Analysis and flood models for Ljubljana Urban Region

Elco Koks & Hans de Moel

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Brief overview

What is flood risk?

Modelling the hazard

Preparing the exposure data

Maximum damages and depth-damage curves

The damage assessment

Applying mitigation measures

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Flood risk

Hazard

Exposure

Vulnerability

x

x

= Risk

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Modelling the hazard: HEC-RAS

Developed by the US Army Corps of Engineers (USACE)

Open access

Allows for modelling river floods

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Step 1: Digital Elevation Map and Cross-Sections

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Step 2: The discharges (in meters per second)

Return period

Ljub1 Ljub7 Podl1 Zorn1 boro1 iska1 iz_side1 izic1 grad1 Suji1

'vhrnika' 'moste' 'razor' 'drenov' 'borovnica' 'iska' 'ig1' 'zelimlje' 'dvor' 'razori'

2 13 55 13 2 10 28 10 14 15 6

10 27 108 23 4 22 53 15 26 34 14

25 31 126 27 4 27 62 16 31 42 19

50 34 136 30 5 30 68 17 34 47 22

100 37 144 32 5 33 74 17 37 52 25

250 39 153 35 6 36 80 17 40 57 28

500 41 158 37 6 38 84 17 42 61 31

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Step 3: Final steps in HEC-RAS

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Step 4: The results, 2010 flood simulated

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Preparing the exposure data: update land-use map

OLD:

NEW:

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Vulnerability: maximum damages and depth-damage curves

Based on JRC study from 2007: curves and maximum damages were tailored to country level. Land-use class

Max Damage (per square

meter)High-density residential: land 25High-density residential: the buildings 400Low-density residential: land 10Low-density residential: the buildings 400Industrial or commercial: land 20Industrial or commercial: the buildings 300Road and rail networks and associated land 8.34Airports 10.58Construction sites 76.73Green urban areas 59.01Sport and leisure facilities 57.57Non-irrigated arable land 0.43Permanently irrigated land 0.42Vineyards 0.4Fruit trees and berry plantations 0.38Pastures 0.4Annual crops associated with permanent crops 0.33Complex cultivation patterns 0.37Land principally occupied by agriculture, with significant areas of natural vegetation 0.25Agro-forestry areas 0.29

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Applying mitigation measures

Raising houses:• +25 cm• +50 cm• +100 cm

Building a dike:• Notranje Gorice

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The results

Baseline Dike + 25 cm +50 cm + 100 cm0

20

40

60

80

100

120

140

RP10

RP50

RP100

RP500

in m

illi

on

s E

uro

Baseline Dike + 25 cm +50 cm + 100 cm0

1

2

3

4

5

6

7

8

9

10

EAD

EAD

in m

illi

on

s E

uro

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Benefit-cost analysis

Cost-benefit ratio of dike at Notranje is > 2

Elevating existing buildings has very low ratio (0.005)

Elevating new buildings has a much higher ratio but is not everywhere > 1

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Concluding remarks

The model is able to model the flood and its consequences

BUT: maximum damages and curves should be tailored more to Slovenian characteristics.

With such models, many more adaptation and mitigation measures can be evaluated

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Questions?

Contact details:

Elco.koks@vu.nl