Runoff characteristics of bare micro catchments in a semi arid area, Kenya

The main objective of the study was to investigate the runoff characteristics of bare micro catchments using the Natural Resources Conservation Service Curve Number (NRCS CN) method. The study was carried out on three rectangular and two triangular bare runoff plots of area 10 m2 constructed on a natural slope of 5% and a typical loamy sand soil. It involved measurement of rainfall and surface run off on storm basis. The curve numbers in the NRCS CN method were first obtained through calibration using observed rainfall and surface runoff data. The calibrated curve numbers were found to be between 97.16 and 99.37 with mean of 98.54. Based on the mean curve number and the soil hydrologic group B, it was found that the bare micro-catchments could be treated as paved surfaces. The treatment of bare runoff plots as paved surfaces was later validated using a different set of rainfall and runoff data. A comparison between computed and observed surface runoff from the runoff plots revealed a close fit (R2 = 0.971). Based on the results, it was concluded that the NRCS CN method could be used to compute surface runoff from bare micro catchments if treated as pave surfaces.