ABSTRACT
The traditional urban practice was to construct lined channels, mainly in order to avoid channel erosion and to provide efficient drainage. Consider water flowing from a pool of water having a constant water level to a channel. The depth of the uniform flow will depend on the slope of the channel; for a mild slope channel the flow is likely to be subcritical with the depth higher than the critical depth. Water depth on floodplains is lower compared to the main channel water depth and for shallower water, the relative roughness is higher. For a very flat topography this is an issue, as the channel should have a slope to convey water downstream by gravity. For the design of a channel, the basic aim is to convey the maximum amount of discharge through a minimum possible area.
