1. ENAC SSIE
/
Three dimensional hydrodynamic
modeling of Lake Geneva
Auteur André Michael
Encadrement Prof. Alfred Johny Wüest1 / Damien Bouffard1
Master 2013
1 Physics of Aquatic Systems Laboratory – Margaretha Kamprad Chair (APHYS)
Main goals
• Validate a 3D numerical simulation of Lake Geneva circulation and thermal structure both in stratified and unstratified period
• Provide a physical interpretation of the results, trying to identify the natural processes causing those results
Physical limnology of Lake Geneva
General circulation
Residual circulation
•Caused by long fetch winds (synoptic winds)
•Wind cause thermocline tilting => Oscillations +
Coriolis force = Cyclonic circulation
•Wind energy -> Potential energy -> Currents
Direct circulation
•Caused by thermal winds
•Wind energy -> Cyclonic currents (faster response)
•Constant currents (≠ residual circulation)
Density
stratification
Result of two
opposing force:
Solar radiation
(stabilizing force)
VS. Wind stress
(mixing force)
Lake Geneva winds
• Long fetch strong winds (Bise NE and Vent SW)
• Thermal winds (lake/land-breeze)
Methods
Model
• Delft3D used: A 3D hydrodynamic computational model
• Used on a curvilinear grid 500m X 500m, with 100
layers (Z-mode)
• Simulation time frame: 1st of March -> 30th of
December 2011.
• Calculation time step is 1 minute
• Meteorological data input: Wind speed and direction, air
temperature, relative humidity, cloud coverage and
solar radiations time series
• Simulations run with spatially homogenous and
heterogeneous winds
Meteorological data and observations
• Buchillon station: Water temperature at 1m and 36m, for the
whole simulation period
• Vidy bay: Currents speed and
direction over the whole
watercolumn and temperature at
bed (65m), for the last month of
simulation only
• SHL2: Monthly temperature
profile
Results
Thermal structure (heterogeneous winds)
Depth[m]
SHL2 Simulation J2
100 150 200 250 300 350
-80
-60
-40
-20
0
Temperature [°C]
5
10
15
20
Depth[m]
SHL2 Simulation J2
100 150 200 250 300 350
-80
-60
-40
-20
0
Temperature [°C]
5
10
15
20
t [Days]
Depth[m]
SHL2 Observations
100 150 200 250 300 350
-80
-60
-40
-20
0
Temperature [°C]
5
10
15
20
Circulation
5 5.1 5.2 5.3 5.4 5.5 5.6
1.15
1.2
1.25
1.3
1.35
1.4
1.45
1.5
1.55
x 10
5 Spring depth averaged mean circulation
5 5.1 5.2 5.3 5.4 5.5 5.6
x 10
5
1.15
1.2
1.25
1.3
1.35
1.4
1.45
1.5
1.55
x 10
5 Summer depth averaged mean circulation
5 5.1 5.2 5.3 5.4 5.5 5.6
x 10
5
1.15
1.2
1.25
1.3
1.35
1.4
1.45
1.5
1.55
x 10
5 Fall depth averaged mean circulation
5 5.1 5.2 5.3 5.4 5.5 5.6
1.15
1.2
1.25
1.3
1.35
1.4
1.45
1.5
1.55
x 10
5 December depth averaged circulation
5 5.1 5.2 5.3 5.4 5.5 5.6
1.15
1.2
1.25
1.3
1.35
1.4
1.45
1.5
1.55
x 10
5
Spring depth averaged mean circulation
5 5.1 5.2 5.3 5.4 5.5 5.6
1.15
1.2
1.25
1.3
1.35
1.4
1.45
1.5
1.55
x 10
5
Summer depthaveraged mean circulation
5 5.1 5.2 5.3 5.4 5.5 5.6
1.15
1.2
1.25
1.3
1.35
1.4
1.45
1.5
1.55
x 10
5 Fall depth averaged mean circulation
5 5.1 5.2 5.3 5.4 5.5 5.6
1.15
1.2
1.25
1.3
1.35
1.4
1.45
1.5
1.55
x 10
5 Winter depth averaged mean circulation
Homogenous wind simulations
Heterogeneous wind simulations
Physical interpretation
• Comparison between homogeneous and heterogeneous winds simulations => roles of long fetch winds and thermal winds in circulation
• Comparison between surface and depth averaged circulation => gyre are rather deep (direct circulation) or superficial (residual circulation)
Bise event
Lake
breeze
Conclusion
• Western anticyclonic gyre: Caused by long fetch winds, strengthened by thermal winds, superficial => Residual circulation
• Eastern cyclonic gyre: Spring and fall, disappeared in summer (patchy circulation), rotation sense inversion in winter under strong SW
winds, penetrates into epilimnion => direct circulation
• Divergence between model and observation at the end of the year: Observed thermocline rise while modeled thermocline get deeper
• Observed thermal structure interpolated from monthly temperature profile, and the last two profile were outliers => misinterpretations?
• Year 2011 unusual from meteorological point of view: shallower themocline at SHL2 since >10 years