Water Quality assessment of Bagmati River in Kathmandu Valley

Abstract

Water quality assessment of Bagmati River in the Kathmandu valley was carried out at pre-monsoon(March and April) and monsoon(July and September)season.The standard methods (APHA 1998 and Trivedy and Goel 1986) were followed for chemical analysis.Five sitesviz. Sundarijal, Aryagh at,Thapathali, Sundarighat and Khokana were selected.The major work of the study was analysis of physical (Temperature, pH, Electrical Conductivity) and chemical (DO, BOD, NO 3 vii -N, PO 4 -P, NH -N) parameters along the Bagmati River, classification of River based on polluted sites, comparing river water quality in past and present and determining the self-dilution capacity. 3 The water quality of Bagmati River was classified using German Water Quality Index and Netherl and Water Quality Index.Based on the German Water Quality Index, the five stations of Bagmati River were classified separately. According to this Index, Sundarij alwas classified as 'low pollution 'zone in both the pre-monsoon and monsoon season while Aryaghat as 'moderate pollution' zone at both the seasons. Similarly, Thapathali was classified as 'very severe pollution' zone inpre-monsoon and 'moderate pollution' zone in monsoon while Sundarighat as 'excessive pollution' zone in pre-monsoon and 'severe pollution' zone in monsoon. Khokana was classified as 'very severe pollution' zone in pre-monsoon and 'moderate' pollution' zone in monsoon.On the other hand, based on the Netherl and Water Quality Index, Sundarijal was classified as 'Excellent' zone in pre-monsoon and monsoon,Aryaghat as 'Bad' zone in pre-monsoon and 'fair' in monsoon season. Thapathali, Sundarighat and Khokana were classified as 'very bad' zone in both the seasons in all these three stations.The chemical parameters were found beyond the natural level in almost all the stations except Sundarijal. Sundarighat was found in worstcondition among all. The water quality trend analysis at past and present indicated degrading condition of river. Self-dilution capacity i.e. additional flow required in the river so as to maintain permissible level of 30mg/L BOD at Sundarijal, Aryaghat and Khokana was calculated as 1.03m 3 /s, 1.74m 3 /s and 17.7m 3 /s; respectively.The level of pollution was found to be more severe in pre-monsoon than that of monsoon season.Key words: Chemical Parameters, Monsoon and Pre-monsoon, Water Quality