Lunch Seminar "Teaching and Research in Integrated Watershed Management for the Ethiopian Highlands"

Understanding the basic hydrology and erosion in the Ethiopian highlands is vital for effective management and utilization of water resources and soil conservation planning. An important question for judging effectiveness of soil and water conservation practices is whether runoff and erosion is affected by land use or topography. To examine this, studies were conducted by  students from the Cornell Master’s program in Integrated Watershed Management at Bahir Dar University in several small watersheds ranging from 100-400 ha in the highlands. Several of these watersheds had long-term records of rainfall and discharge. Water tables were monitored and infiltration rates were compared with rainfall intensities. The results show that the amount of runoff was greater for cropland located on mild to intermediate slopes than for grass and wood lands on the steeper slopes. Water tables were closer to the surface on cropland for the mild to intermediate slopes than on grass and in woods for the steeper slopes.  Infiltration rates that were generally in excess of the rainfall rates imply that when surface runoff was generated it can only occur  when the root zone was saturated. The piezometer readings indicated that saturation occurred at the foot of the steep slopes indicating that gravitational processes are dominant for in most of the landscape with the exception of severely degraded soils. 

Erosion was directly linked to the runoff processes with much greater erosion rates from the bottom of the slope than from the upper parts. This was especially true when large gullies formed in the saturated bottom lands where the soil had very little strength and water pressures were  great when the water table was above the gully bottom.  Although more research is needed on what conservation practices are effective in reducing soil loss when saturation excess dominates the runoff processes, field based research is essential for meaningful teaching of integrated watershed management to students from developing countries.