146
S. Z. QASIM:
3. Temperature
During the premonsoon season of maximum solar radiation and warm weather, the
temperature throughout the water column remains uniform and records its maximum.
With the onset of rains in May, the water temperature decreases and a clear thermal
32
l )
~ 30 r-",,:::re::;z:r
~
::J
e 28
'"
~26
~ 24
22 ~~~~rLrLrLrL~~~~
D
Fig. 5. Average monthly values of water temperature at 3 different depths of the backwater.
Surface: closed circles; mid depth: triangles; bottom: open circles
gradient develops in the water column (Fig. 5). The difference in temperature from the
surface to the bottom may be more than 50 C. The thermal gradient persists until about
September.
4. Salinity
The salinity remains homogeneous throughout the water column during the premonsoon season, indicating that the water is well mixed (Fig. 6). During the monsoon
months large quantities of freshwater enter the estuary, resulting in low salinity water
g
~20
~
'c
'a 10
til
Fig. 6. Average monthly values of salinity at 3 different depths of the backwater. Symbols as in
Fig. 5
at the surface and denser water at the bottom. Because of a clear stratification which
exists during the monsoon months, the surface and bottom waters remain quite distinct.
The stratification is broken up during the postmonsoon months when homogeneous
conditions are gradually restored.