Occurrence of Ground Water                            [Back] [Home]

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

       The Crystalline aquifers :-  The shallow aquifers of the crystalline rocks are made up of the highly decomposed weathered zone or partly weathered and fractured rock.  Thick weathered zone is seen along the midland area either beneath the laterites or exposed.  In the hill ranges, thin weathered zone is seen along topographic lows, area with lesser elevation and gentle slope.  In areas along the hill ranges generally rock exposures are seen.  The depth to water level in this aquifer varies from 2 to 16 mbgl and the yield of the well ranges between 2 to 10 m³ per day.
       The exploratory drilling carried out by Central Ground Water Board in the State in the crystalline formations has indicated that the potential fractures are encountered at depths ranging between 60 to 175 m. bgl.  with yield varying from less than 1 to as much as 35 litres per second (lps).   In Charnockites, more than 40% of the wells have yielded more than 10 lps or above.

       The Tertiary aquifers :-  Ground water occurs under phreatic condition in the shallow zone and under semi-confined to confined conditions in the deeper aquifers. The Tertiary formation of Kerala coast is divided into four distinct beds viz. Alleppey, Vaikom, Quilon and Warkali.  These formations except the Alleppey beds are seen as outcrops and  are lateritised wherever they are exposed.  The maximum thickness of Tertiary sediments is found between Karunagapally and Kattoor and all the four beds are encountered in this area.           
       Ground water is commonly developed through dug wells tapping the sandy zones at shallow depth in the Tertiary sediments.  The depth to water level in this shallow zone ranges from 3.0 to 27 m. bgl and the yield of the well ranges from 500 lpd to 10 m³ per day.
       The Vaikom and Warkali beds form the most potential aquifers in the Tertiary group.  The Alleppey beds have been encountered at deeper levels in the bore holes drilled in the coastal tract of Alleppey district and the formation water is found to be saline and hence, no tube well has been constructed by tapping this formation.           
       In the Vaikom aquifers, the piezometeric level is between 2 m and 20 m above msl. The yield of the tube wells constructed in this formations ranges from 1 to 57 lps.  This bed forms 'auto flow' zones along the coast between Karunagapally in Quilon district and Nattika in Trichur district.  Recent exploration by CGWB has proved good quality ground water zone in this formation in and around Cochin area.
       Warkali aquifers are the most developed aquifer system among the Tertiary group.  The urban and rural water supply in the coastal area between Quilon and Shertalai is mostly dependent on this.  The piezometric head is about 3 m. above msl along the eastern part of the sedimentary basin whereas it is 10 m. below msl in and around Alleppey.  The yield of the wells tapping this formation ranges from 3 to 14 lps.           
       The hydrogeological information on the Quilon beds is very limited.  The formation is considered to be a poor aquifer compared to Vaikom and Warkali beds.

       Laterites :-     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 - 6 m³ per day.  The occurrence and movement of ground water in the laterites are mainly controlled by the topography.  Laterite is a highly porous rock formation, which can form potential aquifers along topographic lows.  However, due to this same porous nature, groundwater is drained from elevated places and slopes at shortest duration after monsoon due to which scarcity is experienced in the elevated places and slopes.  This is the most extensive hydrogeologic unit in the State.  The thickness varies generally from less than a meter to above 20 m.and thicker zones are seen along Malappuram and other northern districts. 

       Alluvium :- 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 100 m. and the depth to water level ranges from less than a meter to 6 m. bgl.  Filter point wells are feasible wherever the saturated thickness exceeds 5 m.       This potential aquifer is extensively developed by dug wells and filter point wells throughout the state and the yield ranges from 5 to 35 m³ per day.