Tallinn sewer system unable to handle torrential rains, flash flooding

Extreme flash flooding in Tallinn on Sunday saw the evacuation of a major shopping mall and some residents take to kayaking and canoeing through the streets. Laagna Road, Tallinn, July 10, 2016. (Kaarel Tooming/ERR)
By Elo Ellermaa, Vahur Lauri
7/11/2016 9:08 PM
Category: News

The sheer amount of precipitation to fall during a brief but torrential rainstorm in the Estonian capital on Sunday was so extraordinary that the city’s sewer system was unable to handle the volume of stormwater created, causing flash flooding in multiple locations across the city, explained Tallinn Waterworks. Analysis to be completed within a couple of weeks should show whether or not the sewer system would need a complete overhaul.

Tallinn Waterworks was able to ascertain on Sunday already that all systems under their management were under control and in good working order, including pumps working at full capacity. According to the waterworks company, however, the amount of rain to fall in a short period of time early Sunday afternoon was exceptional, with 40 millimeters, or over 1.5 inches, of precipitation falling in 40 minutes, reported ETV’s nightly news broadcast “Aktuaalne kaamera.”

Tallinn Waterworks Production Manager Aleksandr Timofejev explained that there was simply so much stormwater that the city’s existing sewage systems were not able to drain it away fast enough. “This is an exceptional case,” he insisted.

Timofejev added that they are working together with the Tallinn Municipal Engineering Services Department in order to better handle such situations in the future.

The Supervisory Foundation of Water Companies in Tallinn has been asked to conduct a thorough analysis during the next couple of weeks, however.

“This will form the basis for whether future plans for public water supply and sewage systems should take a new direction,” noted Timofejev.

Specialist: Tallinn flooding bound to repeat itself

Ain Kendra, a lecturer in the Tallinn University of Technology’s (TTÜ) Department of Road Engineering, warned, however, that such flooding could easily occur in Tallinn again due to issues with sewage system design and limited drainage capacities, among other concerns.

“I think that we should have pipes many times wider to carry stormwater out of the city,” said Kendra. “But that is not a matter of road design, but rather a matter of sewage system design.”

The TTÜ lecturer explained that what traffic planning and stormwater management system planning had in common was that in both cases, one must consider the system as a whole, which in the case of sewage systems meant “that we would have main lines and pipes capable of handling this [stormwater].”

According to Estonian road design standards, flooding such as Sunday’s in Tallinn could occur approximately once every 50 years, and city sewer system standards account for substantially more frequent flooding — once every two years. According to Kendra, however, flooding caused by stormwater actually occurs even more frequently than that.

“There would be nothing unusual about it if this [flooding] were to happen again next week,” he said.

Editor: Aili Sarapik

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