A nine-year study on the benefits and risks of soil and water conservation practices in the humid highlands of Ethiopia: The Debre Mawi watershed

Authors: MHIRE, DEMESEW - Bahir Dar University; DAGNEW, DESSALEGN - Bahir Dar University; GUZMAN, CHRISTIAN - Washington State University; ALEMIE, TILASHWORK - Amhara Regional Agricultural Research Institute; ZEGEYE, ASSEFA - Amhara Regional Agricultural Research Institute; TEBEBU, TIGIST - Cornell University; Langendoen, Eddy; ZAITCHIK, BENJAMIN - Johns Hopkins University; TILAHUN, SEIFU - Bahir Dar University; STEENHUIS, TAMMO - Cornell University

Submitted to: Environmental Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/30/2020
Publication Date: 6/26/2020
Citation: Mhire, D.A., Dagnew, D.C., Guzman, C.D., Alemie, T.C., Zegeye, A.D., Tebebu, T.Y., Langendoen, E.J., Zaitchik, B.F., Tilahun, S.A., Steenhuis, T.S. 2020. A nine-year study on the benefits and risks of soil and water conservation practices in the humid highlands of Ethiopia: The Debre Mawi watershed. Environmental Management. 270 (2020) 110885. https://doi.org/10.1016/j.jenvman.2020.110885.
DOI: https://doi.org/10.1016/j.jenvman.2020.110885

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 have been investigated by an interdisciplinary group of faculty and postgraduate students at Bahir Dar University in cooperation with scientists from Amhara Regional Agricultural Research Institute (Bahir Dar), Cornell University (Ithaca, NY), Johns Hopkins University (Baltimore, MD), and the USDA, ARS, Watershed Physical Processes Research Unit (Oxford, MS). Research findings of the interdisciplinary group were based on research conducted between 2010 and 2018 in the Debre Mawi watershed in the Amhara region south of Lake Tana, Ethiopia. Soil and water conservation practices (SWCPs) mandated by the Ethiopian government have reduced soil loss from the uplands. However, 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. Eucalyptus plantations voluntarily established by farmers on vulnerable bottomlands appear to be effective gully erosion control. Therefore, governmental and non-governmental organizations financing the design and implementation of SWCPs should ensure that SWCPs emphasize the safe removal of excess water from the valley bottoms. This can be accomplished through context-appropriate SWCPs siting, careful attention to drainage in addition to sediment trapping, and/or integration of vegetation.

Technical Abstract: A nine year (2010-2018) field study in the Debre Mawi watershed was carried out to understand the effect of governmental imposed and farmer’s initiated conservation practices. The watershed is located in the sub-humid Ethiopian highlands which experience high and increasing erosion rates despite years of conservation efforts. As a consequence, reservoirs are filling up and soil degradation is enhanced. Warranting the evaluation of conservation practices currently in use. In the Debre Mawi watershed, precipitation, stream discharge, and suspended sediment concentrations were recorded. In addition, ground water depth and total saturated area measurements were taken for selected periods. From 2012 to 2014 government mandated conservation practices consisting 50-cm deep infiltration furrows with bunds downslope were implemented. These furrows were filled in with sediment in 2018. In addition, over the observation period the acreage of eucalyptus trees planted by farmers on the most vulnerable lands tripled to 5% of the total area with most trees full grown in 2018. Observations indicate that conservation practices and the increases acreage of eucalyptus were associated with significant reductions in runoff coefficient and sediment concentrations, and these reductions appear to persist through 2018. At the same time, the measurements also suggest government sponsored infiltration furrows in the saturated bottomlands are ineffective and may concentrate flows and enhance gully erosion while eucalyptus trees appear effective. The results of this observational study point to both the potential benefits of SWCPs in this sub-humid tropical highland region and to emerging long-term risks. If SWCPs are to be pursued in watersheds like Debre Mawi, due attention has to be given to the safe removal of excess water from the valley bottoms. This can be accomplished through context-appropriate SWCPs siting, careful attention to drainage in addition to sediment trapping, and/or integration of vegetation.