Helsinki makes provision for future floods caused by storms

Temporary barrier wall for Market Square; dyke and pumping station for homes in low-lying eastern suburbs

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The City of Helsinki is making a more determined effort than ever before to make provision for future floods. The authorities will be provided with an updated flood map showing contour lines every ten centimetres.
The new map will help the rescue service workers to arrive at critical areas in time with their flood prevention equipment.
The emergency services staff will no longer be taken by surprise if the sea water threatens to rise over the edge of the jetties and into city's Market Square. They will be notified when the sea level rises 90 centimetres above its normal level. During the peak of Wednesday's high winds the sea level rose by 99 centimetres.
An alarm will be given when the water level reaches 110 centimetres above average, which is ten centimetres below the surface of the market square.
The sea water will then be blocked off the market square by temporary flood barriers. They will be built by using sandbags and bales of recycled paper wrapped in plastic.
"The protective wall's field tests were run in August and the wall held well. With one trailer lorry and a forklift truck we can build 120 metres of flood wall in an hour", fire chief Markku Rissanen promises.
The city's sanding trucks have already been equipped with funnels, which, when needed, will enable the quick filling of sandbags. There are no plans to equip the Market Square with permanent flood barriers, but in some low-lying areas embankments and dykes are needed.
The Helsinki Public Works Department will start planning a dyke and a pumping station in the district of Marjaniemi to protect the buildings in the Niittyranta and Koivuniementie areas.
In the districts of Tammisalo and Laajasalo the parkland schemes include banks that will prevent the flood water from entering the streets and yards.
The city geologists have also taken the possibility of a flood into consideration by checking the elevations of tunnel entrances. According to the new regulations the minimum threshold elevation is 2.6 metres from the average sea level.
Presently there are six service tunnels that fall short in this respect and might therefore get flooded. In emergencies the rescue department will block the tunnels with sandbags, but there are plans to modify the entrances in the future.
Helsinki Water is also on its guard. The sewer system overflow points can be blocked to prevent the sea water from entering the system.
The tolerance of the sewer system is sometimes tested by short torrential showers. Reasonable rain, even if it is long in duration, can be handled better.
During the previous major flooding in January 2005, the sea water broke through onto the Market Square and threatened 20 properties in Marjaniemi. In Tammisalo and Laajasalo some yards and low-lying seaside parks were flooded.
At that time the sea level rose in Helsinki by 1.51 metres. In the new map a white line drawn around the sea fronts acts as a reminder of that situation.
Initially the map will be placed in the city's internal information network for the use of various authorities. How outsiders will get to see the map and at what cost is yet to be decided.