In order to minimise pollution of the river Elbe from untreated run-off water stormwater tanks in Johannstadt and Kaditz were built.
Technical data of both installations
Stormwater tank Johannstadt
On 8th October 2001 the stormwater and clarification tank in Johannstadt with a capacity of 12,000m³ was officially put into operation after a two-year construction period.
The underground tank for the storage of wastewater is 50m long by 45m wide and consists of five chambers. The base of the tank is 17m below ground level. The complete tank is covered with soil so that plants can grow on it and a minimum impact on the nature reserve ‘Elbe meadows’ is ensured. The only visible sign of the tank is a 4 x 4m glass building which serves as access point to the underground facilities.
The stormwater tank in Johannstadt stores excess water when extremely wet conditions prevail and the capacity of the Old Town collection sewer is exceeded. Once conditions go back to normal the stored water can then be dosed in a controlled manner to the STW Dresden Kaditz and appropriately treated before being discharged into the river. If the capacity is still not sufficient, the then at least mechanically treated water is released into the river Elbe.
Stormwater tank Kaditz
In March 2002 the construction of the stormwater tank in Kaditz commenced. Two years later six rectangular tanks with a capacity of 6,000m³ each was completed and now provides a total storage capacity of 24,000m³.
If the wastewater flow to the works exceeds 4m³/s the pumps divert the flow to the stormwater tanks. These tanks are designed like primary settlement tanks and work like a mechanical treatment stage. In the unlikely case that the flow is even larger than 13m³/s, then the excess flow is directly discharged into the river Elbe.
Once the flow to the works has dropped below 4m³/s the stored wastewater in the tanks is added to the flow. The stormwater tanks are cleaned with final effluent from the works. A special feature of the stormwater tank in Kaditz is a photovoltaic plant on the roof.