GROUND
WATER INVESTIGATION:
Ground
Water Investigation with UNDP Assistance:
The Ground Water investigation
by the Public Works Department dates back to year 1965. A Ground water
cell was formed to cater to the needs
of the industries around Chennai.
Having felt the need of
systematic investigation in and around Chennai, the Government of
Tamilnadu approached United Nations and the ground water investigations
started with the assistance of UNDP in the following four selected areas.
(i)
Korataliyar and Araniyar basins.
(ii)
Part of Palar Basin
(iii)
Neyveli area (mainly on the east of Panruti along Gedilam)
(iv)
Cauvery Delta.
During the period between
1965-72 with the assistance of U.N.D.P. Ground Water Investigations were
carried out and Ground Water potential in the above said areas was
assessed on scientific basis.
Macro Level Studies (1970-78)
Based on the experience gained under UNDP it was felt necessary that scientific investigations have to be carried out in the entire Tamilnadu. Accordingly a full fledged Ground Water Directorate started functioning since November 1970 and during 1972 the PWD (Ground Water) was upgraded and headed by Chief Engineer (GW). The activities of the ground water department from 1970 can be broadly classified into 3 phases.
Phase
– I (Nov. 1970 –78).
Investigations were carried out at Macro level and basic data like infiltration through rainfall, seepage from applied water for crops, from tanks, from canals etc. were collected. With these parameters the assessment of Groundwater potential and the block wise groundwater assessment was made at macro level for the entire State. This appraisal of Ground Water potential with Panchayat Union blocks as a unit was made to meet out the requirements of A.R.D.C. (Now known as NABARD). The categorisation of areas/blocks as dark, grey and white has been made based on the ground water development. This paved way for the flow of institutional finance for minor irrigation schemes implemented by the Land Development Banks.
Phase
II Micro Level Study (1978-86)
From
the macro level studies conducted during the Ist Phase throughout
Tamilnadu, among 50% of the area was found to be over-developed. But the
field findings such as water level fluctuation and related hydrogeological
conditions existed varied from the assessment made by the macro level
studies, and hence it was decided to carry out micro level survey in all
the blocks bifurcating the blocks into sub-basins/mini water sheds.
In this villagewise study, data like land use pattern, cropping
pattern raised through surface water sources of irrigation, including
rivers, canals tanks etc. ground water structures like dug wells, bore
wells etc. and also the exploitation of ground water from each well is
collected and compiled in a detailed and precise manner. Such studies have
been started from 1978 and completed in the year 1986.
Under
phase III, the investigation of Ground water survey was reoriented on the
following lines:
(i)
Investigation,
monitoring and assessment of the ground water potential.
(ii)
Consultancy services
(iii)
Special Investigations.
Watershed Study
In
order to know the inter-relationship between rainfall, run-off and
infiltration, the various parameters like rainfall, evaporation,
temperature, wind velocity etc. are being observed in mini water sheds by
setting up 65 meteorological stations in almost all the river basins and
15 water sheds in different type of soil characteristics have been
selected for the study.
Drilling
Of Exploratory Bore Wells
As a part of investigation
programme exploratory bore holes are periodically drilled with the
following objectives:
(i)
To explore the sub-surface lithological characteristics
(ii)
To arrive at the sub-surface hydrogeological parameters
(iii)To
find out the quality of Groundwater at different aquifers.
Monitoring
Of Water Levels.
Since
groundwater is a dynamic resource, continuous monitoring of water level is
essential which helps to assess the gravity of the situation during
adverse seasonal condition like drought. For this purpose, about 1746
wells including 618 drought wells spread over the State are under
observation during the first week of every month. In addition to the open
wells, 102 Nos. of automatic water level recorders are installed in some
of the bore wells for continuous monitoring. Under Hydrology Project with
World Bank assistance 852 piezometers have been drilled and in 723
piezometers Water Level
is being monitored by both manual and DWLRs.
Water
Quality Study.
About
4300 water samples are collected from various sources like shallow
observation wells, bore wells, surface water samples etc. and tested for
the suitability of domestic, agriculture and industrial purposes. For
carrying out the above study, four Labs have been established at Chennai,
Madurai, Tiruchi and Pollachi under
the control of the Chief Engineer (State Ground & Surface Water
Resources Data Centre). For general public and other Department water
samples are also analysed at prescribed rates. In addition to the above
services, State Ground & Surface Water Resources Data Centre
undertakes analysis of water samples to find out the suitability for
drinking and irrigation purposes.
Collection Of Data On Groundwater Structures
To assess the Groundwater
potential, well structures are very much essential for the realistic
assessment of Groundwater draft. The
above study has been taken up and it has been proposed to collect the
villagewise well census data from the Village Administrative Officers and
test check them by actual field verification. The target has been fixed as
466 villages per year.
Firm
Up of Irrigation Potentials
It is essential to have an
updated realistic picture on the potential created and utilised as on date
under Minor Irrigation schemes. It
is necessary to use a scientific methodology for assessment of irrigation
potential created and its utilisation.
This work involves the collection of particulars on the irrigation
potential created, irrigation potential utilised the gross area irrigated
and the net area irrigated. In addition, other works like issuing of
Groundwater clearance certificates for the energisation of Agricultural
pump sets are carried out by this Department. However in
2000, Government issued orders exempting the agricultural pumpset
from obtaining N.O.C. from Groundwater Wing of
P.W.D.
Collection of Rainfall Data.
Rainfall data are
continuously collected from 400 rain gauge stations throughout the State
of Tamilnadu. Based on the
data collected the maximum and minimum rainfall with percentage deviation
are being worked out. The Histograms are drawn based on the 70 years
rainfall data. The Isohyetal maps are also prepared to demonstrate the
rainfall pattern in the District.
Saltwater /Fresh Water Interface Studies
In Tamilnadu the length of
the coastal stretch is about 920 km.
The entire stretch has been taken up to find out the salt
water-fresh water interface studies.
Minjur well fields which is located north of Chennai City where the
salt water fresh water interface studies conducted during 1972 was located
3.5km from sea coast and during 1999 this has moved to about 10.0 Km from
sea coast. This has been
confirmed by water quality studies.