Description of the application

The main sewer system of Prague is combined and covers about 60% of the total city area. It consists of 2,360 km of sewers, 54,000 manholes, 140 CSOs and 19 pumping stations. The sewer system is connected with the central WWTP, which has a design flow rate of Q = 6m3/s. Due to the large amount of inter-connections, the type of storage structures and the regular extension of the system, its behaviour is complex. Problem areas identified include the pollution of receiving waters (Vltava River) by combined sewer overflows and the deteriorating condition of the system itself. Flood gates have been installed within the sewers and CSOs are receiving modification in these areas, including slight changes in tank geometry and the installation of pre-treatment devices. Another problem is connected with several local separate sewer systems located on the outskirts of the city.

Lessons learned

In order to assess benefits of the individual CSO reconstruction phases, pollution and hydraulic impacts of overflow were simulated by a computer model (‘REBEKA’) using a 70 year rainfall time series for Prague. REBEKA simulates both emissions from the sewer system (discharge of water, total suspended solids and NH4-N) and water quality standards in the receiving water (frequency of acute water pollution events caused by unionised ammonia NH3). Simulation results for the reconstruction phases revealed a gradual decrease in the average number of overflows per year, overflow volume and duration and the amount of suspended solids discharged in the individual reconstruction phases.

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Last modified: Sept. 12, 2016, 9:18 a.m.