TR-79 : Effect of tributary junction on routing characteristics

Abstract

In accurate routing of floods in river networks using the St. Venant's equations, the junction imposes a computational difficulty because of the mutual backwater effects of the channels joining at the junction. Various methods have been developed to predict the progress of a flood wave along a junction. These have been briefly discussed and the overlapping method using four-point implicit finite difference scheme has been described in detail in this report. Having surveyed the different methodologies and experiences of various authors/implementers, the data requirement needed for finding the solutions to such problems faced by Water Resources Engineers has also been given separately. Conventionally, the downstream backwater effect is simply ignored and the computations for the network are proceeded in a cascading manner towards the downstream, leading to unrealistic results. The overlapping segment method faithfully simulates the flood flow in the network and the computer results agree well with those obtained by the time consuming solution of all the flow equations of the entire network. Conversely, the commonly used sequential cascading channel method produces in-accurate results, particularly when the downstream backwater effect is important and reverse flow occurs.