Mapping groundwater suitability for irrigation using GIS: A Case study of Ilorin, Kwara State, Southwestern Nigeria

Agricultural water in the right quantity and desired quality is needed to drive agrarian revolution in Nigeria. Groundwater, among the forms of water in nature is strategic for Nigeria has it is easy to exploit, readily available not affected by seasonality and the largest natural storage of available freshwater on the planet. The study was aimed at evaluating and mapping irrigation water quality of groundwater system within Ilorin metropolis. Forty-four well samples were collected in triplicates over the dry and wet seasons with their locations georeferenced. The water samples were sent to the laboratory and the results were incorporated into a GIS database in the development of a water map. Six indices, Sodium Adsorption Ratio (SAR), Magnesium Adsorption Ratio (MAR), Permeability Index (PI), Residual Sodium Carbonate (RSC), Kelly's Ratio (KR) and Soluble Sodium Percentage (SSP), were used to evaluate suitability for irrigation. The geo-spatial representation is displayed using Surfer 9 and ARC Map software. The sampling points were concentrated in the southern portion of the study area, with dense settlements and expected anthropogenic activities. The western portion of the study area within the vicinity of Moro river basin reflected general good irrigation water quality and low settlement is prime for irrigated agriculture. The geospatial representations of irrigation water quality developed guides decision makers on the use of various ground water sources within the area. In the same light, it demonstrates high efficiency of GIS in elucidating complex geospatial data through the development of quality maps.