Effect of Channel Shape on Time of Travel and Equilibrium Detention Storage in Channel

Abstract

For a catchment comprising a network of open channels and overland planes, the time of travel and the equilibrium detention storage in the channels have profound effects on the runoff characteristics of the catchment. For channels with long time of travel and large detention storage, they produce smaller catchment outflow, and the converse is true. Intuitively, the shape of the channels must have an effect on both the time of travel and the detention storage. Hence, the channel shape can be used as a means to manage the runoff from a catchment. In this technical note, the effect of channel shape on the time of travel and the equilibrium detention storage has been compared for seven channel shapes. The channels are subject to a uniform lateral inflow and a constant upstream inflow. The seven channel shapes are (1) square; (2) wide rectangular; (3) deep rectangular; (4) triangular; (5) vertical curb; (6) parabolic; and (7) circular. The comparison shows that channels with long time of travel also have large equilibrium detention storage, and vice versa. It also shows that channel shape can cause a sixfold increase in the time of travel, and a fourfold increase in the detention storage. Of the seven channel shapes, the one that produces the longest time of travel and largest detention storage is the deep rectangular channel. Hence, the use of this channel produces smaller catchment outflow. The channel that produces the shortest time of travel and smallest detention storage is the parabolic channel with large flow depth. Hence, the use of this channel produces larger catchment outflow.