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Understanding of runoff sources and sinks coupled with development of rubost models
that provide rapid and less expensive assessment of the impacts of land management on
surface runoff is critical in the management of soil and water resources. In this study, a
stratified sampling procedure was used to set up 51 runoff plots on representative land
use types on the three slope zones in the landscape. On each slope zone a completely
randomized design was utilized. Runoff measurements were done for 120 rainfall events
involving two rain seasons. Three rain gauges with one gauge on each slope zone were
used for rainfall measurements. Infiltration measurements were also conducted on all the
land use types using two single ring infiltrometers. Topsoil samples (20 em deep) were
collected from each runoff plot for laboratory soil spectral analysis.
One way analysis of variance was utilized to investigate the effects of land use types on
surface runoff in each slope zone. Calibration of soil spectral reflectance to mean
seasonal runoff was done using partial least squares (PLS) technique.
Results of the study showed that land use significantly (p=0.001) influenced runoff
generation in on all slope zones. There were differences in seasonal runoff generation
patterns in the lowlands due to the presence of saturated overland flow in the long rainy
season. Results show that runoff generation mechanisms significantly (p=0.001)
influenced surface runoff in the lowlands in the long rainy season.
There were no statistical differences at 5% level of significance among tillage treatments
in the uplands and midlands slope zones. However, runoff from conventionally tilled
areas showed the highest variation (Cv=109%).
There were good correlations (R2>0.70) between surface runoff and soil spectral
reflectance for both rain seasons. However, the model validation of the relationship for
short rains, 2001 had a coefficient of determination ofr2 = 0.54.
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