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 Managementext.coppin@mrw.wallonie.be

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).