|About Andhra Pradesh|
|Andhra Pradesh, the third largest State of the country with a geographical area of 2.75 lakh Sq Kms. has a forest Cover of 23 %. The following table gives the Administrative set up of the State. The State shares its boundaries with Orissa, Tamil Nadu, Chattishgarh, Maharashtra and Karnataka, and on the eastern side is the Bay of Bengal.|
|Although the normal annual rainfall is 940 mm, it has a wide range of distribution in the State. In the drier and interior southern district Ananthapur, it is as low as 552 mm while north eastern coastal regions record normal of more than 1200 mm. The rainfall record shows that droughts are fairly recurrent in the state. The analysis of rainfall during 1974-2007 indicates deficit rainfall in all the 22 years in one or the other parts of the State. The State receives about 66% of rainfall from south-west monsoon (June-September) and about 25% from north-east monsoon (October-December). The remaining 9% is received during winter and summer months.|
|Rivers of the state vis-à-vis watersheds|
|The state has 3 major rivers the Godavari, the Krishna and the Pennar, besides a number of small but splendid rivers of eastern-ghats. The River Godavari with its tributaries Pranahita, Manjeera, Maneru, Indravati, Kinnerasani, Pamuleru and Sileru drains through the northern parts of the State into Bay of Bengal. The river flows through Adilabad, Karimnagar, Nizamabad, Medak, Ranga Reddy, Warangal, Khammam, Krishna, East & West Godavari and Visakhapatnam districts. The River Krishna with its tributaries Tungabhadra, Vedhavati, Hundri, Musi, Paleru and Munneru flows through the central parts of the State. It drains through Anantapur, Kurnool, Mahabubnagar, Ranga Reddy, Nalgonda, Guntur and Krishna districts in to Bay of Bengal. The River Pennar, the third biggest river, with its tributaries Chitravati, Papaghni, Cheyyeru and Pincha drains Rayalaseema region and Nellore district.|
There are in all 40 rivers that drain directly into the sea, and 81 sub basins are recognised as accounting units for the water. However, these sub basins which range in size from 90.65 km2 to 15699 km2 are generally too big for estimation of dynamic groundwater resources. The ideal recommended size of groundwater estimation unit i.e. the catchment is 300 km2. Hence, in 2002, for the purpose of groundwater estimation these accounting units were further sub-divided into 1193 drainage basins that are called watersheds in consonance with the decision of the Groundwater Estimation Committee. However, these divisions are modified in 2004 and arrived at 1229 groundwater assessment units (watersheds) in the state.
|Soils and agro-climatic zones|
|The soils are broadly red, black, alluvial, lateric and coastal sandy types. They support large variety of natural vegetation and in general good for agriculture and horticulture. The climate, rainfall and soil divide the state into 7 climatic zones- High altitude and Tribal area, Kishna-Godavari zone, North coastal zone, Northeren Telangana zone, Scarce rainfall zone, Southern Telangana zone and Southern zone, which are based as much on the water availability as on the type of agriculture that the area can support. Hence, these are properly referred as agro-climatic zones.|
|Agro climatic zones of Andhra Pradesh|
|Geological and Hydrogeological characteristics|
|The state is covered by|
|Archaeans, Pre-Cambrians, Cuddapahs, Kurnools and Deccan traps are categorised as Hard Rocks from groundwater point of view. These rocks have negligible primary porosity. The development and management of aquifers in these diverse formations requires similar techniques. These rocks cover nearly 85% of the State that is about 2.332 lakh km2. The remaining 15% of the area that is 41,160 km2 is underlain by soft rocks Gondwanas, Rajahmundry formations, Recent Alluvium, etc.(Figure: Geological map of Andhra Pradesh).|
|Geological map of Andhra Pradesh|
|In hard rocks average well yields are ranging from 75 to 150 l/m are recorded in these rocks. However, present day mean well yields are around 0.50 ha.m per annum and they are skewed towards lower side. History of the wells shows that till 1970s there were mostly dug wells. Some of them could irrigate up to 10 or 15 acres (4 to 6 ha) of paddy in good monsoon years, especially if the area was served by small irrigation tanks. Wells that could sustain up to 5 acres (2 ha) were quite common. In 1980s the technique of drilling wells was well entrenched and initially some of the dug wells were converted to dug – cum – bore wells along and progressive farmers took up drilling of bore wells. Still it was quite common to find wells (now bore wells) irrigate 5 acres. The mean yield of the bore wells during this period was 2.47 ha.m and that of the dug wells with pumping facility was 0.91 ha.m. But with state’s support through financial institutes for well sinking programme in 1990s, the number of bore wells started proliferating. And simultaneously, during this decade the mean well yields started showing a decline. During this decade (2000s), it is common to see bore wells irrigate less than an hectare of land due to decrease of well yields and deep water table. An implication of this change is tragic wastage of energy. Dug wells that pumped accumulated water from storage required just an hour of pumping to irrigate 2 acres of crop like groundnut. Present day bore well takes 6 to 8 hours of excruciatingly slow pumping to irrigate the same field.|
|Soft and unconsolidated Rocks|
|Gondwana rocks form extensive aquifers and sustain well yields quite beyond their annual replenishment. Tube wells constructed in these rocks have yielded 100 to 1000 l/m for drawdowns ranging from 12 to 38 m. The open wells tapping these formations yield from 10 to 20 m3/day.|
|The Kamthi Sandstones beyond the depth of 250 m bgl are intercalated with shales and clays. Tube-wells constructed within the 200 m depth range yield from 100 l/m to 1000 l/m for draw-downs of 9 to 30 m. Transmissivity of the aquifer varies between 28 and 950 m2/day. The yield of tube wells in the Chinthalapudi Sandstones constructed down to 50 and 150 m bgl vary from 200 to 600 l/m and the transmissivity of the aquifer varies between 150 and 303 m2/day. These aquifers are confined and in some cases potentiometric surface lies above the ground surface giving rise to flowing wells / springs.|
|Rajahmundry sandstones are also good aquifers; the yields of tube-wells tapping these tertiary aquifers down to depths of 300 m vary from 200 to 1500 l/m for drawdowns of 6 to 15 m and transmissivity of the aquifer varies from 90 to 2500 m2/day indicating that these are the finest aquifers in the state.|
The alluvial aquifers have high porosity and permeability. Filter points are most common in this formation. Filter points drilled down to 1.5 to 20 m bgl yield between 150 to 1500 l/m.
In Krishna-Godavari delta the alluvium attains a thickness of more than a few hundreds of metres. However, the deeper aquifers are found to contain highly saline water. The static water level in these formations is generally shallow. Groundwater in the coastal alluvium occurs both under water table and confined conditions and is generally developed by means of dug-wells, filter points and shallow tube wells. The depth to water table in dug wells varies from near surface to about 5 m bgl. Usually the quality of water is the main problem in coastal alluvium. Fresh water bodies occur as pockets and lenses in the top 20 m bgl. Deeper wells can lead to up-conning of salt water and fresh water interface, which can damage the groundwater irretrievably. Hence, the depth of the wells must be restricted to 4 or 5 m bgl. In Delta region of Krishna, it is found that the sediments have connate water, which is not completely flushed out, and as a result the water quality is poor in deeper aquifers – mostly beyond 60 metres bgl.
The vast potential of these aquifers in terms of their ability to give huge quantum of water even when annual abstraction (usage) far exceeds recharge is a cause for concern. It is a political and administrative challenge that the civilised society must address thoughtfully. At present however, a decline of 1 meter per annum is considered quite reasonable for next 25 years and it is hoped that by that time there will be a big shift from agriculture dominated society to industry dominated society that can take better care of its water resources. But studies are needed to devise measures to prevent the depletion and plan artificial recharge with full vigour in these areas. The economy as well as the rainfall of the region should make this easily possible. The decision therefore is to allow well construction in all the soft rock areas of the state unhindered except in aquifers where quality of the water deteriorates rapidly with depth.
|The chemical quality of groundwater exhibits considerable variations from place to place. The geological environment, climate and drainage have profound influence on its quality. Of late pollution by number of sources including the farm chemicals, etc is doing lot of harm and damage to groundwater system. The groundwater in Archaean crystalline rocks is in general neutral to alkaline and the chloride content ranges from 30 to 525 ppm. The quality of groundwater in Cuddapah and Kurnool formations is generally poor and TDS in some of these places exceeds 1000 ppm. The quality of groundwater from Gondwana formations is generally good except in some local patches. The groundwater from Gondwanas in parts of Karimnagar and Warangal is generally alkaline and in places excessively hard. The TDS of groundwater from trap rocks ranges from 200 to 300 ppm in upland areas and from 400 to 700 ppm in valley portions. Groundwater is often brackish to saline in black cotton soils associated with traps.|
In Krishna and Godavari delta the quality of groundwater varies widely. The quality in the shallow zone is generally within potable limits, but deteriorates rapidly with depth. Totally, 30 Mandals (East Godavari 10, Guntur 7 and Krishna 13) are categorized as poor quality areas and estimated separately. The groundwater quality in general is found to be not suitable for irrigation practices in these areas. However, some localized poor groundwater quality areas, identified in Anantapur, Kadapa, Kurnool, Nellore, Guntur and Vishakapatnam are not included in poor groundwater quality areas as groundwater is in use for irrigation. The groundwater quality may vary from place to place and hence there may be pockets of better and usable groundwater in these otherwise poor quality groundwater areas.
|Availability of groundwater:|
|From the groundwater point of view, rock formations in the State can be classified into three distinct categories of (a) hard rocks, (b) soft rocks and (c) alluvial formations. Groundwater in the above rock types occurs under water table, semi-confined or confined conditions. Groundwater is present in secondary porosity of the host rocks limited to the weathered and fractured zones; joints and bedding planes etc., In the soft rocks and alluvium, the inter granular porosity contributes towards occurrence and movement of groundwater.|
Nearly 85% of the State is underlain by hard rocks and the chief contributors of groundwater in these rocks are the fractured systems. These fractured systems as mentioned above are not uniformly distributed and have limited aerial and depth extent.
Rainfall is the source of recharge to groundwater and during the last decade this source has become erratic and sometimes very low. The number of rainy days has also come down. Thus the recharge to groundwater bodies has come down. Apart from this people are resorting to use groundwater more often because, it is economical, easily available and consumes less time to ground a project, in view of the limited surface water resources and their uneven distribution. Thus the strain on groundwater aquifers mostly in upland areas is increasing day by day.
|Trends in groundwater development|
|During the last three decades:|
|Well population increased from 8.0 to 25.0 lakhs. Average annual growth rate of well population in the state is about 50,000 wells per year. Area irrigated through groundwater increased from 10 to 34 lakh hectares. This constitute about 50% of the total area irrigated. About 80% of the drinking water needs are met through groundwater.|
|Ground Water Estimation|
|National water policy enunciates periodic assessment of groundwater resource for quantification, sustainable development and management. The State is divided into 40 drainage basins and 81 sub basins of major and minor rivers. These 81 sub basins are further divided into 1229 groundwater micro basins of 100 to 300 square kilometers size based on local drainage, geomorphology and hydrogeology.|
Due to changing groundwater scenario and addition of more than 50,000 extraction structures every year, it is proposed to take-up revision of estimates at periodic intervals as envisaged in the “National Water Policy
Groundwater resources have reached a very critical stage in Non-Command areas and thoughtful use, conservation and management is required. All the areas of the state that are not served by canal command including the areas in districts like West Godavari to districts like Ananthapur are showing very high usage of the available groundwater and it is reflected in the stage of development which exceeds 70% and which is perceived as the limit to which the aquifers can be safely exploited. Although, the choice would be 40 to 50% if the environmental considerations are applied too. Based on the stage of groundwater development, the groundwater basins have been categorized as Over Exploited (Stage of groundwater development is > 100%), Critical (Stage of groundwater development is 90% to 100%), Semi-Crtical (Stage of groundwater development is 70% to 90%) and Safe (Stage of groundwater development is < 70%)
|Groundwater estimation results|
|Groundwater monitoring – Analysis of water levels:|
|Ground Water Department is monitoring the changes in groundwater regime continuously through a network of purpose built Piezometer wells fitted with Automatic water level recorders in different hydrogeological and geomorphic units. The water levels are recorded every 6th hour and the fluctuations noticed seasonally and annually are analyzed in relation to rainfall, recharge measures, drought and extraction of groundwater in the area. The water level data collected during a particular month will be analyzed and compared with earlier periods for studying the seasonal and annual fluctuations in water levels in relation to rainfall.|
Monday, 24 July 2017
Groundwater Scenario: About Andhra Pradesh
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