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Journal
of Environmental Hydrology ISSN 1058-3912 |
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Electronic
Journal of the International Association for Environmental Hydrology
JEH Volume 12 (2004), Paper 10 Posted June 23, 2004 CHANNEL EROSION IN THE OPA BASIN, SOUTHWESTERN NIGERIA A. Adediji L.K.Jeje Department of Geography, Obafemi Awolowo University, Ile-Ife, Nigeria ABSTRACT This study examines the relationship between topographic attributes and channel sediment yield in nineteen 1st order, five 2nd order, one 3rd order and one 4th order river basin under different land use/vegetation surfaces in the Opa basin, southwestern Nigeria. The study basins were monitored for one year with emphasis on channel specific sediment yield. The results showed that the mean channel sediment yield obtained from 1st order basins in builtup areas, cultivated field crops, cocoa dominated (perennial crops) and degraded forests were 23.09, 10.94, 8.78, and 7.10 t/km2/yr, respectively. The mean channel sediment yield obtained for 2nd order, 3rd order, 4th order and 5th order channels, were 17.11 t/yr (17.69 t/km2/yr), 22.30 t/yr (14.86 t/km2/yr), 481.94 t/yr (18.19 t/km2/yr) and 1727.41 t/yr (25.40 t/km2/yr), respectively. Channel specific sediment yield (SSY) was negatively correlated with basin area (A) and stream length (L) with r-values of –0.601 and –0.606 at a = 0.05. However, relative relief (H-h) and relief ratio (Rh) correlated positively with the channel specific sediment yield. Also, all the land use/vegetation attributes except percent built-up area were negatively related to the rate of sediment yield. In fact, the percent built-up area was positively correlated with SSY (r = 0.659 at a =0.05). The result of the stepwise regression analysis showed that only basin area was included in the equation obtained for the study basins. It accounted for about 40.9 percent of the total variance in the channel specific sediment yield of the streams. The equation obtained for channel specific sediment yield could be used for predicting the rate of channel erosion in an area under similar geology, climate, land use, and vegetation. Reference: Adediji, A. and L.K.Jeje; Channel Erosion in the Opa Basin, Southwestern Nigeria, Journal of Environmental Hydrology, Vol. 12, Paper 10, June 2004. CONTACT: A. Adediji Department of Geography Obafemi Awolowo University Ile-Ife, Nigeria E-mail:remiadediji2003@yahoo.co.uk |
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