TOPOLOGY
DESCRIPTION OF THE POWAI LAKE
Powai
lake (19 O
8' N and 72 O 54' E) situated 55 meters above the
mean sea level (msl) is known as 'Anglers Paradise.' It is meant
exclusively for angling and sports and is located about 27 KM
away in the north-east of Mumbai city. Mumbai city is located
on Mumbai Island of salsette northward and thense the mainland
(Bhagat, 1977). The Island consist of lowlying plain flanked
by two parallel ridges of low hills. The western ridge terminates
in Malabar hill. Colaba, the low peninsula at the end of the
eastern ridge is joined to Mumbal by a substantial cause way (Annon,
1960). It is surrounded by back waters of Arabian sea almost on
all the sides and has few fresh water impoundments. Mumbai muncipality's
drinking water schemes resulted in formation of more fresh water
lakes, Vihar in 1858, Tulsi in 1879 and Powai in 1891 having water
spread area of 7.29. 1.35 and 2.10 sq. km. respectively. Vihar
and Tulsi lake water are used for drinking purpose. But the project
of Powai lake was discarded as the water was found to be inpotable
and the lake was leased out to the Bombay Presidency Angling Association
in the year, 1939 now called 'Maharashtra State Angling Association',
Mumbai for Angling and sports.
Powai
lake was said to be populated by 37 species of fishes (Kulkami,
1947 and Amore, 1955). Bhagat (1977) has listed 32 species in
the lake while Singh Kohli (1991) has listed 1O main fish species
in the lake. Although 10 species of fishes have been found in
the lake, the quality of fishes are represented only in small
numbers. Due to the discharge of waste water into the lake along
with the silt load from the surrounding area due to quarrying
work, it has lost its diverse nature of population. Fishing rights
are given to the Maharashtra State Angling Association. The lake
is stocked with carp fry at the beginning of the monsoon but the
fishing activity is spread all over the year. Maharashtra State
Angling Association release two to five lakh fish fingerlings
speclallv flown in from Calcutta and tended in hatchery in the
lake. This has helped to save the Indian Mahaseer which was on
the verge of extinction (Mid-Day 16th June, 1988).
To
meet developmental demands the mountains of this area have been
cut which resulted in loosening of soil in the area which finally
entered into the lake system. It is estimated that till now about
3000 m3 of silt had been deposited in the lake, as a result of
which the bed of lake has risen upto one meter (as reported in
Mid Day No. 2755 dated 2nd June, 1988). Importance of errosion
and silting, in the lake has been discussed by workers like Pennington
( 1973 ) and McLachian ( 1976 ). Besides the silt people from
nearby slums also defecate and urinate near the lake. The lorry
drivers are also increasingly finding the lake's environs a cood
place to wash their vehicles.
More
than 100 years old Powai lake represents a typical case of environmental
degradation due to urbanisation. The lake is free from industrial
pollution. It is polluted by untreated domestic sewage, silt
from construction and idol immersion. At present the lake is
infested with water hyacinth Eichhornia crassipes
and maintains a permanent bloom of
microcystis sp. and Melosira sp. due to high level
of nutrients and favourable environmental conditions. The Maharashtra
State Angling Association, Powai, spends around Rs. 30,000 to
Rs. 40,000 per annum to clear these hyacinths [ Mid-Day, July
25, 1997 ]. Today the lake is extensively used for fish culture,
bathing and washing purposes and there is an urgent need to undertake
action to conserve the ecosystem.
The
conservation of Powai lake is in the interest of man as its ecological,
aquacultural and touristic value is immense. 21 lakes will be
decorated under the Central Govt's project of purification of
the "Ganga and National Lake Conservation Plan" which
has started before a month. Powai lake of Mumbai has been included
in Central Govt's 'National Lake Conservation Plan'. So this
lake which has been built before 100 years will change its form
now. (As reported in Loksatta dated 7th August 1995).
SOURCES OF WATER TO THE LAKE
The
small streamlets, Dahisur nala and Gopal riverlet are the main
sources to feed the lake with the rain water from the catchment
area (6.68 km 2 ) in the north-east hills. In order to conserve
the rain water a dam of height 10 meter was constructed (of rock-fill
wall) near the Powal garden. When the water in the lake reaches
a level of 6.1 meters, it starts overflowing from this dam. During
the monsoon the water overflow the dam into Vihar-Powai nala and
finally discharges into the backwater of Arabian sea through Mahim
Creek.