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Investigation of the impact of stone bunds on erosion and deposition processes combining conventional and tracer methodology in the Gumara-Maksegnit watershed, northern highlands of Ethiopia

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Title Investigation of the impact of stone bunds on erosion and deposition processes combining conventional and tracer methodology in the Gumara-Maksegnit watershed, northern highlands of Ethiopia
 
Creator Obereder, Eva Maria
 
Subject stone bunds
 
Description Different soil and water conservation methods intend to prevent ongoing land degradation,
which is triggered by rainfall driven soil erosion in the Ethiopian agricultural lands. A
commonly used technique is the construction of stone bunds. Although the expected effect
is a reduction of surface runoff and soil loss, their behaviour and effectiveness is not always
clear and they seem to strongly depend on their age. Thus, the purpose of this research
was to evaluate the impact of graded stone bunds on surface runoff and sediment yield by
using conventional and tracing approaches at different field scales.
In June 2015 two controlled field experiments were set up in the Gumara-Maksegnit
watershed in Northern Ethiopia. Three consecutive runoff plots of 20 x 4 m (length and
width, respectively) along the maximum slope direction were established. Each one was
separated from the downstream one by a stone bund. This “cascade plot” allowed the
measurement of surface runoff along each stone bund and the measurement of overflow
over the lowest stone bund. In order to assess the pathway and spatial distribution of the
sediments different tracers (Magnetite, Hematite and Goethite) were applied in a 40 cm
wide strip at the top of each plot. The second tracer experiment was conducted on the
same hillslope. It consisted of a 20 m long unbounded hillslope, with a 4 m long and 40 cm
wide Magnetite strip placed at the top. At the end of August 2015 and for both trials, soil
samples of 0-2 cm depth were taken in a 1.5 x 1.5 m grid within the area of the cascade
and the hillslope, respectively. For the hillslope experiment additionally soil samples
parallel to the stone bund (above and underneath) were taken along 16 m to assess the
soil movement. Tracer concentrations of soil and sediment samples in both trials were
analysed. Runoff and sediment were collected in weekly intervals from July to September.
The data from surface runoff and soil loss showed a very good correlation, whereas rainfall
and surface runoff were not really correlating. The spatial distribution of magnetite
concentration showed that magnetite was moved from the top of the hillslope over stone
bund 1 but there was almost no dislocation below stone bund 2, indicating that stone
bund 2 was not overtopped by runoff. Consequently, at similar slopes the distance
between the stone bunds should be reduced from 20 m to about 15 m to prevent water
from overtopping. In the hillslope experiment the applied tracer was moved further away
from the top. This can be attributed to higher runoff, as the hillslope experiment was not
bordered at the top end and the sides. Therefore, it allowed runoff from areas above the
investigation site in addition to the runoff on the hillslope. Furthermore, it could be
determined that water and sediment found a way to get through a hole in the stone bund.
 
Date 2016-05-18
2016-12-12T07:03:02Z
2016-12-12T07:03:02Z
 
Type Thesis
 
Identifier https://mel.cgiar.org/dspace/limited
Eva Maria Obereder. (18/5/2016). Investigation of the impact of stone bunds on erosion and deposition processes combining conventional and tracer methodology in the Gumara-Maksegnit watershed, northern highlands of Ethiopia. Vienna, Austria: University of Natural Resources and Life Sciences, Center for Development Research (BOKU - CDR).
https://hdl.handle.net/20.500.11766/5134
Timeless limited access
 
Language en
 
Rights CC-BY-NC-4.0
 
Format PDF
 
Publisher University of Natural Resources and Life Sciences, Center for Development Research (BOKU - CDR)