Multifractal Behaviour of River Networks

A numerical multifractal analysis was performed for five river networks extracted from Calabrian natural basins represented on 1:25000 topographic sheets. The spectrum of generalised fractal dimensions, D(q), and the sequence of mass exponents, tau(q), were obtained using an efficient generalised box-counting algorithm. The multifractal spectrum, f(alpha), was deduced with a Legendre transform. Results show that the nature of the analysed river networks is multifractal, with support dimensions, D(0), ranging between 1.76 and 1.89. The importance of the specific number of digitised points is underlined, in order to define accurately the geometry of river networks through a direct generalised box-counting measure that is not influenced by their topology. The algorithm was also applied to a square portion of the Trionto river network to investigate border effects. Results confirm the multifractal behaviour, but with D(0)=2. Finally, some open mathematical problems related to the assessment of the box-counting dimension are discussed.