Flood: National Platform for Natural Hazards

Floods and debris flows - even before storms and hail - are the natural hazards that repeatedly cause the most property damage in Switzerland each year. Since the middle of the 19th century, much has been done to protect against flooding. However, with the increasing population density and the more frequent occurrence of thunderstorms and heavy rainfall due to climate change, the vulnerability remains.

Alerting

Warning system and alarms

Floods are often caused by various factors, which can also occur in combination: heavy or prolonged rainfall, snowmelt, large volumes of water and debris, erosion and sedimentation. Floods and debris flows (swelling mountain streams that carry debris and earth masses) have caused damage totalling over CHF 13 billion since 1972.

BAFU, Damage caused by natural hazards

Fact sheet «Floods and debris flows”

The floods of 2005 revealed the limits of technical protection measures and heralded a turnaround. Just one week after the storm disaster, the Federal Council launched the Optimisation of Warning and Alerting in the Event of Natural Hazards (OWARNA) project. In collaboration with PLANAT, the project analysed which measures contribute to the reduction and management of such emergencies.

Commission for flood protection

Specifically, the federal government has improved the forecasting models, standardised the warning and hazard levels and optimised alerts in the event of extreme weather events. In 2014, the ‘Natural Hazards Portal’ warning platform was created for the population.

The 2005 floods showed the limits of technical protection measures and heralded a turnaround

Increase in hazard

Increasing risk of flooding

Climate change is having an impact on the risk of flooding: According to current climate scenarios, Switzerland will experience increasingly frequent and intense heavy rainfall. Glaciers will also continue to melt. The risk of flooding and debris flows will increase in future.

NCCS, Swiss waters in the face of climate change

Effective measures

Various bodies are involved in protecting against floods and debris flows: cantons and municipalities with spatial planning and organisational measures. But also homeowners with structural measures or the design of the terrain. The federal government makes personal recommendations on how individuals should behave before, during or after a flood. Examples of measures include

Spatial planning measures

Create hazard and risk maps
Designate hazard areas in the zoning plan
Designate watercourse areas and keep them clear
Do not build over or zone endangered areas

Flood hazard map

Technical measures

Maintain watercourses and existing protective structures
Provide retention measures (flow regulation, retention areas and basins, debris collectors)
Increase channel capacities (dams, widening)
Divert and redirect flood peaks (overload corridors)
Implement measures for bed load management and balance
Stabilise banks and riverbeds
Protect buildings and structures

NCCS, Protect buildings from flooding

Biological measures

Maintain protective forests and lateral slopes of watercourses
Provide erosion-prone banks and riparian zones with vegetation

Organisational measures

Install monitoring and early warning systems
Create and practise alerting concepts
Draw up emergency plans and keep them up to date
Keep mobile protective elements ready

Widened Ticino around Bellinzona

The River Ticino was straightened and canalised at the end of the 19th century to make the land arable. Over the years, the river bed eroded, the protective embankments were damaged and the risk of the plain being flooded increased. Today, the river is being given more space again. The ‘Parco fluviale Ticino Boschetti e Saleggi a Bellinzona’ project serves not only to protect against flooding, but also to promote biodiversity and provide a recreational area.

Parco fluviale Saleggi-Boschetti

Chronicle

Devastating floods and debris flows

1852

The Aare reached its highest level ever recorded and also caused the Rhine to rise sharply. The Seeland was particularly affected by this flood and efforts to correct the waters of the Jura were given new impetus.

ETH-Bibliothek Zürich, Bildarchiv / Fotograf: Unbekannt / Ans_05457-004-AL-FL / Public Domain Mark

Weidenbuhne für Hochwasserschutz und Auflandung (We-Ho)

1981

On 24 July, after heavy rainfall, a debris flow emerged from a small stream and buried a camp with children near Domat-Ems (GR). Many were able to save themselves, but six girls died.

ETH-Bibliothek Zürich, Bildarchiv/Stiftung Luftbild Schweiz / Fotograf: Swissair Photo AG / LBS_R1-900905 / CC BY-SA 4.0

1987

Switzerland was in a state of emergency in August 1987: there was hardly a valley without major damage to streams and rivers, roads, houses, infrastructure or agricultural land. The floods caused damage totalling CHF 800 million.

ETH-Bibliothek Zürich, Bildarchiv / Fotograf: Enz, Dieter; Comet Photo AG (Zürich) / Com_L36-0227-0008-0004 / CC BY-SA 4.0

Attinghausen Allmend, Blick nach Osten (E)

1993

On 24 September, the Saltina in Brig burst its banks after weeks of rainfall and three days of heavy rain. Debris and alluvial wood accumulated on the bridge in the centre of the town, causing a blockage. The flooding left metres of sand and debris on roads, squares and in buildings. Two people lost their lives. The material damage caused by this event totalled over CHF 650 million. 

2005

Six people died in the floods in Switzerland in August 2005. It caused property damage totalling CHF 3 billion and was the natural event with the greatest financial damage since it was systematically recorded in 1972. Around 900 municipalities were affected. Places such as Engelberg and Lauterbrunnen were cut off from the environment for days. In Bern, the Aare burst its banks and flooded the Matte neighbourhood.

Simone Hunziker PLANAT 2005

2007

The flood of 8/9 August was another major event that affected large parts of the Swiss Plateau and the Swiss Jura. The system of the Jura lakes and the underlying Aare, which was considered flood-proof, was overloaded. The Birs swelled into a raging river and flooded the old town centre of Laufen (BL).