Analysis and flood models for Ljubljana Urban Region Elco Koks & Hans de Moel

2 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

3 Flood risk Hazard Exposure Vulnerability x x x x = = Risk

4 Modelling the hazard: HEC-RAS  Developed by the US Army Corps of Engineers (USACE)  Open access  Allows for modelling river floods

5 Step 1: Digital Elevation Map and Cross-Sections

6 Step 2: The discharges (in meters per second) Return period Ljub1Ljub7Podl1Zorn1boro1iska1iz_side1izic1grad1Suji1 'vhrnika''moste''razor''drenov''borovnica''iska''ig1''zelimlje''dvor''razori'

7 Step 3: Final steps in HEC-RAS

8 Step 4: The results, 2010 flood simulated

9 Preparing the exposure data: update land-use map OLD: NEW:

10 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: land25 High-density residential: the buildings400 Low-density residential: land10 Low-density residential: the buildings400 Industrial or commercial: land20 Industrial or commercial: the buildings300 Road and rail networks and associated land8.34 Airports10.58 Construction sites76.73 Green urban areas59.01 Sport and leisure facilities57.57 Non-irrigated arable land0.43 Permanently irrigated land0.42 Vineyards0.4 Fruit trees and berry plantations0.38 Pastures0.4 Annual crops associated with permanent crops 0.33 Complex cultivation patterns0.37 Land principally occupied by agriculture, with significant areas of natural vegetation0.25 Agro-forestry areas0.29

11 Applying mitigation measures  Raising houses: +25 cm +50 cm +100 cm  Building a dike: Notranje Gorice

12 The results

13 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

14 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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