Quelques aspects de la propagation des crues

Some aspects of flood routing

Electricité de France, Centre de Recherches et d'Essais de Chatou.

Résumé

The autor refers to the classic equations of variable flow in rivers and then transforms them by the introduction of reference values, bringing in dimensionless variables. This new form of the T/y system enables the various terms involved to be compared and their relevanee to be discussed. The method of characteristics is next referred to and applied to the dimensionless variables, followed by an account of the evolution of the characteristic curves when the less important parameters are ignored. One of the most interesting cases is that of the diffusion-type flood equation obtained by the elimination of the space and time partial differentials of discharge from the dynamic equation. The system then becomes parabolic and can be reduced to an equation of the heat transfer type. From this are deduced the flood diffusion coefficient and propagation velocity, the latter being composed of two terms, one of which is geometrical and disappear's when the banks are vertical, which is a case where Seddon's formula applies. The author mentions the methods of Bachet and Shoitiro Hayami, which are both based on the diffusion eqnation. In conclusion, the case of a simple flood wave is studied, in which the energy slope is coustant : in this case the system becomes a first order linear partial differential equation which integrates. This case in which the maximum number of terms are left out, though very simplified, nevertheless occurs under actual conditions. It can be recognised by the fact that a single-value Q (Z) relation obtains, which holds good even under flood conditions.