Evaluation of the Impact of Stone Bunds on Soil Loss and Surface Runoff in the Gumara-Maksegnit Watershed, Northern Highlands of Ethiopia
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Stefanie Wakolbinger, Andreas Klik, Reinhard Nolz. (30/5/2016). Evaluation of the Impact of Stone Bunds on Soil Loss and Surface Runoff in the Gumara-Maksegnit Watershed, Northern Highlands of Ethiopia. Vienna, Austria: University of Natural Resources and Life Sciences, Center for Development Research (BOKU - CDR).
Abstract
Ethiopia is highly affected by land degradation and one of the key problems is soil erosion.
It is mainly caused by the rapid population increase, deforestation, low vegetation cover
and unbalanced livestock and crop production. As far as about 85 % of the Ethiopian
population depends on agriculture, it is essential to prevent or reduce further degradation.
In the Northern Highlands of Ethiopia, stone bunds are widely used as a soil and water
conservation measure (SWC). Stone bunds are little embankments of stones along the
contour lines and influence the translation processes of surface runoff.
In June 2015 a field experiment in the Gumara-Maksegnit watershed was carried out to
investigate the impact of stone bunds on surface runoff and soil erosion using 4 m wide
and 20 m long bounded plots monitoring surface runoff and sediment yield with and without
stone bunds. The average slope of the plots is about 8 %. The novel design of the plots
(with stone bunds) allowed the monitoring of runoff along the contour (stone bund) as well
as the bund overflow. The sideflow and overflow were separately collected and routed via
a multi-slot-divider to different storage ponds. Representative samples were taken at a
roughly weekly interval for a sediment concentration assessment. Precipitation was
measured in daily intervals next to the study site.
Total rainfall of the observation period in 2015 (July to September) was 601 mm. During
the same time period plots without stone bunds generated approximately 15 t/ha soil loss,
whereas plots with stone bunds produced approximately 4 t/ha. However, only 19 % of the
sediment from the treated plots was transported over the stone bunds, the rest (81%) either
deposited in front of the bund or moved along and was spilled as sideflow. Throughout the
investigation period 91 mm of surface runoff were produced on the treated plots. This
corresponds to a runoff coefficient of 0.17. Around 30% of this runoff overtopped the stone
bunds, the remaining part ran off along the contour.
Overall, stone bunds can be seen as effective soil and water conservation measures under
the conditions of the Ethiopian Highlands