Hydraulics of slope erosion by overland ow A case study: Nnobi-Onitsha hillslope site, Anambra state S.E. Nigeria

The erosion problem at nnobi was investigated with a view to determine thetypes and major factors responsible for accelerated erosion in the area, in order to developa simple prediction model for the erosion rate. the severe erosion of ground surfaces,such as unpaved road shoulders and bare soil surfaces, in high density areas of southeastern nigeria is a common feature. for many years, hydrologist and engineers have beenfaced with the challenge of producing adequate drainage programs to check the menace oferosion by overland ow. six ume experiments were conducted where erosion rates weremeasured. the rainfall data for the past ten years were obtained and analyzed, a survey ofthe catchment area for each of the gully sites was carried out and soil samples were obtainedfrom the eroding layers of the gullies. analysis of the results show that the area experiencesrainfall of high intensity, with intensities of up to 80 mm/hr being recorded for a durationof 30 minutes. the slope of the land is generally steep, with slope gradient varying from15% to 22%, and soil particles with very low organic and clay content, ranging between0.2 to 0.4 to 1 and 6%, respectively. a mathematical model of hill slope overland ow forthe nnobi experimental watershed, obtained using the saburo [1] equation, to predict theerosion rate, is presented as:e = 0:0158dc:ace(fi)15=8:l3=8:s3=2: