Environmental Engineering Reference
In-Depth Information
community and coral reefs in shallow
water zones. These biotic forms con-
tribute nutrients due to which a wide
spectrum of planktonic diversity exists
in this system. The
ecological and economic point of view.
These are the live matrix of mangrove
ecosystem of Sundarbans on which the
unique spectrum of biological diversity is
embedded. In Indian Sundarbans,
approximately 2,069 km
2
area is occu-
pied by tidal river system. The main
estuaries, from west to east (Fig.
1.13
),
are highlighted in Table
1.3
along with
their salient features.
Estuaries may also be classi
shery potential is
extremely high, and hence, the modern
trend of monoculture (e.g., culture of
Penaeus monodon
) is perhaps a wrong
choice in this system. These productive
systems with varied ecological niches
are suitable for polyculture practice.
(e) Emerging new systems associated with
man: In modern societies, estuaries are
treated as the ultimate sink of different
categories of waste. Estuaries have
varying capacities to handle
ed as tide-
dominated (Fig.
1.14
) and wave-domi-
nated (Fig.
1.15
) estuary on the basis of
several important (positive and negative)
hydrological processes (Table
1.4
).
Tide-dominated estuaries are very common in
the tropical region. During high-tide condition,
the coastal vegetation preferably the mangroves
is partially drowned and the substratum becomes
totally invisible (Fig.
1.16
). However, during
low-tide condition, the substratum gets exposed
(Fig.
1.17
), and several varieties of saline
creepers and herbs are seen (Figs.
1.18
and
1.19
).
The astronomical tide at the estuarine mouth
determines the nature of
'
material depending on the size of the
system,
'
degradable
ow patterns, hydrological
parameters, microbial load, type of estu-
ary and the climatic zone. Materials such
as treated sewage and pulp mill wastes,
seafood and other food processing
wastes, petroleum wastes and dredging
spoil can be decomposed and dispersed
provided that (i) the system is not stres-
sed by poison (insecticides, acids, etc.)
and that (ii) the rate of input is controlled
at low to moderate levels and not sub-
jected to sudden shocks produced by
periodic massive dumping. Of all the
man made changes, impounding estua-
rine water has perhaps the greatest effect.
It must be recognized that impounded
waters are a completely different type of
ecosystem that have nearly no natural
capacity for waste treatment. In countries
such as India and Bangladesh, huge
numbers of impounded waterbodies have
been created to promote shrimp or tiger
prawn (
fl
ow in an estuary near its
mouth. The tide along the coast of India is mixed,
i.e., it consists of a mixture of oscillations with a
period of about 12.5 h (semi-diurnal oscillation)
and with a period of about a day (diurnal oscilla-
tion). The range is particularly high in gulfs such
as the Gulf of Kutch or the Gulf of Khambhat or a
channel like the Hooghly River, all of which get
narrower away from their sea end.
fl
1.2
Fluid Movements
in the Oceans and Estuaries
1.2.1 Waves
) culture in the
coastal areas, due to which the ecology
and environment of the surrounding
areas have been greatly damaged.
The estuaries adjacent to the Bay of
Bengal are extremely important from the
Penaeus monodon
Waves are generally produced by the action of
wind blowing across the surface of the ocean and
are formed as a result of the transfer of energy
from the wind to the water. Winds can generate
waves as small as a ripple or as high as 30 m.
