The Impact of Soil Erosion in the Upper Blue Nile on Downstream Reservoir Sedimentation

Population growth in the Blue Nile Basin has led to fast land-use changes from forest to agricultural land, which resulted in speeding up the soil erosion processes producing highly negative impacts on the local soil fertility and agricultural productivity. The eroded sediment is transported downstream by water and sinks in the lower basin where it significantly reduces reservoir storage and irrigation canals capacity. The only effective solution to mitigate the sedimentation problem is to limit the sediment inputs from upstream by locally implementing erosion control practices. However, given the vastness and remoteness of the involved areas, this first requires the knowledge of the most critical zones. The book identifies the sources of the sediment depositing in the Lower Blue Nile Basin and quantifies the amounts involved providing essential information for the planning and implementation of any interventions aiming at reducing soil erosion. The methods used consist of extensive field work covering most of the basin, watershed, hydrodynamic and morphodynamic modelling and, for the first time, the mineralogical analysis of the sediment at the sources and sinks. The method is successful in indentifying the areas providing most of the transported sediment, where it is recommended to start with erosion control practices.Hydraulic EngineeringCivil Engineering and Geoscience

Modelling of sedimentation processes inside Roseires Reservoir (Sudan) (abstract)

Roseires Reservoir is located on the Blue Nile River, in Sudan (figure 1). It is the first trap to the sediments coming from the upper catchment in Ethiopia, which suffers from high erosion and desertification problems. The reservoir lost already more than one third of its storage capacity due to sedimentation in the last four decades. This is a big economical loss to Sudan, in addition to the high maintenance costs of sediment clearance in front of the turbines to facilitate hydropower production.Hydraulic EngineeringCivil Engineering and Geoscience

Quantification of water uses along the Blue Nile River network using a one dimension (1D) hydrodynamic model

In the Nile River Basin, upstream runoff variability is an acute issue to downstream countries, since these countries are almost entirely dependent on Nile waters. Cooperative management of the Nile waters has become urgent, considering climate variations (Conway, 2005; Yates & Strzepek, 1998 a) and the necessity to use the water resource for irrigation and hydropower. The Grand Ethiopian Renaissance Dam is currently under construction in Ethiopia not far from the border with Sudan (The dam speech, 2011; Hassaballah et al., 2011). The water resource in the Blue Nile River Basin is under increasing pressure due to rapid population and economic growth, which is often aggravated by a lack of coordinated management and governance. Incomplete knowledge of water uses and needs is the main obstacle for proper management of the water resource in poorly studied river basins. Hydrodynamic models, supported by field measurements, are often the most appropriate tool to study the water distribution in river networks, under high and low flow conditions, taking into account water uses, presence of structures, like weir and dams, as well as physical features, like the complex river network geometry. The objective of this research is to study the water distribution along the entire Blue Nile River system to quantify the availability of the water resource at all flow conditions.Hydraulic EngineeringCivil Engineering and Geoscience

Modelling of sedimentation processes inside Roseires Reservoir (Sudan)

Roseires Reservoir, located on the Blue Nile River in Sudan, is the first trap to the sediments coming from the vast upper river catchment in Ethiopia, which suffers from high erosion and desertification problems. The reservoir has already lost more than one-third of its storage capacity due to sedimentation in the last four decades. Appropriate management of the eroded soils in the upper basin could mitigate this problem. In order to do that, the areas providing the highest sediment volumes to the river have to be identified, since they should have priority with respect to the application of erosion control practices. This requires studying the sedimentation record inside Roseires Reservoir in order to assess when and how much sediment is deposited and to identify its source. This paper deals with the identification of deposition time and soil stratification inside the reservoir, based on historical bathymetric data, numerical modelling and newly acquired soil data. The remoteness of the study area and the extreme climate result in coring campaigns being expensive and difficult. Therefore, these activities need to be optimised and coring locations selected beforehand. This was done by combining bathymetric data and the results of a depth-averaged morphodynamic model recording the vertical stratification in sediment deposits. The model allowed for recognising the areas that are potentially subject to neither net erosion nor bar migration during the lifespan of the reservoir. Verification of these results was carried out by analysing sediment stratification from the data collected during the subsequent field campaign.Hydraulic EngineeringCivil Engineering and Geoscience

Modelling of sedimentation processes inside Roseires Reservoir (Sudan) (discussion)

Discussion paper. Roseires Reservoir, located on the Blue Nile River, in Sudan, is the first trap to the sediments coming from the upper catchment in Ethiopia, which suffers from high erosion and desertification problems. The reservoir lost already more than one third of its 5 storage capacity due to sedimentation in the last four decades. Appropriate management of the eroded area in the upper basin could mitigate this problem. In order to do that, the areas providing the highest sediment volumes to the river have to be identified, since they should have priority with respect to the application of erosion control practices. This requires studying the sedimentation record inside Roseires Reservoir, 10 with the aim of identifying when and how much sediment from a certain area is deposited. The identification of deposition time is derived from soil stratification inside the reservoir. This requires expensive coring campaigns that need to be optimized. The most promising sampling coring areas were therefore selected beforehand by combining bathymetric data and the results of a depth-averaged morphodynamic model able 15 to record vertical stratification in sediment deposits. The model allowed recognising the areas that are potentially neither subject to net erosion nor to bar migration during the life span of the reservoir. Verification of these results was carried out by analysing sediment stratification from the data collected in subsequent field campaign.Hydraulic EngineeringCivil Engineering and Geoscience