ABSTRACT
Agricultural sector is the prime consumer of ground water resources in the state and country. The rapid increase in ground water irrigated area in last few years, in Chhattisgarh state has brought 0.41 Mha of land under ground water irrigation. The increased ground water draft sharply leading to sectoral decline in ground water level .The decline ground level has threaten the sustainability of hand pumps, the principal source of drinking water and life line of rural water supply system. Artificial recharge to ground water is the best possiblesolution to the above problem. Central Ground Water Board through its network monitoring stations all over the state, ground water sampling, exploration, detailed hydrogeological studies in specific areas has generated large data base on hydrogeological condition of the state.
In the present paper an attempt has been made to incorporate the available data base to demarcate the suitable area for Artificial Recharge in the state applying the GIS technique. A total of 7049 sq.km area in 23 isolated pocket spread in 49 blocks of 15 districts has been identified using six thematic layers by GIS technique. The artificial recharge can provide additional secured irrigation to 87320 ha land on expenditure of nearly Rs 5140 million and improve the sustainability of ground water abstraction structures. Since in Durg district the stage of ground water development is highest within the state and seven out of 12 block of Durg district and three out of four block of Dhamtari district are categorized under “Semi Critical” hence special emphasis has been given to deal with Durg and Dhamtari district.
INTRODUCTION
The increase in ground water utilization in the last decade for agricultural activities through adoption of bore wells has resulted in a six-fold increase in ground water draft in the last 20 years in Chhattisgarh. During the year 1990 the ground water draft was 60830 ham, it has increased to 359772 ham in 2009, resulting in an overall increase in stage of ground water development from 3.31% to 31%. The present stage of development of ground water in the state varies from 2% in Bijapur to 69% in Durg district. The ground water irrigated areahas increased more than 6 times in last decade from 0.087 Mha to 0.41 Mha. Overall increase in the irrigated area of State during last decade has mostly been contributed through ground water. The development has not been uniform and steady in the State. Due to multifarious reasons the development has been slow in certain area but it has galloped in other places. Out of 146 blocks of Chhattisgarh, the stage of ground water development is still less than 30% in 104 blocks, between 30-50% in 19 blocks and more than 50% only in 23 blocks. However there are only 14 ‘semi-critical’ blocks (Balod, Bemetra, Baramkela, Rajnandgaon, Gurur, Durg, Dhamtari, Dhamdha, Kurud, Patan, Pandaria, Nagri, Saja and Belha ) and no ‘critical’ or ‘over exploited’ blocks as per the latest (2009) resource estimation in the State. During 1990 stage of ground water development was lower than 33% in all the blocks. When compared with earlier resource estimation of 1990’s it shows two to nine fold increase in the stage of ground water development among those 74 blocks wherepresently the ground water development is more than 30%. (State report 2009)
Chhattisgarh State requires assured irrigation for sustainable agricultural productivity and to mitigate the effect of incessant drought condition. This is possible by adopting ground water development in 104 blocks where the stage of ground water development is still below 50%. Adopting rainwater harvesting and artificial recharge practice, simultaneously in those blocks where ground water development is presently above 50% and in those blocks where the sustainability of the abstraction structures is under threat in lean period, can enhance the sustainability.
Durg district having the highest ground water development within the state, where seven out of tewlve blocks fall under semi-critical areas, need special emphasis to mitigate the emerging challenge of development with scientific ground water management practice. Durg is located on Mahanadi plains where the population density is high. Being plain land and scanty forest cover the availability of agricultural land is higher. The districts occupied with rocks of Chhattisgarh Supergroup, mainly karstic limestone, gypsiferous and calcareous shale, which are potential aquifer. Simultaneously Durg is socio-economically advance district of the state. All these above conditions are conducive for rapid growth of ground water recourses in the district. Three out of four block of Dhamtari district are also categorised as semi critical required attention. Nagri block of Dhamtari district situated on granitic terrain and having largely unconfined aquifer where rainwater harvesting can bevery useful for managed aquifer storage.
Application of modern technique like GIS can help to identify the pockets of areas where immediate attention has to be given for proper ground water resource management to mitigate the emerging ground water problems.
METHODOLOGY
To demarcate suitable sites of Artificial Recharge in Chhattisgarh six different thematic layers were prepared from the available and field data generated by monitoring through well-established network of 381 monitoring stations all over the state (Year book 2005) and other hydrogeological studies.
a) Post monsoon depth to water level (DTW) map was prepared using Mapinfo 6.5 with vertical mapper keeping 3 m interval. The grid map was generated using Natural Neighborhood statistical package from table extracted from Oracle database. Vadose zone available for recharge is calculated based on decadal post monsoon depth to water level data (November) separately for every 3 m interval. Vadose zone available below 3 m ground level has been considered suitable for recharge
b) The decadal ground water trend of post monsoon level is generated using November (1995-2004) ground water level data through Mapinfo 6.5. with vertical mapper. Areas showing fall in ground water level @ > 10 cm/year has been considered for artificial recharge.
c) The stage of ground water development was calculated for all the 146 blocks using GEC 1997 norms.(CGWB, 2005)
d) The geological map prepared by GSI (and modified by various works) on 1:250000 scale has been used for identification of aquifer along with the back ground hydrogeologic information available for all the major rock type with CGWB including specific yield for various rock type.
e) All the above hydrogeological layers were superimposed on administrative map of Chhattisgarh State along with water shed map, using Mapinfo 6.5.
f) Using the GIS facility, the areas were demarcated having more than 3m post monsoon ground water level with a falling trend in post monsoon period @ > 10 cm/year or having stage of ground water development as semi critical. Logical and scientific discrimination is applied with the marked area keeping the land use and population density criteria in mind to restrict the earmarked area.
g) Finally the marked areas were superimposed on geological and geomorphological map to propose suitable method of Artificial Recharge.
h) Based on the volume of Vadose zone calculated separately for each watershed (AISLS1990), and availability of surplus subsurface runoff in that particular watershed, the number of Artificial Recharge structure were finalized.
i) Budgetary requirement for construction of Artificial Recharge structure were calculated based on guideline provided by CGWB New Delhi.(CGWB, 2002)
j) The work presented here is a team effort of all the scientific officers of CGWB, NCCR, Raipur.
DISCUSSIONS
Identification of area
Over the years, traditional rainwater harvesting through structures like tanks and village ponds has been practiced. In order to cope with recurrence of drought and water depletion, a massive “Watershed Development Programme” was launched by Government of India in 1975 in drought prone areas, focus was laid on sustainable effort to harmonize the use of water, soil, forest resources, with the emphasis on holistic planning on basin/ sub basin level.
Based on data of National Hydrograph Stations established by CGWB to monitor the fluctuation of ground water levels in different hydrogeological situations, a trend analysis was carried out for the decade between 1995 and 2004. A total area of 7049 sq.km. in Chhattisgarh shows declining trend in ground water levels. 23 major watersheds have been identified in Chhattisgarh in which declining trend of more than 0.1 m/yr was recorded. (Fig 1) These watersheds have been identified for construction of suitable artificial rechargestructures to augment the available ground water resources.
Sub-surface storage space and water requirement
To estimate the sub surface storage and space available, a map was prepared on the basis of average post monsoon depth to water level for the period 1995-2004. The decadal post monsoon average depth to water level is predominantly in the range of 3 to 6 m below ground level. Based on this map the volume of unsaturated zone available for recharge (Vadose zone to 3 m below ground level) was calculated for each of the 23 identified watersheds. A total 456mcm volume of vodose zone was calculated based on the specificyield of the rock types in the watersheds of Chhattishgarh state (CGWB 1984).The requirement of water to fully saturate the vadose zone upto 3 m below ground level was worked out for each watershed at 75% efficiency considered for recharge structures. The total requirement of water to saturate the sub-surface storage space worked out to be 606 mcm for the entire State ( Table 1 ).
Source water availability
The availability of surplus monsoon runoff was estimated for 23 identified watersheds mainly on the basis of data from State Irrigation Department. The total availability of source water for recharge worked out to be 16658 mcm, which is much more than the total requirement to create the sub-surface storage. However, for each watershed the requirement vis-à-vis the availability was seen and the least of the two was considered as available source water for harnessing artificial recharge structures. The total quantum of source water, whichcan be utilized for creation of sub-surface storage worked out to be 601 mcm for all the 23 identified watersheds.
Recharge structures
The suitable artificial recharge structures in the State are gully plugs, gabion structures, contour bunds in the upper reaches of the watersheds, percolation tanks, nala bunds in the runoff zones and recharge shafts, gravity head wells in down stream areas. The main artificial recharge structures are given below and estimated number of feasible structures and their cost are described in Table 2.
Percolation Tanks
Percolation tank is the main artificial recharge structure proposed for effective utilisation of the surplus monsoon runoff. In hard rock areas only 50% of the total estimated surplus surface water resources have been considered for storage in the percolation tanks. As per the hydrogeological conditions in Chhattisgarh an average percolation tank has filling capacity of 0.1 mcm. It can actually store 200% of the capacity due to multiple filling during the monsoon. Unit average gross storage capacity of 0.2 mcm has been considered forthe percolation tank . The average cost of such structure has been considered as Rs.20 Lakh. The number of feasible percolation tank in each identified watershed is presented in Table 2. The total percolation tanks feasible in Chhattisgarh are 1470 costing Rs. 2940 million.
Nala Bunds
There is a large scope for constructing Nala bunds/Cement plugs in various second order streams in State. About 25 % of surplus monsoon runoff can be utilized by recharging through these structures. The average capacity of Nala bunds/Cement plugs has been considered as 0.03 mcm. The average cost of each structure has been taken as Rs.1.0 lakh. It is estimated that 5050 Nala bund/Cement plugs can be constructed in the State at the cost of Rs 505 million.
Recharge Shafts & Gravity Head Recharge Wells
These structures are feasible in villages and urban pockets. About 10% of the surplus monsoon runoff can be utilized through these structures. The average recharge capacity through recharges shafts, gravity head recharge through dug wells during an operational period of 60 days in monsoon and post monsoon period is considered as 0.01 mcm. The average cost of structure may be taken as Rs.2.5 Lacs. The number of structuresand their cost for each identified watershed is calculated and presented in Table 2. For the entire State the feasible structures are 6060 costing Rs.1515 million.
Gully Plugs, Contour Bunds, Gabion Structures
These are mainly soil conserving structures help to increase the soil moisture with limited recharge to ground water. It is estimated that 15% of total water available for recharge can be utilized through these structures, which have an average storage capacity of 0.005 mcm. The average cost of each structure is taken as Rs.10,000/-. The structures feasible in each identified watershed has been estimated and presented in Table 2. For the entire State feasible structures total up to 18180 costing Rs 182 million.
Cost estimates and benefits
The main artificial recharge structure in the 23 identified watershed are percolation tanks, Nala bund/ Cement plugs, Recharge shaft/Gravity head recharge wells and water conservation structures like gully plug, contour bund and gabion structures. The total cost of these artificial recharge structures works out to Rs 5142 million. The benefit from the proposed plan would be in terms of creation of additional irrigation potential in ruralareas and supplementing drinking water needs in urban areas.An additional irrigation potential of 873 Sq km would be created.
RESULTS AND CONCLUSIONS
Application of GIS technique to demarcate suitable areas for artificial recharge of ground water in Chhattisgarh by using six thematic layers namely i) decadal post monsoon depth to water level ii) decadal post monsoon water level trend iii) stage of ground water development iv) watershed v) geology and vi) geomorphology has brought out nearly 7049 sq.km area in 15 district in 23 isolated pockets. Total 456 mcm vadose zone is available for artificial recharge of ground water. These 23 identified areas were spread over 49 blocks and 15watersheds. Out of these 15 watersheds 9 were from Mahanadi basin, where ground water development is maximum. The identified area needs 606 mcm of water to saturation, which is only3.6% of the available surplus runoff. For these 23 pockets, the total structure recommended are 1470 percolation tanks, 5050 cement plugs, 6060 gravity head recharge structures and 18180 rainwater harvesting structures. The construction of these structures required nearly 514crors of rupees and will generate peoples participation and rural employment. This also brings additional 87320 ha of land under assured irrigation and will enhance sustainability of ground water structures, particularly of hand pumps for drinking water supply.
In Durg district three areas have been identified in 8 out of 12 blocks for artificial recharge covering nearly 1188 sq.km area. Based on the aquifer character of karstified limestone and gypsiferous shale gravity head recharge wells are assume to be the best effective artificial recharge structure for Durg district. It is suggested that gravity head recharge wells may be constructed in existing irrigation tanks or in combination with stop dam/check dam so that the deeper aquifer are recharged properly during the lean period for more effectiveresults. Site selection for these gravity head recharge wells must be done in a scientific manner for success of the project. Artificial Recharge in gypsiferous aquifers of Saja and Bemetra block will also improve the quality of ground water making it soft by dilution.
The area identified for artificial recharge in the present paper is based on the regional level studies. Before implementation of above recommendations in the selected 23 areas micro level field investigations are to be carried out.
ACKNOWLEDGMENT
The authors are thankful to the Shri Sushil Gupta, Chairman, CGWB for allowing to publish the paper. The Regional Director, CGWB, NCCR Raipur is thankfully acknowledged for guidance and for the logistic support.
REFERENCE
- AISLS,1990 –Watershed atlas of India, All India soil and land use survey,
- Deptt. Agriculture and Cooperation, New Delhi
- CGWB 1984- Manual on Artificial Recharge of Ground Water, CGWB, Faridabad.
- CGWB 2002- Master plan for artificial recharge , CGWB, Faridabad.
- CGWB 2011- Dynamic Ground water Resources of Chhattisgarh, CGWB, Raipur
- State report 2006 -Hydrogeology of Chhattisgarh, unpublished report ,CGWB Raipur,
- Year book 2005- Unpublished report. CGWB Raipur
Arunangshu Mukherjee, J.R.Verma and Dinesh Tewari
Central Ground Water Board
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