
• Appendix 11 shows the measured velocities. The first part shows the results without macroroughness
(Appendix 11.1 to 11.3) and the second part the ones with vertical ribs (Appendix
11.4 to 11.6). Each part first gives the tangential velocities, then the velocity vectors in
the cross-section (radial and vertical velocity components) and finally the 3D-velocity vectors
in the bend. For the 3D-plots, the bend is represented as a prismatic block. The velocity
profiles are located every 15° at cross-sections from 10° to 85°. All presented velocity measurements
were made at an initial bed slope of 0.50%. The influence of the macro-roughness
is shown for a discharge of 210 l/s. Due to the big number of measurement points
over the depth (128 points), only every 4th point was used for the vector plots to facilitate
the reading.
• Appendix 12 gives the results of the genetic programming used to search for a new scour
formula.
5.3.2 Observations during the tests
a) Development of the scour and point bars
For the tests without macro-roughness, the scour process started in general at discharges between
100 and 140 l/s (see § 5.2). At a discharge of 150 l/s, sediment transport was observed over the
whole cross-section (except for the flattest bed slope of 0.35%, where a discharge of about
180 l/s was needed to move the sediments). The formation of the first scour hole started almost at
the final location of the second scour hole at the downstream end of the channel and moved with
increasing discharge in the upstream direction where it started oscillating around its final position
between 30° and 45°. For the main test, which were started directly at the final discharge (150, 180
1.Since straight and curved parts of the channel had to be merged on one plot, the same distance
unit had to be used for the horizontal axis. Since the main interest is the behavior in the bend, an
angular reference was chosen. The distances in the straight parts were converted to angles corresponding
to a position on a bend located on the center line of the channel.
EPFL Ph.D thesis 2632 - Daniel S. Hersberger November 9, 2002 / page 109