Hydraulic conditions in isothermal lakes

Abstract

The paper considers the forms of water movement that occur in unstratified lakes. Although not dealing directly with ecological implications, it is hoped that it will encourage the inclusion of observations of underwater weather as part of normal limnological routine. It is particularly concerned to show what observations are most effective in revealing hydraulic conditions.Relations between wind, lake geometry and wave characteristics are examined. Factors determining the steady, wind-driven circulation are reviewed and examined in sequence: the action of wind on a water surface and the current directly generated by the wind drag; the effect of the earth's rotation; the need to balance the tlow in and out of any part of the lake; the influence of lake morphometry. A simple model of lake circulation is developed that may help in the interpretation of on-lake observations. Some other features of isothermal motion are discussed including the horizontal currents associated with unsteady wind conditions (seiches).The possible interaction between waves and currents are discussed. A tentative classification of hydraulic conditions in terms of wind speed, lake depth and fetch is suggested as a basis for forming hypotheses about the motion prior to on-lake observations and as a possible starting point for a comparative approach.

Contribution of sediment focussing to heterogeneity of organic carbon and phosphorus burial in small lakes

“…Using the method of Smith (1979), a theoretical profile of wind-induced current speed with water depth was generated for different wind speeds (Fig. 6).…”

“…Indicative wind-induced current speeds were calculated from 2008 wind data, using the method of Smith (1979) …”

“…These currents are directly related to the strength of the wind blowing over the lake surface (Smith, 1979). At a simplified level, during isothermal conditions, current speed declines exponentially with depth and, as described by the law of the conservation of mass, a return current is generated in the opposing direction (Smith, 1979). These currents cause resuspension below the wavemixed layer and are important in the offshore transport of sediments in large lakes (Lemmin & Imboden, 1987;Hawley et al, 1996;Hawley & Lee, 1999).…”

“…These currents are directly related to the strength of the wind blowing over the lake surface (Smith, 1979). At a simplified level, during isothermal conditions, current speed declines exponentially with depth and, as described by the law of the conservation of mass, a return current is generated in the opposing direction (Smith, 1979).…”

Three‐dimensional hydrodynamic and sediment transport modeling to test the sediment focusing hypothesis in upland lakes

“…One of the few model studies is that by Mackay et al (2012), who showed that wind-driven currents were sufficient to mobilize small sediment grains at all depths (up to 8.5 m) within Esthwaite Water. However, their study uses a simple analytical relation between wind forcing and the surface current and its decay with depth (Smith 1979).…”