A method leading to an automated creation and update of a flood risk mapFlood cartography project - Plan PLUIES
Bertrand COPPIN3rd International Symposium on Integrated
Water Resources [email protected]
Bochum - Germany - 26/28 September 2006
Context
Methodology
FRANCE
FLANDERS
BRUSSELS
Grand Duchy of
LUXEMBOURG
GERMANY
MeuseTournai
MonsCharleroi
Namur
Liège
Arlon
Escaut
Sambre
- P.L.I. (Plan de Localisation Informatique)A digitized cadastre (graphic file representing the limits of cadastral parcels on the scale of 1 :10.000) associated with the cadastral matrix (alphanumeric database). To know the declared use of parcels (building, farming, industry, wooded area, etc.).
Major Rivers
Elevation (in metres)
0 - 50
50 - 150
150 - 300
300 - 450
450 - 700
Major Towns
Legend
Wallonia, with its 3.4 million inhabitants, and 16.844 km², has one of the highest population density in Europe.Streams, rivers and waterways - with very different hydrologic workings - fit in with a various relief : between the Plaine hennuyère in the west, which is under an altitude of 50 m, and the ardenian massif in the east, reaching 694 m at its highest point.At the institutional level, Belgium is a federal state made up of three Regions : the Walloon Region, the Flemish Region and the region of Brussels Capitale. Each has its own public services and competences.
I
L
L L
M
M
M
H
H H
L M H
L
M
H
Hazard
Vulnerability- Unbuilt parcels
- Other unbuilt parcels, very little sensible to flood
Housing, firms, agricultural buildings, sports centre, hospitals,transformers, schools, motorways, major roads...
Outdoor sports installations, loading platforms, cemeteries, secondary roads...
Farmland (meadows, cultivations, tree nurseries), private or public gardens, sports grounds...
Wasteland, woods, disused quarries, "natural" spaces...
Levels ofvulnerability Type of uses Examples of uses
Very rare
Rare
Frequent
T = 25 years
T = 50 years
T = or > 100 years
Recurrence
SubmersionFrequencyof floods
return periodQ T
Depth (D)
Extent of water surface
flow velocity (V)
Duration of flood (Du)
Protection
Catch -
yes
Catch +
V > 1 m/s
Du > 3 days
Embankments, pumping, movable flood walls
yes
0 = D < 0,3 = D < 1,3 = D (m)
M H H
M M M
M
L M H
H
M
L
( >2x/10 years)
The main basis data
- Flood hazard mapping To delimit hazard areas according to three values.
Picture 5 : Extract of the damage risk map (watershed "Dyle-Gette")
Photo 2 :
The Vesdre (Province de Liège)
Floods in January 2003 in the Walloon Region :
Photo 1 :
The Eau Blanche (Province deNamur)
Data processing
- 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 3 : Matrix to determine the damage risk
The risk value reflects the extent of damages on vulnerable elements.
Picture 4 : Sketch extract of data processing
Basis data (blue balloons) are integrated in this pattern and processed in geoprocessing units (orange oblongs). New data (green balloons) are created in output. These latters are used again to provide other transformation processes. This cycle keeps going till reaching the layer of damage risk.
Table 1 : Bringing together uses according to vulnerability levelsUses (elements sensible to flood) are filed according to four levels of vulnerability, depending on their propensity to submit damages.Vulnerability has been determined on the basis of a multicriteria analysis, by taking into account direct and indirect damages, tangible and intangible costs.
Raw data are integrated and modeled into a Geographic Information System (G.I.S.). The processing string which is created allows to automate the production. Script is written in a python programming language.
Step 2 : Mapping
Step 1 : Determination of damage risk
An overall and cross-disciplinary project of floods fight
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 of floods prevention and fight against their effects on the disaster victims. 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.
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, the damage risk's. This work should be completed in the middle of year 2007.The flood risk map should achieve various aims.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 "Plan PLUIES" actions :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;2 - to reduce vulnerability : identify building lands located in flood areas;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.
H = HighM = ModerateL = LowI = Insignificant
Picture 1 : The Walloon Region
L L
High
Moderate
Low
Insignificant
Picture 2 : Sketch of hazard determining
Flood hazard by overflowing is made up of areas in which floods are expected to occur in a more or less extended and frequently way, due to natural overflowing of waterways.The hazard value is determined by the combination of two factors : the recurrence of a flood (periodicity or occurrence) and its water surface elevation.Several methods are being used : hydrologic statistics, hydraulic modeling, ground studies and hydropedology.
Scale 1 : 10.000
I
I - All the buildings used as housing or linked to an economic or leasure activity - Community or major public services equipments- Major highways, railways
- Light superstructures or movable equipments - Community or minor public services equipments
I
Legend
HighModerateLowInsignificant
* Unbuilt lands at the moment, situated in an urbanizable area of the Plan de secteur
HighModerate
Highways
Major highwaysSecondary highways
(The filling's colour varies according to the risk value)
Damage risk
Potential damage risk*
Risk area Stretch of water Water body
(The sign's colour varies according to the risk value)
Administration
Historic building
Hospital
SchoolE
Patr.
Adm
Police
Ponctual risk
Table 2 : Overall philosophyof the mapping work
RESTRAINTS- deadlineLife cycle of the project for mapping the flood risk zones : three years. Most of the hazard maps are produced at the end of the project.
AIMS MEANS
- Work out a method allowing to produce, within some months, the damage risk maps.
- available resourcesRestricted available means (staff and budget)
- servicing in the hereafterNecessity for a regular and simplified update of the maps, after the end of the project
The development of an automated method.- Avoid the new data production;- enhance data produced by public services;- use the data in vectorial form;- reduce the manual data processing.
- The use of starting data independent of the project and managed externally.
- Allow the futur staff (untrained) to produce the maps.Knowledge management : structure and file knowledge linked to the production of maps (enhance metadata, formalize the procedure by creating a servicing fi le).