NUMERICAL METHODS OF FLOOD ROUTING

Abstract

The story of man's progress is closely linked with the exploitation of rivers. Development of great civilizations on the river banks and location of some of the largest cities on the river banks, testify to this fact. Ever since the dawn of civilization rivers have been the major source to fulfil the water requirements of mankind. Unfortunately, while rivers do briny much-needed water to the millions who are settled on their banks, they can also bring calamity in the form of floods. Floods claim hundreds of lives besides causing severe property damage in our country every year. The study of floods is important for the design of flood control projects and flood ferecasting systems. The technique which is used for predicting the temporal and spatial variation of a flood wave, as it traverses through a river system, is called Ftood Rou-ting. In other words it is the techique of computing the flow parameters at some location from the known parameters at an upstream location. 1.2 FLOOD ROUTING The object of flood routing is to know the effect of system dynamics and system storage on the shape and movement of the flood wave. The basic problem is to solve unsteady flow equations and then to find out the new shape of the flood hydrograph at a downstream location. - 2 - Methods for-tolving these euqations depend very much on the selection of the form of these equations. These various methods can broadly be classified under two headings as below : i) Hydrologic Methods . ii) Hydraulic Methods. Hydrologic methods are based upon the solution of continuity equation with the help of a suitable relationship for the channel storage. These methods do not take into account the momentum equation. On the other hand, hydraulic routing procedures take into account both, continuity and momentum equations. Hence it is obvious that hydraulic routing techniques are more accurate and applicable in a variety of situations, as compared to hydrologic routing. The solution of the St. Venant's equations may be obtained using any one of the following hydraulic methods : i) Method of characteristics ii) Explicit Finite- Difference scheme iii) Implicit finite-difference scheme. Of those, the implicit scheme is often pr,zferred on account of its advantages over the other methods, so fOr as stability, choice of longer time steps etc is concerned. Although the details of implicit scheme are well documented , ':(2;3,8) raki, the program based on this method even for a single channel is not readily available in the literature