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Chapter 7 - Establishing an empirical formula
750 m
740 m
730 m
720 m
Figure 7.16: Measured water and bed elevation (scale model) along the left bank (wall) upstream the bridge
(Wilerbrücke); Schutzelement 1 is the vertical side wall equiped with trapezoidal ribs [Kuster et al,
1992, Appendix G, Plan 30]
Figure 7.17: Cross section in the scour hole, upstream the bridge[Kuster et al., 1992, Appendix F, Plan 22]
The following characteristics of the reach were used for the computations: R c = 110 m,
B = 30 m, A≅ 150 m 2 , S 0 = 2.6 %, d 90 = 0.60 m, σ = 10 , φ = 38 °, V ≅ 4 m/s,
Fr = 0.7 , θ = 0.110 and θ cr = 0.047 .
The mean water depth upstream the bend equiped with macro-roughness is obtained taking into
account the influence of the wall roughness (see section 3.3 on page 31) is of 3.8 m. Taking also
into account the backwater curve in the Reuss River (Fig. 7.17), a water depth of h m ≅ 5 m is
found. The hydraulic radius is of R h = 4.3 m. The (experimentally scour depth is of
h smax ,
= 10.9 m.
page 184 / November 9, 2002
Wall roughness effects on flow and scouring