Abstract:
An understandmg of flow mechanism near an abstraction well is important for
successful exploitation of groundwater resources. Properly planned and carefully conducted
pumping tests provide basic information for the solution of many groundwater flow problems.
Pumping test data are normally analysed using conventional curve-matching techniques.
Although little information about the aquifer behaviour can be gained from this analysis, yet
a far greater understanding can be achieved using numerical models.
The two zone numerical model described by Rathod and Rushton (199'1) has been
further developed and applied to interpret three pumping tests conducted in an alluvial aquifer
in central Bangladesh. The model could reproduce the significant features of the aquifer
behaviour and the overall agreement between the observed drawdowns and model results was
very good. The important features of the flow mechanisms include: vertical components of
flow in the vicinity of the well, leakage from overlying layer with fall of water table, well
storage and well losses. The values of transmissivity and storage coefficient, as derived from
numerical analysis, for the three test sites ranged from 940 to 1510 m2/day and 0.0006 to
0.001 respectively. Thk vertical hydraulic conductivity of the overlying layer was found to . . .
vary from 0.005 to 0.007 m/day.
The model has also been used to predict the response of the aquifer to pumping over
a typical growing season. The results show significant drawdowns both at the pumped well
and at outer boundary. Unless sufficient recharge takes place during the monsoon, the
groundwater head will fall year by year. Since these predictions were made based on a model
which had been verified only for a short period the results should be treated as an indication
of the likely trend. Nevertheless, such information are quite useful for successful
development of groundwater resources in the study area.
