Accuracy of water quality predictions with loading scenarios of forest industry waste waters

The environmental effects of the Finnish industrial loadings are in practic e decided by water courts as they give permits. In decision-making they use an inspection procedure. Since 1970s in Finland within this procedure one method of environmental evaluation has been the application of numerical wa ter quality models. At the Kokemaenjoki watercourse water quality effects o f the paper and pulp mills in Mantta, Lielahti and Valkeakoski were studied with two or three dimensional water quality models. On the basis of these results the costs and benefits of different loading options were considered . Now, after more than a decade, the response of the lake waters to the nut rient and BOD loading can be seen in the water quality monitoring results. We used these observations and studied the accuracy and limitations of thes e early water quality models. (C) 1999 Published by Elsevier Science Ltd on behalf of the IAWQ. All rights reserved.