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Chapter 1 - Introduction
1.1 Context
The floods of 1987 in the Reuss River Valley, 1987 and 1993 in the Rhone River Valley and 1997
at Sachseln in Switzerland caused catastrophic damages in villages and on infrastructures in these
densely populated areas. Due to the limited space, the banks of mountain rivers crossing settlements
and villages have often to be protected with walls against dangerous bank erosions. Compared
to the riverbed, these walls are rather smooth; therefore high flow velocities occur along the
walls and cause deep scouring near their foundations. At extreme floods the foundation of the
bank walls can be undercut by scouring which results in failure of the protection wall. Especially
walls in river bends are endangered because of the increased scouring action in bends. Failure of
the foundation and consequently of the protection wall, will allow uncontrolled lateral bank erosion,
which will result in serious destruction of buildings and infrastructures. If the endangered
walls at the river banks are furnished with roughness elements as vertical ribs, scouring along the
walls can be reduced considerably.
This fact was observed during the design of the protection measures in the Reuss River Valley
(flood event of 1987) and Saas Valley (flood event of 1993). The protection walls at Gurtnellen-
Wiler (Reuss River in Canton Uri) were equipped with vertical ribs, tested and optimized with qualitative
scale model tests (KUSTER, JÄGGI, BEZZOLA, 1992 and JÄGGI, BEZZOLA, KUSTER, 1996,
SCHLEISS, 2000).
Figure 1.1: Hydraulic scale model of the Reuss River, Gurtnellen, Switzerland [Kuster et al., 1992]
page 2 / November 9, 2002
Wall roughness effects on flow and scouring