Le coefficient de compacite de Gravelius: analyse critique d'un indice de forme des bassins versants

Traditionally, to characterize a drainage basin, various shape indices are proposed that may be used for inter-basin comparison and possibly for estimation of unmeasured characteristics. The index most commonly referred to is the compactness coefficient proposed by Gravelius. This is the ratio of the perimeter of the watershed to the circumference of a circle whose area is equal to that of the given drainage basin. The fractal geometry approach makes the validity of such indices questionable. Indeed, in the above definition, the only well-defined size is the surface of the basin. Although there is, of course, uncertainty in its measurement, it is possible to determine, for example, its lower and upper bounds. The perimeter measurement, on the other hand, is completely dependent on its measurement gauge, and, thus, has no characteristics that might detract from the value of the indices calculated from it.