41.4 Routing - nptel - Indian Institute of Technology Madras

Hydraulics Prof. B.S. Thandaveswara
(c) Stage hydrograph (f3(h) h is the depth);
(d) Outflow rating curve (f4 (H), H is the head); and
(e) Storage function (a function of elevation)
Reservoir routing can be accomplished with any one of the hydrologic routing methods
(puls, storage indication method) based on the equation
Indian Institute of Technology Madras
dS
= I - Q
dt
in which
I is the inflow into the reservoir, Q is the outflow from the reservoir and,
dS is the rate of change of storage in the reservoir
dt
Commonly used method is modified Puls method.
The other method for solving equation is Standard Runge - Kutta method, in which the
water surface elevation and water spread area are used. This approach does not
require the computation of special storage outflow (as in the case of modified Puls
method), but is more closely related to hydraulics of flow through the reservoir. The 3 rd
Order Runge - Kutta method involves dividing each time step interval into three
increments and calculating successive values of water surface elevation and reservoir
discharge. This method has proved to be easier for programming and computations as
the trial and error procedure is eliminated.
Determination of breach outflow hydrograph requires knowledge of rate of breaching.
Models for this purpose are available in standard commercial software.
41.4.3 Channel Routing
This is a mathematical procedure used for tracking the flow along the channel. This
involves the determination of discharge, water surface elevation, and time of arrival of
peak, along the channel reaches, by using St. Venant's equation. i.e. unsteady free
surface flow equation. One may note that, kinematic wave approximation also known as