On What is Explained by the Form of a Channel Network

Abstract

The paper studies the relation between the structure of river networks and the features of their geomorphologic hydrologic response. The hydrologic response of a channel network is defined by decomposing the process of runoff formation into two distinct contributions, one accounting for the mechanisms of travel time within individual reaches (hydrodynamic dispersion), and the other accounting for the morphology of the network structure (geomorphological dispersion). The variance of the resulting travel time distributions is shown to be made up by two additive contributions corresponding to the two dispersion mechanisms considered. The geomorphologic dispersion coefficient is shown to depend on the ratios of bifurcation, length and area of the network suggesting that, at the scale of organized network, heterogeneities other than those related to the convection field shape the dispersive character of transport. In particular, a significant application of the general solution to Hortonian channel networks suggests that models based on accurate specification of the geometry and the topology of the network and a simplified dynamics capture the foremost features of the travel time distributions in a broad range of dispersivities within individual reaches. We then conclude that the form of a network explains most features of the hydrologic response of its drainage basin.