Flow retarders, using a flexible hydrostatic butterfly-valve system in the main sewer, have proved to be the most reliable and economic solution to preventing flooding in Feldkirch in periods of extreme rainfall.
Straub expertise guided the project from the planning stage right through to connection of the concrete chambers into the sewer network, including provision of comprehensive documentation. The highly efficient Straub-Flex 3LS pipe coupling reduced the installation time for a single flow retarder to less than one hour.
The challenge:
In recent years, many regions of the world — including alpine countries — have suffered from unpredictable weather patterns. Nestled in the Austrian Alps, Feldkirch has repeatedly had to struggle with the problem of the inability of downstream levels of the sewer system to cope with the excessive volumes of storm water.
Flooded streets, cellars and basements in the surrounding residential areas have been the costly and unpleasant consequence. Feldkirch city engineers were faced with a choice: to either construct additional, high-capacity storm-water reservoirs; or to expand the at-risk areas of the sewer system to ensure that even extreme rainfall would not overload them.
Following extensive investigation and costing studies, the decision was taken to install flow retarders, linked into the main sewer by means of Straub pipe couplings. In situations of threatening flooding, the flow retarders are able to control the flow of flood water upstream of the critical areas of the sewer system.
In comparison with the stormwater reservoir alternative, this elegant and safe solution has saved the city of Feldkirch more than EUR 4 million.
The solution:
A total of five flow retarders were installed in the Gisingen district of Feldkirch.
Three of these are rigid flow retarders; they were installed in sections of the sewer system with pipe diameters of 1690 or 2400 mm. The two larger ones, which this article focuses on, are equipped with a flexible hydrostatic butterfly- valve system, and are linked into the sewer network by means of 2400 mm joint spigots.
