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Projects / Programmes source: ARIS

Geophysical and Ecological Approach to Dispersion of a Sewage Plume

Research activity

Code Science Field Subfield
1.02.07  Natural sciences and mathematics  Physics  Biophysics 

Code Science Field
P500  Natural sciences and mathematics  Geophysics, physical oceanography, meteorology 
Keywords
sewage, coastal waters, submarine outfall, dispersion, dilution, stratification, tides
Evaluation (rules)
source: COBISS
Researchers (3)
no. Code Name and surname Research area Role Period No. of publicationsNo. of publications
1.  05226  PhD Vlado Malačič  Hydrology  Head  1998 - 1999  366 
2.  00112  PhD Rudolf Rajar  Civil engineering  Researcher  1998 - 1999  366 
3.  06202  PhD Tomaž Vrhovec  Physics  Researcher  1999  208 
Organisations (3)
no. Code Research organisation City Registration number No. of publicationsNo. of publications
1.  0105  National Institute of Biology  Ljubljana  5055784  13,335 
2.  0792  University of Ljubljana, Faculty of Civil and Geodetic Engineering  Ljubljana  1626981  26,383 
3.  1554  University of Ljubljana, Faculty of Mathematics and Physics  Ljubljana  1627007  33,822 
Abstract
The applied research project deals with the analysis of wastewater field, which spreads into the sea from two diffusers of the submarine outfall near Piran. Numerical models were developed for the simulation of diffusers'' hydraulics and of initial dilution of a buoyant plume, which spreads from the diffuser''s orifices towards the wastewater field laying above. The wastewater field is formed within the water column in a layer of neutral buoyancy in density-stratified environment. There, the secondary dilution process starts, where currents spread the wastewater patch on a larger scale. The near-field survey of the wastewater distribution was monitored ten times from 1997 to 1998 with a fine-scale CTD probe, on which sensors for oxygen and fluorescence (chlorophyll-a) were additionaly installed. Surveys covered the area of 780 m × 740 m with 31 vertical profiles. On a central station the concentrations of nutrients and faecal coliforms were analysed in the water samples taken from at least ten depths. The vertical resolution of the free-falling CTD probe with a speed of 1 m/s is 2.5 cm, therefore anomalies in salinity (less than 0.2 PSU) and temperature (less than 0.3 °C) were detected in layers of wastewater fields which originate from two diffusers. These anomalies corresponded to a signifficant increase in ammonia and faecal coliforms. Since during the enhanced summer stratification of the shallow Gulf of Trieste the thickness of the layer of neutral buoyancy could be less than 0.5 m, the wastewater field is hardly detectable with ''standard'' CTD probes of lower resolution. In 1999 the secondary dilution process will be estimated on the basis of current measurements. Tidal currents at the place of sewage spreading will also be analysed from the results of a 2D numerical model of the northern Adriatic Sea.
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