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1 Addisie, M. B.; Ayele, G. K.; Gessess, A. A.; Tilahun, S. A.; Moges, M. M.; Schmitter, Petra S.; Steenhuis, T. S. 2015. Hydro-geomorphological features at gully heads in the humid northern Ethiopian Highlands, Birr Watershed. Paper presented at the 3rd International Conference on the Advancements of Science and Technology [ICAST], Bahir Dar, Ethiopia, 8-9 May 2015. 7p.
Hydrogeology ; Geomorphology ; Morphology ; Humid zones ; Highlands ; Watersheds ; Water table ; Soil properties ; Gully erosion ; Landscape ; Case studies / Ethiopia / Ethiopian Highlands / Birr Watershed
(Location: IWMI HQ Call no: e-copy only Record No: H047312)
(0.36 MB)
The study was conducted in the Birr watershed at twelve gully heads located close to each other. The survey includes measurements of morphological features, soil properties, water table elevations and catchment characteristics including erosion at each gully head. The analysis showed that gully head morphology could be explained by the role of different gully head controlling factors. The result suggested the maximum rate of head cut retreat reaches from 0 to 22.5m. There was no head retreat recorded from the arrested heads relative to unprotected heads. Compared to semiarid highlands of northern Ethiopia, the average short term head cut retreat was 12 fold greater. From the direct shear test, angle of internal friction by far greater than the slope of gully heads which are located at flat lands. The width depth ratio showed that the shallow depth heads were controlled by fluvial erosion whereas for the deep gully heads both fluvial and mass wasting due tension cracks are operating. In this study a significant power relationship established between the volume of the gully head and the length of retreat at the active gullies with V = 4.85 L1.05 (R2 = 0.91 and P= 0.042) which is different from the relation obtained from the entire gully system as a result of varies controlling factors.
2 Addisie, M. B.; Ayele, G. K.; Gessess, A. A.; Tilahun, S. A.; Zegeye, A. D.; Moges, M. M. [NARS]; Schmitter, Petra; Langendoen, E. J.; Steenhuis, T. S. 2015. Hydrological and morphological factors at gully heads in the humid northern Ethiopian Highlands, Birr watershed [Abstract only] In Nyssen J., Enyew A., Poesen J et al. (Eds.). International Conference on Tropical Lakes in a Changing Environment: Water, Land, Biology, Climate and Humans (TropiLakes), Bahir Dar, Ethiopia, 23-29 September 2015. Book of Abstracts. Bahir Dar, Ethiopia: Bahir Dar University. pp.72.
Hydrological factors ; Gully erosion ; Humid climate ; Water table ; Watersheds ; Highlands ; Soils / Ethiopia / Birr Watershed / Ethiopian Highlands
(Location: IWMI HQ Call no: e-copy only Record No: H047416)
(0.10 MB)
In the Ethiopian highlands, gully erosion is severe. Although attempts to prevent gullying, it remains a challenge. Our objectives are to understand better the processes that control gully head cut retreat. The study was conducted in Birr watershed located at South West of Bahir Dar, Ethiopia. Twelve gully heads were selected and monitored from July to October, 2014. We measured gully head morphology, length of recession via pegging technique, soil analysis to determine soil shear strength, physical and chemical properties, water table elevations and catchment physical characteristics. Two active gully head cuts were arrested with stone riprap after regarding at 450. The result shows that the maximum rate of head cut retreat was between 0 to 22.5m. There was no head retreat observed from the protected heads compared with unprotected heads. The average short term head cut retreat was much greater than that observed in semiarid highlands of northern Ethiopia. The greater gulley rate of recession in the humid monsoon climate is likely caused by the water table that was above the gully bottom. In August when the soil became saturated, about 45% of head cut migration occurred. Thus the water table contributed to the slumping of gully heads and weakened the strength of the soil cohesion. The soil shear strength test result shows, angle of internal friction was by far greater than the slope of gully heads where heads are located in the periodically saturated flat lands. The width depth ratio showed that the shallow depth heads were controlled by fluvial erosion whereas for the deep gully heads both fluvial and mass wasting due to tension cracks was the main driving force. Both the water table control and protecting the head cuts of shallow gullies plays a key role in reducing the sediment contribution of gully in the humid Ethiopian highlands.
3 Addisie, M. B.; Ayele, G. K.; Gessess, A. A.; Tilahun, S. A.; Zegeye, A. D.; Moges, M. M.; Schmitter, Petra; Langendoen, E. J.; Steenhuis, T. S. 2017. Gully head retreat in the sub-humid Ethiopian Highlands: the Ene-Chilala Catchment. Land Degradation and Development, 28(5):1579-1588. [doi: https://doi.org/10.1002/ldr.2688]
Gully erosion ; Erosion control ; Humid zones ; Highlands ; Catchment areas ; Sedimentation ; Wet season ; Monitoring ; Soil texture / East Africa / Ethiopia / Ene-Chilala Catchment
(Location: IWMI HQ Call no: e-copy only Record No: H048152)
In the northern highlands of Ethiopia, gully erosion is severe. Despite many efforts to implement gully prevention measures, controlling gully erosion remains a challenge. The objective is to better understand the regional gully erosion processes and to prevent gully head retreat. The study was conducted in the Ene-Chilala catchment in the sub-humid headwaters of the Birr River located southwest of Bahir Dar, Ethiopia. Twelve gully heads were monitored during the 2014 and 2015 rainy monsoon phase. We measured gully head morphology and retreat length, soil shear strength, ground water table levels, and catchment physical characteristics. Two active gully head cuts were treated in 2014 and an additional three head cuts in 2015 by regrading their slope to 45° and covering them with stone riprap. These treatments halted the gully head advance. The untreated gullies were actively eroding due to groundwater at shallow depths. The largest head retreat was 22.5 m, of which about half occurred in August of the first year when the surrounding soil was fully saturated. Lowering both the water table and protecting the gully heads can play a key role in reducing gully expansion and soil loss due to gully erosion in the Ethiopian highlands.
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