Field Steady State Infiltration Rates of Soils in Kumba - Cameroon: Validation of Some Empirical Predictive Infiltration Models and GIS Applications

Kumba capital of Meme Division, one of the largest cocoa cash crop producing areas in Cameroon, is a typically agrarian town that needs a good understanding of the soil properties of the area. The evaluation of steady state infiltration rates of soils is important in agriculture, groundwater resources preservation and civil engineering to; increase the availability of data, determine regions of aquifer recharge and discharge, infer soil types, evaluate soil suitability for agriculture and provide another tool for generating water resources management parameters in the area. The double ring infiltrometer method was used to measure field infiltration rates from which steady state infiltration rates were determined. The steady state infiltration rates were compared to those determined using empirical predictive models to rate these models’ performance in Kumba. There is significant spatial variation in the steady state infiltration rates (vertical saturated hydraulic conductivities) in the vadose zone of the phreatic aquiferous formations in Kumba. The steady state infiltration rate values range from 0.01-0.96 m/d. Inferred soil types are 7.7% sandy soils, 26.9% sandy silty soils, 19.2% loam and 42.3% clays and 3.8% sodic clayey soils. Infiltration rate classes determined are; very slow to slow (46.1%), slow to moderately slow (19.2%), moderately-slow-to-moderatelyrapid (19.2%), moderately rapid to rapid (7.7%) and very rapid (7.7%). Soil’s suitability for surface irrigation is 38.5% optimum, 7.7% suitable, 34.6% marginally suitable and 7.7% unsuitable. 7.7% of soils are suitable and 34.6 % marginally suitable for rice cultivation. Recharge zones are located towards the south and southwestern parts of Kumba. Comparing measured and predictive model-estimated infiltration rates, the Kostiakov model gives the best prediction for the final infiltration rate in Kumba.