Water quality modelling of sewers. A case study
1995
Heip, L. | Assel, J. van | Mus, I. | Swartenbroekx, P. (Aquafin, Aartselaar (Belgium))
In Flanders (Belgium) much effort is being put into complying with the EC Urban Waste Water Treatment Directive (CEC 1991). Aquafin, as the responsible for building and operating the sewer infrastructure including WWTPs (waste water treatment plants) for domestic sewerage in Flanders, is one of the major forces towards this goal. Since most of Flanders sewers are combined, CSOs (combined sewer overflows) contribute to a large extent to the pollution of surface waters. At the moment sewers are being designed on a mere quantitative basis to prevent flooding, including limiting the number of spill-events to seven a year. The organic load associated with an event is not taken into consideration. The present day design tools include powerful software, computing the hydraulic behaviour of a sewer system on the basis of the full St.-Venant equations. With these tools,incorporated in the Hydronaut-software package, new sewers are designed and existing sewers optimized on an overflow spill frequency criterion. The aim of the EC-funded SPI098/2 Sprint program in Flanders is to develop an engineering procedure extending the Hydronaut-procedure to qualitative design. Thus the load generated by CSOs can be taken into account and limiting this load can eventually become an important design criterion. The development of this procedure is based on a case study in the catchment of Tielt (Belgium), where a sampling and monitoring campaign is being performed on four overflows. The results of this campaign form the basis for verification and calibration of the HydroworksDM software, a software package combining hydraulic and pollutant transport calculations.
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