Abstract

Groundwater is one of the earth's most widely distributed and most important resources. It is more widely and easily available than surface water, relatively unpolluted in most cases, and safe for human consumption. As groundwater development intensifies, well owners become more interested in the response of aquifers to heavy pumping, whereas initially they were concerned with the delineation and exploration of aquifers. Competition for available resources has brought about the concept of optimization of aquifer-potentials and their response to development, as inevitable tools for effective groundwater exploration and exploitation.

The calibrated Ameki and Nanka ground-water flow models were used to simulate the potential effect of water-management plans on hydraulic heads and ground-water movement in the Ameki and Nanka domains. The Ameki and Nanka formation were optimized by incorporating the MODFLOW Finite Difference Groundwater Flow Model into a Groundwater Management (GWM) linear optimization program. For this purpose, each of the problem domains/aquifers was sub-divided into cells based on the number of observation wells. The Ameki formation was treated as a five-cell model while the Nanka aquifer was divided into a seven-cell model. The total water demand, D, was projected using a population growth rate of 2.5%/year, firstly from the base year to year-2005, and then year-2030, for the aquifers within the study area, using the Nigerian 1991 population census figures as the from the Petroleum Trust Fund (PTF) sponsored feasibility studies report on Provision of Rural Water Supply for Anambra State, which were found to be in close agreement. The aquifers were assumed to be homogenous and replenished from precipitation at a rate of 2005 mm/yr. The average cost of pumping and conveyance of water to the consumers, in each case, was assumed to be 1.5MU/m³.

The permissible drawdown in Observation Wells 'A' to 'E' varied from 8.80m to 23.00m at a minimized optimal cost of pumping of 36.09 x 10⁶ MU/yr in the Ameki Groundwater Management Model, while for the Nanka Management Model, the permissible drawdown in Observation Wells 'A' to 'G' varied between 15.10m to 19.50m at a minimized cost of pumping of 22.40 x 10⁶MU/yr.

The Ameki and Nanka aquifer domains could support drafts of 24.06 Mm³/yr and 14.93 Mm³/yr respectively, without violating the lower limit constraints on water levels.

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