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 50
Relationship Between Temperature and Viscosity
in Pure Water
40
30
20
10
0
0.6
0.8
1.0
1.2
1.4
1.6
1.8
Viscosity (dyne-sec per sq. cm)
Figure 1.2.7. The relationship between temperature and viscosity for pure
water
1.2.6
MIXES
The physical properties of water contribute to stratification, stability and energy budgets in
lakes. Because water warmer than 4EC is less dense, warmer waters usually exist nearer the surface.
But because water colder than 4EC is also less dense, some temperate lakes have colder waters at the
surface (mostly during the winter months). Under both these conditions, the lakes are thermally
stratified and considered stable.
In the Southeast, thermal stability usually begins in the spring and continues into the fall. During
the fall Lake Hartwell, for example, cools at the surface and experiences cooler inflows. The total
energy content of the lake decreases. At the lake surface, the cooling produces shallow instability and
wind or convective mixing can occur at progressively greater depths. In Lake Hartwell, this process
begins around September and continues through December. When the lake finally achieves a uniform
temperature, surface to bottom, through cooling and mixing, the lake is said to be isothermal.
1.2-15
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