ASSESSMENT OF SLOPE MOVEMENTS FROM GOHA –TSION TO DEJEN
(BLUE NILE) GORGE, ETHIOPIA.

ABSTRACT

The likelihood of slope movements in Abay gorge (Blue Nile Basin) is directly or indirectly related to the geology, geomorphology, climate and human activities. The occurrence of soft rocks containing clays within limestones, sandstones and gypsum, the intersection of joints, the missing of some lithologic units due to minor process of faulting accompanied by extensive river erosion, and the deep penetrative weathering effect are the main geologic factors that are considered as possible causes of landslides and rockfalls. Steep and concave slopes are also characterized by active mass movements especially at the time of heavy rainfall and anomalously high thunder showers. The day to day agricultural activity of residents of the area together with the high expansion rate of settlements towards valleys and adjacent hill sides allow the problem to deserve serious consideration in the past two years. Moreover, some factors like fluctuation of ground water level and traffic volume are considered to be landslide accelerators.

In this study, terrains are classified with respect to the type of movement and the material involved as zones of landslides and rockfall. The former is further divided into three zones (stable, semi-stable and unstable) on the basis of their degree of stability. Possible remedial measures are recommended based on the site conditions of the disturbed zones and the existing tight budgetary constraints. Accordingly, drainage control and spring development are effective ways of mitigating landslide problems in localities where rotational slope movements are dominant. Relocation of the route line is the most reasonable corrective measure for the displaced road section of Gilgele. Restraints (engineering structures) are equally important especially in minor rotational slides and planar movements that encroach up on the shoulders of settlements and roadside. Selective vegetation systems, reduction of unplanned activities of human beings and description regarding perception of landslide hazards are all recommended to solve the problem of slope instability in the Abay gorge.

Note: The report is available at the Central Technical Library of the ESTC.

(Report 1997)

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