40
Exercise 3
turbulence generated and entrainment of water (and contained nutrients, gases,
organisms) from one stratum to another?
7. With continued strong winds, bring about complete mixing. While applying dye
crystals, observe the patterns of destratification and, in general, how much energy is
required for this disruption. Determine the density of the fully mixed "lake" with the
hydrometer.
Apparatus and Supplies
1. The experiments of this exercise should be done with a lake model constructed
longer and narrower than typical aquaria. An excellent model has been made of 1cm Plexiglas' acrylic sheeting with dimensions of 180 x 60 x 20 cm. Smaller models,
made with redwood framing and glass sides, also have been used effectively. The
ends of the "lake" are built up with inert materials (e.g., styrofoam) to produce an
ellipsoidal morphology common in natural basins. The volumes of the final
epilimnion, metalimnion, and hypolimnion can be calculated readily from the
resulting trapezoidal shapes.
2. In the example given, the epilimnion consists of approximately 601 of water without
sugar additions (p;::::: 1.000); ca. 301 forms the metalimnion, to which red food
coloring and sugar are added carefully to yield a density of 1.015 to 1.018; and the
hypolimnion contains ca. 631 of water with blue food coloring and sufficient sugar to
yield a density of 1.035 to 1.040 g/cm 3 .
3. A strong blower, such as a vacuum cleaner, to generate wind-driven surface currents.
4. A stopwatch.
5. Catechol violet or methylene blue crystals (as in Lake Modell)
6. Hydrometer in the range of 1.000 to 1.070.
Calculations
Proceed as in Lake Modell to calculate (a) the stability of the lake, (b) the resistance to
mixing, and (c) the theoretical perods of the internal seiches. Make plots of the density
versus depth and compare all of these results with those of the other lake models.
ADDITIONAL MODELS
A supply of polyurethane pieces will be available for those wishing to construct basins
of various morphologies. This material can be cut easily with a hot knife and the rough
parts smoothed with the flat blade of the hot knife. Care should be taken to have the
dimensions of any form you cut about 2 cm wider and longer than those of the
aquarium so that it will hold itself at any desired level without additional support. As
example studies, the following are suggested as both instructive and feasible:
1. Simultaneous action of wind and "sun" on the thermal properties of lakes.
2. Production of multiple thermoclines.
3. Effect of sills and other bottom configurations (e.g., multiple depressions,
submersed lakemounts) on water movements.
4. Determination of eddy conductivity coefficients from temperature measurements
with continuous wind in the absence of the heat lamp.
5. Determination of eddy diffusivity coefficients from dye concentrations with wind in
the absence and presence of the heat lamp.
Exercise 3
turbulence generated and entrainment of water (and contained nutrients, gases,
organisms) from one stratum to another?
7. With continued strong winds, bring about complete mixing. While applying dye
crystals, observe the patterns of destratification and, in general, how much energy is
required for this disruption. Determine the density of the fully mixed "lake" with the
hydrometer.
Apparatus and Supplies
1. The experiments of this exercise should be done with a lake model constructed
longer and narrower than typical aquaria. An excellent model has been made of 1cm Plexiglas' acrylic sheeting with dimensions of 180 x 60 x 20 cm. Smaller models,
made with redwood framing and glass sides, also have been used effectively. The
ends of the "lake" are built up with inert materials (e.g., styrofoam) to produce an
ellipsoidal morphology common in natural basins. The volumes of the final
epilimnion, metalimnion, and hypolimnion can be calculated readily from the
resulting trapezoidal shapes.
2. In the example given, the epilimnion consists of approximately 601 of water without
sugar additions (p;::::: 1.000); ca. 301 forms the metalimnion, to which red food
coloring and sugar are added carefully to yield a density of 1.015 to 1.018; and the
hypolimnion contains ca. 631 of water with blue food coloring and sufficient sugar to
yield a density of 1.035 to 1.040 g/cm 3 .
3. A strong blower, such as a vacuum cleaner, to generate wind-driven surface currents.
4. A stopwatch.
5. Catechol violet or methylene blue crystals (as in Lake Modell)
6. Hydrometer in the range of 1.000 to 1.070.
Calculations
Proceed as in Lake Modell to calculate (a) the stability of the lake, (b) the resistance to
mixing, and (c) the theoretical perods of the internal seiches. Make plots of the density
versus depth and compare all of these results with those of the other lake models.
ADDITIONAL MODELS
A supply of polyurethane pieces will be available for those wishing to construct basins
of various morphologies. This material can be cut easily with a hot knife and the rough
parts smoothed with the flat blade of the hot knife. Care should be taken to have the
dimensions of any form you cut about 2 cm wider and longer than those of the
aquarium so that it will hold itself at any desired level without additional support. As
example studies, the following are suggested as both instructive and feasible:
1. Simultaneous action of wind and "sun" on the thermal properties of lakes.
2. Production of multiple thermoclines.
3. Effect of sills and other bottom configurations (e.g., multiple depressions,
submersed lakemounts) on water movements.
4. Determination of eddy conductivity coefficients from temperature measurements
with continuous wind in the absence of the heat lamp.
5. Determination of eddy diffusivity coefficients from dye concentrations with wind in
the absence and presence of the heat lamp.