Abstract:
The groundwater depletion is an emerging problem worldwide due to changes in
climate and an increase in urbanization. Two major water-bearing formations Nari of
Oligocene and Gaj of Miocene age were used as study area which was exposed near Karachi,
Pakistan. These formations consist of limestone and sandstone with intercalation of thick
layers of mudstone.
This research work is divided into two parts the first part composed of groundwater
budgeting by using a classical equation. The inflow of groundwater in the formations was
calculated by thermo-pluviometric data of the study area and water loss of Hub Dam. The
potential of evapotranspiration (P.E.T) was calculated by the Thornthwaite method, matrix
effect by the coefficient of infiltration potential (C.I.P) and runoff by the coefficient of
infiltration potential weighted with the slope (C.I.P.S). The precipitation on the exposure of
the formations was estimated by the ArcGIS integration method. The groundwater inflow
from Hub Dam was estimated by using twenty years of annual water loss data by removing
P.E.T. The total mean annual inflow of groundwater in the formations was 2414.12 US
Gallons per Second (G.P.S). The annual mean outflow was estimated by calculation of
groundwater usage of industries and domestic purposes and the mean annual groundwater
outflow was 5562.61 US G.P.S. and an annual deficit of groundwater was 3148.5 US G.P.S,
which make it a total discharge of 56%. The second part of the thesis composed of validating
the groundwater budget by developing groundwater maps, a graph of the past twenty year’s
water table and their comparison with the Standard Precipitation Index (S.P.I). For making
groundwater maps Direct Current Electrical Resistivity (D.C.E.R) and static water level data
from existing industrial wells were used, followed by ArcGIS integration. The D.C.E.R data
indicates A-Type and K-Type sub-surface with high resistivity in the three-layer model of
IPI2win, which shows the dry sub-surface of existing ground level to 200 m with hard rocks.
The average water table of residential areas in 2019 was 60 m and in industrial areas was 130
m. The oscillation of the groundwater table of the last twenty years and the deficit of
groundwater budget show an alarming condition for the future. If the same scenario persists,
then by 2025, the water table will decline up to 140 m.
