|
|||||
|
|
|||||
|
|||||
|
|||||
|
|||||
|
|
Water
is the vital element of life and truthful companion of humanity. It is the most
abundant element on the earth, covering about 1400 million cubic kilometers, of
which only 0.03% is usable – the rest forming part of oceans and polar
ice-caps. Urban domestic and industrial consumers are using larger amounts of
water and consequently depleting the available resources. The goal should be to
promote water use and management in such a way that society’s needs are met
while at the same time, water resources are protected. Non availability of
adequate drinking water due to progressively depleting surface and groundwater
is a big challenge to the water management system.
Even
today, more than 90% of our rural population is primarily dependent upon
groundwater. Water supplies from groundwater sources are becoming increasingly
important, but they are threatened by unplanned exploitation and by
contamination from many sources. Protection and conservation of groundwater is
therefore a top priority task, particularly in such regions of limited available
water resources.
Groundwater
is derived from precipitation on the earth’s surface that gradually percolates
to the sub-soil through the porous strata or openings through rock formations.
The process of infiltration of water and subsequent water movement is an
exceedingly complex process. The aquifer complex transports the groundwater from
areas of replenishment to areas of need.
Groundwater
recharge, in a general sense, is the downward flow of water reaching the water
table, forming an addition to the groundwater reservoir. Recharge of groundwater
may occur naturally from precipitation, rivers, canals and lakes and as
man-induced phenomena via such activities as irrigation and urbanisation.
Quantification of the current rate of natural groundwater recharge is thus a
basic prerequisite for efficient groundwater resource management and is
particularly vital in arid and semi-arid where such resources are key to
economic development.
Urbanization
has profound impacts on the hydrological cycle, effecting changes in groundwater
recharge mechanisms. The provision of water supply, sanitation and drainage are
the key elements of the
urbanisation process. A common factor to most urbanisation is that it results in
–
(i)
Impermeabilisation of a significant proportion of land surface, and
(ii)
Major water imports from outside the urban limits.
Urbanisation
also causes major changes in the frequency and volume of recharge, although
these changes cannot be measured directly and are thus difficult to quantify.
Some urbanisation processes also cause radical changes in the quality of the
recharge. The changes in recharge caused by urbanisation in turn influence the
groundwater levels and flow regimes in the underlying aquifers.
A
field investigation has been carried out for three successive water years over
Bangalore (rural and urban) district for recharge assessment.
The district covers an area of 8039 sq.km and falls in between north
latitude 12°15˘
- 13°
31˘
and east longitude 77°
4˘
and 77°
59˘.
The population in the district is 9.7 million according to 2001 census. The
district receives annually about 879mm of rainfall.
The
central groundwater board (CGWB) has issued guidelines (1997) to assess the
groundwater resource adopting two methods viz.,
i.
based on water table fluctuation data
ii.
rainfall infiltration data
Here
in our study in Bangalore, water table fluctuation method has been adopted. Data
on geomorphology, geology, soils, land use, rainfall, infiltration, water table,
fluctuations, specific yield, evaporation losses, utilisable losses, other
inputs have been considered during the study.
Also,
monsoon and non-monsoon seasonal recharge values are quantified for 59 rain
gauge stations. The probable percentage of rainfall contributing to groundwater
recharge for the area receiving less than 700 mm annual rainfall, has been
assessed to vary from 3 to 5. The steps and methodology followed and data
utilised for assessing quantum of rainfall recharged into the aquifers are
presented in the paper.
Address:
Department of Civil Engineering,
S.J. College of Engineering, Mysore. Karnataka. India
Department of Civil Engineering,
Bangalore University, Jnanabharathi Campus,
Bangalore. Karnataka. India
UGC-DSA Centre, Department of Mathematics,
Bangalore University, Central College Campus,
Bangalore. Karnataka. India
Phone: 2220483 E-mail: granganna@yahoo.com
