Review of the occurrences and influencing factors of landslides in the highlands of Ethiopia: With implications for infrastructural development

The hilly and mountainous terrains of the highlands of Ethiopia are frequently affected by rainfall-induced landslides of different types and sizes. The major types of landslides reported to have been triggered by heavy rainfalls include debris/earth slides, debris/earth flows and, and medium to large-scale rockslides. Though rockfalls are common in the Ethiopian highlands no association is made with rainfalls. Review of the previous studies revealed that landslide hazards have been causing: loss of human lives, failure of engineering structures, damage on agricultural lands and on the natural environment. Medium to large-scale rockslides were reported in areas underlain by Paleozoic glacial sediments and volcanic rocks. Evaluation of the relationship between landslides and various influencing factors show that the debris/earth slides/flows have prevailed in: (a) areas which are underlain by Paleozoic glacial sediments, shales, and basalt flows, (b) hillslopes characterized by slope angles in the range 15-45 degrees, (c) terrains represented by concave shapes with some on planar surfaces, (d) areas affected by active gully erosion/artificial excavations, and (e) places represented by sparse or no vegetation cover with deeper roots. With regard to the triggering mechanisms, most of the rainfall-induced landslides have taken place in the late periods of the rainy seasons (late August to early September) following heavy rainfalls indicating that process is related to raise in groundwater level coupled with a certain intensity of rainfall event. Ethiopia is currently involved in massive infrastructural development (including roads and railways), urban development and extensive natural resources management. In this whole socio-economic development, landslides and landslide-generated ground failures need to be given due attention in order to reduce losses from such hazards and create safe geo-environment.Key words: Review, Landslides, Highlands, Ethiopi

Soil and water managements and landscapes: Africa RISING science, innovations and technologies with scaling potential from the Ethiopian highlands

United States Agency for International Developmen

Integrated landscape management: Africa RISING R4D experiences in the Ethiopian highlands

United States Agency for International Developmen

Soil erosion assessment in Ethiopia: A review

Soil erosion is a critical problem affecting rural livelihoods in Ethiopia. Large numbers of studies have been undertaken to identify critical areas of soil loss and prioritize conservation options. With the advancement of geospatial analysis techniques, the use of spatially distributed soil erosion assessment options has become increasingly common. The lack of database and documentation related to soil erosion assessment undermines coordination leading to duplication of efforts and in some instances generating contradictory results. The purpose of this study is to (1) review existing knowledge related to the extent and spatial distribution of soil erosion, (2) document the associated methods employed to assess soil erosion, and (3) assess the spatio-temporal dynamics of soil erosion and the determinant factors in Ethiopia. The review shows that there are about 170 peer-reviewed papers published in scientific journals related to soil erosion in Ethiopia. In those scientific articles, 15 different approaches were used to assess soil loss and sediment yield at different scales. Considering the data set, soil loss rate in Ethiopia varies between 0 and 220 t ha–1 y–1, and sediment yield ranges between 2 and 70 t ha–1 y–1. Based on the database, the national average gross soil erosion rate is estimated to be 38 t ha–1 y–1, while the net sediment yield is about 26 t ha–1 y–1. Generally, the observed gross soil loss is slightly lower than the mean value from cultivated lands reported in previous estimates (42 t ha–1 y–1) by Hurni (1993). The estimate made using the Revised Universal Soil Loss Equation gives the highest soil loss (51 t ha–1 y–1), while that based on field-survey approaches gives the lowest (20 t ha–1 y–1). The highest average net soil loss rate (40 t ha–1 y–1) is obtained using plot-level measurements, while the lowest (18 t ha–1 y–1) is obtained using the AGricultural Non-Point Source pollution model. The highest average soil erosion rate is observed in the moist agro-ecological zone (57 ± 7.8 t ha–1 y–1), while the lowest is obtained in the submoist (23.6 ± 2.7 t ha–1 y–1) following the arid zone (28.8 ± 6.5 t ha–1 y–1). The wide range of soil erosion estimates imply spatio-temporal dynamics of soil erosion in the country, which is mainly a reflection of heterogeneity of the various sites, mainly associated with different values of cover and management factors. Such knowledge can enable making informed conservation decisions by focusing on critical hotspots

Evaluation of the Velocity Parameter Estimation Methods in a Geomorphological Instantaneous Unit Hydrograph (GIUH) Model for Simulating Flood Hydrograph in Ungauged Catchments

Runoff data is crucial for development of water resources. Runoff data is however rarely available for ungauged catchments, especially in developing countries. Geomorphological instantaneous unit hydrographs (GIUH) models can be used for predicting runoff in poorly gauged catchments, but a challenge with these models is estimating the dynamic velocity parameter. In this study, three GIUH models were developed based on estimation of flow velocity using calibration of Manning’s n (GIUH-cal), peak discharge (GIUH-pq) and 30-min rain intensity (GIUH-I30). The objectives of this study were to (a) assess suitability of a GIUH model for simulating runoff in Gule catchment, northern Ethiopia and (b) evaluate performance of three velocity parameter estimation methods in simulating runoff using GIUH models. Runoff hydrographs of the GIUH models matched well with observed hygrographs for most rain events. The GIUH-cal model had the best performance, 18 out of 20 rain events resulting in Nash–Sutcliffe model efficiency (NSE) values of 0.53 to 0.95. The GIUH-pq and GIUH-I30 models performed satisfactorily with 12 of the 20 rain events resulting in NSE values greater than 0.50. Overall, the GIUH models underestimated peak discharge compared to observed data. The GIUH models were moderately sensitive to changes in flow velocity. Peak discharge and time to peak discharge were highly sensitive to changes in flow velocity. The developed GIUH models could be used for simulating flood hydrographs of the Gule catchment. Particularly, the GIUH-I30 model will be very useful for estimating direct surface runoff in the absence of streamflow data