KLIWA-Workshop "Extreme Hochwasser"
Floods and climate change; Dutch experiences along the Rhine and the
Referent: Dr. Marcel de Wit - RIZA, Arnheim (Niederlande)
The Netherlands are situated in the delta of the Rhine and the Meuse.
Without flood protection large parts of the country would be regularly
inundated. Flood protection in the Netherlands is based on design discharges
with a given probability of occurrence. Along the non-tidal, embanked parts of
the Rhine and Meuse an occurrence frequency of once every 1,250 years is used.
The corresponding discharge has been obtained by analysing observed annual
maximum discharges and peak over threshold discharges. The observed discharge
record is relatively short: starting in 1901 for the Rhine and 1911 for the
Meuse. This implies that new observations can substantially effect the
calculated design discharge. In 2001 the design discharge for the river Rhine
has been updated from 15,000 m³/s to 16,000 m³/s and the design discharge for
the river Meuse has been updated from 3,650 m³/s to 3,800 m³/s. The current
policy is to handle this increase by creating more space for the river rather
than increasing the level of the dikes. At present large scale measures to
increase space for the river are partly in preparation and partly under
Preparing for a future with climate change
There is a growing concern that climate change will lead to an increase of
precipitation and as a result an increase of the frequency and magnitude of
floods in the Rhine and Meuse. Based on climate change scenarios it is argued
that by the end of the 21th Century the design discharges may increase to
18,000 m³/s (Rhine) and 4,600 m³/s (Meuse). These estimates have been used as a
boundary condition for long term outlooks of flood risks along the Dutch
Major aim of these outlooks is
to evaluate whether the current measures are sustainable, and
to reserve space along the river that can be used in case the present
measures appear to be insufficient. The recent floods, research activities,
and political statements have triggered a lively public discussion on
climate change and flood management in the Netherlands.