Resilience measure: Stormwater retention tank


Stormwater tanks are an effective way of reducing peak flow and equalising flow rates from storm water runoffs in the sewer system. Placed strategically, stormwater tanks mean better utilisation of the existing sewer system, allow for intelligent management of storm water flows, and ultimately save on infrastructure investments. Stormwater tanks can be relatively easily adapted to the sewer system, and during heavy rain the sewer system is relieved by guiding excess storm water to the stormwater tank for temporary storage.
(GRUNDFOS, Design of StormWater Tanks, accessed on Sept. 2016)

Co-benefits and impacts

Stormwater tanks are a cost-effective solution, because sewer lines are already constructed and generally have a substantially remaining lifetime, and replacing existing pipes in an urban environment is "in addition to being very expensive" troublesome.
(GRUNDFOS, Design of StormWater Tanks, accessed on Sept. 2016)


Storm water is collected in the sewer network. A sewer network can either be a combined system or a separate stormwater system. The latter is of no interest for this guideline, as the storm water from this system is often guided directly to the recipient or into wet retention ponds. However, storm water from the combined sewer system is a more complex issue and can cause environmental, aesthetic and hygiene problems for the recipients, in the form of combined sewer overflows of untreated wastewater, because the systems are not constructed to cope with these large water flows. Retention time of the stored water is controlled by available space in the sewer system, and this determines when water from the tank can be conveyed back. This can normally be done immediately after the storm water runoff event and the tank can be empty within 24-48 hours after the first inflow. Especially for combined sewerage systems, during extended periods of detention, unintended issues such as odour problems might arise, resulting from the combination of wastewater quality, temperature and time.
(GRUNDFOS, Design of StormWater Tanks, accessed on Sept. 2016)

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Last modified: Sept. 20, 2016, 6:48 a.m.