Abstract:
The Wabe River is a perennial river that is one of the water contributors for the Gibe III dam.
It is used for various purposes such as agriculture, recreation, and domestic use. However, the
potential pollution of the river has increased due to the stream from a brewery industry, and its
impact on the self-purification capacity of the river has not been studied. Therefore, the
objective of this study was to evaluate the quality of the stream from the industry and simulate
its impact on the self-purification capacity of the Wabe River using QUAL2Kw.
Sample collection was conducted during the dry season from December to January. The
sampling points of the river water included one upstream location approximately 450m from
the mixing point, the mixing point of the stream and river, and four downstream points. The
samples were measured in the field and laboratory according to respective standard analysis
methods. Various parameters such as COD, BOD5, DO, alkalinity, pH, TSS, TP, TN, soluble
phosphate, ammonia, nitrate, nitrite, and water temperature were analyzed. In the development
of the self-purification simulation model, river velocity and discharge were measured using
velocity area methods, and the required river geometry was extracted with the help of ArcGIS
10.8 and HEC-RAS.
The analytical results for the stream from industry showed high concentrations of BOD5
(354.3±96.6 mg/l), TSS (457±251 mg/l), TP (22.72±2.17 mg/l), and COD (600±167.6 mg/l),
which exceeded the limits set by the EPA. However, since there are no presented standards for
other parameters in the EPA, a comparison could not be made. The quality of the river, except
for TSS and nitrite nitrogen concentration, was found to be good according to the US.EPA
(2003) standards. TSS concentrations in all sampling points and nitrite nitrogen concentrations
from S-3 to S-6 exceeded US.EPA (2003) standards due to discharge of waste, less dilution
and decomposition of matter. The QUAL2Kw simulation showed good agreement with
observed values, except for COD, NH3-N, and TSS parameters, which raised concerns about
the ecological health of the river. It is recommended that the respective government/body/
should take periodic regulatory actions to ensure that stream from the industry are safely
released. The use of QUAL2Kw will aid in decision-making processes.
