Improving efficacy of landscape interventions in the (sub) humid Ethiopian highlands by improved understanding of runoff processes

Authors: TEBEBU, TIGIST - Cornell University; STEENHUIS, TAMMO - Cornell University; DAGNEW, DESSALEGN - Bahir Dar University; GUZMAN, CHRISTIAN - Cornell University; BAYABIL, HAIMANOTE - Cornell University; ZEGEYE, ASSEFA - Cornell University; Collick, Amy; LANGAN, SIMON - International Water Management Institute, East Africa And Nile Basin Office; MCALLISTER, CHARLOTTE - International Development Research Centre; Langendoen, Eddy; TILAHUN, SEIFU - Bahir Dar University

Submitted to: Frontiers in Earth Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/10/2015
Publication Date: 9/2/2015
Citation: Tebebu, T.Y., Steenhuis, T.S., Dagnew, D.C., Guzman, C.D., Bayabil, H.K., Zegeye, A.D., Collick, A.S., Langan, S., Mcallister, C., Langendoen, E.J., Tilahun, S.A. 2015. Improving efficacy of landscape interventions in the (sub) humid Ethiopian highlands by improved understanding of runoff processes. Frontiers in Earth Science. 3:49 doi: 10.3389/feart.2015.00049.

Interpretive Summary: Despite millions of dollars invested in soil and water conservation practices and other landscape interventions in the sub humid Ethiopian highlands, sediment concentration in Ethiopian rivers is increasing. Possible ways to reverse the current trend has been investigated by an interdisciplinary group of faculty and postgraduate students at Bahir Dar University in cooperation with scientists from International Irrigation Management Institute (Addis Ababa), Amhara Regional Agricultural Research Institute (Bahir Dar), Cornell University (Ithaca, NY) and the USDA, ARS, Watershed Physical Processes Research Unit. Research findings of the interdisciplinary group were based on research conducted in the Debra Mewi, Maybar, Anjeni and other watersheds in the Amhara region south of Lake Tana, Ethiopia. Based on the understanding of the hydrology of Ethiopian highlands, priority in landscape interventions should be given to re-vegetation of the degraded areas so as to reduce the sediment concentration originating from these source areas. Additionally, efforts should be directed to gully rehabilitation in the saturated bottom landscape. The rehabilitation may consist of vegetating shallow gullies and stabilizing head cuts of deeper gullies by decreasing the slope of the head cuts and then protecting the chutes. Finally, research should be carried out in increasing the infiltration of the upland soil. This will reduce the direct runoff during the rainy season and increase baseflow during the dry season by connecting the land surface to the original deep flow paths that still exists below about 60 cm.

Technical Abstract: Despite millions of dollars invested in soil and water conservation practices and other landscape interventions in the Ethiopian highlands and billions of hours of food-for-work farm labor, sediment concentration in rivers is increasing. Possible ways to reverse the current trend have been investigated by an interdisciplinary group of faculty and postgraduate students at Bahir Dar University in cooperation with scientists from the International Water Management Institute (Addis Ababa), Amhara Regional Agricultural Research Institute (Bahir Dar), Cornell University (Ithaca, NY) and the U.S. Department of Agriculture-Agricultural Research Service, Watershed Physical Processes Research Unit (Oxford, MS). This paper reports on the research findings of the interdisciplinary group conducted in the Debre Mewi, Maybar, Anjeni and other watersheds of the past six years. Based on the understanding of the hydrology of Ethiopian (sub) humid highlands, we provide a novel concept about sources of surface runoff and sediment and about mechanisms that govern the erosion processes. With this concept we introduce approaches of best soil and water conservation practices. The approach highlights the fact that priority in landscape interventions should be given to re-vegetation of the degraded areas so as to reduce the sediment concentration contributions originating from these source areas. Additionally, efforts should be directed to gully rehabilitation in the saturated bottom landscape. The rehabilitation may consist of vegetating shallow gullies and stabilizing head cuts of deeper gullies by decreasing the slope of the head cuts and then protecting the chutes. Finally, research should be carried out in increasing the infiltration of the upland areas and the hardpan layer in soils. This will reduce the direct runoff during the rainy season and increase baseflow during the dry season by connecting the land surface to the original deep flow paths that still exist below about 60 cm.