GOVERNMENT OF TAMIL NADU

PUBLIC WORKS DEPARTMENT

 WATER RESOURCES ORGANISATION

 

MASTER PLAN  FOR ‘ARTIFICIAL  RECHARGE  TO GROUND WATER’

 IN TAMIL NADU.

 

MASTER PLAN FOR

‘ARTIFICIAL RECHARGE TO GROUND WATER’ IN TAMIL NADU’

.

Introduction:

Groundwater as a dependable source and its proximity to various users has led to indiscriminate extraction of this precious natural resource for agricultural, domestic and industrial uses. The speedy and uncontrolled usage of ground water has caused many problems. The intensive ground water development has resulted in depletion in water levels, deterioration in water quality and availability of this scarce resource. Proliferation in ground water extraction resulted in increase in the stage of development in Tamil Nadu from 63% to 85% between 1992 and 2004 as per the ground water assessment made by the Ground Water Wing of TNPWD. Similarly the nos. of over-exploited and critical blocks has increased from 89 blocks to 175 blocks. Groundwater quality in coastal area has also been affected due to excessive groundwater development. Also over exploitation near the coast has led to sea water intrusion. The development of groundwater resources in these areas therefore need to be regulated and augmented through suitable measures to provide sustainability. Rainfall being the main source of recharge to groundwater, it is essential that substantial volumes of surplus monsoon run-off that flows out into the sea has to be conserved and recharged to groundwater reservoir.

 

The efficacy of the surface water bodies such as tanks, canals as a means of natural recharge to groundwater has drastically reduced simply because the water levels in those areas are too deep. Hence the need of the hour is for ‘Artificial Recharge’ systems that convey the fresh rainwater into the aquifer. In other words, the basic purpose of artificial recharge of ground water is to restore supplies from the aquifers depleted due to excessive ground water development. The artificial recharge to ground water aims at augmentation of ground water reservoir by modifying the natural movement of surface water utilizing suitable civil construction techniques.The Artificial recharge techniques inter-relate and integrate the source water to ground water reservoir. The benefits are rise in water level and consequent increase in storage of the ground water reservoir.

 

Concept of augmenting ground water or sub surface reservoir:

 

The sub surface reservoirs are very attractive and technically feasible alternatives for storing surplus monsoon run off. The sub surface storages have advantages of being free from the adverse effects like inundation of large surface area, loss of cultivable land, displacement of local population, evaporation losses and sensitivity to earthquakes. No gigantic structures are needed to store water. The structures required for recharging ground water reservoirs are of small dimensions and cost effective such as check dams, percolation tanks, surface spreading basins, pits, sub surface dykes etc.

 

Basic requirement for Artificial Recharge projects:

     The basic requirements for artificial recharge to ground water are: -

a)     Availability of non-committed surplus run-off in space and time

b)     Identification of suitable geological environment and sites for creating sub-surface reservoir through cost effective artificial recharge techniques.

Source  of  Water availability:

The source water availability, one of the prime requisites for ground water recharge can be assessed by analyzing the monsoon rainfall pattern, its frequency, number of rainy days maximum rainfall in a day and its variation in space and time. The variations in rainfall pattern in space and time can be considered for assessing the surplus surface water availability.

Hydro-geological aspects:

Detailed knowledge of geological and hydrological features of the area is necessary for adequately selecting the site and the type of recharge structure. The hydro-geological situation in each area needs to be appraised with a view to assess the recharge capabilities of the underlying hydro-geological formations. For assessing the requirement of water for sub-surface storage, the entire thickness of the vadose zone upto 3 m below ground level is to be considered as the upper 3 m of unsaturated zone may cause adverse environmental impact viz., water logging, soil salinity etc.

Need for Artificial Recharge Projects:

The natural recharge of ground water is very slow and could not keep pace with the excessive continued exploitation of ground water. This over-exploitation of ground water resulted in declining ground water levels and depleted the ground water resources in some of the areas. In order to augment the natural supply of ground water, the artificial recharge of ground water is essential.The rainfall occurrence is limited to a few days in a year. The natural recharge to ground water reservoir in restricted to this period only. The artificial recharge techniques aim at increasing the recharge period in the post monsoon season and provide additional recharge. This results in providing sustainability to ground water development during the lean season.Thus there is a need for a systematic implementation of artificial projects for augmenting ground water under various hydro-geological conditions.

Planning of Artificial Recharge Projects:

 

Identification of areas:

The Artificial Recharge projects are site specific and the replication of the techniques from areas are to be based on the local hydro-geological and hydrological environments. The first step in planning the project is to demarcate the area of recharge.The Artificial Recharge of Ground Water is normally taken in areas i) where the water levels are declining on regular basis ii) where the substantial amount of aquifer has already been de-saturated iii) where availability of ground water is inadequate in lean months and iv) where salinity ingress is taking place. In Tamil Nadu, the potential recharge areas have been identified from the zonation maps prepared using Remote Sensing and GIS techniques by Institute of Remote Sensing, Anna University in association with Department of Rural Development, Government of Tamil Nadu and Tamil Nadu Water Supply and Drainage Board.

Factors to be considered:

 

Hydro-meteorological Factors:  

            The data on rainfall intensity, number of rainy days etc. help in deciding the capacity and design of the artificial recharge structures.

Hydrological Factors:  

The details like quantity of water available for artificial recharge as source water for recharge have to be worked out by carrying out hydrological investigations in that area viz., water shed/sub basin/basin.

Soil-Infiltration factors:

            The information on the infiltration capacity of the soil at a particular point under given set of conditions is important while adopting water spreading methods for artificial recharge. The infiltration capacity depends on soil type moisture content, organic matter, vegetable cover season air entrapment, formations of surface seals crusts etc.

Hydro-geological factors:  

            The hydrogeology of an area is of prime importance in successful implementation of any 'Artificial Recharge Scheme'. The data on sub-surface hydro-geological units, their thickness and depth of occurrence are essential to decide on the location and type of structures to be constructed in the field.

Geophysical factors:

            These techniques are highly suitable and effective means of determining the characteristic formational features for suitable site selection for artificial recharge structures. Also this technique is mostly adopted to assess the unknown sub-surface hydro-geological conditions economically, adequately and unambiguously.

 

Other factors:

           

            The quality of raw waters available for recharge should be free from chemical and bacteriological effects. Also the water should be silt free.

 The impact assessment studies carried out on the already constructed artificial recharge structures reveal that percolation tanks, check dams, recharge shafts are effective structures in hard rock areas whereas recharge trench and recharge tube wells are effective in case of alluvial areas. In coastal areas tidal regulators are effective in controlling seawater ingress. In case of urban areas and hilly terrains with high rainfall rooftop rain water structures are effective. These aspects are to be kept in mind while formulating the artificial recharge schemes.

 

 

 

Artificial Recharge Techniques:

 

The Artificial Recharge Techniques can be broadly categorized as follows:-

Design of Artificial Recharge Structures:

            Different Artificial Recharge Structures are to be proposed to suit different hydro-geological conditions as below:-

Check dams:

            Check dams are constructed across small streams having gentle slope and are feasible both in hard rock as well as alluvial formation. The site selected for check dam should have sufficient thickness of permeable bed or weathered formation to facilitate recharge of stored water within short span of time. The water stored in these structures is mostly confined to stream course and the height is normally around 2 metres.

Percolation Ponds:

These structures are artificially created surface water body submerging highly permeable land areas so that the surface run-off is   made to percolate and recharge the ground water recharge. The percolation   tanks should be located on the downstream side of run-off zone with land slope between 3 to 5%.The capacity of a percolation tank should be governed by the percolation capacity of the strata in the tank rather than the yield of the catchment. These structures are suitable for both in alluvial and hard rock areas. In the case of hard rock areas submergence area should have high permeability with the degree and extent of weathering of rocks should be uniform and not just localized. Percolation tanks with wells and shafts can also be constructed in areas where shallow or superficial formations are highly impermeable or clayey.

 

Percolation tanks are normally constructed on second order or third order steams since the catchment so also the submergence area would be smaller.Designed capacity should not normally be more than 50% of the total quantum of rainfall in catchment. The benefited area should have sufficient number of wells and cultivable land to develop the recharged water.

Recharge shafts:

Recharge shaft is an artificial recharge structure which penetrates the overlying impervious strata and provides effective access of surface water to recharge the aquifer. These structures are ideally suited for areas with deep water levels.

Sub surface Dykes:

            The main purpose or sub surface dyke is to prevent the flow of ground water out of the sub basin and to increase the storage within the aquifer. These structures will ensure supply during the period of need.

 Nalla Bunds:

These are small bunds of weirs constructed across second order streams in areas having gentler slopes. These nalla bunds store water confining to stream course.

Tanks as Recharge structures:

Small village tanks can be modified for enhancing ground water recharge after detailed studies.

Dug well recharge:

In rural areas, the rain water runoff can be channelised and recharged to dug wells through a filter. The quality of source water including the silt content should be such that the quality of ground water reservoir is not deteriorated. The recharge water is guided through a pipe to the bottom of the well, below the water level to avoid scouring of bottom and entrapment of air bubbles in the aquifer.

Roof top rain water harvesting:

In urban areas, the roof top rain water harvesting can be adopted for recharge of ground water. This method of water harvesting requires connecting the outlet pipes from roof top to divert the water to either existing wells/tube wells/bore wells or specially constructed wells.

 

Tamil Nadu scenario of Ground Water:

 

Tamil Nadu is an agrarian state spreading over an area of 1,30,300 sq.km  and has been divided into 31 districts, which are further divided into 385 blocks. The State is characterized by diverse climatic, physiographic and hydro-geologic conditions 73% of the geographical area is underlain by hard rock formations and 27% occupy sedimentary formations.

 

The predominant source of water for the State is rainfall from both the southwest and northeast monsoons. The average rainfall in the state in a water year (June to May) is 961.8 mm. The utilizable surface water resources are 23,371 MCM (825 TMC). The annual replenishable ground water resource in the state is 23,070 MCM (815 TMC). In Tamil Nadu 95% of the surface water resources have been utilized and the only alternative is 'Ground Water'. The Ground Water Development in the State has shown a phenomenal increase from 7.9 lakhs wells to 20 lakhs wells between 1951 to 1990. This has further increased to 37 lakhs during 2004. The increase in number of ground water abstraction structures is due to implementation of technically viable schemes for development of the resource backed by liberal funding from institutional finance agencies, improvement in availability of electric power and diesel, good quality seeds, fertilizers, Government subsidies etc.

The stage of ground water development as on March 2004 in the State is 85% and the quantum available for future development is 3076 MCM (15%). Based on the stage of development, the blocks have been categorized in terms of its exploitation for various uses in 385 blocks of the State. They are as below: -

Over exploited                       142     (>100%)

Critical                                      33      (>90% but < 100%)

Semi-critical                            57      (>70% but <90%)

Safe                                        145     (<70%)

Saline blocks                             8

Total                                        385 blocks.

 

Over-exploitation of ground water has resulted in declining ground water levels, shortage in water supply increased pumping lifts and consequent increase in power consumption.

 

The stage of ground water development of this magnitude viz. 85% with such optimal planning has resulted in creating deleterious effects in terms of ground water depletion and quality deterioration.The combination of these challenges needs a suitable management approach. Augmentation of ground water through Artificial Recharge is one such approach to overcome the problems of ground water scarcity.

 

Need for a Master Plan for Artificial Recharge:

 

In Tamil Nadu various departments like PWD, Agricultural Engg.Dept. Tamil Nadu Water Supply and Drainage Board, Rural Development, Metro Water and Forest Department have been implementing different 'Artificial Recharge Schemes' like Check Dams, Percolation Ponds, Recharge Shafts, Tidal regulators, Recharge tube wells and rain water structures. So far the Agricultural Engineering Dept. has implemented 4753 check dams, 10996 Percolation ponds and 12564 Farm ponds since 1984. Similarly, TWAD Board has implemented 3666 check dams since 2001. The Forest Department has executed 25600 check dams and 2540 percolation ponds so far under various projects. The impact assessment studies conducted by the TWAD Board on some of the artificial schemes revealed that there was a substantial increase in water level from 2.50 metres to 12 metres in those areas. Similarly the impact assessment studies conducted by the Agricultural Engineering Department and Forest Department also revealed that there was a substantial increase in water levels and in turn indicating the increase in groundwater potential. These success stories emphasize the need for taking up the Artificial Recharge Schemes in a larger way so as to augment the ground water through Artificial recharge so as to prevent the semi-critical areas numbering 57 blocks becoming critical blocks. Also the implementation of Artificial Recharge Schemes will improve the ground water potential which will enable the over-exploited and critical blocks to revert back to semi-critical and safe blocks. Hence the Artificial Recharge schemes are to be taken in a large scale wherever feasible for which a systematic approach based on a Master Plan is the need of the hour.

 

Methodology for preparation of the Master Plan:

1)     The most favourable areas for artificial recharge structures are identified and prioritized based on the ‘Stage of Ground Water development’ of that area.

2)     The numbers and suitable types of structures are proposed based on the storage capacity and efficiency considering the storage space and available source water for recharge.

3)     The cost estimates of different types of artificial recharge structures were worked out to arrive at the total cost.

 

Identification of feasible areas and types of structures to be                provided:

In several areas of the state where rainfall is high, considerable variability of rains in terms of their onset, distribution and amount over space and time result in uncertainty about availability of water for rain fed crops. In hilly terrains, steep slopes result in heavy run-off and low infiltration, resulting in shortage of water during summer season. In all such areas, there is an urgent need to take steps for augmentation of ground water resources through appropriate techniques to provide assured supply of water for irrigation, industrial and domestic needs.

The areas characterized both declining trend and depletion in depth to water table are ideal sites for ‘Artificial recharge to Ground Water’.

The potential recharge areas and the type of recharge structures to be provided are being identified with the help of zonation maps prepared using Remote Sensing and GIS techniques by the Institute of Remote Sensing, Anna University and funded by the Department of Rural Development and TWAD

Recharge structures:

Recharge structures proposed depending upon the topography, hydro-geological conditions, check dams, percolation ponds will be appropriate for recharging the aquifer. It has been considered that 70% of the available sub storage would be recharged through percolation ponds and the remaining 30% through check dams. In certain areas, for example, in Cuddalore district, the terrain is not suitable for check dams and hence only percolation ponds are to be adopted. In urban areas, roof top rainwater harvesting is to be adopted. Apart from these sub-surface barriers, providing recharge shafts/pits, Farm ponds, Recharge tanks, Desilting of Tanks etc. can also be adopted depending upon the site conditions.

Way Forward:

Implementation of Artificial Recharge Schemes in Tamil Nadu:

 

The implementation of Artificial Recharge schemes has to be carried out in systematic and holistic manner as per the Master Plan by the respective agencies like PWD, Agricultural Engineering Department, TWAD Board, Chennai Metro Water Supply and Sewage Board and Forest Department in a period of three years. As already indicated different departments have been implementing the 'Artificial Recharge of Ground Water' schemes, to make the schemes of this nature well planned on scientific basis and also to create data base, it is desirable to notify the 'State Ground & Surface Water Resources Data Centre (SG&SWRDC) WRO as a nodal department at the state level. The Nodal Agency identified as the 'State Ground and Surface Water Resources Data Centre, WRO has to monitor the implementation of all the recharge schemes. To popularize these schemes in a big way and to ensure their success, this programme has to be made a people's programme.

 

Benefits anticipated:

The implementation of Artificial Recharge Schemes in a systematic and scientific manner will enhance the ground water potential in the affected areas. The problems like depletion in water levels and deterioration in water quality caused due to over-exploitation will be tackled by augmentation of ground water through Artificial Recharge. In our State, out of 385 blocks, 175 blocks are over-exploited and critical where the stage of ground water development is more than 90%. The situation in these over-exploited and critical blocks constituting 45.45% will improve by the implementation of the proposed artificial recharge schemes. The augmentation of the ground water through the Artificial Recharge measures coupled with management and regulatory measures will improve the ground water scenario in the State and these affected blocks may revert back to semi-critical and safe blocks respectively. Apart from this, immediate steps are required to be taken to prevent the semi-critical blocks numbering 57 blocks (14.80%) from becoming critical and over-exploited blocks. In Tamil Nadu, various departments like PWD, Agricultural Engineering, TWAD Board, Panchayats were implementing artificial recharge schemes. Forest department is implementing similar schemes in the Reserved  Forests. The sectoral allocation of water to various uses will be supplemented and go a longway in tackling the problems of over-exploitation of ground water in the State.

 Total Cost:

The total cost of artificial recharge structures to be taken up in the years 2008-09, 2009-10 & 2010-11  will be Rs. 550 Crores of which the amount sanctioned for the year  2008-09 will be Rs. 100 Crores.

              ‘His Excellency, the Governor of Tamilnadu addressed in the Legislative Assembly on 23.01.2008 that the schemes for implementation in the water deficit areas for storing the unutilized water in rivers, river lets and streams and utilizing it round the year for drinking water and agricultural purposes. Hence this Master Plan is prepared.

 

The Administrative Sanction for this scheme  has been issued by the Tamilnadu Government  vide its order mentioned below.

 “G.O. Ms No 198,  PW(R2)Dept. dt  10-6-2008.”

 The break up details of the amount sanctioned for 2008-09  for different Government Agencies are as follow.

 a)   Water Resources Organaisation (PWD)      Rs     48   Crores.

 b)   State Ground and Surface Water

      Resources Data Centre (PWD)                       Rs       2   Crores.

 c)    TWAD Board                                                   Rs     24   Crores.

 d)  Agricultural  Engineering Department             Rs     25  Crores.

 e)  Forest  Department                                            Rs       1  Crore.

                                                                                ______________ 

                                                             Total           Rs 100  Croress.

                                                                              

 

 

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