D-BAUG - Departement Bau, Umwelt und Geomatik - ETH Zürich

Highlights ▪ Resources
Flood control measures at the “Kleine
Emme” River
Physical experiments on drift wood retention
at the‘Kleine Emme’River near Malters,
Canton Lucerne.
The 2005 flood event caused large damages in many regions
in Switzerland and so in the area of the Kleine Emme
River. Initiated by this event, a combined approach including
hydro power production and drift wood retention with
a diversion channel and a drift wood rack (Fig. 1) for the
Malters river stretch at the Kleine Emme has been projected.
The Canton Lucerne has assigned the VAW to test
and optimize the given configuration with the help of a
physical model on a 1:50 scale with focus on flood protection
aspects and the efficiency of the drift wood retention.
The experiments showed that, with the given configuration,
the intended efficiency of 50 % of retained drift wood
can be achieved; however, certain flood protection aspects
were not fulfilled.To improve the situation, a new concept
regarding the direction of the approach flow towards the
drift wood rack (parallel instead of frontal approach flow)
(Fig. 2) has been tested.The parallel approach flow in combination
with an area of recirculating flow, led to the same
efficiency of retained drift wood, plus strongly improved
flood safety conditions.This improvement can be explained
by a reduced tendency of the drift wood for piling up in
front of the drift wood rack with parallel approach flow,
leading to reduced backwater effects.
The final design includes a second drift wood rack downstream
of the first one, which increases the drift wood retention
efficiency by approximately 10 %, resulting in a total
retention efficiency of roughly 2/3 of the oncoming
drift wood.
62 ▪ D-BAUG Annual Report 2009
Flood protection project “Linth 2000”
Hybrid modelling of a spillway to prevent
dam breaks at the Linth Canal.
by S. Tamagni, V. Weitbrecht / VAW by P. Seitz, Th. Berchtold, V. Weitbrecht, D. Vetsch / VAW
Since river engineering and flood protection concepts are
designed to work properly not only under design conditions,
but as well for the overload scenario, the flood protection
project “Linth 2000” is investigated at the VAW using
a hybrid modelling approach, where physical and
numerical experiments are combined. A regulated overfall
weir in an 800 m long newly built local river widening is
planned to limit the downstream discharge in the Linth
Canal. The spillway is designed to reduce the peak flow of
500 m 3 /s in the canal to a maximum of 420 m 3 /s. The
mean discharge in the Linth Canal is about 54.6 m 3 /s.
In the laboratory, the physical model on a 1:30 scale covers
90 m 2 . It includes parts of the local widening, the spillway
and the runoff in the stream course downstream of the
spillway (Fig. 3).
To assess upstream boundary conditions for the physical
model, numerical simulations are performed covering a
larger flow domain up- and downstream of the local
widening (Fig. 3). In the numerical model, the water levels,
the bed shear stress and the averaged flow velocities are
calculated for several flood scenarios. In the physical model,
the functionality of the spillway and the riverbed stability
are tested. For the numerical computations, the modular
software BASEMENT that has been developed at VAW is
used.