Factors that determine water movement. Morphometry Structure of stratification Wind patterns

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1 Water Movement

2 Factors that determine water movement Morphometry Structure of stratification Wind patterns

3 Turbulent and laminar flow Laminar flow - smooth, unidirectional flow Low velocity Rare in nature Turbulent flow - disordered, multidirectional flow Vortex formation occurs Mixing occurs perpendicular to current

4 Eddy diffusion and conductivity Heat conduction and turbulent mixing are similar Coefficient of eddy diffusion (Kz) is a measure of the rate of exchange or intensity of mixing across a plane Coefficients of eddy diffusion decrease with increasing stability of stratification

5 Surface waves (progressive waves) Frictional movement of wind over water sets water in motion and surface into oscillation, producing traveling surface waves Short surface waves have cycloid movement with mostly horizontal translocation Neighboring cycloid waves move synchronously to produce a traveling wave

7 Surface waves (progressive waves) Cycloid diameter is decreased by 50% for every depth increase of λ/9 h is commonly 5% of λ When h/λ ratio exceeds 1/10, the peak collapses and forms whitecaps

8 Surface waves (progressive waves) Where wavelength is more than 20 times the water depth, the waves become shallow water waves or long waves Wave height of the highest waves on a lake is roughly proportional to the square root of the fetch

9 Surface waves (progressive waves) As deep water waves become shallow water waves, wavelength decreases Wave height decreases slightly then increases markedly and becomes asymmetrical and unstable Plunging breaker Spilling breaker

10 Surface currents Currents are non-periodic water movements generated from external forces Wind Changes in atmospheric pressure Horizontal density gradients Influx of water into a lake

11 Coriolis Effect Geostrophic effects of the deflecting (Coriolis) force due to the earth's rotation are found in all currents in moderate to large lakes In the Northern Hemisphere, surface currents are deflected to the right relative to the direction of the wind In general, current speed is approximately 2% of wind speed that generates them

12 Langmuir Circulation Sporadic, turbulent transport is sometimes organized into vertical, helical currents in upper layers of the lake Streaks form in a parallel direction to the wind Streaks coincide with areas of surface convergence and downward movement Streaks are marked by windrows of aggregated particulate matter Areas between streaks are zones of upwelling

14 Langmuir Circulation Langmuir circulation occurs in large lakes at wind speeds greater than 2 or 3 m/sec and less than 7 m/sec Algae and zooplankton aggregate in the streaks

15 Metalimnetic entrainment After prolonged periods of wind, wind drift causes water to pile up at the downwind end of the lake When it reaches the metalimnion, it flows back (against the wind direction) along the metalimnion Increased mixing occurs along the interface Upon equilibrium, the metalimnion is lowered

17 Long standing waves Displacement of the entire water mass generates rhythmic motions, including oscillations of the water surface and the internal structure Motions take the form of very long waves with wavelengths of the same order as basin dimensions

18 Long standing waves Surface and the thermocline oscillate up and down like a see saw These oscillations (standing waves) are called seiches

19 Long standing waves Seiches are caused by wind-induced tilting of the water surface When the wind stops, water flows back Oscillates around one or more nodal points No vertical movement occurs at the nodal point Maximum vertical movement occurs at the antinodal point Nodal point is actually a line that runs the width of the lake

20 Long standing waves Surface seiche is a long standing wave associated with the air-water interface Periodicity of vertical movement is a function of the length and depth of the basin Amplitude is small compared to internal seiche

21 Long standing waves Internal seiche When a lake is stratified, water layers oscillate relative to each other and create an internal seiche

Ocean Circulation. Si Hui Lee and Frances Wen. You can access ME at

Ocean Circulation. Si Hui Lee and Frances Wen. You can access ME at Ocean Circulation Si Hui Lee and Frances Wen You can access ME at http://tinyurl.com/oceancirculation Earth - the blue planet - 71% area covered by the oceans - 3/4 of ocean area between 3000-6000m deep