HR: 0800h
AN: H21A-1318    [Abstracts]
TI: Hydrologic and Erosional Response to Natural Rainfall and Effects of Conservation and Rehabilitation Measures in a Degraded Dry Sub-Humid Watershed of the Ethiopian Highlands
AU: * McHugh, O V
EM: ovm2@cornell.edu
AF: Department of Biological and Environmental Engineering, Cornell University, 76 Riley Robb Hall, Ithaca, NY 14853 United States
AU: Liu, B M
EM: bml33@cornell.edu
AF: Department of Biological and Environmental Engineering, Cornell University, 76 Riley Robb Hall, Ithaca, NY 14853 United States
AU: Steenhuis, T S
EM: tss1@cornell.edu
AF: Department of Biological and Environmental Engineering, Cornell University, 76 Riley Robb Hall, Ithaca, NY 14853 United States
AB: A good understanding of runoff and erosion under actual field conditions is essential for effective planning of land conservation in the Ethiopian highlands. Hydrologic and sediment yield response to natural rainfall was measured during 3 rainy seasons (2003-2004) at plot and catchment scales with and without conservation practices. Results show that as expected surface runoff generation and erosion rates are significantly influenced by rainfall intensity, land use, scale of measurement, land slope, and the presence or not of conservation measures. Seasonal runoff coefficient and sediment yield were significantly better correlated to number of storms with high 30-minute maximum rainfall intensity (I₃₀ > 20 mm h^-1) than to total seasonal rainfall depth. Under conventional management systems cropland on slopes greater than 3 % generated significantly more (over twice) surface runoff and sediment yield compared with shrub and open forest grazing land on steep slopes (34 %). Plot measured surface runoff coefficients (for crop and grazing land uses which cover over 90 % of the catchment area) exceeded total catchment streamflow discharge demonstrating a scale effect. The observed scale effect, a stronger correlation of runoff with maximum rainfall intensity than rainfall depth and average rainfall intensity, and observed significant increases in runoff with steeper land slopes indicate that Hortonian overland flow is the primary runoff generation mechanism in the study zone. Concerning slope effects, cropland on mild slopes produced relatively low seasonal sediment yields (< 2 t ha^-1) regardless of seasonal rainfall intensity and land preparation practice. However, sediment yield was drastically high (up to 35 t ha^-1) on steep slopes (9 -11 %) especially during seasons with several high intensity rainfall events. The community protected open forest grazing area soil loss was low at sustainable levels (< 2.2 t ha^-1 season^-1) during all seasons while the shrub grazing land exceeded sustainable soil loss rates (7.4 t ha^-1 season^-1) during a season with high intensity rainfall. Gully rehabilitation (installation of sandbag and gabion checkdams, planting of various types of vegetation, and protection from livestock grazing) and hillside conservation (areas with bench terracing, planted tree seedlings, and small area closure from livestock grazing) resulted in significantly lower catchment peak streamflow discharge and longer duration streamflow compared to a catchment in the same watershed without these measures. Cropland tied ridge and no till conservation practices reduced surface runoff and soil loss during seasons with moderate rainfall intensities, but tied ridges performed similarly or worse than conventional tillage during seasons with many high intensity storms and on steep slopes (> 9 %). Subsoiling performed statistically similar to tillage with the conventional maresha plow, but considerably increased soil loss rates on moderate and steep slopes (3-11 %).
DE: 1815 Erosion
DE: 1850 Overland flow
DE: 1879 Watershed
DE: 6329 Project evaluation
DE: 9305 Africa
SC: Hydrology [H]
MN: Fall Meeting 2005