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Katholieke Universiteit Leuven (2017)

Identification of sediment sources in the Tekeze catchment, northern Ethiopia

D’Hoore, Ward

Titre : Identification of sediment sources in the Tekeze catchment, northern Ethiopia

Auteur : D’Hoore, Ward

Université de soutenance : Katholieke Universiteit Leuven

Grade : Master of Geography 2017

Résumé
The northern Ethiopian highlands are one of the areas in the world with the highest sediment loads of rivers. The combination of steep slopes, erosive rainfall, severe land degradation are important causes of high soil erosion rates. Sediment is infilling the reservoir behind the large Tekeze dam, constructed in 2009. This dam provides hydro-power and is also used for irrigation purposes and water supply during droughts. The aim of this thesis was to detect sediment sources in the Tekeze catchment (ca. 30,600 km²) in northern Ethiopia to assist local authorities and policy makers to apply targeted soil and water conservation (SWC) measures to reduce soil erosion on-site and to increase the life-expectancy of the reservoir. Recent research indicated that SWC measures like stone bunds, conservation trenches, check dams and micro-basins can effectively reduce soil erosion. In this perspective, a modelling approach was used to detect sediment sources and to estimate soil loss rates due to three various erosion processes (i.e. sheet and rill erosion , gully erosion and landslide erosion). Results show that the spatial distribution of sheet and rill erosion in the semi-arid Tekeze catchment is controlled by rock fragment cover. The distribution of rock fragments in the catchment is mainly controlled by slope and elevation. The modelled average soil loss rates are high. Gully erosion is mainly controlled by grain size, vegetation cover and contributing drainage area. However, coping with the wide variety of gully types is a challenge. Despite high uncertainties of the model, soil loss due to gully erosion was from the same order of magnitude of sheet and rill erosion. Landslides within the catchment are typically shallow and located on steep slopes but can nevertheless be important local source of sediments. An integrated map of the various erosion processes shows the most critical locations in the catchment for erosion. This thesis is a call for the development of integrated soil erosion prediction models at the large catchment scale. Referring to the aim of this thesis the produced maps can assist local catchment management teams in the Tekeze catchment to detect the main sediment source areas and to apply effective and targeted SWC measures on the erosion hotspot locations. This (i) to reduce sediment yield and (ii) to restore most degraded landscapes and hence to increase the livelihood of people.

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Page publiée le 13 décembre 2018