Groundwater modeling of unconfined aquifer system of crystalline area - a case study in Lapsiya watershed (Hazaribagh)

This paper on the GIS Development site discusses the findings of a  modeling exercise that was attempted in Lapasiya watershed, Hazaribagh, India. This modeling was an attempt to replicate the behaviors of natural groundwater or hydrologic system by defining the essential features of the system in some controlled physical or mathematical manner. Modeling can play an extremely important role in the management of hydrologic and groundwater system.

The long term planning and management of groundwater needs understanding groundwater interaction with surface water, recharge, seepaze process, intake and rate of withdrawal in space and time and its long term effect on the aquifer system to achieve the sustainability. The entire exercise becomes complex process and it is outside preview of static modeling exercise such as DBTM approach. Several attempts have been made through computer modeling in alluvial plain of India, but less stress has been made for the modeling of the aquifer in hard rock area.

Objectives of  the modeling exercise included:

• To simulate the condition similar to aquifer behaviors with time. The water table or equi-potential surface remains near to the surface after the monsoon; water table starts falling down from Nov. onwards andreaches maximum depth in the month of May/ June. After onset of monsoon, water table comes up.
• To budget the groundwater resources
• To find out the suitable area for bore well development and optimization of pumping rate and duration. In study area, 20 deep bore wells have been identified through geo-hydrological and geophysical survey. However,  their sustainability cannot be determined on long term basis.
• To determine the sensitivity of the model in terms of the various input parameters i.e. recharge/ evapo-transpiration,hydraulic conductivity. So more stresses should be given in collection of field data.

The study concluded that the modeling exercise of unconfined aquifer system of hard rock area in Indian condition was possible and that the model could be simulated to near real field condition. The study found
that:

• Model accuracy was very much dependent aquifer geometry.
• Groundwater reserve estimation of the entire aquifer system could be determined from the modeling.
• The model could be further improved if more and more spatial data on input parameter i.e. hydraulic conductivity, recharge, base-flow in the river, were to collected and inputted into the model for better control.
• Modeling was a complex exercise and thus a lot of discussion with experts and consultation was required.

Groundwater modeling of unconfined aquifer system can thus provide solution for estimating the available groundwater resource, optimizing the pumping rate and identifying suitable locations/ area where there will less adverse effects on the aquifer system in long duration pumping. The pumping rate of pumps can be optimised in the upper reaches to check groundwater seepage in the drainage channel. The modeling exercise has given better understanding of the aquifer behavior with change in different input parameter.