Modelling of two low lying urban watersheds in the greater Colombo area fou drainage and environment improvement

Abstract

The increase ih urban populations is demanding more and more land for living and hence there are widespread land cover and land use interventions as solutions to over-come the scarcity of land. This creates uncontrolled flooding causing enormous problems to the environment. Realistic drainage planning in urban areas requires the capability to incorporate land use changes, requires the ability to look at varying channel conditions, and should consider the concepts of storm water and domestic water discharges and the effects of downstream controls that affects the flow. Most urban watersheds in the City'of Colombo in Sri Lanka and its vicinity are low-lying but in the literature, one finds only limited application of hydrologic models to low lying watersheds in Sri Lanka. In this study two urban watersheds in the Greater Colombo region were mathematically modelled considering the land cover, canal properties, intermittent storage, and tidal and backwater effects, to identify the parameters that could be used for design purposes: The modelling effort established the Tiydrodynamic and watershed models through a systematic calibration and verification procedures and the results indicated very good reproduction of observed hydrographs. The present work is considered a very important contribution towards the urban drainage and environment improvement ..