As a water conservation measure, Government has given an unprecedented thought to proposals such as RainWater Harvesting. Keeping this in view, CMWSSB has decided to embark upon popularising the RWH techniques among the residents of Chennai city, as also in the neighbouring areas.
Considering the importance of Rainwater harvesting in conserving the precious ground water resource, the Board has taken initiative to constitute a fully dedicated "Rainwater Harvesting Cell". The main objective of the Cell is to create awareness and to offer technical assistance free of cost to the residents and also to provide to the citizens 'cost effective solutions'. CMWSSB has created several models, detailed designs etc., which are available in the form of brochures, booklets and are being distributed to the public. In the recent past, we have also tried to disseminate related information through electronic and print media quite vigorously. An Information Centre on RWH was opened from 10.8.2001 onwards at the CMWSS Board Head Office.
Efforts were taken to convert the Rainwater Harvesting campaign launched by the Government as people's movement. A number of seminars/ workshops and exhibitions were organised involving various Government agencies, NGOs and private individuals. As a result of this intensive campaign the Rainwater Harvesting has become popular in Chennai city and the people are adopting it on their own.
Realizing the importance on regulatory mechanism for providing rainwater harvesting CMWSSB has made the installation of Rainwater Harvesting structures as a compulsory pre-requisite for providing water and sewer connections for all the new buildings.
Regular training programme are being conducted at the Metrowater Resources Centre for the benefit of public, private engineers and building workers.
A list of Resource Persons has been prepared and made available. Details on RWH have also been put up on the Metrowater website.
The initiatives taken by CMWSSB can be categorised into macro level and micro level initiatives. At macro level the Board has constructed a number of check dams to recharge ground water in wellfield area and also have constructed injection wells to arrest saline water intrusion in one of its wellfield close to coast.
At micro level, this Board have taken a no. of steps to popularise RWH at individual house hold level in Chennai city. This Board has also implemented RWH in the public buildings such as Raj Bhavan, Children's Park, Egmore Museum, Presidency College, Stanley Hospital, Nochikuppam slum and Lady Willingdon Higher Secondary School to create models for demonstration. In Chennai city, a total no.of 38,218 RWH structures have been constructed by individuals and in Government Buildings.
Macro Level Groundwater System :
(i) A.K. Basin Aquifers :
During early 1965, extensive hydrogeological studies were taken up as part of UNDP Project in the Araniar - Koratalaiyar Basin (A.K.Basin) to assess the ground water potential. The studies resulted in the commissioning of three Wellfields (in 1969) namely, Minjur, Panjetty and Tamaraipakkam for extraction of 125 mld (27.5 mgd) of ground water. During early eighties, a reassessment of ground water potential was carried out again with UNDP assistance and this resulted in the commissioning of three new Wellfields (in 1989) namely, Poondi, Kannigaiper and Flood Plains to extract about 55 mld (12 mgd) of ground water. Presently, Metrowater is exploiting all the six Wellfields.
(ii) Southern Coastal Aquifer :
Based on the survey conducted by the Geological Survey of India (GSI) during 1975-77 and subsequent studies made by the UNDP and Metrowater Board, it has been established that the narrow coastal stretch which extends upto 20 Kms from Thiruvanmiyur to Muttukkadu along the New Mahabalipuram road on the southern side of Chennai city has a shallow water table aquifer with a potential of 4.5 mgd. Based on this shallow wells have been constructed to extract around 1.5 mgd to 2 mgd of ground water to supplement the city water supply.
Water level depletion and low yield
Though it was estimated that a total quantity of 180 mld (39.5 mgd) of ground water could be extracted from all the six Wellfields, in A.K.Basin the actual yield become reduced year by year and during the year 1990, it become only 50% of the original estimate.
This is due to the fast rate of depletion of water level caused by continuous extraction mainly by farmers,low rainfall and frequent drought periods. During the same time it was observed that sea water intrusion upto 9 km inland took place into the Minjur aquifer which is located very near to the coast (Bay of Bengal).
Construction of Checkdams and Injection wells
In order to keep the sustainable yield of the aquifers and to arrest sea water intrusion certain long term measures such as (i) construction of checkdams across River Koratalaiyar and (ii) construction of Injection wells in Minjur Aquifer have been initiated.
Based on the recommendations of the UNDP studies, construction of these check dams across the Koratalaiyar river has been taken up in order to harness the flood waters available during the monsoon periods for recharge purposes.
Out of the five locations, two checkdams are constructed already and one is nearing completion.Periodic water level monitoring shows that the water level in the nearest wellfield (aquifers) increased considerably due to the recharge effect of the checkdams thereby increase the yield of the wells.
Again based on the UNDP study recommendations, it was decided to construct a battery of recharging wells to arrest sea water intrusion in Minjur aquifer and an injection experiment was conducted to assess the intake capacity of the recharge well. Based on the positive results obtained, 15 injection wells of 350mm dia and 45m depth were constructed to create an artificial barrier of fresh water in the Minjur aquifer. In addition 10 observation wells were also constructed for the purpose of monitoring the quality of ground water. Periodical monitoring of water quality shows considerable improvement in the quality of ground water and therefore it is possible to maintain optimum level of extraction in Minjur Wellfield.
Implementation of Groundwater Regulation Act
On the basis of clear evidence of sea water intrusion into the Minjur aquifer, the Tamilnadu Government realised the necessity of saving the coastal aquifers and other ground water potential zones in and around the city and enacted legislation to regulate and control the extraction, use or transportation of ground water.
The Act which came into force with effect from 15.2.88 has been named as "The Chennai Metropolitan Area Groundwater (Regulation) Act, 27 of 1987". A total number of 243 revenue villages of the neighbouring two districts and the city of Chennai are included in the scheduled areas of the Act. The competent authorities to implement the Act are (i) CMWSS Board for Chennai city and (ii) the respective Revenue Divisional Officers/Sub-Collectors for the other revenue villages.
The Act envisages (i) Registration of existing wells (ii) Regulation of sinking new wells (iii) Issue of licences to extract ground water for non-domestic purpose and (iv) Issue of licences for transportation through goods vehicles. Licences were issued by the Revenue officials on payment of prescribed fees after getting technical clearance from CMWSSB.
Impact of macro level initiatives
- It is, due to the implementation of the Groundwater Regulation Act, the water table in the southern part of the city which was on an average depth of 8 metres before 1988, as risen upto an average depth 4 metres below ground level which means that there is about 4 metres nett increase.
- After the implementation of the Act coupled with other measures such as construction of check dams across Koratalaiyar river, there has been phenomenal increase / rise in the ground water table.
- As a matter of fact, during the year 2000-2001, Metrowater Board has been able to increase the drawl from 55 mld to the present 100 mld of water (50% of city supply) from these Wellfields only due to the measures undertaken by the CMWSS during the last 5 to 6 years.
Feature studies :
In order to reassess the ground water potential in the Arani-Koratalaiyar river basin a detailed restudy of the entire river basin has to be taken up by the Board with the assistance of the World Bank.
- To create public awareness on the importance of RWH among the public
- To popularise simple and cost effective RWH methods in order to attract larger participation of the public.
- To offer technical guidance/assistance about the methods to be adopted based on the local geological formations and site conditions.
- To monitor water level and water level quality in the Rainwater Harvested areas and wells (both existing and proposed areas/wells).
- To assure proper maintenance of the RWH structures after installation.
- To do and undertake anything which would promote RWH (both in individual houses and public places).