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

Highlights ▪ Infrastructure Systems
Renewal of the hydropower station
Rüchlig in Aarau
Hybrid investigations to optimize the
hydraulic structures of the planned power
plant Rüchlig.
The hydropower station Rüchlig is situated on the river Aare in
Aarau. It is operated by the Nordostschweizerische Kraftwerke
AG (NOK).The powerhouse and the main weir are separated by
a small island called Zurlindeninsel. In connection with the imminent
renewal of the concession, it is intended to rehabilitate
the existent power station Rüchlig, to improve the flood protection
in the city of Aarau, and to increase the residual flow.
The existing powerhouse will be replaced by a new powerhouse
with two units on the left hand side of the power channel.
On the right hand side a gated flood weir will be built. In
the future the flood protection will be improved by discharging
a much higher flow through the power channel during a flood
event.
Numerical model experiments
The numerical model covers the whole concession area and will
provide information on the expected behaviour of the flow
during normal operation and in case of a flood. New water
level-discharge-relations and net heads will be determined.
For flood events the freeboard and bed shear stress in the
channel are examined.The extreme situation of an emergency
shut-down of the turbines is investigated by means of up- and
downsurge calculations (Fig. 1).
The model is calibrated on the basis of measured water leveldischarge-relations
at six different measuring points.
The simulations are carried out with the software program
BASEMENT. BASEMENT has been developed at VAW and is used
for the simulation of transient flow in open channels.
Physical model experiments
The physical model of the powerhouse simulates a local section
of the channel including the flood weir and the powerhouse at a
scale of 1:30 (Fig. 2). The boundary conditions are based on numerical
simulation results. The main focus is on the design of
the power intake, the weir structures and the dividing pier.
56 ▪ D-BAUG Annual Report 2009
Hydraulics of dike breaching
Flood events during the past years resul-
ted in increased dike failures due to over-
topping.
by E. Rühli, N. Mache, A. Lais, D. Vetsch / VAW by L. Schmocker,W.H. Hager / VAW
Dikes along rivers are designed to protect a valley including its
population and property from floods. However, many dikes
have not been maintained during decades and flood events
during the past years resulted in increased dike failures due
to overtopping. Breaching of a dike can lead to extensive
flooding of nearby areas along with both monetary and human
losses.An accurate prediction of the dike failure process
is essential to develop effective emergency action plans or establish
adequate safety measurements.
The dike breach process is therefore systematically investigated
in a hydraulic model at VAW. A small scale model dike
was inserted in a model channel and subsequently completely
eroded due to overtopping.The small scale model allows
testing a wide range of parameters affecting the dike
breach process with a comparatively small effort. Of particular
interest are the dike erosion process, the dike failure time
and the resulting outflow. Figure 3 shows a typical temporal
advance of the dike breach. The water inflow results in dike
crest overtopping at time t = 0 s. Its erosion starts at t = 2 s.
At time t = 10 s almost half of the dike is eroded and at t = 100 s
the original dike is completely destroyed.