Environmental Engineering Reference
In-Depth Information
Fig. 1.11
Spatio-temporal variation of salinity in eastern Indian Sundarbans
Fig. 1.12
Future trend of
surface water salinity in
eastern Indian Sundarbans
18.00
16.00
Eastern sector
14.00
12.00
10.00
8.00
6.00
1980
1990
2000
2010
2020
2030
2040
2050
(b) Fjord-type estuaries: The deep U-
shaped indentures due glacial erosion
with a shallow sill at their mouth formed
by terminal glacial deposits, e.g., Nor-
way, British Columbia and Alaska.
(c) Bar-built estuaries: These are shallow
basins often partly exposed at low tide
enclosed by a chain of offshore bars or
barrier islands, broken at intervals by
inlets. These bars are sometimes depos-
ited offshore or are remnants of former
coastal dunes, e.g., North Carolina and
Georgia.
(d) Estuaries produced by tectonic pro-
cesses: Geological faulting or local
subsidence results in the formation of
coastal indented structures, e.g., San
Francisco Bay.
3. On the basis of water circulation and
stratication:
(a) Highly stratied or
'
salt-wedge
'
estu-
ary: When the freshwater discharge
from the rivers dominates over the tidal
action, the freshwater tends to over
ow
the heavier salt water which forms a
'
fl
extending along the bottom for
a considerable distance upstream. This
fl
wedge
'
ow of freshwater is again governed by
the Coriolis force, which forces the
freshwater to move strongly along the
right shore (if the observer faces the sea
in the Northern Hemisphere and vice
versa in the Southern Hemisphere). Such
'
strati
ed
'
or
'
bilayered
'
estuary will
exhibit a salinity pro
le with a
'
halo-
cline
'
or zone of sharp change in salinity
