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Understanding runoff processes in a basin is of paramount importance for the effective planning and management of water resources, in particular in data-scarce regions such as the Upper Blue Nile. Hydrological models representing the underlying hydrological processes can predict river discharges from ungauged catchments and allow for an understanding of the rainfall-runoff processes in those catchments. In this paper, such a conceptual process-based hydrological model is developed and applied to the upper Gumara and Gilgel Abay catchments (both located within the Upper Blue Nile Basin, the Lake Tana sub-basin) to study the runoff mechanisms and rainfall-runoff processes in the basin. Topography is considered as a proxy for the variability of most of the catchment characteristics. We divided the catchments into different runoff production areas using topographic criteria. Impermeable surfaces (rock outcrops and hard soil pans, common in the Upper Blue Nile Basin) were considered separately in the conceptual model. Based on model results, it can be inferred that about 65% of the runoff appears in the form of interflow in the Gumara study catchment, and baseflow constitutes the larger proportion of runoff (44-48 %) in the Gilgel Abay catchment. Direct runoff represents a smaller fraction of the runoff in both catchments (18-19% for the Gumara, and 20% for the Gilgel Abay) and most of this direct runoff is generated through infiltration excess runoff mechanism from the impermeable rocks or hard soil pans. The study reveals that the hillslopes are recharge areas (sources of interflow and deep percolation) and direct runoff as saturated excess flow prevails from the flat slope areas. Overall, the model study suggests that identifying the catchments into different runoff production areas based on topography and including the impermeable rocky areas separately in the modeling process mimics the rainfall-runoff process in the Upper Blue Nile Basin well and yields a useful result for operational management of water resources in this data-scarce region. [ABSTRACT FROM AUTHOR]

ABSTRACT The combined effects of erosive rains, steep slopes and human land use have caused severe land degradation in the Ethiopian Highlands for several thousand years, but since the 1970s, however, land rehabilitation programmes have been established to try to reverse deterioration. In order to characterize and quantify the transformations in the north Ethiopian Highlands, a study was carried out over 8884 km2 of the Tigray Highlands of northern Ethiopia. Using Landsat Multispectral Scanner and later Thematic Mapper imagery (1972, 1984/1986 and 2000), historical terrestrial photographs (1974-1975) and fieldwork (2008), we prepared land use and cover maps. For assessing the use of the historical terrestrial photographs, Landsat images from 1972 were classified using two different methods, namely conventional change detection (image differencing) and ground truthing (using the historical photographs of 1974-1975). Results show that the use of terrestrial photographs is promising, as the classification accuracy based on this method (Kappa coefficient 0·54) is better than the classification accuracy of the method based on image differencing (Kappa coefficient 0·46). Major land use and cover changes indicate the following: (1) a gradual but significant decline in bare ground (32 per cent in 1972 to 8 per cent in 2000); (2) a significant increase of bushland (25 to 43 per cent) and total forest area (including eucalypt plantations, 2·6 to 6·3 per cent); and (3) creation of numerous lakes and ponds. The dominant change trajectory (27 per cent of the study area) indicates a gradual or recent vegetation increase. These changes can be linked to the population growth and the introduction of land rehabilitation initiatives, complemented by growing awareness of land holders. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

With the recovery of the European beaver ( Castor fiber) and their capacity to engineer fluvial landscapes, questions arise as to how they influence sediment transport, including the spatio-temporal trends and patterns of sedimentation in beaver ponds. The Chevral river (Ardennes, Belgium) contains two beaver dam sequences, which appeared in 2004. Volumes of sediment deposited behind the dams were measured, and grain-size distribution patterns were determined. Flow discharges and sediment fluxes were measured at the inflow and outflow of each dam sequence. Between 2004 and 2011, 1710.1 m3 of sediment was deposited behind the beaver dams, with an average sediment thickness of 25.1 cm. The thickness of the sediment layer was significantly ( p < 0.001) related to the area of the beaver ponds. Along the stream, beaver pond sediment thickness displayed a sinusoidal deposition pattern, in which ponds with thick sediment layers were preceded by a series of ponds with thinner sediment layers. A downstream textural coarsening in the dam sequences was also observed, probably because of dam failures subsequent to surges. Differences in sediment flux between the inflow and outflow at the beaver pond sequence were related to the river hydrograph, with deposition taking place during the rising limbs and slight erosion during the falling limbs. The 7-year-old sequences have filtered 190.19 ton of sediment out of the Chevral river, which is of the same order of magnitude as the 374.4 ton measured in pond deposits, with the difference between the values corresponding to beaver excavations (60.24 ton), inflow from small tributaries, and runoff from the valley flanks. Hydrogeomorphic effects of C. fiber and Castor canadensis activity are similar in magnitude. The detailed analysis of sedimentation in beaver pond sequences confirms the potential of beavers to contribute to river and wetland restoration, and catchment management. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In the Northern Ethiopian Highlands, ca. 33% of the land is cropland, which is mainly cultivated by smallholders who based on indigenous knowledge plan their cropping system on the basis of spatio-temporal variability in rainfall. To understand the relationships between rainfall variability and cropping systems, a field campaign was undertaken in the rainy season of 2009 when 118 farmers were interviewed at different locations with different environmental characteristics. Five cropping systems were identified, each having a distinct cropping season length and crop association. Cropping systems with shorter cropping seasons were generally on the valleysides, whereas longer cycles occurred in the valley bottoms. The length of cropping season also increased from north-northeast to south-southwest. Crop associations within cropping systems also varied with altitude. Cropping systems changed in response to variation in annual rainfall. This resulted in shifts of cropping systems at catchment and regional scales, with cropping systems having longer cropping seasons where there was greater annual precipitation. The results were scaled up to the whole region by modelling the spatial distribution of cropping systems at a 8 × 8 km² resolution over the period 1996-2009. The results indicate that indigenous knowledge is important when assessing the impact of climatic variability on agricultural production and that large inter-annual variability in the duration of crop cover in Northern Ethiopia might be an important, although generally overlooked, explanatory factor for explaining previous land degradation cycles. [ABSTRACT FROM AUTHOR]

ABSTRACT Most regional-scale soil erosion models are spatially lumped and hence have limited application to practical problems such as the evaluation of the spatial variability of soil erosion and sediment delivery within a catchment. Therefore, the objectives of this study were as follows: (i) to calibrate and assess the performance of a spatially distributed WATEM/SEDEM model in predicting absolute sediment yield and specific sediment yield from 12 catchments in Tigray (Ethiopia) by using two different sediment transport capacity equations (original and modified) and (ii) to assess the performance of WATEM/SEDEM for the identification of critical sediment source areas needed for targeting catchment management. The performance of the two model versions for sediment yield was found promising for the 12 catchments. For both versions, model performance for the nine catchments with limited gully erosion was clearly better than the performance obtained when including the three catchments with significant gully erosion. Moreover, there is no significant difference (alpha 5 per cent) between the performances of the two model versions. Cultivated lands were found to be on average five times more prone to erosion than bush-shrub lands. The predicted soil loss values in most parts of Gindae catchment are generally high as compared with the soil formation rates. This emphasises the importance of implementing appropriate soil and water conservation measures in critical sediment source areas prioritising the steepest part of the catchment (i.e. areas with slope >50 per cent). The applicability of the WATEM/SEDEM model to environments where gully erosion is important requires the incorporation of permanent gully and bank gully erosion in the model structure. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Accelerated soil erosion leads to sedimentation in reservoirs and a decline in their life span. As many reservoirs in northern Ethiopia are dry at the end of the dry season, we were able to evaluate the potential of using reservoir sediments for land reclamation. Stripped land from which construction material for the reservoirs had been excavated was covered with 0, 15 and 30 cm of sediment and planted with a local garlic cultivar ( Allium sativum). The applied reservoir sediments had low to medium organic C and total N contents and were high in available P and exchangeable cations. The yield of garlic increased with additional available water and the application of sediments. The results show that total biomass and bulb yield were three times higher on the reclaimed plots than on the control ones (11.7 t/ha vs. 3.6 t/ha for the biomass; 7.7 t/ha vs. 2.0 t/ha for the yield). When sediment transport and labour costs were taken into account, plots with 15 cm of sediments had in the first cropping season a cost-benefit ratio of 3, whilst those with 30 cm had a cost-benefit ratio of 0.9. This study demonstrates that the use of relatively small quantities of reservoir sediments is an economically viable strategy for land reclamation. The result can be improvement in income for resource-poor farmers by as much as 76%, and the life expectancy of the reservoirs is also increased. [ABSTRACT FROM AUTHOR]

The aim of conservation agriculture (CA) is to improve soil quality and crop yield whilst reducing runoff and topsoil erosion. An experiment was carried out in a rainfed field using a permanent raised bed planting system for 3 yr (2005-2007) in Adigudem, northern Ethiopia in order to evaluate the effect of CA on runoff, soil loss and crop yield. CA practices were introduced in fields with Vertisols in a randomized complete block design on permanent 5 × 19 m plots. Three treatments were evaluated: (1) conventional tillage (CT) with a minimum of three tillage operations and removal of crop residues, (2) terwah (TER) that was similar to CT except that contour furrows were included at 1.5 m intervals, and (3) derdero+ (DER+), which consists of permanent raised beds with a furrow and bed system, retention of 30% of standing crop residues and zero tillage on the top of the bed. All ploughing as well as the maintenance of the furrows of the permanent raised beds was done using a local ard plough called maresha. Results from monitoring over 3 yr showed that soil loss and runoff were significantly higher ( P < 0.05) in CT followed by TER and DER+. Average soil losses of 5.2, 20.1 and 24.2 t/ha were recorded from DER+, TER and CT, respectively. Runoff was 46.3, 76.3 and 98.1 mm from DER+, TER and CT, respectively. Grain yield was significantly lower ( P < 0.05) in DER+ under teff in 2006, probably due to the high sensitivity of teff to weeds. The yield of wheat in 2007 was significantly higher in DER+ followed by TER. The terwah system is recommended as a first measure for wider adoption to reduce runoff and soil loss and to increase crop yield. The long-term goal is to achieve a derdero+ system, i.e. a permanent raised bed planting system along with the application of crop residues. [ABSTRACT FROM AUTHOR]

The article presents a discussion about the use of land and soil at the Tigray Highlands in Dogu'a Tembien, Northern Ethiopia. The study focused on soil type, land use and crop production system. Type of soils found within the area are vertisols, vertic cambisols, cumulic regosols and calcaric regosols. The study found that population growth is affecting natural resources of the Ethiopian Highlands resulting land degradation. It is also noted that a decline in natural vegetation is also impacting sustainability of traditional agricultural systems.

The article presents information on a study which examined sediment-bound nutrient exports from several catchments and reservoirs in Tigray, Northern Ethiopia. The study assessed the spatial variability in nutrient content in the catchment soils and the deposited sediment in the reservoirs. The fertility status of the deposited sediment and its potential use for land reclamation of the surrounding degraded croplands was evaluated. It also assessed the rate of nutrient export and compared the Ethiopian situation with a high-input region. The potential for carbon sequestration in the deposited sediment was explored. The costs of land degradation by soil erosion were also quantified.

Large, deep-seated landslides are common features in the Flemish Ardennes (Belgium). As most of these old (>100 years) landslides are located under forest in this hilly region, aerial photograph interpretation is not an appropriate landslide mapping method. This study tested the potential of LIDAR (Light Detection and Ranging) images for mapping old landslides under forest. Landslide inventory maps were created for a 125 km² area by applying the expert knowledge of seven geomorphologists to LIDAR-derived hillshade, slope and contour line maps in a GIS environment. Each of the seven LIDAR-based landslide inventories was compared (i) with the other six, (ii) with a detailed field survey-based inventory, and (iii) with a comparable study in which topographic data were extracted from a topographical map. The combination of the percentage of field landslides indicated by an expert and the percentage of positional discrepancies (expressed in terms of positional mismatch) were used to evaluate the quality of the LIDAR-based inventory maps. High-quality LIDAR-derived landslide inventory maps contain more than 70 per cent of the landslides mapped during the field survey, and have positional discrepancies smaller than 70 per cent when compared with the field survey-based inventory map. Four experts and the combination map of all experts satisfied these criteria. Together the seven experts indicated all landslides mapped in the field. Importantly, LIDAR enabled the experts to find ten new landslides and to correct the boundaries of eleven (of the 77) landslides mapped during the field survey. Hence, this study showed that large-scale LIDAR-derived maps analysed by experienced geomorphologists can significantly improve field survey-based inventories of landslides with a subdued morphology in hilly regions. [ABSTRACT FROM AUTHOR]

Abstract: Distinct rock fragment displacements occur on the ambas, or structurally determined stepped mountains of the Northern Ethiopian Highlands. This paper describes the rock fragment detachment from cliffs by rockfall, quantifies its annual rate, and identifies factors controlling rock fragment movement on the scree slopes. It further presents a conceptual model explaining rock fragment cover at the soil surface in these landscapes. In the May Zegzeg catchment (Dogu''a Tembien district, Tigray), rockfall from cliffs and rock fragment movement on debris slopes by runoff and livestock trampling were monitored over a 4-year period (1998–2001). Rockfall and rock fragment transport mainly induced by livestock trampling appear to be important geomorphic processes. Along a 1500-m long section of the Amba Aradam sandstone cliff, at least 80 t of rocks are detached yearly and fall over a mean vertical distance of 24 m resulting in a mean annual cliff retreat rate of 0.37 mm y−1. Yearly unit rock fragment transport rates on scree slopes ranged between 23.1 and 37.9 kg m−1 y−1. This process is virtually stopped when exclosures are established. Corresponding mean rock fragment transport coefficients K are 32–69 kg m−1 y−1 on rangeland but only 3.9 kg m−1 y−1 in densely vegetated exclosures. A conceptual model indicates that besides rockfall from cliffs and argillipedoturbation, all factors and processes of rock fragment redistribution in the study area are of anthropogenic origin. [Copyright &y& Elsevier]

In Tigray (Northern Ethiopia, significant achievements were made, mainly from 1994 to 2002, on the development of agriculture through irrigation by employing seasonally harvested runoff using earth dams. However, most of the implemented schemes are not serving the intended purpose well because of constraints associated with both pre- and post-implementation. Sediment deposition in reservoirs is a serious off-site consequence of soil erosion in the region. However, the extent of the problem is not well studied. Moreover, there are no sufficient and reliable sediment-yield data for Northern Ethiopia, which are important for designing new reservoirs and for implementing soil conservation practices. This study addresses those problems by undertaking: (1) a survey and evaluation of the general characteristics and problems of 54 recently built reservoirs and the characteristics of their respective catchments; and (2) a detailed sediment survey in ten reservoirs and related catchment characteristics. A field survey in 2002-2003, a review of technical reports and interviews were the bases for this study. Most of the reservoirs are under risk of insufficient inflow, excessive seepage and sediment deposition. These problems are mainly attributed to the use of a poor database on hydrology and sediment yield, and the lack of adaptable methodologies for assessing controlling factors at the planning stage. The reservoir survey, which is the first of its kind in Ethiopia, also indicates that specific sediment yield (SSY) varies significantly between catchments: i.e. from 237 to 1817 t km-2 y-1 with an average of 909 (± 500) t km-2 y-1. The high spatial variability is mainly associated with differences in lithology, cover, extent of gully network and human activities. Therefore, adapting an average SSY value for the whole region is not recommended for future planning purposes. The sediment deposition problem is significant: i.e. 70 per cent of the study reservoirs have important siltation problems so that they will end their useful life well before the dam design period. Hence, sediment management in reservoirs could be an effective approach towards maintaining the existing storage capacity. For the realization of sustainable land and water development in Tigray, sufficient and reliable database building, development and standardization of appropriate methodologies for predicting sediment yield and capacity building of designers needs to be given top priority. Moreover, awareness creation among policy makers, donors and beneficiaries is also important for action. [ABSTRACT FROM AUTHOR]