The structure and scaling of river networks characterized using fracta
l dimensions related to Horton's laws is assessed. The Hortonian scali
ng framework is shown to be limited in that strict self similarity is
only possible for structurally Hortonian networks. Dimension estimates
using the Hortonian scaling system are biased and do not admit space
filling. Tokunaga cyclicity presents an alternative way to characteriz
e network scaling that does not suffer from these problems. Fractal di
mensions are presented in terms of Tokunaga cyclicity parameters.