Of Chhattisgarh’s near two crore population, 80 per cent are heavily dependant on agriculture and allied activities as recently documented in the State Focus Paper by NABARD. The net sown area is 34 per cent of the total geographical area of the State, while the net irrigated area is just 24 per cent of the net sown area, rainfed paddy constituting the staple crop.
Although there is tremendous scope for judicious groundwater development in many parts of the State, dwindling water levels in several pockets is raising a sense of alarm. The present paper summarises various aspects of groundwater resources of the State to enable a better understanding of the potential available, its characteristics, state of development and quality.
Physiography The State can be divided into 3 distinct zones – Bastar Plateau, covering districts of Kanker, Bastar and Dantewara, mostly covered by forests with an average elevation between 700 and 800 m; Chhattisgarh Plains, spread over the central part of the State with an average elevation of 400m, and; Northern Hill Region, covering parts of Surguja, Koriya, Korba, Bilaspur, Jashpur and Raigarh Districts. The main rivers in the central region are Mahanadi and its tributaries, while River Indravati, a tributary of Godavari drains the southern part. Tributaries of the Ganga – Son, Gopad, Rihand etc. drain the northern part and river Sankh, a tributary of the river Bramhani drains a small portion along the northeastern part of the State.
Geohydrologic setting Geological formations in Chhattisgarh can be grouped into five broad hydrostratigraphic units – Precambrian crystallines; Precambrian sedimentaries; semiconsolidated sedimentaries (Gondwanas and Lametas); Deccan Traps and; unconsolidated sediments (alluvium and colluvium). Further, depending on the prevailing porosity type, the rocks have been divided into two broad types – hard rocks with fractured/fissured porosity and – soft rocks with primary porosity. Gondwanas, Lametas and unconsolidated sediments form soft rocks the rest is hard rock.
The Precambrian crystalline province, covering nearly 55 per cent of the State has the least potential with respect to groundwater yield and development. The Precambrian sedimentaries occupy nearly 28 per cent of the State and groundwater potential zones are confined to weathered mantle, caverns, fractures and formation contacts. Karsts, though few, form repository of groundwater in these terrains. The semiconsolidated sedimentaries covering nearly 16 per cent the area and form thick and extensive unconfined to confined aquifers down to 300 mbgl. Groundwater development in this area is moderate and development is restricted to upper aquifers (within 120m). The Deccan traps occupies a small area and the weathered part of the traps is converted to laterites and can yield substantial water to the dug wells. Unconsolidated formations of quaternary age have thin unconfined aquifers with thickness upto 30m and locally forms potential aquifers.
Groundwater quality The groundwater in the State is both suitable for irrigation and potable. However, there are instances of contamination, which are mostly geogenic in nature.
Sulphate The high calcium sulphate caused due to dissolution of gypsum produces is responsible for permanent hardness in groundwater. The overall sulphate content in groundwater, spread over an area of more than 3000 sq.kms, is above the permissible limit recommended for drinking water norms, causing gastro intestinal disorders.
Iron The presence of iron in groundwater may be found in all the districts of Chhattisgarh and iron contamination is one of the biggest problems of the State. Iron ingestion in large quantities results in a condition known as haemochromatosios wherein tissue damage results from iron accumulation. Besides, such water is usually unpalatable and stains laundry and plumbing fixtures.
Fluoride This naturally occurring substance in high concentration causes endemic fluorosis, a severe bone disease. While high value of fluoride in potable water cause mottling of teeth and fluorosis, low values of fluoride causes dental carries and teeth decay. Distribution of fluoride in groundwater in the State is sporadic in nature and the concentration of the fluoride above permissible is associated with granites/gneisses of Archaean age.
Arsenic Higher concentration of arsenic above the permissible limit (0.05 mg/l) in drinking water causes arsenical dermatosis (black spots, eruptions and even cracking of skin), arsenicosis, hyperkeratoris and melanosis. The highest concentration of 1.89 mg/l was reported at the Koudikasa village. There are 11 villages in Chowki block of Rajnandgaon district where arsenic levels above 0.05 mg/l are found.
Groundwater level monitoring is a scientific surveillance system to observe the periodic and long-term changes. At present a network of 540 observation wells have been established by Centre Ground Water Board (CGWB) all over the State (May 2008) The water level reflects cumulative effect of natural recharge-discharge condition and draft. The water table fluctuation is dependent on rainfall infiltration, consumptive use, topography, soil characteristics, temperature, humidity, lithology of the formation etc.
Water Level Fluctuations: About 96 per cent of the monitored wells exhibit rise in water level in November 2008 when compared to water levels during May 2008. About 25 per cent of the monitored wells exhibit rise in the range of 0 to 2m in parts of all the districts. In 41 per cent of the monitored wells rise is in the range of 2 to 4m whereas the remaining 30 per cent of the observation wells show rise of more than 4 m. The maximum rise of 14.19 m was recorded in Devri observation well of Kanker district. Maximum fall of 1.73 m was recorded in Khati observation well of Durg district.
Water Level Trends: Long-term water level trends were analysed using water level data of individual wells for separate periods for the last 10 years (1999-2008). A rise or fall of more than 15 cm/year was considered significant. Analysis of trends shows that for the pre-monsoon (May) period water levels in 20 per cent of the area record falling trends while 68 per cent show no significant rise or fall was observed. In 12 per cent of the area water levels show a rising trend. Similarly, for post monsoon period (November) water levels in 48 per cent of the area show falling trends. In 49 per cent no significant rise or fall was observed and in 3 per cent water levels showed a rising trend.
Development and management of the groundwater resources of the State has to be taken up keeping in view its varied hydrogeological characteristics. Special thrust to groundwater development has to be given for irrigation of the areas where stage of groundwater development is less than 50 per cent. There is an urgent need to educate people to utilise many developmental schemes of the government, and simultaneously grow proficient in rain water harvesting and artificial recharge. Concurrently, serious conservation measures and legislation need to be put in place in areas of intensive groundwater development such as the semi-critical blocks in Durg, Bilaspur and Dhamtari Districts, urban areas, mining and industrial areas etc.