Application of QUAL2kw and Forecasting models for assessment of pollutants in upper Athi River catchment in Kenya

Abstract

Water pollution in the Athi river drainage basin, the fourth largest drainage basin in Kenya, has the potential of adversely impacting the aquatic biota and communities living downstream of the river. The upper part of the basin has experienced rapid industrialization in the recent past and there has also been increased encroachment of wetlands and forests for agriculture and settlement to cater for the increased population. The objective of this study was geared towards the generation of scenarios to predict future water quality trends in the upper parts of the Athi river basin. The prediction of the future water quality trends was undertaken in two phases: (i) the development of longitudinal water quality profile using QUAL2Kw model and (ii) prediction of the future water quality trends using the SPSS Forecasting tool. The collection of water quality data in established sampling stations located in the upper parts of the basin was carried out between January and December 2018. The archival data for the period 2015-2018 was obtained from Water Resources Authority (WRA) database for the determination of future trends in selected water quality parameters. The correlation analysis between the observed and predicted water quality parameters yielded strong R2 values for temperature-0.82, electrical conductivity-0.99, total dissolved solids-0.94, biochemical oxygen demand-0.66, chlorophyll a-0.89, total nitrogen-0.75 and total phosphorous-0.94. The standard error ranged between 0.01-0.42, indicating that the model is reliable for predicting water quality parameters in the river. The available archival monthly data from 2015 to 2018 were averaged for time series forecasting to generate future water quality scenarios of the river for the period 2019-2030. The results showed that dissolved oxygen exhibit a decreasing trend in future indicating depletion of oxygen in water. There will also be significant increasing trends for Electrical Conductivity, Total Suspended Solids, Biochemical Oxygen Demand and Iron in future. There is a risk that the pollutants will increase to unsafe levels in the Athi River if appropriate management actions are not taken by the concerned agencies