Abstract
Ndarugu River, Kenya, during its course through the different agricultural and industrial areas of Gatundu, Gachororo and Juja farms, receives untreated industrial, domestic and agricultural waste of point source discharges from coffee and tea factories. During wet season the water is also polluted by non-point (diffuse) sources created by runoff carrying soil, fertilizer and pesticide residues from the catchment area. This study involved the calibration of water quality model QUAL2K to predict the water quality of this segment of the river. The model was calibrated and validated for flow discharge (Q), temperature (T°), flow velocity (V), biochemical oxygen demand (BOD5), dissolved oxygen (DO) and nitrate (NO3-N), using data collected and analyzed during field and laboratory measurements done in July and November-December 2013. The model was then used in simulation and its performance was evaluated using statistical criteria based on correlation coefficient (R2) and standard errors (SE) between the observed and simulated data. The model reflected the field data quite well with minor exceptions. In spite of these minor differences between the measured and simulated data set at some points, the calibration and validation results are acceptable especially for developing countries where the financial resources for frequent monitoring works and higher accuracy data analysis are very limited. The water is being polluted by the human activities in the catchment. There is need for proper control of wastewater by various techniques, and preliminary treatment of waste discharges prior to effluent disposal. Management of the watershed is necessary so as to protect the river from the adverse impacts of agricultural activities and save it from further deterioration.
Highlights
Intensive developments of industry, agricultural production and ever intensive urbanization have led to the increase in number of pollutants and the amount of wastewater which pollute water flows
In most of the studies carried out in the application of QUAL2K model, it was observed that the model represented the field data quite well and this reasonable modeling guarantees the use of QUAL2K for future river water quality options [5]
The aim of the study was to model the water quality of the polluted segment of Ndarugu River by the comprehensive application of water quality model QUAL2K and evaluate the performance of the model using statistics based on correlation coefficient (R2) and standard error (SE)
Summary
Agricultural production and ever intensive urbanization have led to the increase in number of pollutants and the amount of wastewater which pollute water flows. Agricultural and industrial wastewater into the rivers with little or no treatment prior to discharge is a common practice in many developing countries. This has caused a serious concern over the deterioration of river water quality. One of the major inadequacies is the lack of provision for conversion of algal death to carbonaceous biochemical oxygen demand (CBOD) Another limitation of this model is that the river section has to be segmented in to equal lengths reaches and equal the number of elements in each reach. The aim of the study was to model the water quality of the polluted segment of Ndarugu River by the comprehensive application of water quality model QUAL2K and evaluate the performance of the model using statistics based on correlation coefficient (R2) and standard error (SE)
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