Basin‐scale motion in stratified Upper Lake Constance

Abstract

This paper describes experimental and modeled wind-induced oscillations in Upper Lake Constance with an emphasis on a coherent understanding of the basin-scale internal dynamics in this example of a large and stratified lake. Data were collected with eight Lake Diagnostic Systems (LDSs) consisting of thermistor chains and wind anemometers. The isotherm displacements as measured by the LDSs were interpreted using the three-dimensional hydrodynamic Estuary and Lake Computer Model (ELCOM). Three types of basin-scale waves were found to dominate the wave motion: the vertical mode-one Kelvin wave that had an observed period around 90 h, two vertical mode-one Poincaré waves that had periods near 8 h and 12 h, and a vertical mode-two Poincaré wave that had a period near 14 h. After strong westerly winds, upwelling of cold bottom water was observed east of the Sill of Mainau, where the lake's two subbasins connect. The width and length ratios of the subbasins, spatial variations of the wind field, and rotational effects over the lake are shown to play critical roles in the details of the upwelling structure. A sudden fall of the isotherms in Lake Ü berlingen formed a surge. The reflection of the surge from the northwestern boundary induced a vertical mode-two response leading to an intrusion in the metalimnion that caused a three-layer velocity structure in the smaller subbasin.

Interbasin exchange and mixing in the hypolimnion of a large lake: The role of long internal waves

“…The temperature equation is solved simultaneously. Models based on these equations have been shown to compare reasonably well with time series of measured flow properties as well as with the low wave-number part of measured spectra (Laval et al 2003;Rueda et al 2003;Appt et al 2004).…”

“…1a) present a consistent picture of a lake dominated by the presence of several modes of wind-forced long internal waves modified by the Earth's rotation (Mortimer 1974;Bäuerle 1985;Lemmin et al 2005) and by a broad spectrum of short internal waves (Thorpe et al 1996; Thorpe and Lemmin 1999;Thorpe and Umlauf 2002). The occurrence of long internal waves, most notably internal Kelvin-type and Poincaré-type waves, is a typical and well-known feature also observed in other lakes of comparable size and has been documented in numerous field studies and numerical experiments (Umlauf et al 1999;Rueda et al 2003;Appt et al 2004).…”

“…Previous modeling studies of long interval wave motions in large lakes were either purely numerical in nature (e.g., Beletsky et al 1997;Umlauf et al 1999) or compared model results with the thermal signatures of internal waves (Hodges et al 2000;Pan et al 2002;Appt et al 2004). Lemckert et al (2004) studied velocity profiles derived from a microstructure probe in a turbulent BBL induced by basin-scale internal waves but did not attempt to compare their results with a numerical model.…”

“…The occurrence of a turbulent BBL is also chemically relevant; Lorke et al (2003) pointed out that such turbulent boundary layers are of crucial importance for the oxygen transport through the viscous sublayer toward the sediment Our results are likely to be applicable to other large lakes with a well-defined side basin. For example, recent studies on Lake Constance, Western Europe's second largest lake, revealed that Kelvin-type waves after wind events may lead to strong (several 10s of meters) vertical thermocline excursions in the Lake of Ü berlingen, an elongated side basin of Lake Constance with a similar geometry as the side basin of Lake Geneva (Appt et al 2004). Even though these authors did not directly measure current speeds, their simulations clearly show that, after strong wind events, the observed thermocline excursions in the side basin imply strong exchange currents with the main basin of Lake Constance.…”

Predicting effects of reservoir expansion with three-dimensional modeling: Case study of Los Vaqueros Reservoir

“…ELCOM and CAEDYM have been validated in many applications throughout the world, including lakes (Hodges et al 1999, Laval et al 2003a, Appt et al 2004, river estuaries Hamilton 1997), tidal lagoons (Spillman et al 2008), and other coastal ocean systems (Laval et al 2003b). …”