Managing flood risk in coastal cities through an integrated modellingframework supporting stakeholders’ involvement: the case of Rethymno, Crete

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C. MAKROPOULOSV. TSOUKALA K. BELIBASSAKIS A. LYKOU M. CHONDROS P. GOURGOURA D. NIKOLOPOULOS

Managing flood risk in coastal cities through an integrated modelling framework supporting stakeholders’ involvement: the case of Rethymno, Crete

C. Makropoulos, V. Tsoukala, K. Belibassakis, A. Lykou, M. Chondros, P. Gourgoura, D. Nikolopoulos

As part of36th IAHR WORLD CONGRESS 28 June–3 July 2015 Delft & The Hague, the Netherlands

Special One-Day Session on Coasts at threat in Europe 30-06-2015

AcknowledgementThe research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under Grant agreement n°603663 for the research project PEARL (Preparing for Extreme And Rare events in coastaL regions). The research and its conclusions reflect only the views of the authors and the European Union is not liable for any use that may be made of the information contained herein.

http://www.pearl-fp7.eu/

PEARL projectResearch & work within PEARL

• The aim of PEARL is to develop adaptive risk management strategies for coastal communities against extreme hydro-meteorological events minimising social, economic and environmental impacts & increasing the resilience of Coastal Regions in Europe

• Rethymo City in Crete(Greece) is one of the7 EU coastal case studies

• Ultimate goal is the development of an actionableroadmap for flood riskmanagement by enabling stakeholders’ involvement & grasping their perspectiveneeds and ambitions

Rethymno case studyOverview Rethymno

Population: 32.468 (Census 2011)Density : 140,12 pop./km2Artificial Surfaces

Agricultural areas&

Forest and semi natural surfaces

Corine land cover 2000

L ≈ 7,5 kM

L ≈ 2,0 kM

• Region of Crete• 3rd most populous urban area of the island• Commercial, administrative, cultural & touristic activities are being developed

along the north coast

Mean absolute altitude:15 m

Problem description

Erosion & sediment transport

Violent wave overtopping

• High N-NW winds & Great Fetches• Sea level change• Storm surges 145 km2

• Heavy precipitation• Flash floods• Pluvial floods

• Storm water flow through the city• Numerous streams cross it• Transition form steep slopes at

the upstream rural area to the flat urban zone

Multiple stressors have always posed flood threats causing an on going risk to its residents,homes, business & public infrastructure

Major historic flood events

• February 29th, 1968• February 6th, 1984

Archontakis, 2013

• October 28th, 1991• November 10th, 1999

(Photos depicting events’ impacts)

Mainly related to heavy precipitation, exceedance of rivers’ & drainage systems’ capacity or inability of flow routing due to lack of maintenance

Mitigation measures were selected

The flood events led to adverse human, material, economic and environmental effects and eventually to the selection of prevention and mitigation measures:• Arrangement and diversion of streams and torrents• Construction of circular stormwater drainage collectors • Construction of internal-primary drainage network• Construction of flood control dams

Nonetheless,Based on recent flood events, there is a growing realisation that focusing exclusively on engineering mitigation measures and treating problems in an ad hoc, isolated fashion is no longer a viable option

Archontakis, 2013

Recent Flood Events (1/3)occurred during autumn-winter period

• Flash flood (event October 24th, 2014)

a collection of articles and videos about flooding in Rethymnoavailable at PEARL’s website: http://www.pearl-fp7.eu/casestudies/greece/

Water entered shops and restaurants in the Old Town of Rethymno, the drainage network inlets had been covered by citizens during summer months in order to avoid odour, no maintenance from Authorities side was clamed by others

Recent Flood Events (2/3)occurred during autumn-winter period

a collection of articles and videos about flooding in Rethymnoavailable at PEARL’s website: http://www.pearl-fp7.eu/casestudies/greece/

• Overtopping (event January 1st, 2015 )• Overtopping (event January 13th, 2015)The windward wave breakwater was damaged once more, debris were transferred all over the surrounding roads, right in front of the coast guard buildings.

Recent Flood Events (3/3)occurred during autumn-winter period

a collection of articles and videos about flooding in Rethymnoavailable at PEARL’s website: http://www.pearl-fp7.eu/casestudies/greece/

• Overtopping ( event February 10th, 2015)

Same phenomena as the previous events on January, a car was swept away from the surrounding roads and ended up in the Old Venetian Harbour

Damages (1/2)recorded after the recent events

a collection of articles and videos about flooding in Rethymnoavailable at PEARL’s website: http://www.pearl-fp7.eu/casestudies/greece/

• Extensive structural damages from the event on January 13th, 2015 (just after they had repaired the windward breakwater from previous ones)

Previous damages: photo taken on January 4th, 2014

Damages (2/2)recorded after the recent events

a collection of articles and videos about flooding in Rethymnoavailable at PEARL’s website: http://www.pearl-fp7.eu/casestudies/greece/

Extensive structural damages from the event on February 10th, 2015• To public infrastructures• To local business facilities• To citizens’ property

Rethymno within PEARLunderstanding flood risk under different hydro-meteorological scenarios

Modelling extreme events individually or in coincidence through an integrated modelling framework: Estimation of atmospheric variables and development of climate change scenarios Estimation of Wave Characteristics (4-level downscaling approach ) Modelling of nearshore response to hurricane impacts and storms (e.g. storm

surges, wave propagation, sediment transport, erosion, wave diffraction and refraction, etc.)

Catchment hydrological modelling (incl. Hydraulic calculations of natural channels networks

Urban flood modelling (incl. surface flow & stormwater network)

SWAN MIKE 21

EURTOP

MIKE 11, MIKE URBAN, MIKE 21 FM

Combination of floods highlight the need for the estimation of hazard due to combined roots and causes

Step 1

Step 2

Step 3

Step 4

From the coast

Classification of storm events(Weak, Moderate, Significant, Severe, Extreme)

Hydrodynamic field in shallower regions Wave run up Wave overtopping

• Preprocessing of geospatial data• Modification of DEM (DEM: 2 m,

DSM: 0.8m) • Subbasin & river

network delineation• Estimation of Stream

& Subbasincharacteristics

• Estimation of hydrological parameters• Derivation of necessary input data for

hydrologic/hydraulic simulation

13 River BasinsTotal area: 145 km2

Total length of river network: 390 km

DSM: 0.8m

DEM: 2 m

Moving inland: data

Setting up coupled hydraulic models for 1D/2D simulationfor the urban area (MIKE 11, MIKE 21 FM & later MIKE URBAN)enabling hazard assessment from flooding derived from the sea, rivers, urban, drainage and sewer systems

Downstream boundary conditions along the coastline provided by the multi-scale coastal modellling framework

Moving inland: Models

Stakeholders involvementcreating common images, grasping their needs and ambitions

• Flow of information between authorities – Stakeholder’s analysis & Sociogram• Comprehension of their perception of flood risk• Engaging them towards the development of specific & actionable roadmaps –

establishment of the Learning & Action Alliances

Meeting with Municipal Water Supply & Sewerage Company Meeting with the Municipal Port Authority

Meeting with Civil Protection Volunteer Team

Modelling stakeholder actions: ABM approach

The agents (local authorities & Stakeholders):• Inspect the existing flood protection measures• Get information regarding the foreseen flood risk

and the available funding resources• Get information regarding the assessment

of new measures • Interact with the stakeholders• Choose to maintain existing and/or

implement new measures of flood protection

The ABM includes:• Responsible authorities’ behavioural rules for implementation

and maintenance of flood resilience measures based on multi-criteria assessment

• Stakeholders’ procedures for defending their interests• Authorities and stakeholders cooperation rules based on

iterated N-Prisoner’s Dilemma games• Link with flood risk assessment for assessing the effect of the

Rethymno’s authorities’ response to flood risk

Getting stakeholder to actWater Detective app (developed by Hydrologic)

Web based front endPEARL’s platform

PostgreSQL/PostGIS

HR’s WD portal

Flood related crowdsourcing citizens’ report

Visualisation of geo-referenced information

Possible rerouting to responsible authorities and provision of alerts

Rethymno within the PEARL platforman interface between the developed tools and the stakeholders

Access to the Knowledge Base for resilience measures, strategies & tools supporting their selection & enabling end users to find solution to flood problems

Visualisation of all types of result e.g. flood inundation maps, future urban growth scenarios, social behaviour, flood reports etc.

An interactive platform enabling visualisation of the effect of the alternative choices on risk situations by giving access to a library of possible future that will assist future analysis and decision making processes of the local authorities

Scenario Manager application per Case

A common space for knowledge & lessons learned sharing among all PEAR’s CS & stakeholders

Managing flood risk in coastal cities through an integrated modellingframework supporting stakeholders’ involvement: the case of Rethymno, Crete

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C. MAKROPOULOSV. TSOUKALA K. BELIBASSAKIS A. LYKOU M. CHONDROS P. GOURGOURA D. NIKOLOPOULOS