Earthquakes, floods, rockfall processes, debris flows and avalanches can cause massive damage to buildings and endanger human life. Damage can be prevented at relatively little expense.
Text: Lucienne Rey
The mess took the young owners unawares: no sooner had they moved into their new house in Rain (LU) than they had to clear out the basement again – and dispose of everything that had been destroyed. Heavy rain had caused a layer of water, which was only a few centimetres deep but covering an entire field, to run down the slope and into the basement of the new building, through lightwells and down the basement steps. Around 130,000 Swiss francs of damage was caused to the building. Added to this was the cost of the ruined furniture, which came to around 80,000 Swiss francs.
Disastrous surface runoff
What came as a surprise to the homeowners was not completely unexpected for Antoine Magnollay, who works in the FOEN’s Flood Protection Section. Surface runoff is a widespread, frequent occurrence: “30 to 50 percent of damage caused by flooding is due to surface runoff”, he says. It may look less spectacular than a river that has burst its banks, but the effects are just as devastating. The good news is that the problem can be largely controlled at relatively little expense.
A valuable tool for tackling surface runoff is the surface runoff risk map, which has been available for the whole of Switzerland since 2018. It shows the areas that might be at risk from runoff after heavy downpours. The Canton of Lucerne helped develop and test the map, which went live there in 2016. “The map shows the natural topography and illustrates where the water will flow”, says Markus Wigger from the Lucerne cantonal building insurance company. Building experts use the runoff map in conjunction with the hazard maps (for floods, landslides, rockfall processes and avalanches) to work out if there is any risk of flooding for construction projects and to suggest possible protective measures. For a building project, this could mean planning corridors to divert or channel off water in a controlled manner. “It is certainly possible to design this kind of landscape attractively so that it also benefits biodiversity”, Markus Wigger explains. Provided they are planned in good time, the costs for such measures are negligible and are definitely much lower than clean-up costs once damage has occurred.
When the planning application for the housing estate in Rain was submitted in 2015, the surface runoff map was not yet ready. The protective measures implemented after the event cost 12,000 Swiss francs – a fraction of the costs caused by the floods. A permanent flood kerb along the plot boundary now stops any surface water and diverts it past the housing estate. The low concrete wall is barely noticeable, does not impair the appearance or function of the building or plot and allows the residents to sleep easy during heavy downpours.
When it comes to protecting buildings from the destructive effects of earthquakes, the protective measures for new buildings generally have little impact on the appearance of a property or on the budget – provided earthquake protection is included in the plans from the beginning, in close collaboration with the architects and the engineering company.
Expenditure on earthquake-resistant provisions in new builds accounts for no more than one percent of the total building costs”, says Friederike Braune from the FOEN’s Prevention of Major Accidents and Earthquake Mitigation Section, who has published numerous information sheets and guidelines on this topic.
Since 2003, new buildings in Switzerland must take account of earthquake impacts. Existing buildings have to be checked for earthquake safety and, if it is found to be insufficient, they must be upgraded accordingly. Earthquakes can occur anywhere in Switzerland, although very powerful earthquakes, like those that occur in Italy, are less common. Up to 1,500 earthquakes are registered in Switzerland each year. According to the Swiss Seismological Service (SED), 20 to 30 of these – those with a magnitude of 2.5 or more – can be felt by the population.
The new housing project on the Hanroareal site in Liestal (BL) demonstrates that earthquake-resistant construction does not require trade-offs in terms of aesthetics or the choice of materials. A gently curved long house with 40 apartments was even built with a construction material not commonly used in apartment buildings: the walls are timber frames with composite wood panels clamped to each side. This sheathing gives the building the desired static properties. Division walls, which run through all floors of the building, give it the necessary stability. The outer wall, a facade perforated with numerous small windows, balconies and apartment entrances, is particularly innovative. “In standard architecture, wall elements without openings act as buttresses against wind and earthquake effects”, explains Martin Geiser, an earthquake engineering professor who researches the earthquake behaviour of timber buildings at Bern University of Applied Sciences (BFH). “The perforated facade is reinforced around the windows so that the entire wall now acts as a buttress and not just the elements without openings”, says Geiser, who tested the stability of the new wall in the BFH laboratory in Biel.
In the case of existing properties, deficits in earthquake resistance can often be tackled when repairs and conversion work are carried out. In Geneva, a project to add additional floors to a 1950s apartment block was seen as an opportunity to improve the earthquake protection of the entire building (see photo). Firstly, a fine metal frame placed on top of the existing brickwork minimises the additional weight of the three new storeys. On the courtyard and street side of the building, frames of glued-laminated timber were anchored onto the existing walls to stabilise the structure of the entire building and protect it against the impacts of earthquakes.
“When adding extra floors to the apartment building, we were not only able to extend its life and improve the quality of the space, but also increase the earthquake protection”, says Giovanni Accardo, the contracted construction engineer from INGENI SA. The building was praised during an award ceremony by the Swiss Foundation for Structural Dynamics and Seismic Engineering – and it shows that even with existing buildings, if project managers work together closely, it is possible to combine attractive architecture with earthquake protection.
Help with protective measures
People who want to secure a building against gravitational natural disasters such as floods, avalanches and debris flows may be eligible for support from the public authorities. A number of cantons provide financial assistance and will cover between 20 and 50 percent of the costs of protecting existing properties. For a building to be eligible, the insurance company must have checked and approved the planned measures. An interactive map at schutz-vor-naturgefahren.ch/bauherr/unterstuetzung/fachstellen.html (in German and French) shows the specialist departments that can help in each canton. Some insurance companies also offer financial support. There are currently no grants available for measures to protect against earthquakes.
Last modification 03.06.2020