D28: Internal seiche mixing study - Hydromod

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Integrated Water Resource Management for Important Deep European Lakes and their Catchment Areas EUROLAKES D28: Internal seiche mixing study FP5_Contract No.: EVK1-CT1999-00004 Version: 1.2 Date: 24.08.2004 File: D28.doc Page 20 of 92 2.5 CONCLUSIONS The analysed measurements are shown the existence of internal gravity wave in the Lac du Bourget with a period between 40hours to 80 hours depending on the vertical stratification structure. The simulation using the TELEMAC-3D model is used to reproduce one seiche event on the Lac du Bourget. The numerical results are in a quite good qualitative agreement with the measurements. The numerical results are given some interesting new information about the hydraulic respond of the lake under wind forcing. After the generation of the internal seiches, the wave propagation is showing a rotating structure, due to the Coriolis influence, with an amphidromic point at the middle of the lake (Figure 16). In spite of the bad representation of the bathymetry along the coast, the maximum dissipation of the internal wave illustrated by the two figures (Figure 17 and Figure 18) is located all around the coastline of the lake. And the maximum vertical velocity is less than 1. 10 -3 m/s. 2.6 REFERENCES Bournet PE. 1996. Contribution à l’étude hydrodynamique et thermique du Lac du Bourget. PhD Thesis. Janin JM, Lepeintre F, and Pechon P. 1992. TELEMAC-3D: a finite element code to solve 3D free surface flows problems. Proceedings of computer modelling of seas and Coastal regions. Southampton, UK.
Integrated Water Resource Management for Important Deep European Lakes and their Catchment Areas EUROLAKES D28: Internal seiche mixing study 3 INTERNAL SEICHES AND MIXING IN LAC LÉMAN 3.1 THE LAC LÉMAN ENVIRONMENT FP5_Contract No.: EVK1-CT1999-00004 Version: 1.2 Date: 24.08.2004 File: D28.doc Page 21 of 92 The Lac Léman (Figure 19) is a warm monomictic lake situated between Switzerland and France. It is curved in shape and composed of two main basins: a deep central eastern basin (310 m maximum depth, 157 m mean depth, mean width 10 km) called Grand Lac ("big lake") and a relatively small and narrow section in the west called Petit Lac ("small lake," maximum depth 70 m; mean width around 4 km). The lake has a total length of 70.2 km and a width of 13.8 km in the central part which corresponds to 2.4 Rossby radii under typical summer stratification conditions. The eastern part of the lake is surrounded by high mountains sheltering it from most strong winds. The central and western part of the lake form part of the Swiss central plateau. The windfield over the lake is affected by the mountains and the plateau. It is consequently dominated by events of strong winds from the northeast and southwest which may last from several hours to several days. The winds from the northeast have been observed to cause thermocline depressions of more than 20 m in the Petit Lac (Lemmin and D'Adamo 1996). These wind events can be considered as the principal forcing to initiate internal seiches. � �� Figure 19 : Map of the Lac Léman (Lake Geneva) with surrounding topography and positions of recording stations discussed in this text. Depth contours are given with reference to the water surface level which is at an elevation of 371 m above sea level. ��
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D28: Internal seiche mixing study - Hydromod

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