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.

  Phase III (Year from 1987 onwards).

 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. Manual water levels are monitored during the first week of every month from all open wells and piezometers.

 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.