Direct effects of dominant winds on residence and travel times in the wide and open lacustrine embayment: Vidy Bay (Lake Geneva, Switzerland)

Abstract

Numerical simulations were carried out to determine the residence (or flushing) time of water in Vidy Bay (north shore of Lake Geneva) for different meteorological conditions. A hydrodynamic model (Delft3D-FLOW) was applied to simulate the flow field in the embayment during 2010 and January 2011. Using these results, particle tracking was applied to estimate transport of wastewater effluent discharged into the embayment. The model predictions compared well with published field measurements of dissolved species (as given by electrical conductivity profiles) within the wastewater. The pelagic boundary of the embayment was defined by the largest within-bay gyre. Based on this definition, particle tracking was used to quantify the residence time under dominant wind conditions. Similarly, particle tracking was used to determine the travel time (i.e., time to exit the embayment) for each of Vidy Bay's three inflows (stream, stormwater and wastewater effluent). Although the wind field over the lake is variable, current patterns in the embayment can be simulated using the hydrodynamic model forced by a spatially uniform wind field. For a given wind speed, the main factor influencing residence and travel times is the wind angle. The presence of gyres leads to high mean residence times with large variability. As the wind direction becomes more aligned with the shoreline (i.e., with increasing westerly or easterly components), longshore currents dominate. These disrupt gyre formation and markedly reduce the mean and variability of embayment residence time. The numerical model was utilized to assess the potential for plume movement (in plan) from above the wastewater effluent outfall towards one of Lausanne's drinking water intakes. In the most direct pathway, westward longshore currents can move water from the embayment to the water column above the intake location.

Wastewater as a point source of antibiotic-resistance genes in the sediment of a freshwater lake

“…Low ARG levels detected at locations close to the shore further east (EG1 and NC15) would support the hypothesis that the Chamberonne plume is partly responsible for the extension of the ARG contamination in the south-western direction. This is also supported by current measurements in Vidy Bay in 2010, which revealed 45% of the currents moving west-southwest (Razmi et al, 2013).…”

“…Currents are influenced by changing wind regimes, stratification and bathymetry and vary in direction and speed with depth (Wü est and Lorke, 2003;Righetti et al, 2011). For Vidy Bay, it has recently been shown that near-shore gyres can occur (which enhance the retention time of water and pollutants in the bay) and that neither of two dominant wind regimes produce a consistent current pattern (Razmi et al, 2013). However, westward shore-parallel currents can disrupt gyre formation and move water from near the STEP site to the water column above the DWP, with a dilution factor of about 100 (Razmi et al, 2013).…”

“…For Vidy Bay, it has recently been shown that near-shore gyres can occur (which enhance the retention time of water and pollutants in the bay) and that neither of two dominant wind regimes produce a consistent current pattern (Razmi et al, 2013). However, westward shore-parallel currents can disrupt gyre formation and move water from near the STEP site to the water column above the DWP, with a dilution factor of about 100 (Razmi et al, 2013). In previous studies, tracer released from the WWTP during holomixis reached surface waters at the DWP site (NC13) within 48 h, whereas no tracers were detected when thermal stratification precluded upwelling (Wildi and Rossi, 1997; 1.E-07…”

Into the abyss of Lake Geneva: the elemo interdisciplinary field investigation using the MIR submersibles

“…The concentration of detected pharmaceuticals was found to decrease with increasing distance from the WWTP outlet. An assessment based on the cumulative risk exerted by all measured substances indicated that the wastewater caused a zone of potential ecotoxicological risk that extended well into the deep lake and also in the direction of the St. Sulpice drinking water intake of the City of Lausanne (Hoerger et al 2014, Razmi et al 2014, Bonvin et al 2013). This unique survey was possible because during the dives, the scientists inside the MIR submersibles observed in real time proxy wastewater indicators, such as conductivity and could guide the MIRs along the wastewater plume trajectory.…”

Assessing water quality in lake Naivasha

“…Several computational hydrodynamic models have been developed (Fan, 1988;Razmi et al, 2013;Rodi, 2006;Teeter et al, 2001;Wolfgang, 2006). Reviews of the existing hydrodynamic models can be found in (Elfrink and Baldock, 2002;Nakato, 1990;Onishi, 1994;Papanicolaou et al, 2008;Przedwojski et al, 1995;Spasojevic and Holly, 2000).…”