Estimation of Aquifer Parameters of Limestone Aquifers – A Case Study in Thirunelvely and Kondavil of the Jaffna District

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)