engleski

Split submarine outfall impact assessment and pollutant transport modelling

Split (Southern Croatia) submarine outfall, whose construction will begin in September 2001, represent a key disposal facility of centralized Split/Solin Bithern Basin sewerage system, which drains the area with some 60.000 inhabitants. Construction of this outfall will enable all preliminarly treated communal wastewater to be discharged into the Brac channel via 2, 750 m long HDPe pipeline, ending up at a depth of 36 m. In order to check the consequences of various discharge scenarios, the outfall operation impact has been preliminarly tested by means of 3-D mathematical and hydraulic model. Performed test confirm that the submerged morphological barrier, located westward to the planned outfall diffuser section location, contributes to the complexity of sea currents pattern in the wastewater discharge zone, while characteristic energy dampening effect due to seasonal seawater column stratification represents a favourable factor for submarine release of wastewater. This paper presents results of both physical and mathematical modelling experiments in typical hydrodinamic and oceanographic conditions in the Brac channel, where various driving forces act simultaneously. Results obtained by two models, both in terms of modelled currents fields and spatial extent of the pollution filed, has lead to a conclusion that reasonably high safety factors (in terms of meeting prescribed coastal water bacteriological quality standards) can be obtained with the proposed optimized outfall length. That conclusion is further strenghtened by the fact that expected outfall intermittent operation regime will enable flusing of the mixing zone between two consecutive discharge batches, so even better results than presented herein are expected in real situations.

submarine outfall; 3-D mathematical and hydraulic model; optimized outfall length

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