Abstract:
Eutrophication is a trouble that alter the ecological integrity of any water resources at global,
regional and local scale including Ethiopia resulted by P that exported and loaded from
agricultural-based catchment. Gilgel Gibe I watershed is agriculture –based catchment found
in the south-western part of Ethiopia, in Oromia Regional State. This catchment is exhibited
to this problem as a result of agricultural intensification with P concentration beyond the limit
(0.86 mg/l).Therefore, the objectives of this study were to assess the transport pathways,
quantify the amount of P load and to identify the prone sub-basins that were responsible for a
significant P load utilizing SWAT model on this study area. To achieve this, a longitudinal
desk study design was followed after all necessary input data was collected, analyzed and
prepared.
The GIS- Arc SWAT interface was applied to distinguish and classify the land use, soil and
slope of the area and found the LU as Generic (AGLI) ( Agriculture, Agro-silvi-cultural,
Agro-pastoral) 91.46%,Forest Evergreen (FRSE) ( Silvi-culture) 2.69%,Forest Mixed (FRST)
(Forest with coffee under and coffee under tree),2.89%,Pasture (PAST) (Grass land),
2.75%,Urban (URBN) (Residential) 0.21% and dominant soil as Eutric Nitosols (Ne13-3b)
65%, Eutric Vertisols (Ne12-2c) 35%.Further the model performance was evaluated and
found the model was satisfactory to be applied over the area for water resources management
for sustainable social and economic development. Following this, the pathways of P was
assessed and found that the organic form of (Org P) was the dominant exportation mechanism
and accounts around 77.2% of paths. Similarly, the maximum total P load was also
investigated and found as 4.4 × 10 ହ
tons/year on 2009 and corresponding minimum total
load was around 5.7 × 10 ସ
tons /year and holds 4.4% load on 2007.The prone sub-basins
which were significantly responsible for high P load wereidentified.Lastly, conclusions and
recommendations would be offered based on study findings.
