IMPACTS OF URBANISATION ON WATER BODIES

Abstract

The rapidly urbanizing Udaipur city, in the south of Rajasthan, has an interlinked man-made lake system which is now under threat because of increase in Impervious Surface Area (ISA)[1]. The Ahar catchment in which Udaipur lies has seen a rise in built-up area from 6.93% to 18.20% in the past 20 years. In order to reduce the negative impacts of urbanization on the receiving water bodies, spatial planning must be integrated with water management. In response to a better understanding of ISA, the adoption of Water Sensitive Urban Design (WSUD) is promising for large urban developments.[2] The study tried to explore the potential for improvement of stormwater quality which in turn will help in ameliorating the receiving water bodies by Water Sensitive Retrofitting. Water quality assessment of the lakes showed high Nitrate content because of which lakes are infested with aquatic weeds and algae. Urban Hydrology Model, EPA-SWMM is used to model the effects of parks in an existing urban catchment of Udaipur as networks of bio-retention devices. ERDAS 2014 is used to generate imperviousness which was found to be the most sensitive of all parameters. ArcMap 10.2.2 is used to calculate runoff manually for validation. The results demonstrated the potential for increasing the utilitarian value of many public parks by verifying the capacity for significantly improving urban stormwater quality. 10-20% of park area for 30 large sized public parks was reserved for bio-retention which resulted in about 14.48 tonnes/yr reduction in Nitrate content from stormwater. It showed an overall nitrogen removal efficiency of 6.4%. The runoff was reduced by 5.3% and the peak value reduced by 7.2% with a delay in peak of about 1 hour. It was found that the subcatchment with ISA 88% has the nitrogen load of 2.57 tonnes/yr per sq.km while the subcatchment with ISA 6% has a nitrogen load of 0.09 tonnes/yr per sq.km. Nitrogen content is also high in the subcatchments in which agricultural area is high although ISA is reasonably low. There is a growing consensus on the rising need of a more sustainable urban water management, for which different concepts have stemmed, but empirical validation of the same is limited, it being a complex and data demanding study. [3]