Soil Resistance to Overland Flow at Ibiekuma Watershed in South Central Nigeria

摘要

Understanding and proper modeling of overland flow hydraulic parameters is essential in the development of process-based erosion models and evaluation of surface runoff under field situations. In this study, field measurement of significant overland flow parameters was conducted on a 3×7 m twin-runoff plots within Ibiekuma watershed in south-central Nigeria. Parameterization of the resistance model involved: a detailed topographic survey of the plots using a 1×1 m cell grid and evaluation of the median particle size; small plot experiments to determine parameters of the Green and Ampt infiltration model and small plot experiments to determine parameter estimate for the dynamic friction factor. With the friction factor varying between 0.0006 and 0.0016 depending on the median particle size, the soil resistance to surface flow at Ibiekuma catchment is considerably low. The rate of runoff produced after the ensuing infiltration and attainment of rainfall-infiltration excess is high with an attendant high level of erodibility of the superficial soil. A neurosolution in a spread sheet environment of the data collected established the relationship between the friction factor and median particle size of the soil in the area as f = 3E 06 Gm2 0.0002 Gm + 0.0039 where, f and Gm are the friction factor and the median particle size, respectively.