Wad Medani, Sudan
Wad Medani, Sudan

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Tesemma Z.K.,Bahir Dar University | Mohamed Y.A.,International Water Management Institute | Mohamed Y.A.,UNESCO-IHE Institute for Water Education | Mohamed Y.A.,Hydraulic Research Station | And 2 more authors.
Hydrological Processes | Year: 2010

Most of the water from the Nile originates in Ethiopia but there is no agreement on how land degradation or climate change affects the future flow in downstream countries. The objective of this paper is to improve the understanding of future conditions by analysing historical trends. During the period 1964-2003, the average monthly basin-wide precipitation and monthly discharge data were collected and analysed statistically for two stations in the upper 30% of the Blue Nile Basin and monthly and 10-day discharge data of one station at the Sudan-Ethiopia border. A rainfall-runoff model examined the causes for observed trends. The results show that, while there was no significant trend in the seasonal and annual basin-wide average rainfall, significant increases in discharge during the long rainy season (June to September) were observed at all three stations. In the upper Blue Nile, the short rainy season flow (March to May) increased, while the dry season flow (October to February) stayed the same. At the Sudan border, the dry season flow decreased significantly with no change in the short rainy season flow. The difference in response was likely due to the construction of weir in the 1990s at the Lake Tana outlet that affected the upper Blue Nile discharge significantly but affected less than 10% of the discharge at the Sudan border. The rainfall-runoff model reproduced the observed trends, assuming that an additional 10% of the hillsides were eroded in the 40-year time span and generated overland flow instead of interflow and base flow. Models concerning future trends in the Nile cannot assume that the landscape runoff processes will remain static. © 2010 John Wiley & Sons, Ltd..

Omer A.Y.A.,UNESCO IHE | Omer A.Y.A.,Dams Implementation Unit of Ministry of Water Resources and Electricity | Ali Y.S.A.,UNESCO IHE | Ali Y.S.A.,Hydraulic Research Station | And 6 more authors.
Earth Surface Dynamics | Year: 2015

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. © 2015 Author(s).

Mohamed Y.,Hydraulic Research Station | Mohamed Y.,Technical University of Delft | Savenije H.H.G.,Technical University of Delft
Wetlands Ecology and Management | Year: 2014

The Sudd wetland is a huge swampy area (30,000-40,000 km2), with vegetation composed mainly of papyrus, water hyacinth and grasslands. It is located in South Sudan, and is of vital importance for livelihoods, ecosystem services and water resources. Half of the White Nile flow evaporates when passing through the Sudd (~16,000 106 m3/year). Historically, this phenomenon triggered several water conservation projects in the Nile region (the Jonglei Canal Project). However, the available information on the hydrology of the Sudd is very limited, and mostly outdated. This paper investigates the long term dynamics of the Sudd hydroclimatology (water balance components), and how it affects the wetland areal extent. The water balance results show that the extent of the Sudd wetland area is determined both by the regional climate (outflow from Lake Victoria) and the local climate, represented by precipitation and evaporation over the wetland itself. The long term trends of the Sudd hydrology from 1900 to 2000 have been analyzed with the Mann-Kendall test statistics. The water flows into and out of the Sudd demonstrate a statistically significant increasing trends during the last 100 years. This can be attributed to increasing rainfall over Lake Victoria in the early 1960s. The daily maximum and minimum temperature in the Sudd shows an increasing trend of 0.6 and 1.5 °C, respectively, over the last 100 years. However, this has not caused any change of the wetland actual evaporation (open water evaporation plus plant transpiration). The impact of the temperature rise has likely been compensated by a reduction of the relative humidity and solar radiation over the wetland. The statistical test shows that both relative humidity and solar radiation (sunshine hours) has significantly decreased, each reduced by 10 % over the last 50 year. The precipitation over the Sudd showed no significant change during the last 100 years. On the other hand, the areal extent of the Sudd wetland increased by 19,000 km2 (80 %) during the last 100 years, as a result of the increased inflows. The long term variability of the Sudd areal extent provides new results and deeper insights of the two-way land surface climate feedbacks, and informs wetland conservation and water resources management for this important tropical wetland. © 2014 Springer Science+Business Media Dordrecht.

Uhlenbrook S.,UNESCO IHE | Uhlenbrook S.,Technical University of Delft | Mohamed Y.,UNESCO IHE | Mohamed Y.,Technical University of Delft | And 2 more authors.
Hydrology and Earth System Sciences | Year: 2010

Understanding catchment hydrological processes is essential for water resources management, in particular in data scarce regions. The Gilgel Abay catchment (a major tributary into Lake Tana, source of the Blue Nile) is undergoing intensive plans for water management, which is part of larger development plans in the Blue Nile basin in Ethiopia. To obtain a better understanding of the water balance dynamics and runoff generation mechanisms and to evaluate model transferability, catchment modeling has been conducted using the conceptual hydrological model HBV. Accordingly, the catchment of the Gilgel Abay has been divided into two gauged sub-catchments (Upper Gilgel Abay and Koga) and the un-gauged part of the catchment. All available data sets were tested for stationarity, consistency and homogeneity and the data limitations (quality and quantity) are discussed. Manual calibration of the daily models for three different catchment representations, i.e. (i) lumped, (ii) lumped with multiple vegetation zones, and (iii) semi-distributed with multiple vegetation and elevation zones, showed good to satisfactory model performances with Nash-Sutcliffe efficiencies Reff > 0.75 and > 0.6 for the Upper Gilgel Abay and Koga sub-catchments, respectively. Better model results could not be obtained with manual calibration, very likely due to the limited data quality and model insufficiencies. Increasing the computation time step to 15 and 30 days improved the model performance in both sub-catchments to R eff > 0.8. Model parameter transferability tests have been conducted by interchanging parameters sets between the two gauged sub-catchments. Results showed poor performances for the daily models (0.30 < Reff < 0.67), but better performances for the 15 and 30 days models, Reff > 0.80. The transferability tests together with a sensitivity analysis using Monte Carlo simulations (more than 1 million model runs per catchment representation) explained the different hydrologic responses of the two sub-catchments, which seems to be mainly caused by the presence of dambos in Koga sub-catchment. It is concluded that daily model transferability is not feasible, while it can produce acceptable results for the 15 and 30 days models. This is very useful for water resources planning and management, but not sufficient to capture detailed hydrological processes in an ungauged area. © Author(s) 2010.

Hamid S.H.,Hydraulic Research Station | Mohamed A.A.,University of Gezira | Mohamed Y.A.,International Water Management Institute IWMI
Irrigation and Drainage | Year: 2011

The underperformance problem of large-scale irrigation systems particularly in developing countries, has adversely affected levels of production of those systems. The fact that these irrigation systems are not managed in response to their performance has been identified as the main reason behind their malfunctioning. A performance-oriented management approach is demonstrated here to help irrigation system managers take the right decisions, through continuous in-season performance assessment. The Advanced Very High Resolution Radiometer satellite images of the National Oceanic and Atmospheric Administration (NOAA-AVHRR) for the year 2000, complemented by water release data, were used to assess the performance of the Rahad irrigation scheme, Sudan (126 000ha), on a 10-day time step. The Surface Energy Balance Algorithm (SEBAL) was used to process the NOAA-AVHRR images. The decisions on irrigation water allocation are guided by maps of the relative water supply and soil moisture content generated for the last time step. Further decision support could be realized using the performance indicators of the system and the soil water balance for the given time step. A semiautomatic computer program was developed which can be easily used by field staff to support their management decisions. It is anticipated that the application of such an approach will improve the performance of large-scale irrigation systems, and support development of a performance-oriented management culture among the staff of these irrigation systems. Copyright © 2009 John Wiley & Sons, Ltd.

Kiptala J.K.,UNESCO-IHE Institute for Water Education | Kiptala J.K.,Jomo Kenyatta University of Agriculture and Technology | Mohamed Y.,UNESCO-IHE Institute for Water Education | Mohamed Y.,Technical University of Delft | And 5 more authors.
Water Resources Research | Year: 2013

Evapotranspiration (ET) accounts for a substantial amount of the water use in river basins particular in the tropics and arid regions. However, accurate estimation still remains a challenge especially in large spatially heterogeneous and data scarce areas including the Upper Pangani River Basin in Eastern Africa. Using multitemporal Moderate-resolution Imaging Spectroradiometer (MODIS) and Surface Energy Balance Algorithm of Land (SEBAL) model, 138 images were analyzed at 250 m, 8 day scales to estimate actual ET for 16 land use types for the period 2008-2010. A good agreement was attained for the SEBAL results from various validations. For open water evaporation, the estimated ET for Nyumba ya Mungu (NyM) reservoir showed a good correlations (R=0.95; R 2=0.91; Mean Absolute Error (MAE) and Root Means Square Error (RMSE) of less than 5%) to pan evaporation using an optimized pan coefficient of 0.81. An absolute relative error of 2% was also achieved from the mean annual water balance estimates of the reservoir. The estimated ET for various agricultural land uses indicated a consistent pattern with the seasonal variability of the crop coefficient (Kc) based on Penman-Monteith equation. In addition, ET estimates for the mountainous areas has been significantly suppressed at the higher elevations (above 2300 m a.s.l.), which is consistent with the decrease in potential evaporation. The calculated surface outflow (Qs) through a water balance analysis resulted in a bias of 12% to the observed discharge at the outlet of the river basin. The bias was within 13% uncertainty range at 95% confidence interval for Qs. SEBAL ET estimates were also compared with global ET from MODIS 16 algorithm (R=0.74; R2=0.32; RMSE of 34% and MAE of 28%) and comparatively significant in variance at 95% confidence level. The interseasonal and intraseasonal ET fluxes derived have shown the level of water use for various land use types under different climate conditions. The evaporative water use in the river basin accounted for 94% to the annual precipitation for the period of study. The results have a potential for use in hydrological analysis and water accounting. © 2013. American Geophysical Union. All Rights Reserved.

Kiptala J.K.,UNESCO-IHE Institute for Water Education | Kiptala J.K.,Jomo Kenyatta University of Agriculture and Technology | Mohamed Y.,UNESCO-IHE Institute for Water Education | Mohamed Y.,Technical University of Delft | And 7 more authors.
Physics and Chemistry of the Earth | Year: 2013

In arid and semi-arid areas, evaporation fluxes are the largest component of the hydrological cycle, with runoff coefficient rarely exceeding 10%. These fluxes are a function of land use and land management and as such an essential component for integrated water resources management. Spatially distributed land use and land cover (LULC) maps distinguishing not only natural land cover but also management practices such as irrigation are therefore essential for comprehensive water management analysis in a river basin. Through remote sensing, LULC can be classified using its unique phenological variability observed over time. For this purpose, sixteen LULC types have been classified in the Upper Pangani River Basin (the headwaters of the Pangani River Basin in Tanzania) using MODIS vegetation satellite data. Ninety-four images based on 8. day temporal and 250. m spatial resolutions were analyzed for the hydrological years 2009 and 2010. Unsupervised and supervised clustering techniques were utilized to identify various LULC types with aid of ground information on crop calendar and the land features of the river basin. Ground truthing data were obtained during two rainfall seasons to assess the classification accuracy. The results showed an overall classification accuracy of 85%, with the producer's accuracy of 83% and user's accuracy of 86% for confidence level of 98% in the analysis. The overall Kappa coefficient of 0.85 also showed good agreement between the LULC and the ground data. The land suitability classification based on FAO-SYS framework for the various LULC types were also consistent with the derived classification results. The existing local database on total smallholder irrigation development and sugarcane cultivation (large scale irrigation) showed a 74% and 95% variation respectively to the LULC classification and showed fairly good geographical distribution. The LULC information provides an essential boundary condition for establishing the water use and management of green and blue water resources in the water stress Pangani River Basin. © 2013 Elsevier Ltd.

Tekleab S.,UNESCO-IHE Institute for Water Education | Tekleab S.,Addis Ababa Institute of Technology | Tekleab S.,Hawassa University | Tekleab S.,Technical University of Delft | And 7 more authors.
Hydrological Processes | Year: 2014

The objective of this study was to quantify the impacts of land use/land cover (LULC) change on the hydrology of the Jedeb, an agricultural dominated mesoscale catchment, in the Abay/Upper Blue Nile basin, Ethiopia. Two methods have been used. First, the trends of certain daily flow variability parameters were evaluated to detect statistical significance of the change of the hydrologic response. Second, a conceptual monthly hydrological model was used to detect changes in the model parameters over different periods to infer LULC change. The results from the statistical analysis of the daily flows between 1973 and 2010 reveal a significant change in the response of the catchment. Peak flow is enhanced, i.e. response appears to be flashier. There is a significant increase in the rise and fall rates of the flow hydrograph, as well as the number of low-flow pulses below a threshold level. The discharge pulses show a declining duration with time. The model result depicts a change in model parameters over different periods, which could be attributed to an LULC change. The model parameters representing soil moisture conditions indicated a gradual decreasing trend, implying limited storage capacity likely attributed to increasing agricultural farming practices in the catchment. This resulted in more surface runoff and less infiltration into the soil layers. The results of the monthly flow duration curve analysis indicated large changes of the flow regime. The high flow has increased by 45% between the 1990s and 2000s, whereas the reduction in low flows was larger: a 15% decrease between 1970s and 1980s, 39% between 1980s and 1990s and up to 71% between 1990s and 2000s. These results, could guide informed catchment management practices to reduce surface runoff and augment soil moisture level in the Jedeb catchment. © 2013 John Wiley & Sons, Ltd.

Betrie G.D.,UNESCO-IHE Institute for Water Education | Betrie G.D.,Technical University of Delft | Mohamed Y.A.,UNESCO-IHE Institute for Water Education | Mohamed Y.A.,Technical University of Delft | And 3 more authors.
Hydrology and Earth System Sciences | Year: 2011

Soil erosion/sedimentation is an immense problem that has threatened water resources development in the Nile river basin, particularly in the Eastern Nile (Ethiopia, Sudan and Egypt). An insight into soil erosion/sedimentation mechanisms and mitigation methods plays an imperative role for the sustainable water resources development in the region. This paper presents daily sediment yield simulations in the Upper Blue Nile under different Best Management Practice (BMP) scenarios. Scenarios applied in this paper are (i) maintaining existing conditions, (ii) introducing filter strips, (iii) applying stone bunds (parallel terraces), and (iv) reforestation. The Soil and Water Assessment Tool (SWAT) was used to model soil erosion, identify soil erosion prone areas and assess the impact of BMPs on sediment reduction. For the existing conditions scenario, the model results showed a satisfactory agreement between daily observed and simulated sediment concentrations as indicated by Nash-Sutcliffe efficiency greater than 0.83. The simulation results showed that applying filter strips, stone bunds and reforestation scenarios reduced the current sediment yields both at the subbasins and the basin outlets. However, a precise interpretation of the quantitative results may not be appropriate because some physical processes are not well represented in the SWAT model. © Author(s) 2011.

Gebremicael T.G.,UNESCO-IHE Institute for Water Education | Mohamed Y.A.,UNESCO-IHE Institute for Water Education | Mohamed Y.A.,Technical University of Delft | Mohamed Y.A.,Hydraulic Research Station | And 5 more authors.
Journal of Hydrology | Year: 2013

The landuse/cover changes in the Ethiopian highlands have significantly increased the variability of runoff and sediment fluxes of the Blue Nile River during the last few decades. The objectives of this study were (i) to understand the long-term variations of runoff and sediment fluxes using statistical models, (ii) to interpret and corroborate the statistical results using a physically-based hydrological model, Soil and Water Assessment Tool (SWAT), and (iii) to validate the interpretation of SWAT results by assessing changes of landuse maps. Firstly, Mann-Kendall and Pettitt tests were used to test the trends of Blue Nile flow (1970-2009) and sediment load (1980-2009) at the outlet of the Upper Blue Nile basin at El Diem station. These tests showed statistically significant increasing trends of annual stream flow, wet season stream flow and sediment load at 5% confidence level. The dry season flow showed a significant decrease in the trend. However, during the same period the annual rainfall over the basin showed no significant trends. The results of the statistical tests were sensitive to the time domain. Secondly, the SWAT model was used to simulate the runoff and sediment fluxes in the early 1970s and at the end of the time series in 2000s in order to interpret the physical causes of the trends and corroborate the statistical results. A comparison of model parameter values between the 1970s and 2000s shows significant change, which could explain catchment response changes over the 28. years of record. Thirdly, a comparison of landuse maps of 1970s against 2000s shows conversion of vegetation cover into agriculture and grass lands over wide areas of the Upper Blue Nile basin. The combined results of the statistical tests, the SWAT model, and landuse change detection are consistent with the hypothesis that landuse change has caused a significant change of runoff and sediment load from the Upper Blue Nile during the last four decades. This is an important finding to inform optimal water resources management in the basin, both upstream in the Ethiopian highlands, and further downstream in the plains of Sudan and Egypt. © 2012 Elsevier B.V.

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