engleski

The water Quality Prognosis of the River Drava

The river Drava is the biggest drinking water supplier, as well as essential with its water for agriculture, industry, fishing, river navigation, tourism and recreation, furthermore it is used for energy production. Since the river is also a big waste water recipient, its protection is of the great importance. The waste water coming frorn the city of Osijek itself and neighbouring urban areas together with industry waste water is discharged into the river without being treated, causing a significant pollution worsening the water quality, so that at this point it does not meet the prescribed II. class criteria. The paper describes the downstream water quality prognosis of the river Drava, determined with the classical one-dimensional Streeter-Phelps model, that takes into account only biochemical processes decomposition and reaeration. Since the waste water outfall is 12.1 km far from the Drava river mouth in the Danube river, the complete waste water mixing with river water doos not occure, it was necessary to extend Streeter-Phelps- model with the following formulas: with Lapsev's formula for the initial hydraulic dilution, Froll and Rodzirel's formula for waste and belonging river water mixing coefficient (subsequent dilution) as well as Potapov's formula for turbulent diffusion coefficient. The developed model has been applied in order to predict the river water quality, Osijek waste water discharge condition directly, without waste water treatment plant as well as to determine waste water discharge condition using the the water treatment plant and also to examine senasonal discharge conditions. The required waste water treatment degree was determined taking into account the river Drava ability for self-purification as well as proposed Croatian regulations for waste water discharge into the rivers and sea (according to European Community regulations).

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