1 Continental J. Engineering Sciences 6 (3): 1 - 6, 2011 ISSN: 2141 – 4068 © Wilolud Journals, 2011 http://www.wiloludjournal.com ` Printed in Nigeria ESTIMATION OF GROUND WATER RECHARGE AT NCAM, ILORIN FOR IMPROVED IRRIGATION MANAGEMENT. Makanjuola, M. B., James David, T. A. Makar and I. E. Ahaneku Department of Land and Water Engineering Management, National Centre for Agricultural Mechanization (NCAM), Ilorin. ABSTRACT The recharge rate is a very important parameter required in the successful development of ground water resources, as often, it is this rate that can be safely abstracted as safe yield from wells and boreholes. Groundwater recharge was estimated for 2 wells located in areas representing the different land uses at NCAM using the water table fluctuation method. The yield from sites A and B were 0.02 – 0.2 m 3 /hr and 0.008 – 0.03 m 3 /hr respectively while the peak scheme water demand required for producing dry season vegetables for 0.5ha was obtained as 0.002 m 3 /s. Achieving better understanding of the mechanisms that control groundwater recharge is crucial towards improving groundwater management. KEYWORDS: groundwater recharge, over-extraction, yield, water demand INTRODUCTION Water is indispensable to all life on earth. Fresh water is constantly formed newly through a phenomenon known as hydrological cycle. Groundwater, on the other hand, is a replenishable resource widely distributed under the ground. It is free from pollution and can be developed with small capital cost in the least possible time (Raghunath, 1991). It allows the practice of intensive irrigation with possibilities of double or triple cropping, including commercial crops. In addition, supplemental irrigation during periods of deficient surface supply can be practiced thus making all year round farming possible. Rainfall is the principal source for replenishment of moisture in the soil water system and recharge of ground water. Groundwater recharge or deep drainage or deep percolation is a hydrologic process where water moves downwards from surface water to groundwater. It is also the process whereby water below the land surface is replenished by either direct infiltration of rainfall or by leakage from surface water bodies like streams and lakes. The amount of moisture that will eventually reach the water table depends on the rate and duration of rainfall, the subsequent conditions at the upper boundary, the antecedent soil moisture conditions, the water table depth and the soil type. A good aquifer is capable of transmitting water through its pores at a rate sufficient for economic extraction by wells. The recharge rate varies both spatially and temporally. Factors influencing groundwater recharge include characteristics of the recharge beds, such as topography, land use and vegetation cover, existing soil moisture and the ability of the recharge beds and aquifer materials to capture and transmit water (Bureau of Rural Science, 2007). Agricultural land uses as categorized by US, EPA (2008) include: Cropland; Irrigated cropland; Range and pasture; Orchards; Permanent hay land; Specialty crop production; and Nursery crop production. Zhang and Schilling (2006) observed that grass cover lowered the water table, reduced soil moisture through ET losses, and thus reduced groundwater recharge. The key factors controlling groundwater recharge are highlighted as: climatic, the amount and intensity of rainfall and evaporation; soil and aquifer hydraulic properties; type and amount of vegetation cover and types of land use; topography, in particular the slope of the land surface; the nature and geometry of aquifers in the catchment; residual (or antecedent) soil moisture stored in the soil profile from previous rainfall events. The recharge rate is a very important parameter required in the successful development of ground water resources, as often, it is this rate that can be safely abstracted as safe yield from wells and boreholes. Quantification of the rate of natural ground water recharge is a pre-requisite for efficient ground water resource management. It is particularly important in regions with large demands for ground water supplies, where such resources are the keys to economic development. Few studies deal explicitly with groundwater recharge in temperate and humid zones, because recharge is normally included in regional groundwater investigations as