Simulation of Flow Regime of Dibdibba Dandy Aquifer inSafwan-Zubair Area, South of Iraq

Abstract

A two-dimensional model is constructed to simulate the flow regime of the
upper part of Dibdibba sandy aquifer in Safwan-Zubair area, south of Iraq. Although
the Dibdibba Formation is a multi-layer system in the surveyed area, the suggested
conceptual model which is advocated to simulate the flow regime of aquifer is fixed
for one layer, i.e., the activity of the deeper aquifer is negligible. The model is
calibrated using trial and error procedure in two stages: steady state followed by
transient state. The outcome of the calibration process demonstrated considerable
spatial variations in transmissivities and storativites of the aquifer system. A very
good similarity between the observed and simulated groundwater levels in the steady
state calibration is observed. A reasonable representation of the hydraulic gradient
over the mode area which consistent with relative magnitude of hydraulic
conductivies is obtained during this calibration stage. Transient calibration is
undertaken to calibrate the aquifer storage parameter after the steady state calibration
is achieved. The transient calibration results are evaluated by comparing water levels
at eight observation wells. Good matches are observed for all cases. The reliabilities
of calibrated parameters are checked through sensitivity analysis. Verification test is
also added to ensure that the calibrated model could be an adequate counterpart of
the actual groundwater system and to verify the reliability of the model results. The
model is verified against the measured heads during June 2000. The verified model
is utilized to predict behaviour of the aquifer over a planning horizon of 10 years
(2000-2010) under two developments scenarios. The management plans are
undertaken with continuity of existing trend of growth of pumping wells, i.e., 200
wells per year and without growth and still the situation is similar to that in year
2000. The first run indicates that the decline of groundwater heads of about one
meter in the central part of the area and of about 0.5 meter in the northern and
western parts is expected. The outcome of the second run demonstrates that no
significant changes from 2000 status have occured. The calibrated model can be
used, if necessary data is available, to establish the responses of the aquifer to
artificial recharge which is suggested to enhance the water availability and rebalance
the aquifer in other context.