Poster published at the 3rd International Symposium on Integrated Water Ressources Management (Sept 2006 - Bochum, Germany)

1. A method leading to an automated creation and update of a flood risk map
Flood cartography project - Plan PLUIES
Bertrand COPPIN
3rd International Symposium on Integrated
ext.coppin@mrw.wallonie.be Water Resources Management
Bochum - Germany - 26/28 September 2006
Context
Floods in January 2003 in the Walloon Region : An overall and cross-disciplinary project of floods fight Picture 1 : The Walloon Region
Wallonia, with its 3.4 million inhabitants, and
Photo 1 :
Having to face the repetition of floods and the spreading damages on its territory, the Walloon Government, in January 2003, launched the "Plan PLUIES", an overall project 16.844 km², has one of the highest population
FLANDERS
The Eau Blanche of floods prevention and fight against their effects on the disaster victims. density in Europe.
(Province de Twenty-seven initiatives have been put into action. One of the main's, consists in a map-making of the areas where floods are caused by overflowing of the rivers. Streams, rivers and waterways - with very
BRUSSELS
Namur) GERMANY different hydrologic workings - fit in with a
Being started in early 2004, the flood cartography project aims at putting two major issues in perspective : on the one hand, the mapping of flood hazard; on the other hand, Tournai
Liège
various relief : between the Plaine hennuyère
Es
ca
u se
u
Me
in the west, which is under an altitude of 50 m,
t
Namur
the damage risk's. This work should be completed in the middle of year 2007.
Mons
Charleroi
e
br
Sa m
and the ardenian massif in the east, reaching
The flood risk map should achieve various aims. Legend
FRANCE 694 m at its highest point.
By localising and organising the areas into a hierarchy, according to their damage risk level, the map will constitute an helpful decision tool by bringing into play the different Major Rivers
Photo 2 :
Major Towns At the institutional level, Belgium is a federal
"Plan PLUIES" actions : Elevation (in metres) Grand Duchy of
The Vesdre 0 - 50
LUXEMBOURG state made up of three Regions : the Walloon
1 - to fit out the rivers banks and the alluvial plains : localize the areas to be protected and those that could be flooded, or over-flooded deliberately;
(Province 50 - 150
Region, the Flemish Region and the region of
2 - to reduce vulnerability : identify building lands located in flood areas;
150 - 300
Arlon
de Liège) 300 - 450
Brussels Capitale. Each has its own public
3 - to improve crisis management : delimit areas that have to be protected as a priority, that is to say, those where damages are at the highest. 450 - 700
services and competences.
Methodology
Step 1 : Determination of damage risk
Hazard H = High
M = Moderate Levels of Bringing together uses
Picture 2 : Sketch of hazard determining Recurrence vulnerability Type of uses Examples of uses Table 1 :
L = Low
according to vulnerability
Flood hazard by overflowing is made up of
T = 25 years
H M H H F requent
( >2x/1 0 years) H I M H H I = Insignificant
- All the buildings used as housing or linked to
an economic or leasure activity
Housing, firms, agricultural
buildings, sports centre, hospitals,
levels
areas in which floods are expected to occur M M M M Rare High - Community or major public services transformers, schools, motorways, Uses (elements sensible to
equipments
in a more or less extended and frequently flood) are filed according to four
I L M H major roads...
T = 50 years
- Major highways, railways
way, due to natural overflowing of waterways. T = or > 100 years
L L L M Very rare
M levels of vulnerability, depending
The hazard value is determined by the L M H Submersio n - Light superstructures or movable equipments on their propensity to submit
Outdoor sports installations, loading
I L L M damages.
Frequency - Community or minor public services
return period Moderate platforms, cemeteries, secondary
combination of two factors : the recurrence of
a flood (periodicity or occurrence) and its
QT
Depth (D) 0 = D < 0,3 = D < 1,3 = D (m)
Catch +
of floods
L equipments roads... Vulnerability has been
Extent of yes
Farmland (meadows, cultivations,
determined on the basis of a
water surface elevation. water surface Vulnerability
Several methods are being used : hydrologic Catch - flow velocity (V) V > 1 m/s I L M H Low - Unbuilt parcels tree nurseries), private or public
gardens, sports grounds...
multicriteria analysis, by taking
into account direct and indirect
statistics, hydraulic modeling, ground studies Duration of flood (Du) Du > 3 days
damages, tangible and
Wasteland, woods, disused
and hydropedology. Picture 3 : Matrix to determine the damage risk Insignificant - Other unbuilt parcels, very little sensible to flood
quarries, "natural" spaces...
yes Pro tection Embankments, pumping, movable flood walls intangible costs.
The risk value reflects the extent of damages on vulnerable elements.
Step 2 : Mapping Picture 5 : Extract of the damage risk map (watershed "Dyle-Gette")
RESTRAINTS AIMS MEANS Table 2 :
Overall Legend Ponctual risk (The sign's colour varies
- deadline philosophy according to the risk value)
Life cycle of the project for mapping the flood risk zones : of the Damage risk
- Work out a method allowing to produce, within some months, the Adm
Administration
three years. Most of the hazard maps are produced at the mapping Hospital
end of the project.
damage risk maps. High
work Moderate E School
The development of an automated method. Low
Patr. Historic building
- Avoid the new data production; Police
- available resources - enhance data produced by public services; Insignificant
Restricted available means (staff and budget) - use the data in vectorial form; Potential damage risk* Highways (The filling's colour varies
- reduce the manual data processing. according to the risk value)
* Unbuilt lands at the
High moment, situated in an Major highways
- servicing in the hereafter - The use of starting data independent of the project and managed externally. Moderate
urbanizable area of the
Plan de secteur Secondary highways
Necessity for a regular and simplified update of the maps, Knowledge management : structure and file knowledge linked to the production of
- Allow the futur staff (untrained) to produce the maps. Risk area Stretch of water Water body
after the end of the project maps (enhance metadata, formalize the procedure by creating a servicing file).
The main basis data Data processing
- P.L.I. (Plan de Localisation Informatique) Raw data are integrated and modeled into a Geographic Information System (G.I.S.). The
A digitized cadastre (graphic file representing the limits of cadastral parcels processing string which is created allows to automate the production. Script is written in a python
on the scale of 1 :10.000) associated with the cadastral matrix (alphanumeric programming language.
database).
To know the declared use of parcels (building, farming, industry, wooded
area, etc.).
- P.I.C.C. (Projet Informatique de Cartographie Continue)
A detailed and precise vectorial database (scale 1:1000) of buildings,
localised fittings, and highways.
To underscore some elements particularly sensible (fire station, old
people's home, supplying drinkable water or electricity, etc.) and determine
the nature of communication ways.
- Plan de secteur
Statutory document, on a scale of 1:10.000, defining ground allocation
(constructible and unconstructible areas, farming areas, natural areas, etc.).
To localize building lands where vulnerability could potentially increase..
Picture 4 : Sketch extract of data processing
Basis data (blue balloons) are integrated in this pattern and processed in geoprocessing
- Flood hazard mapping units (orange oblongs). New data (green balloons) are created in output. These latters are Scale 1 : 10.000
To delimit hazard areas according to three values. used again to provide other transformation processes. This cycle keeps going till reaching
the layer of damage risk.