ABSTRACT
The process of computing the reservoir stage, storage volumes and outflow rates corresponding to a particular hydrograph of inflow is commonly referred to as flood routing. Flood routing studies are required in the design of spillways of reservoirs. The spillway capacity is fixed, taking into consideration the moderation caused by the flood absorption capacity of the reservoir, which is the capacity between the full reservoir and high flood level. The spillway is thus designed for discharging a flood peak at less than the peak of the incoming flood. Looking at it, from another angle, flood routing studies may be used to find out the high flood level, for a given spillway for a design flood. Maximum reservoir elevations, obtained by routing a particular hydrograph through a reservoir reflects the integrated effect of-(i) initial reservoir level, (ii) rate and volume of inflow into the reservoir, (iii) rate of outflow, (iv) discharge of regulating outlets, power penstock, and (v) surcharge storage and rate of overflow. In flood control reservoirs, flood routing studies are used to arrive at the most economical combination of storage and outflow capacity such that for the design flood, the outflow from the reservoir does not exceed the safe bankful capacity of the downstream channel. In a flood forecasting system flood routing studies are used to compute the probable flood levels with respect to time at downstream points, corresponding to a flood wave entering the valley at an upstream point.
