EVALUATION OF POLLUTION REDUCTION SCENARIOS IN A RIVER BASIN - APPLICATION OF LONG-TERM WATER-QUALITY SIMULATIONS

Because of stricter environmental regulations for surface water qualit y in Flanders, large efforts are made for the construction of sewers a nd water treatment plants. The present methodology to determine the ne cessary pollutant load reductions is based on the combination of simpl e mass balances, the 90-percentile discharge and neglects the self-pur ification capacity of the surface water. This method is very easy to a pply but offers little guarantee that the goals set will be met. A sus tainable river basin management requires a methodology to evaluate dif ferent options in pollution abatement strategies. Only by this, the av ailable resources can be applied in the most advantageous, sustainable way. In this paper, a methodology is proposed to evaluate water quali ty based on dynamic modelling. This methodology is illustrated by mean s of a case study on the river Dender. Continuous and simultaneous mea surements via 3 places along the river were used to calibrate and vali date the model. Continuous simulations over a period of four years gua rantee that, in contrast with traditional event type simulations, most discharge and hydrometeorologic conditions are taken into account. At tention was given to the occurrence of extreme events. These events wi ll determine the global ecological condition of the river. CDF-curves (Concentrated-Duration-Frequency) make it possible to gain insight in the duration and the frequency of occurrence of events with inadmissib le concentrations of dissolved oxygen and ammonia. Besides simulations taking into account the present loads, differrent pollutant abatement strategies were analysed and compared. The applied methodology offers the possibility to evaluate the impact of different strategies and to locate present and future problems. (C) 1997 IAWQ. Published by Elsev ier Science Ltd.