Assessment of variation in water quality at Right Bank Outfall Drain, including Manchar lake, Sindh, Pakistan

Abstract

ABSTRACT Right Bank Outfall Drain (RBOD) is a drainage canal being built on the right side of river Indus, Sindh Pakistan and will carry saline water from Balochistan and Northern Sindh to Arabian Sea coast. It is still at different stages for completion. Thirteen samples were collected from RBOD III and RBOD I (Hairdin Pumping Stations, Balochistan to Sehwan, Manchar lake, Sindh), and a reference sample was collected from river Indus at Kotri Barrage. The sampling scheme was repeated three times in 2009 and 11 samples were collected from RBOD I during 2018. The water samples were analysed for about 27–41 different parameters, including physicochemical, cations, anions, trace metals and the presence of microbiological organisms. The variation in the water quality was examined pre- and post-monsoon season and flows of water at Kotri Barrage. A significant variation was observed in quality of water pre and post monsoon. Higher concentrations were reported during pre-monsoon season. The water quality index (WQI) indicated that most of the samples were within poor water category for both drinking and irrigation purposes. Gibb’s diagrams demonstrated that evaporation was dominant (85.7%) on the hydrochemistry of the water samples. The Cd, Pb, Ni, Cr and As crossed the permissible limits at a number of sampling stations. The water samples were also examined for multivariate analysis including principal component analysis (PCA), cluster analysis, piper diagrams and coefficient of variation. Chloride (Cl−) and sodium were dominant, followed by calcium, magnesium, sulphate and bicarbonate. The average values of analyses (n = 4) indicated RSD within 4.0%. The samples were examined for possible use for irrigation and 53–92% samples collected from RBOD (n = 14) were within unsuitable category for irrigation.