Ground Water of Kerala - District Brochures

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From the point of view of water resources Kerala is having both abundance and scarecity. The average annual rainfall of the state is 3000mm, the bulk of which (70%) is received during the South-West monsoon which sets in by June and extends upto September. The state also get rains from the North-East monsoon during October to December.However the spatial and temporal distribution pattern is mainly responsible for the frequent floods and droughts in Kerala. The average annual rainfall in the lowland of Kerala ranges from 900mm in the south to 3500mm in the north. In the midland, annual rainfall ranges from 1400mm in the south to about 6000mm in the north. In the highland, annual rainfall varies from 2500mm in the south to about 6000mm in the north. Kerala has got 41 west-flowing and 3 east-flowing were originating from the Western Ghats. The total annual yield of all these rivers together is 78.041 Million Cubic Meters (MCM) of which 70,323 MCM is in Kerala. The peculiarity of the rivers flowing across Kerala is short length of the river and the elevational difference between the high and the low land leading to quick flow of water collected from the river basin and quickly discharged into the Lakshsdweep sea, the state has not been able to utilise the river water sources to a major extent. The major portion of the runoff through the rivers takes place during the monsoon seasons. 67.29% of the surface water area of 3.61 lakh hectares is constituted by brackish water lakes, backwaters and estuaries.

On a rough estimate, the source wise dependence by rural households for domestic water supply dependent on traditional ground water systems is 80%, 10-15% use piped water supply systems, and 5% use traditional-surface and other systems.

Fresh water availability in Kerala

Kerala is rich with 44 rivers which together yield 70300Mm³of water annually. However the total utilizable yield is estimated to be 42000Mm³, only 60% of the annual yield. Kerala possess only four medium rivers and 40 minor rivers.

In the all india perspective the rivers of kerala are not so significant than even the largest of them cannot find a place among the major Indian rivers. With respect to the national norm kerala does not have a single major river and has only four medium rivers. The combined discharge of these four rivers is less than half of that of river Krishna. The remaining fourty rivers are only minor ones, the combined discharge of all of them together is only about one-third of that of Godavari. western ghats from where the river originate is devoid of snow and therefore these river systems do not have the benefit of water supplied during the summer seasons as in the north Indian rivers.The water potential of riverbasins in kerala is in the table

Groundwater has been the mainstay for meeting the domestic needs of more than 80% of rural and 50% of urban population besides, fulfilling the irrigation needs of around 50% of irrigated agriculture. The ease and simplicity of its extraction has played an important role un its development. Recent the problems of decline in water table, contamination of groundwater, seawater intrusion etc. are being reported at many places.

Hydrogeology

Kerala State is a narrow stretch of land covering 38863 sq.km area bordering the Lakshadweep Sea on the western side and Tamil Nadu Karnataka Station the eastern side. The length of the State from north to south is 560km and the average width is 70km with a maximum of 125km. it lies between North latitudes 08 0 18' and 12 0 48' and east longitudes 74 0 52' and 77 0 22'.

Occurrence of Groundwater

Ground water occurs under phreatic, semi-confined and confined conditions in the above formations. The weathers crystallines, laterites and the alluvial formations from the major phreatic aquifers, whereas the deep fractures in the crystallines and the granular zones in the Tertiary sedimentary formations form the semi-confined and confined aquifers.

Along the hill ranges, the crystalline rocks are covered by thin weathered zone. Thick zones of weathered crystallines are seen along midland region. The depth to water level in the weathered crystallines in the midland area ranges from 3 to 16mbgl. The midland area sustains medium capacity dug wells for irrigation. Mostly dug wells that can cater to domestic needs are feasible along topographic lows. Bore wells tapping deeper fractured aquifer are feasible along potential fractures in the midland and hill ranges. Potential fractures are seen down to 240m and the most productive zone is between 60 and 175m and the discharge of bore wells range between 36,000 and 1,25,000 lph.

Of the four Tertiary beds, the two beds viz. the Vaikom and Warkali beds are potential aquifers. The Alleppey beds at the bottom contains bhrackish water as inferred from electrical logs, whereas, the Quilon beds are poor aquifers. The Vaikom aquifer is seen all along the coast between Quilon and Ponnani and the piezometric surface ranges from 1 to 18 m above msl. The aquifer is extensively developed between Quilon and Kayamkulam. The aquifer contains fresh water south of Karuvatta in Alleppey district and also north of chellanum in Ernakumal district. The Warkalai aquifer is seen south of Cochin . The piezometric head in the aquifer varies from 2.6m above msl to 10m above msl. The aquifer is largely developed in and around Alleppey and in Kuttanad area.

Laterites are the most widely distributed lithological unit in the State and the thickness of this formation varies from a few meters to about 30m. The depth to water level in the formation ranges from less than a meter to 25 mbgl. Laterite forms potential aquifers along valleys and can sustain medium duty irrigation wells with the yields in the range of 0.5-6m3 per day.

The alluvium forms potential aquifer along the coastal plains and ground water occurs under phreatic and semi-confined conditions in this aquifer. The thickness of this formation varies from few meters to above 100m and the depth to water level ranges from less than a meter to 6m bgl. Filter point wells are feasible wherever the saturated thickness exceeds 5m.

Depth to water levels

The depth to water level was monitored from 866 NHS distributed throughout the State during the months of January, April, August, November, 2001. The water level measured during the month of April is considered to be pre-monsoon water level and the data of November months are considered to be post monsoon water level.\

The depth to water level mostly depends upon the hydro geological conditions of the area as well as topography, rainfall pattern, etc. In coastal plains the depth to water level is generally restricted to 6 m bgl. In midland areas, where the undulating topography is seen, the depth to water level generally varies from near ground level to 15m bgl. The variation is mostly due to topographical variations, thickness of lateritic overburden etc. In select areas where laterites are underlain by sedimentary aquifers of Tertiary age, the water level goes very deep, even to the extent of 55.0m.bgl.

Ground water potential of Kerala

The ground water potential of Kerala is very low as compared to that of many other states in the country. The estimated ground water balance is 5590Mm³. Dug wells are the major ground water extraction structure in Kerala. The dug wells have a maximum depth of about 10 to 15 meters and have a diameter of about 1 to 2 meters in coastal region and 2 to 6 meters in the midland and high land. The open well density in Kerala is perhaps the highest in the country – 200 wells per sq.km in the coastal region, 150 wells per sq.km in the midland and 70 wells per sq.km in the high land. The ground water withdrawal is estimated as 980Mm³ and the State Ground Water Department calculate the effective recharge as 8134 sq Mm³.The ground water level receding drastically during the summer months and drying up of wells are common features of the ground water levels in many parts of Kerala. The ground water replenishment and hence the levels depends also on the geo-morphological, physical and chemical properties of the soil in general, The depth of water level in Kerala state varies from few cm bgl to 56 M bgl and most of the area fall under 0-20 M bgl. The depth of the water level in the weathered crystalline of midland areas in Kerala varies from 3- 16 M bgl. The midland area sustains medium capacity dugwells. Borewells tapping deeper fractured aquifer are feasible along potential features in the midland and hill ranges. Potential fractures are seen down to 240 M and the most productive zone is between 60 M and 175 M. The discharge of borewells range between 3,600 Iph and 1,25,000 Iph. In laterites, which is the most widely distributed lithological area in the state having a thickness from a 3 M to 30 M, the depth of water level ranges from less than a meter to 25 M.bgl. Lateries from potential aquifer along valleys and can sustain wells with yields in the range of 0.5 M³ to 6 M³ per day. Along the coastal plains the ground water occurs at depth ranging from less than a meter to 6 M.bgl. Filter point wells are feasible wherever the saturated availability indicate that ground water depths are farthest for laterite regions and shallowest for coastal alluvium during all times of the year. The availability of the groundwater level between the post and ore monsoon levels varies widely. The water level fluctuations in the post monsoon and ore monsoon vary between coastal alluvium, river alluvium and valley hills.

The National Water Policy of the Government of India states that the non conventional method for utilization of water such as through artificial recharge to ground water and traditional water conservation practices like rainwater harvesting need to be practiced to increase the utilizable water resources. The rainwater harvesting can be effected by in-situ-Harvesting and artificial recharge to ground water is the process of diverting the surface water into suitable geological formation. The common structures are percolation tanks, khadins, check dam/Anicut, sub-surface dams and injection wells. The ground water storage is the best method for water harvesting as it not only involves filtration of surface but is also safe from evaporation losses, natural catastrophes etc.

Central Ground Water Board has implemented various artificial recharge schemes in Kerala like surface dykes, percolation tanks, and of top rainwater harvesting. Four sub-suface dams were constructed at Palghat district (Anaganadi, Bhabaji Nagar, Alanallur and Ottappalam), one at Ernakulam(Odakali), one at Kottayam(Neezhir) one at Quilon (Sandanadapuram) and two at Trivandrum district(Mampazhakara and Ayiolam). Central Ground Water Board has constructed two percolation tanks, one at Chirakulam of Kottayam district and another one at Kadapallam of Kasaragod district. Roof top rainwater harvesting schemes were implemented at two places viz. Ezhimala and Mayyilcolony of Kannur district. The artificial recharge structures have given satisfactory results and the groundwater condition in the area has improved considerably.

Rainwater harvesting is the viable solution in the monsoon rich state of Kerala. The common structures feasible for Kerala are sub-surface dykes, nala bunds, check dams. The traditional water conservation structures like natural ponds, reservoirs should be desilted and cleaned. Participatory watershed development programmes should be implemented in the State. Mass awareness programme on ground water conservation should be arranged at Panchayat level in all districts.

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Apart from rivers and wells sources like tanks, ponds, springs and surangams are also use in Kerala for providing water for drinking as well as irrigation. It is estimated that Kerala has approximately 995tanks and ponds having more than 15000 Mm³ summer storage. Natural springs occurring in the highland regions of Kerala state have the potential to be developed as good sources for drinking water supply and also for limited small scale irrigation, especially in remote and under developed areas. A total of 236 springs have been identified in the state. Kasaragode district in Northern Kerala has 510 special kind of water harvesting structure called Surangams which have >111pm discharge.

Ramsar cites in Kerala