Estimation of Aquifer Characteristics using Resistivity ...

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Sep 14, 2016 - Majid Khan, Asam Farid, Paul Quinn, Zulfiqar Ahmad. [email protected]. Department of Earth Sciences Quaid-i-AzamUniversity, 45320, ...
9/14/2016

Estimation of Aquifer Characteristics using Resistivity Data and Implications for Groundwater Flow in Kohat Plain, Pakistan Majid Khan, Asam Farid, Paul Quinn, Zulfiqar Ahmad [email protected] Department of Earth Sciences Quaid-i-Azam University, 45320, Islamabad, Pakistan Colorado School of Mines, Department of Geology and Geological Engineering, Denver, Colorado, United States The Petroleum Institute, ADNOC, Abu Dhabi.

Introduction Kohat Plain is a large drainage basin occupying more than 2500 Km. One of the active zone for exploration of hydrocarbons. Geology of late Quaternary alluvial sediments has been evaluated by using geoelectrical and hydrological methods, which have its implications for the ground water flow system in the Kohat Plain. Hydrogeology of Kohat Plain is important for the characterization of aquifer system and developing numerical groundwater flow models to predict the future availability of the water resources. To serve this purpose 160 Vertical Electrical Soundings data has been reprocessed and interpreted in addition to geophysical logs and pumping test data. Conventionally, the aquifer parameters are obtained by the analysis of pumping test data which provide limited spatial information and turn out to be costly and time consuming. Lithologs from the boreholes describe that the lithology of the subsurface is highly heterogeneous and consists of mixtures of gravel, sand, boulders and clay, drilling many boreholes may turn out to be impractical in terms of cost and time. The most common method used for estimating the hydraulic properties of the aquifer are the pump tests, however hydraulic properties of aquifers are computed numerically from Dar Zarrouk parameters which is applied to a basin wide area with values greater than 10,000 Ω-m2 showing coarse grained sediments having fresh water. An attempt has been made to estimate hydraulic conductivity of the aquifer system by establishing a relationship between pump test results and vertical electrical soundings by using regression technique. Resistivity contour maps at different depth interval and resistivity profiles indicate that sedimentation pattern of alluvial deposits of the Kohat Plain is extremely erratic and heterogeneous. At resistivities lower than 40 ohm-m clay with boulders or sandstone thickness is bound to be too slight. The values of resistivity 30 to 40 ohm-m may however yet be of importance in areas with great layer thickness. The analysis of numerical models shows good agreement between simulated and observed heads. The values of hydraulic heads from simulations show that water levels are continuously dropping due to large removal of groundwater in the vicinity of Kohat Plain, Pakistan.

Base Map of the Study Area

Resistivity Models and Historic Groundwater Status

Resistivity Distribution at various Depths and DZ Parameters

Iso-Resistivity Map of Kohat Plain at 20 meters depth (Geosoft, 2012)

Hydraulic Characteristics and 3D Numerical GW Flow Model

Transmissivity Contour Map of Kohat Plain (Geosoft, 2012)

Modeled Resistivity Curves and Correlation with Borehole WA-10 (IP2Win)

Geological Set up

Location Map and Accessibility

XXXXXXXX Iso-Resistivity Map of Kohat Plain at 100 meters depth (Geosoft, 2012)

Location Map and access to Kohat Plain along with 3D DEM. Data Source: Geosoft 2012.

Lithological Correlation of few boreholes within Alluvium Cover

Regional Groundwater fluctuations (Pre-Modeling period) (WAPDA. 1984)

Transverse Resistance Contour Map of Kohat Plain (Geosoft, 2012)

Hydraulic Conductivity Contour Map of Kohat Plain (Geosoft, 2012)

Numerical Groundwater Flow Model of Kohat Plain (Visual MODFLOW, 2011.1.1)

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