Abstract
The productiveness of an aquifer is determined by its aquifer parameters such as specific yield and permeability. Due to the complicated features of the large diameter wells and inadequate resources to conduct pumping tests in observation bore holes, estimating aquifer parameters for better use and management of groundwater resources is extremely difficult. The conventional pumping test; distance drawdown method was not possible in the Chunnagam limestone aquifers to determine the above said parameters because there was no drawdown in observation boreholes even at 3 m distance. Hence, alternatively the single well test was performed in specific places; Thirunelvely and Kondavil. The water level measurements were made by a dip water meter with respect to time during the pumping and recovery phase. A semi-log plot of field drawdown data versus time is made to evaluate the transmissivity of the aquifer. The relationship between residual drawdown and time was used to find the specific yield. The radial flow numerical model previously used to estimate aquifer parameters using large diameter wells in the dry zone of Sri Lanka was used to compare the results obtained by the single well test in the study area. The hydraulic conductivity and specific yield estimated by the single well test agrees with the values obtained by the radial flow numerical model when the model results were matched with the field results. Therefore the single well test in the large diameter wells is reliable and cost effective to estimate aquifers parameters in limestone aquifers when observation bore hole data is not available. The transmissivity value of the Thirunelvely area was higher (274.88 m2/day) when compared with Kondavil (126.5 m2/day) and the specific yield was 0.221 and 0.201 respectively in the Thirunelvely and Kondavil areas. DOI: http://dx.doi.org/10.4038/ouslj.v6i0.4115 OUSL Journal (2010) Vol. 6, (pp. 75- 90)
Highlights
Large diameter dug wells are the main source of water supply in many areas of the world for domestic and agricultural purposes (Herbert and Kitching, 1981 & Ruston and Holt, 1981)
Groundwater from dug wells has been the source of drinking water for a vast majority of the population of Sri Lanka for thousands of years
The occurrence of groundwater and its potential mainly depend on the characteristics and distribution of varying litho – stratigraphical units of subsurface geological formations. This is controlled to a great extent by the temporal distribution of rainfall in Sri Lanka which is distinctively bimodal in pattern
Summary
Large diameter dug wells are the main source of water supply in many areas of the world for domestic and agricultural purposes (Herbert and Kitching, 1981 & Ruston and Holt, 1981). Groundwater from dug wells has been the source of drinking water for a vast majority of the population of Sri Lanka for thousands of years (De Silva and Weatherhead, 1994). The occurrence of groundwater and its potential mainly depend on the characteristics and distribution of varying litho – stratigraphical units of subsurface geological formations. This is controlled to a great extent by the temporal distribution of rainfall in Sri Lanka which is distinctively bimodal in pattern. The Jaffna Peninsula is underlain by highly fractured and karstified lime stone of the miocene age (Arumugam, 1968)
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