Effect on Water Quality due to Residential Development – A Case Study on Kolonnawa Canal

Abstract

Due to the increasing number of residential buildings in Colombo and its suburbs, the wastewater volume generated and discharged by them is also to be increased. It would affect water bodies and would eventually lead them to be heavily polluted. As the canal network which is a part of the surface drainage system in Colombo acts to drain out the flood water from Colombo to the sea and Kelani river while providing and receiving water from urban wetlands, their water quality should be properly monitored and controlled. This study attempted to measure surface water quality in Kolonnawa canal, find out the Grey Water Footprint (GWF) and analyse the effect caused by the domestic wastewater discharged into Kolonnawa canal and its marsh. This study is conducted by using water quality parameters including pH, Temperature, Dissolved Oxygen (DO), Biochemical Oxygen Demand (BOD), Total Dissolved Solid (TDS), Electrical Conductivity (EC), Salinity, Resistivity, Chemical Oxygen Demand (COD), NO3-N and PO4-P and ultimately finding the GWF by collecting 3 sets of samples from 8 locations at 10-day intervals. Test results indicated DO, BOD and COD as downgrading water quality parameters showcasing major differences from allowable water quality standard values. GWF is calculated as 131.25 m3/s, a considerably high discharge rate which could only be achieved in flood situations. According to the water quality results and site investigations, it was concluded that the Kolonnawa canal receives a considerable load of pollutants from its sub-catchment and domestic originated greywater is a major contributor