Publications by Ulrich Lemmin | EPFL Graph Search

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Experimental results are presented of the mean flow and turbulence characteristics in the near field of a plane wall jet issuing from a nozzle onto flat and concave walls consisting of fixed sand beds. This is a flow configuration of interest for sediment ...

Cold-water Density Currents (CDCs) resulting from winter differential cooling and flowing down lateral slopes of a lake (winter cascading) can entrain sediment and contribute to cross-shore transport to its deeper layers. Field investigations along Lake Geneva’s northern shore reveal how CDCs induce sediment resuspension. Acoustic backscattering demonstrated that sediment resuspension is absent at 10-m depth on the steep slope (~30°) just beyond the edge of the shallow coastal shelf where CDCs were initiate

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 (Delft3DFLOW) was applied to simulate the flow field in the ...

Diel Vertical Migration (DVM), a widespread zooplankton behavior in freshwater and marine systems, affects ecological interactions and biogeochemical cycles. In lakes, DVM has mainly been studied in the upper 50 m of the water column. However, based on aco ...

Understanding coastal plane jets which occur when a body of water discharges into an ocean or a lake through a channel or outlet is important, since they play a significant role in sediment, nutrient, and pollutant exchange. This study investigates the nea ...

We examine the dynamics of turbulence subgrid (or sub-filter) scales over a lake surface and the implications for large-eddy simulations (LES) of the atmospheric boundary layer. The analysis is based on measurements obtained during the Lake-Atmosphere Turb ...

Two complementary measurement systems – built upon an autonomous floating craft and a tethered balloon – for lake research and monitoring are presented. The autonomous vehicle was assembled on a catamaran for stability, and is capable of handling a variety ...

The dynamics of spatial heterogeneity of lake surface water temperature (LSWT) at subpixel satellite scale O(1 m) and its effect on the surface cooling estimation at typical satellite pixel areas O(1 km2) were investigated using an airborne platform. The m ...

River inflows have a major influence on lake water quality through their input of sediments, nutrients and contaminants. It is therefore essential to determine their pathways, their mixing with ambient waters and the amount and type of Suspended Particulate Matter (SPM) they carry. Two field campaigns during the stratified period took place in Lake Geneva, Switzerland, in the vicinity of the Rhône River plume, at high and intermediate river discharge. Currents, water and sediment fluxes, temperature, turbid

Reliable estimates of air-water exchange of momentum, heat, and gas are vital for understanding boundary layer dynamics and for developing accurate global and regional climate and weather forecasting models. Spatiotemporal variability of physical processes, below and above the water surface and at the interface, contribute to the uncertainty of these estimates. Air-side exchange processes are closely related to various phenomena in the Atmospheric Boundary Layer (ABL), which frequently manifest themselves a

The logarithmic layer of double-averaged (in time and space) streamwise velocity profiles obtained from field measurements made in the Swiss rivers, Venoge and Chamberonne is parameterized and discussed. Velocity measurements were made using a 3D Acoustic ...

The spatiotemporal surface heat flux (SurHF) distribution over Lake Geneva, the largest lake in Western Europe, was estimated for a 7‐year period (2008–2014). Data sources included hourly maps of over‐the‐lake assimilated meteorological data from a validat ...

Numerical simulations were carried out to examine the effect of different horizontal aspect ratios on wind-induced circulation within open, wide and deep lacustrine embayments. Two adjacent embayments in Lake Geneva, Switzerland, located between Morges and Lausanne on the north shore of the lake, were compared. These embayments were selected because of their similar exposure with respect to wind forcing. However, their aspect ratios are different, making them ideal case studies to evaluate the impact of the

In Lake Geneva, a deep peri-Alpine lake in Switzerland, the sublacustrine Rhône River delta presents a deep canyon, the Rhône Canyon. Previous studies and recent observations show that low-velocity underflows and high-velocity turbidity currents pass frequently in the Rhône Canyon. The former carry little sediment, are long-lasting, slow moving and typically occur in winter when the lake is destratified, whereas the latter are sediment-rich, short-lived and occasionally generate high velocities. In the pres

Numerical simulations were carried out to investigate gyres within open lacustrine embayments subjected to parallel-to-shore currents. In such embayments, gyre formation occurs due to flow separation at the embayment’s upstream edge. High momentum fluid fr ...

In large lakes subject to the Coriolis force, basin-scale gyres and mesoscale eddies, i.e. rotating coherent water masses, play a key role in spreading biochemical materials and energy throughout the lake. In order to assess the spatial and temporal extent ...

Although internal seiches are ubiquitous in large, deep lakes, little is known about the effect of higher vertical-mode seiches on deepwater dynamics. Here, by combining entire summer season current and temperature observations and 3D numerical modeling, w ...

Extensive areas of the bottom of Lake Geneva are covered with bedforms that have been referred to as pillow-hollows and quilted-cover pattern by prior observers, as well as with sediment waves and trenches. These structures are decimeter to meter scale. A large dataset of video recording and stereographic camera imagery of the lake bottom was recently acquired during a campaign with the Russian MIR submersibles. We present a classification of the different types of sediment structures with a focus on distin

Shear velocity u(*) is an important parameter in geophysical flows, in particular with respect to sediment transport dynamics. In this study, we investigate the feasibility of applying five standard methods [the logarithmic mean velocity profile, the Reyno ...

In the Rhône canyon of Lake Geneva (Figure 1), turbidity currents are occasionally present in summer. Based on velocity measurements in the canyon and discharge measurements at Porte du Scex in the Rhône 6 km upstream of Lake Geneva (Figure 1), Lambert and Giovanoli (1988) hypothesized that Rhône River floods and slides of sublacustrine deltaic deposits are the main causes of these turbidity currents. Here, we present another type of initiation: A strong sediment event along the sediment cascade of the Rhôn

Ulrich Lemmin

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Near-field flow structure of a confined wall jet on flat and concave rough walls

Sediment resuspension in Cold Density Currents cascading down lateral slopes of Lake Geneva

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

Identifying and quantifying unexpected deep zooplankton diel vertical migration in a large deep lake

Tracking the Nearfield Evolution of an Initially Shallow, Neutrally Buoyant Plane Jet Over a Sloping Bottom Boundary

Subgrid-Scale Dynamics of Water Vapour, Heat, and Momentum over a Lake

A low-cost, autonomous mobile platform for limnological investigations, supported by high-resolution mesoscale airborne imagery

Surface Water Temperature Heterogeneity at Subpixel Satellite Scales and Its Effect on the Surface Cooling Estimates of a Large Lake: Airborne Remote Sensing Results From Lake Geneva

Nearfield development of the negatively buoyant Rhône River inflow into Lake Geneva as an interflow: suspended particulate matter and associated fluxes

Signatures of coherent flow structures in the atmospheric surface layer over Lake Geneva

Parameterization of the logarithmic layer of double-averaged streamwise velocity profiles in gravel-bed river flows

The Importance of Systematic Spatial Variability in the Surface Heat Flux of a Large Lake: A Multiannual Analysis for Lake Geneva

Circulation patterns in open, wide and deep lacustrine embayments with different aspect ratios

Sediment transfer in the Rhône River Basin, Switzerland: the role of localized severe Alpine storm events on triggering turbidity currents in Lake Geneva

Gyre formation in open and deep lacustrine embayments: The example of Lake Geneva, Switzerland

Basin-scale gyres and mesoscale eddies in large lakes: A novel procedure for their detection and characterization, assessed in Lake Geneva

Strong bottom currents in large, deep Lake Geneva generated by higher vertical-mode Poincaré waves

Morphology of pillow-hollow and quilted-cover bedforms in Lake Geneva, Switzerland

Shear velocity estimates in rough-bed open-channel flow

Sediment connectivity in the Rhône basin: From an isolated thunderstorm at Illgraben to a tubidity current in deep Lake Geneva