EFFECT OF DIFFERENT LAND USE ON INFILTRATION RATES WITHIN MINNA METROPOLITAN AREA OF SOUTHERN GUINEA SAVANNAH ZONE, NIGERIA

Abstract

This project studied the effect of urban forest types, vegetation configuration and soil properties on soil infiltration. In the study, 6 locations were considered; Undeveloped land, Farm land, Grazing land, Gardened land, Paved compound and Paved road side with 5 samples from each location in Minna City, Niger State to investigate the soil infiltration characteristics of urban soil and its influencing factors. The results showed that the steady infiltration rates of urban soil were highly variable. High variations in the final infiltration rates were observed for different vegetation patterns and compaction degrees (22.02, 17.06, 13.45). Land with shrubs and grasses had the highest infiltration rate and places with bare land had the lowest infiltration rate (7.14). In addition, the results showed that the soil infiltration rate decreased with an increase in the bulk density and with a reduction in the soil organic matter content and non-capillary porosity. The soil infiltration rate also had significantly positive relationships with the total porosity and saturated soil water content. Urban soil compaction contributed to low soil infiltration rates. Considering the effect of the land use practices on soil properties, the soils differ considerably between the six locations; that is, the undeveloped land, Farm land, Garden, Grazing land, paved compound and paved road side. The soil at the undeveloped site is a deep, well-drained soil which consist of 56% sand, 25% clay and 31% silt which makes it predominantly sandy-loam. The soil at the farm land is dominated with loamy soil with relatively high degree of homogeneity both vertically across depths and horizontally from one sample locus to the next. The soil texture at grazing land from five different samples collected showed sandy clay, silty loam, clay loam, silty loam and sandy loam, while, Paved compound and paved road side had sandy clay composition which had a high surface runoff and low infiltration (7.78, 7.45, 7.29).These results also demonstrated that the effect of soil texture on infiltration rate was probably masked by the land use practices and soil management, which agrees with the fact that water infiltration into the soil is highly sensitive to land use and soil management. Three infiltration models were applied (Horton, Kostiakov and Philip) and their performances were evaluated based on Root Mean Square Error (RMSE) and coefficient of determination (R2 ). The Philip model with the least RMSE values of 0.79 cmh-1 and R2 of 0.97 most closely predicted the measured infiltration. Kostiakov and Horton models provided less accurate estimates of the measured infiltration with least RMSE values of 4.63 and 5.13 and R2 of 0.92 and 0.91, respectively. To increase the infiltration rate and water storage volume of urban soil, proper techniques to minimize and mitigate soil compaction should be used. These findings can provide useful information for urban planners about how to maximize the water volume of urban soil and decrease urban instantaneous flooding.