The Udunuwara-Yatinuwara water supply scheme of the National Water Supply and Drainage Board abstracts water through a riverbed filtration system located in a bifurcated channel of the Mahaweli River at Peradeniya. The diverted flow through the channel has become inadequate to supply the abstraction demand during the periods of low river flow. The flow pattern in the river and the discharge through the channel are investigated by the application of a two-dimensional depthaveraged flow computational model to a 450 m long river reach including the channel. The model was set up, calibrated and verified for the reach using measurements carried out at the site. The model was applied to ascertain the possibility of increasing the flow through the channel during low flow in the river by changing the river bed level in the reach.