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You are here : eLibrary : IAHR World Congress Proceedings : 36th Congress - The Hague (2015) ALL CONTENT : Extreme events, natural variability and climate change : Generation of sets of synthetic events by multivariate stratified sampling
Generation of sets of synthetic events by multivariate stratified sampling
In order to develop optimized flood risk management plans for the Upper Scheldt and Lys/Leie basins, two major
French/Belgian rivers with a confluence in the city of Ghent, a full probabilistic risk approach has been applied.
Risk analysis requires considering the entire frequency domain of flood consequences. Hence statistical extrapolation is
necessary. This was done by generating 2.500 extreme synthetic events for the river system. First, a continuous
simulation of 28 years time series of recorded regional rainfall has been run through lumped hydrological models,
simulating soil saturation conditions and yielding in joint occurrences of rainfall-runoff discharges at the different inflow
locations. Next, for each catchment an extreme value distribution is fitted to the runoff discharges. Joint occurrences of
extreme events in the Upper Scheldt and the Lys are taken into account by a bivariate extreme value copula. The bivariate
discharge domain of the copula is then stratified in 100 classes. For each class synthetic hydrographs for both rivers are
constructed, with a joint frequency of occurrence that is calculated from the copula function. Synthetic hydrographs are
derived from the combination of a standardized profile for baseflow and surface runoff, which is first shaped by a profile
variation and then scaled with the discharge class. The standardized profiles are the mean expected baseflow and surface
runoff hydrographs computed by normalizing all recorded extreme events. A probability distribution is fitted to the
standardized events, yielding 5 profile classes through a second stratification. Next, the tidal water level variation at the
downstream boundary, statistically modeled with a conditional distribution, was again stratified in 5 classes, eventually
producing 100x5x5 = 2.500 sets of synthetic events. For each set the corresponding multivariate frequency of occurrence
is computed.
All events are run through the hydrodynamic model of the river system. At this point, empirical frequency distributions can
be drawn for flood depths in the floodplains. As a validation, these distributions are plotted against simulations of recorded
extreme historical events, displaying good similarity.
This methodology has the advantage that it determines a statistical distribution of consequences, rather than assigning
frequencies to hydrodynamic boundary conditions.
File Size : 6,238,388 bytes
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Chapter : IAHR World Congress Proceedings
Category : 36th Congress - The Hague (2015) ALL CONTENT
Article : Extreme events, natural variability and climate change
Date Published : 14/08/2015
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