Title: | A multi basin SWAT model analysis of runoff and sedimentation in the Blue Nile, Ethiopia |
Authors: | Easton, Z.M., D.R. Fuka, E.D. White, A.S. Collick, B. Biruk Ashagre, M. McCartney, S.B. Awulachew, A.A. Ahmed and T.S. Steenhuis |
Year: | 2010 |
Journal: | Hydrology and Earth System Sciences |
Volume (Issue): | 14(10) |
Pages: | 1827-1841 |
Article ID: | |
DOI: | 10.5194/hess-14-1827-2010 |
URL (non-DOI journals): | |
Model: | SWAT-WB |
Broad Application Category: | hydrologic and pollutant |
Primary Application Category: | variable source area/saturation excess hydrology |
Secondary Application Category: | sediment loss and transport |
Watershed Description: | 312,000 km^2 Blue Nile in Ethiopia |
Calibration Summary: | |
Validation Summary: | |
General Comments: | |
Abstract: | A multi basin analysis of runoff and erosion in
the Blue Nile Basin, Ethiopia was conducted to elucidate
sources of runoff and sediment. Erosion is arguably the most
critical problem in the Blue Nile Basin, as it limits agricultural
productivity in Ethiopia, degrades benthos in the Nile,
and results in sedimentation of dams in downstream countries.
A modified version of the Soil and Water Assessment
Tool (SWAT) model was developed to predict runoff and sediment
losses from the Ethiopian Blue Nile Basin. The model
simulates saturation excess runoff from the landscape using
a simple daily water balance coupled to a topographic wetness
index in ways that are consistent with observed runoff
processes in the basin. The spatial distribution of landscape
erosion is thus simulated more correctly. The model was
parameterized in a nested design for flow at eight and sediment
at three locations in the basin. Subbasins ranged in size
from 1.3 to 174 000 km^2, and interestingly, the partitioning
of runoff and infiltrating flow could be predicted by topographic
information. Model predictions showed reasonable
accuracy (Nash Sutcliffe Efficiencies ranged from 0.53–0.92)
with measured data across all sites except Kessie, where the
water budget could not be closed; however, the timing of flow
was well captured. Runoff losses increased with rainfall during
the monsoonal season and were greatest from areas with
shallow soils and large contributing areas. Analysis of model
results indicate that upland landscape erosion dominated sediment
delivery to the main stem of the Blue Nile in the early
part of the growing season when tillage occurs and before
the soil was wetted up and plant cover was established. Once
plant cover was established in mid August landscape erosion
was negligible and sediment export was dominated by channel
processes and re-suspension of landscape sediment deposited
early in the growing season. These results imply that
targeting small areas of the landscape where runoff is produced
can be the most effective at controlling erosion and
protecting water resources. However, it is not clear what can
be done to manage channel erosion, particularly in first order
streams in the basin. |
Language: | English |
Keywords: | |