How viable is it to understand the tidal flushing and fresh water
circulation issues in marine water bodies at designing stage? Nakheel, one of
the world’s leading property developer, failed to foresee the water stagnant issues
which came up in 2002 during the construction of Palm Jumeirah. Ultimately,
they brought changes to the design in the middle of the construction phase,
which was to include further openings in the sea wall to allow proper flushing
and water circulation. The South African financial giant and the business
magnate Sol Kerzner never realised he had a design fault in his pioneering
Resort Project-One & Only Reethi Rah in Maldives. Later, the elongated
octopus shaped island was cut across, opening a channel for water circulation
from one side of the island to the other to save one of the island’s beaches
from water stagnation.
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| One and Only Reethirah Maldives (L), Palm Jumeirah (R) |
Undoubtedly, tackling tidal flushing and fresh water
circulation issues in marine water bodies is never easy. Especially for us, who
are very much limited in resources, who lack true local monsoonal data to feed
a simulation model and where EIAs serve more as a jurisdiction rather than a
technical justification of the design.
However, increasing
concern over environmental problems and water quality in small coastal basins,
harbours, and marinas has resulted in the need for an improved prediction
mechanism of tidal flushing and circulation in proposed new Harbours. There had
been cases like the recent case in Hdh. Vaikaradhoo harbour where frequently
fishes die in huge numbers. Inadequate tidal flushing of harbours lead to poor
water quality which intern causes death of several fishes occupying the
harbour. When there is increased light intensity and warm water due to poor
circulation, with the available nutrients it can lead to an algal bloom worsening
the condition further. A prevailing public health hazard could be the outcome
of such a case.
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| Hdh.Vaikaradhoo Harbour. |
Provision
of wave protection is the primary objective of a Harbour. Our Harbours are
typically protected from waves on the seaward side by breakwaters, leaving a
small, 20-30m entrance channel. Since almost all of our present-day harbour
breakwater’s are constructed by placing 800-1200T armour rocks, it is assumed
that adequate tidal
flushing and circulation will be possible through the breakwater and channel.
How important of a design consideration it is to understand the internal
hydraulics governing the tidal flushing and circulation of a harbor, we leave
it mostly based on our assumption. Fortunately, most of the times we have been
on the safe side without an environmental disaster due to inadequate flushing
within the harbor.
It is highly important to adopt ways
which can prevent technical glitches in the designs of enclosed marine water
bodies for fresh water circulation. If natural flushing is impossible, a
periodic mechanical flushing system should be in included.
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