Strömungsdynamische Untersuchungen im Zürich- und im Luganersee Ein Vergleich von Feldmessungen mit Resultaten theoretischer Modelle

Density distribution and temperature and current data which were measured in Lake of Zürich and Lake of Lugano in two summer field programs are scrutinized and interpreted by means of hydrodynamic models. Barotropic surface seiches and baroclinic internal seiches are studied using a one-and two-layer model and measured data permit identification of the respective resonant periods. Wind induced barotropic and baroclinic circulation dynamics is also studied by means of three-dimensional finite difference models of the hydrodynamic viscous equations on the rotating earth. In general the predictions of these models agree favorably with observed data.     

Structure,diversity and stability of two oligochaete communities according to sedimentary inputs in Lake Geneva (Switzerland)

Two oligochaete communities were sampled monthly during one year in two 35 m deep locations of Lake Geneva (Switzerland). Organic sedimentation was lower and less variable in station 1 than in station 2 (157 versus 214 g C m⁻²yr⁻¹). The oligochaete community in station 1 was more diverse and more stable (persistent over time) than in station 2, as long as the organic sedimentation was low. Diversity and stability decreased in station 1 when the organic sedimentation increased, and during anOscillatoria bloom. The less diverse community in station 2 was more resistent to these changes. Diversity was associated with environmental stability, but resistance to perturbation was greater in the simpler community which is adapted to changing environmental conditions. The value of oligochaete communities as an indicator of the level of eutrophication was reassessed according to our present data. Changes in the structure of oligochaete communities were related to changes in sedimentation processes.     

Experimental investigation into the influence of stratification on the passive earth pressure

In this paper, the effect of inhomogeneous soil condition on the passive earth pressure is studied by using model tests. The model tests are carried out with two soil layers. The tests are compared with the corresponding results for homogenous soil. The shear band formation is identified with Particle Image Velocimetry measurements.     

平流及层结在阿尔卑湖泊风成扩散问题中的作用

A semi-implicit semi-spectral hydrodynamic primitive equation model is used to study tracer diffusion in homogeneous and stratified lakes. Impulsively applied spatially uniform wind is applied in the long direction of a rectangular basin with constant depth and Lake Constance. Tracer mass is released at various locations of the free surface and its spreading under the action of dijfusion and advection is studied. We show that for homogeneous basins the tracer quickly spreads over the entire water depth. Inertial waves can also be detected in the tracer concentration. On the other hand for stratified waters the tracer mass is largely confined to the epilimnion with occasional penetration into the hypolimnion where large downwelling occurs. Here Kelvinand Poincar ''e-type wave dynamics is discernable in the tracer-concentratwn-time series, the former more conspicuously at nearshore, the latter at off-shore positions.     

On internal wave dynamics in the northern basin of the lake of Lugano

Abstract

Data collected from the Lake of Lugano during 3 July to 17 August 1979 are analysed for internal gravity wave motions. We demonstrate that a two-layer linear model is capable of explaining the internal wave response. A numerical finite difference procedure is used to determine the seiche periods and eigenfunctions of this model. The computed results (periods and phase differences between station pair interfacial displacements are then compared with the measured data. This comparison demonstrates that four conspicuous internal mode periods can be identified with fair to excellent statistical coherence between data-set pairs and that even higher order modes can be detected but with less statistical confidence. This identification proves that for the Lake of Lugano, no recourse has to be made to multi-layer models that would account for higher order baroclinicity.     

The surface seiches of Lake of Lugano

A computational analysis of the periods and structure of surface seiches of the southern basin of Lake of Lugano and its experimental verification from three simultaneous water gauge recordings, mounted along the shores in Agno, Morcote and Riva S. Vitale, is given. The first five theoretical modes are calculated with a finite element code of the tidal equations; it yields the eigenperiods and co-range and co-tidal lines, which are graphically displayed and discussed in detail. Experimental verification is from recordings taken during February/March 1982. Inspection by eye allows identification of the five lowest order modes, partly including interstation phase shift. Power spectral analysis of three-time series and interstation phase difference and coherence spectra allow identification of higher order modes, probably up to order 13. Agreement between the theoretically predicted and the experimentally determined periods is excellent for all calculated modes. Computational results for the four lowest modes and their structure of the northern basin of Lake of Lugano are also presented and experimentally verified with records taken from an event in August 1979. Agreement is again excellent.