scholarly journals Budgeting suspended sediment fluxes in tropical monsoonal watersheds with limited data: the Lake Tana basin

2018 ◽  
Vol 66 (1) ◽  
pp. 65-78 ◽  
Author(s):  
Fasikaw A. Zimale ◽  
Mamaru A. Moges ◽  
Muluken L. Alemu ◽  
Essayas K. Ayana ◽  
Solomon S. Demissie ◽  
...  
Keyword(s):  
Management Practices ◽  
Sediment Budget ◽  
Model Parameters ◽  
Lake Tana ◽  
Discharge Data ◽  
Flood Plains ◽  
Sediment Fluxes ◽  
Data Limitations ◽  
Lakes And Reservoirs ◽  
Lake Tana Basin

Abstract Soil erosion decreases soil fertility of the uplands and causes siltation of lakes and reservoirs; the lakes and reservoirs in tropical monsoonal African highlands are especially affected by sedimentation. Efforts in reducing loads by designing management practices are hampered by lack of quantitative data on the relationship of erosion in the watersheds and sediment accumulation on flood plains, lakes and reservoirs. The objective of this study is to develop a prototype quantitative method for estimating sediment budget for tropical monsoon lakes with limited observational data. Four watersheds in the Lake Tana basin were selected for this study. The Parameter Efficient Distributed (PED) model that has shown to perform well in the Ethiopian highlands is used to overcome the data limitations and recreate the missing sediment fluxes. PED model parameters are calibrated using daily discharge data and the occasionally collected sediment concentration when establishing the sediment rating curves for the major rivers. The calibrated model parameters are then used to predict the sediment budget for the 1994-2009 period. Sediment retained in the lake is determined from two bathymetric surveys taken 20 years apart whereas the sediment leaving the lake is calculated based on measured discharge and observed sediment concentrations. Results show that annually on average 34 t/ha/year of sediment is removed from the gauged part of the Lake Tana watersheds. Depending on the up-scaling method from the gauged to the ungauged part, 21 to 32 t/ha/year (equivalent to 24-38 Mt/year) is transported from the upland watersheds of which 46% to 65% is retained in the flood plains and 93% to 96% is trapped on the flood plains and in the lake. Thus, only 4-7% of all sediment produced in the watersheds leaves the Lake Tana Basin.

scholarly journals Calculating the sediment budget of a tropical lake in the Blue Nile basin: Lake Tana

2016 ◽  
Author(s):  
F. A. Zimale ◽  
M. A. Mogus ◽  
M. L. Alemu ◽  
E. K. Ayana ◽  
S. S. Demissie ◽  
...  
Keyword(s):  
Sediment Concentration ◽  
Sediment Budget ◽  
Model Parameters ◽  
Lake Tana ◽  
Discharge Data ◽  
Blue Nile Basin ◽  
Lakes And Reservoirs ◽  
African Highlands ◽  
Upper Estimate ◽  
The Impact

Abstract. Soil erosion decreases soil fertility of the uplands and causes siltation of lakes and reservoirs. However, very little data exists to quantify accurately the impact of sediment on lakes in tropical monsoonal areas in the African highlands. Lake Tana is one of these lakes in Ethiopia. The objective of this study is to quantify the sediment budget for Lake Tana watershed with limited observational data. To overcome these limitations we use the Parameter Efficient Distributed (PED) model that has shown to perform well in the Ethiopian highlands. PED model parameters are calibrated using daily discharge data and sediment concentration infrequently measured for establishing sediment rating curves for the major rivers. The calibrated model parameters are then used to predict the sediment budget for the period 1994–2009. Sediment retained in the lake is calculated from two bathymetric taken 15 years apart and the sediment leaving the lake is based on measured discharge and observed sediment concentrations. Results show that annually on average 34 Mg/ha/year of sediment is removed from the gauged part of the Lake Tana watersheds. Depending on the up scaling method, 14 to 32 Mg/ha/year is transported from the watershed of which 82% to 96% (with the upper estimate more likely) is trapped on the floodplains and in the lake.

scholarly journals Establishing Stage–Discharge Rating Curves in Developing Countries: Lake Tana Basin, Ethiopia

Hydrology ◽  
2022 ◽  
Vol 9 (1) ◽  
pp. 13
Author(s):  
Teshager A. Negatu ◽  
Fasikaw A. Zimale ◽  
Tammo S. Steenhuis
Keyword(s):  
Developing Countries ◽  
Ecological Research ◽  
Alluvial Channels ◽  
Rating Curve ◽  
Lake Tana ◽  
Discharge Data ◽  
Streamflow Data ◽  
Rating Curves ◽  
Lake Tana Basin ◽  
Discharge Curves

A significant constraint in water resource development in developing countries is the lack of accurate river discharge data. Stage–discharge measurements are infrequent, and rating curves are not updated after major storms. Therefore, the objective is to develop accurate stage–discharge rating curves with limited measurements. The Lake Tana basin in the upper reaches of the Blue Nile in the Ethiopian Highlands is typical for the lack of reliable streamflow data in Africa. On average, one stage–discharge measurement per year is available for the 21 gaging stations over 60 years or less. To obtain accurate and unique stage–discharge curves, the discharge was expressed as a function of the water level and a time-dependent offset from zero. The offset was expressed as polynomial functions of time (up to order 4). The rating curve constants and the coefficients for the polynomial were found by minimizing the errors between observed and predicted fluxes for the available stage–discharge data. It resulted in unique rating curves with R2 > 0.85 for the four main rivers. One of the river bottoms of the alluvial channels increased in height by up to 3 m in 60 years. In the upland channels, most offsets changed by less than 50 cm. The unique rating curves that account for temporal riverbed changes can aid civil engineers in the design of reservoirs, water managers in improving reservoir management, programmers in calibration and validation of hydrology models and scientists in ecological research.

scholarly journals Calibration and evaluation of a semi-distributed watershed model of Sub-Saharan Africa using GRACE data

2012 ◽  
Vol 16 (9) ◽  
pp. 3083-3099 ◽  
Author(s):  
H. Xie ◽  
L. Longuevergne ◽  
C. Ringler ◽  
B. R. Scanlon
Keyword(s):  
Regional Scale ◽  
Water Storage ◽  
Hydrologic Model ◽  
Sub Saharan Africa ◽  
Model Parameters ◽  
Total Water ◽  
Discharge Data ◽  
Model Based ◽  
Grace Data ◽  
Sub Saharan

Abstract. Irrigation development is rapidly expanding in mostly rainfed Sub-Saharan Africa. This expansion underscores the need for a more comprehensive understanding of water resources beyond surface water. Gravity Recovery and Climate Experiment (GRACE) satellites provide valuable information on spatio-temporal variability in water storage. The objective of this study was to calibrate and evaluate a semi-distributed regional-scale hydrologic model based on the Soil and Water Assessment Tool (SWAT) code for basins in Sub-Saharan Africa using seven-year (July 2002–April 2009) 10-day GRACE data and multi-site river discharge data. The analysis was conducted in a multi-criteria framework. In spite of the uncertainty arising from the tradeoff in optimising model parameters with respect to two non-commensurable criteria defined for two fluxes, SWAT was found to perform well in simulating total water storage variability in most areas of Sub-Saharan Africa, which have semi-arid and sub-humid climates, and that among various water storages represented in SWAT, water storage variations in soil, vadose zone and groundwater are dominant. The study also showed that the simulated total water storage variations tend to have less agreement with GRACE data in arid and equatorial humid regions, and model-based partitioning of total water storage variations into different water storage compartments may be highly uncertain. Thus, future work will be needed for model enhancement in these areas with inferior model fit and for uncertainty reduction in component-wise estimation of water storage variations.

scholarly journals Application of HEC-HMS Model for Flow Simulation in the Lake Tana Basin: The Case of Gilgel Abay Catchment, Upper Blue Nile Basin, Ethiopia

Hydrology ◽  
2019 ◽  
Vol 6 (1) ◽  
pp. 21 ◽  
Author(s):  
Bitew G. Tassew ◽  
Mulugeta A. Belete ◽  
K. Miegel
Keyword(s):  
Sensitivity Analysis ◽  
Relative Error ◽  
Soil Conservation ◽  
Curve Number ◽  
Soil Conservation Service ◽  
Nile Basin ◽  
Lake Tana ◽  
Blue Nile ◽  
Blue Nile Basin ◽  
Lake Tana Basin

Understanding the complex relationships between rainfall and runoff processes is necessary for the proper estimation of the quantity of runoff generated in a watershed. The surface runoff was simulated using the Hydrologic Modelling System (HEC-HMS) for the Gilgel Abay Catchment (1609 km2), Upper Blue Nile Basin, Ethiopia. The catchment was delineated and its properties were extracted from a 30 m × 30 m Digital Elevation Model (DEM) of the Lake Tana Basin. The meteorological model was developed within HEC-HMS from rainfall data and the control specifications defined the period and time step of the simulation run. To account for the loss, runoff estimation, and flow routing, Soil Conservation Service Curve Number (SCS-CN), Soil Conservation Service Unit Hydrograph (SCS-UH) and Muskingum methods were used respectively. The rainfall-runoff simulation was conducted using six extreme daily time series events. Initial results showed that there is a clear difference between the observed and simulated peak flows and the total volume. Thereafter, a model calibration with an optimization method and sensitivity analysis was carried out. The result of the sensitivity analysis showed that the curve number is the sensitive parameter. In addition, the model validation results showed a reasonable difference in peak flow (Relative Error in peak, REP = 1.49%) and total volume (Relative Error in volume, REV = 2.38%). The comparison of the observed and simulated hydrographs and the model performance (NSE = 0.884) and their correlation (R2 = 0.925) showed that the model is appropriate for hydrological simulations in the Gilgel Abay Catchment.

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