Physical:

Properties effected by heat:

1.density

2.viscosity

3.vapor pressure

4.solubility

1.and 2.- Stokes Law - settling of solids in a non-turbulent medium.

We see that an increase in temperature decreases f and and thus vt increases.This may improve water treatment sligtly.Increasing temperature effects location and amount of sediment deposit.

Very slight density differences (0.001-0.002) may cause stratification - also dependent on depth and water movement.Impedes vertical mixing and oxygen transfer.

May cause short circuiting in reservoirs wich in turn effect discharge temperatures.

3. Evaporation rates increase with increase in vapour pressure.Caused by difference in water vapor pressure between air and water, and also by wind velocity.

F = evaporation flux (kg m-2 s-1)

L = latent heat (J kg-1)

C = empirical evaporation coefficient

W = wind speed (m s-1)

es = vapor pressure of saturated air in temperatures of surface water (Pa)

ea = vapor pressure of overlying air (Pa)

We may illustrate the effect of varying surface temperatures by holding all terms in the above equation constant except es.

L = 2.44*106 J kg-1

C = 11.4 (typical)

W = 4.47 m s-1

ea = 999 Pa (air temp. of 294.3 K and RH = 40%)

TH2O (K)  es (Pa)   F(Kg m-2      
                    s-1)          

283.1     1210.5    1.07*10-5     

288.7     1750.0    3.61*10-5     

294.3     2473.7    7.01*10-5     

299.8     3447.3    1.16*10-4     

305.4     4750.0    1.78*10-4     


4. Most living organisms depend on oxygen in one form or another.Relation of water temperature to gas solubility is an important aspect of thermal polution.

Solubility is directly proporcional to parcial pressure at a given temperature under equilibrium conditions.

Temperature changes cause complicated adjustements on the dynamic oxygen balance in waters and make it difficult to relate absolutely the dissolved oxygen and other factors to oxygen demand, such as, atmospheric reareation, photosyntetic production, diffusion, mixing,etc.

Since waters seldom carry a saturated value of water, temperature rise will decrease the holding capacity wich is already less than optimum.

Recent evidence shows that increased temperatures may increase nitrogen levels so as to seriously effect fish life.

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