Inreservoir flood routingonly the storage effects are considered, as the
influence of impulsive motion of the inflow on the momentum of the outflow
is neglected and with the assumption of a horizontal water surface the storage
effects are quickly transmitted (Section 4.3); in river (channel) flood routing
the combined effect of storage, resistance and acceleration is manifest.
There are three possible approaches to channel flood routing.
- The hydraulic method (exact dynamic solution)is based on a numeri-
cal solution of the finite difference form of the Saint Venant
equation(s) (equations (8.11)–(8.14)); its further discussion is outside
the scope of this text, but see for example Abbott and Minns (1998)
and Cunge, Holly and Verwey (1980). For this method data on
channel shape and friction coefficients are required.
- Diffusion analogy (approximate dynamic solution)is based on the
analogy between the flood transformation and the dispersion–
diffusion process. Depending on the approximation of the full
dynamic equation various methods have been developed (e.g. the
variable parameter diffusion method). The determination of various
parameters requires knowledge of at least one flood event and of the
340 RIVER ENGINEERING
Fig. 8.6 Thin-crested weirs
