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1. Overview
2. Urban flooding
3. Natural Topography Flooding
Theme Area 3 is devoted to Flood Propagation
modelling in extreme flooding scenarios. The main objective
is to produce reliable modelling techniques and methods for
the propagation of extreme flood waves across natural environments
and urban areas. The mathematical framework upon which models
will be based are the Shallow Water Equations (SWE). The following
objectives will be addressed:
- Study the flow characteristics in
urban areas and natural valleys. Flow in streets and intersections,
around buildings, in steep sloping complex valleys.
- Test and compare different modelling techniques
and assess their validity as well as identify best approaches.
- Check the accuracy and validate different methods
proposed.
- Perform case studies on actual catastrophic flood
scenarios.
The work plan has been broadly divided into two major areas:
Urban Flooding and Natural Topography Flooding, attending
to their different characteristics. However the adopted strategy
is similar to both and encompasses experimental as well as
computational work.
Experimental work in this area will
cover flow around buildings and a model
city that will constitute benchmarks
for mathematical modelling testing. In particular:
- The isolated building test
case aims at studying the flow characteristics around
a model building withstanding a strong dam break wave at
different angles with respect to the incoming flow direction.
The experiment has been conceived and set up at Université
Catholique de Louvain (UCL) and is carried out in a laboratory
channel where the model building is placed. The data obtained
comprise water depth history and velocity vectors at several
locations around the building and its wake obtained by conductivity
probes and digital imaging techniques respectively.
- The model city flooding
experiment addresses global flow conditions in the streets,
crossings and around buildings upon flood wave arrival at
a city like pattern of ordered buildings. The experiment
has been carried out by ENEL-CESI at its Milano facilities
and will provide data for mathematical model benchmarking.
Data obtained comprise water depth versus time at some ten
probe locations, in and around the city area.
Computational work in this topic aims at representing
global and local flow conditions in the flooded region and
at estimating the level of uncertainty in computed figures.
This will be achieved through:
- Formulation of strategies and techniques to adequately
represent severe flooding in urban scenarios. Mathematical
models will include both one dimensional (channel network
like) and two dimensional representations of a city. In the
two dimensional case several alternatives will be explored:
From a rough representation of the urban area as a reduced
conveyance zone to a detailed meshing of the city topology.
The effect of buildings can be modelled as bottom or boundary
condition based.
- Validation of the concepts and models described above
against laboratory data. The
isolated building test case and The model city flooding
experiment will be used as benchmarks.
These will be open to non partners of the IMPACT project.
- A case study will be set
up regarding an actual city flooding event. The different
models set up by the project partners or other organisations
willing to participate will be tested.
3. Natural topography flooding
Work in this area will run along the same
lines as in Urban flooding. Modelling tasks will be complemented
with experimental data. Within the computational issues that
will be addresses stand:
- Modelling of abrupt slopes and deviation from the
Shallow Water approximation, including model singularities,
such as bottom steps or hydraulic structures.
- Accurate representation of wetting and drying processes.
These effects are essential to a realistic propagation of
the flood wave and has important direct implication on the
validity of numerical solutions, for instance regarding mass
conservation.
- Quantification of mesh influence in the computed
results. Since the SWE approximation is not a complete mathematical
description of flood flow, convergence to a numerical solution
in the mathematical sense does not guarantee a more accurate
representation of the flood.
- Coupling one and two dimensional models can be a
fruitful strategy when abrupt mountain brooks or gorges join
open river valleys or flood plains. It can help obtain a better
representation and save computational effort.
Laboratory work will be conducted to clarify
some fundamental issues and also to create a database for
mathematical model benchmarking.
The following experiments will be conducted:
- Experiments will be carried out at UCL in an instrumented
flume with a bump. These will be devoted to obtain data on
the propagation of flood waves over steep slopes and on the
wetting and drying processes. Data will comprise time history
of water depth at several probe locations as well as velocities.
- Data about global flood characteristics in a real
topography will be obtained from the instrumented physical
model of Toce river valley owned by ENEL-CESI.
Finally past flooding events will be investigated
and data collected in order to prepare a case
study of flood propagation in a real valley where the
mathematical models will be applied and tested in real life
scale and conditions.
For any queries regarding the Flood Propagation
Theme Area, or in order to participate in the benchmarking
campaigns of IMPACT project, please contact the IMPACT project
coordinator Mark
Morris or the theme area leader Francisco
Alcrudo.
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