Comparison of different impact based guidelines for CSOs in the Benesov case study, Czech Republic

摘要: In this paper results of the application of three impact-based guidelines for CSOs (German, Austrian and Swiss) are compared in the Benesov case study (14 000 inhabitants, 125 hared, 7 CSOs). Both the present state as well as the outlook situation after the connection of further subcatchments designed traditionally to comply CSO dilution ratio 1: 5 were assessed. The numerical assessment was enhanced for the biological-ecological evaluation of Benesovsky Creek. All three guidelines applied give the same statement: Benesovsky Creek suffers from significant hydraulic stress already below the uppermost CSO, however, CSO discharges do not cause considerable acute water quality impacts thanks to the low pH. Only the Swiss guideline identified problems with turbidity and accumulation of suspended solids in the streambed agreeing with the field survey. The biological-ecological assessment of Benesovsky Creek confirmed the gradual degradation of the benthic invertebrate community below each CSO outlet. However, the stream biological status is poor already above Benesov and also the channel regulation between CSO3 and WWTP takes part on its deterioration. The planned measures are going to bring a significant reduction of the chronic pollution loading of Benesovsky Creek, however, the hydraulic stress will remain nearly the same and acute water quality impacts will become slightly more significant (but EQS will not be violated).