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

Demesew A Mhiret; Dessalegn C Dagnew; Christian D Guzman; Tilashwork C Alemie; Assefa D Zegeye; Tigist Y Tebebu; Eddy J Langendoen; Benjamin F Zaitchik; Seifu A Tilahun; Tammo S Steenhuis

doi:10.1016/j.jenvman.2020.110885

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

J Environ Manage. 2020 Sep 15:270:110885. doi: 10.1016/j.jenvman.2020.110885. Epub 2020 Jun 26.

Affiliations

¹ Faculty of Civil and Water Resources Engineering, Bahir Dar Institute of Technology, Bahir Dar University, P.O. Box 26, Bahir Dar, Ethiopia; Blue Nile Water Institute, Bahir Dar University, P.O. Box 79, Bahir Dar, Ethiopia.
² Blue Nile Water Institute, Bahir Dar University, P.O. Box 79, Bahir Dar, Ethiopia; Institute of Disaster Risk Management and Food Security Studies, Bahir Dar University, P.O. Box 5501, Bahir Dar, Ethiopia.
³ Department of Civil and Environmental Engineering, University of Massachusetts, Amherst, MA, 01003, USA.
⁴ Amhara Region Agricultural Research Institute, Bahir Dar, Ethiopia.
⁵ Department of Biological and Environmental Engineering, Cornell University, 14850, Ithaca, NY, USA.
⁶ United States Department of Agriculture, Agricultural Research Service, Oxford, MS, USA.
⁷ Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD, 21218, USA.
⁸ Faculty of Civil and Water Resources Engineering, Bahir Dar Institute of Technology, Bahir Dar University, P.O. Box 26, Bahir Dar, Ethiopia.
⁹ Faculty of Civil and Water Resources Engineering, Bahir Dar Institute of Technology, Bahir Dar University, P.O. Box 26, Bahir Dar, Ethiopia; Department of Biological and Environmental Engineering, Cornell University, 14850, Ithaca, NY, USA. Electronic address: tss1@cornell.edu.

PMID: 32721323
DOI: 10.1016/j.jenvman.2020.110885

Abstract

A nine-year (2010-2018) field study in the Debre Mawi watershed was conducted to understand the effect of governmentally-imposed and farmer-initiated conservation practices. The watershed is in the sub-humid Ethiopian Highlands which experience high and increasing erosion rates despite years of conservation efforts. Consequently, reservoirs are filling up with sediment and soil degradation is enhanced, calling for the evaluation of conservation practices currently in use. The few past long-term experimental studies on structural practices are inconclusive. In addition, only anecdotal information is available for streamflow and sediment loss. Precipitation, stream discharge, and suspended sediment concentrations were recorded manually in the Debre Mawi watershed during the nine-year period. Groundwater depth and total saturated area measurements were taken for selected periods. From 2012 to 2014, government-mandated conservation practices were constructed, which consisted of 50-cm-deep infiltration furrows with bunds downslope. These furrows were filled in with sediment by 2018. At the same time, the acreage of eucalyptus trees planted by farmers on the most vulnerable lands tripled to 5% of the total area with most trees fully grown in 2018. Runoff coefficients and sediment concentrations decreased steadily throughout the nine years. In the saturated bottomlands, the observations suggested that government-sponsored infiltration furrows in the saturated bottomlands were 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 conservation practices in this sub-humid tropical highland region and to emerging long-term risks. If structural conservation is to be pursued in watersheds like Debre Mawi, due attention must be given to the safe removal of excess water from the valley bottoms. The vegetative farmer-initiated practice of planting eucalyptus trees effectively reduced streamflow and erosion, but at the same time, might dry up wells during the dry monsoon phase which should be investigated further.

Keywords: Runoff; Soil and water conservation practices; Soil degradation; Soil erosion.

Publication types

Observational Study

MeSH terms

Conservation of Natural Resources
Conservation of Water Resources*
Environmental Monitoring
Ethiopia
Geologic Sediments
Risk Assessment
Soil*

Substances

Soil