The collective impacts of rapid urbanization, poor pollution management practices and insufficient sanitation infrastructure have driven the water quality deterioration in Little Akaki River (LAR), Ethiopia. Water quality modeling using QUAL2Kw was conducted in the LAR aimed at selecting the optimal water quality improvement and pollution load reduction approaches based on the evaluation of five scenarios: modification of point sources (PS) load (S1), modification of nonpoint sources (NPS) load (S2), simultaneous modification of PS and NPS load (S3), application of local oxygenators and fish passages using cascaded rock ramps (S4), and an integrated scenario (S5). Despite the evaluation of S1 resulting in an average load reduction of Biochemical Oxygen Demand (BOD) (17.72%), PO₄-P (37.47%), NO₃-N (19.63%), the water quality objective (WQO) in LAR could not be attained. Similarly, though significant improvement of pollution load was found by S2 and S3 evaluation, it did not secure the permissible BOD and PO₄-P pollution load in the LAR. Besides, as part of an instream measure, a scenario evaluated using the application of rock ramps (S4) resulted in significant reduction of BOD load. All the individual scenarios were not successful and hence an integration of scenarios (S5) was evaluated in LAR that gave a relatively higher pollutant load reduction rate and ultimately was found a better approach to improve pollution loads in the river. In conclusion, pollution load management and control strategy integrally incorporating the use of source-based wastewater treatment, control of diffuse pollution sources through the application of best management practices and the application of instream measures such as the use of cascaded rock ramps could be a feasible approach for better river water quality management, pollution reduction, aquatic life protection and secure sustainable development in the LAR catchment.

中文翻译：

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基于情景的水质模型在埃塞俄比亚小阿卡基河中选择最佳的减污负荷和水质改善方法

快速城市化，不良的污染管理做法和不足的卫生基础设施共同造成的影响，导致埃塞俄比亚小阿卡基河（LAR）的水质恶化。在LAR中使用QUAL2Kw进行水质建模，旨在基于以下5种情况的评估来选择最佳的水质改善和减少污染负荷的方法：修改点源（PS）负荷（S1），修改非点源（NPS）负荷（S2），同时修改PS和NPS负荷（S3），使用级联岩石坡道应用局部充氧器和鱼道（S4）以及综合方案（S5）。尽管对S1进行了评估，但生化需氧量（BOD）（17.72％），PO ₄ -P（37.47％），NO ₃的平均负荷降低了-N（19.63％），则无法达到LAR中的水质指标（WQO）。同样，尽管通过S2和S3评估发现污染负荷得到了显着改善，但它并未确保允许的BOD和PO ₄LAR中的-P污染负荷。此外，作为入流措施的一部分，使用岩石坡道（S4）进行评估的方案可显着降低BOD负荷。所有单个方案均未成功，因此在LAR中对方案（S5）进行了评估，从而获得了相对较高的污染物减少率，最终发现了一种改善河流中污染负荷的更好方法。总之，将污染负荷管理和控制策略整合在一起，包括采用基于源的废水处理，通过采用最佳管理实践来控制弥散性污染源以及采用诸如级联岩石坡道之类的下游措施，这是可行的。更好地管理河流水质，减少污染的方法，