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| Titel |
Surface and subsurface flow effect on permanent gully formation and upland erosion near Lake Tana in the northern highlands of Ethiopia |
| VerfasserIn |
T. Y. Tebebu, A. Z. Abiy, A. D. Zegeye, H. E. Dahlke, Z. M. Easton, S. A. Tilahun, A. S. Collick, S. Kidnau, S. Moges, F. Dadgari, T. S. Steenhuis |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 14, no. 11 ; Nr. 14, no. 11 (2010-11-05), S.2207-2217 |
| Datensatznummer |
250012478
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| Publikation (Nr.) |
 copernicus.org/hess-14-2207-2010.pdf |
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| Zusammenfassung |
| Gully formation in the Ethiopian Highlands has been identified as a major
source of sediment in water bodies, and results in sever land degradation.
Loss of soil from gully erosion reduces agricultural productivity and
grazing land availability, and is one of the major causes of reservoir
siltation in the Nile Basin. This study was conducted in the 523 ha
Debre-Mawi watershed south of Bahir Dar, Ethiopia, where gullies are
actively forming in the landscape. Historic gully development in a section
of the Debre-Mawi watershed was estimated with semi structured farmer
interviews, remotely sensed imagery, and measurements of current gully
volumes. Gully formation was assessed by instrumenting the gully and
surrounding area to measure water table levels and soil physical properties.
Gully formation began in the late 1980's following the removal of indigenous
vegetation, leading to an increase in surface and subsurface runoff from the
hillsides. A comparison of the gully area, estimated from a 0.58 m
resolution QuickBird image, with the current gully area mapped with a GPS,
indicated that the total eroded area of the gully increased from 0.65 ha in
2005 to 1.0 ha in 2007 and 1.43 ha in 2008. The gully erosion rate,
calculated from cross-sectional transect measurements, between 2007 and 2008
was 530 t ha−1 yr−1 in the 17.4 ha area contributing to the gully,
equivalent to over 4 cm soil loss over the contributing area. As a
comparison, we also measured rill and interrill erosion rates in a nearby
section of the watershed, gully erosion rates were approximately 20 times
the measured rill and interrill rates. Depths to the water table measured
with piezometers showed that in the actively eroding sections of the gully
the water table was above the gully bottom and, in stable gully sections the
water table was below the gully bottom during the rainy season. The elevated
water table appears to facilitate the slumping of gully walls, which causes
the gully to widen and to migrate up the hillside. |
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