Stream regularization index. A morphometric approach to quantify the longitudinal profile regularization stage

Abstract

Fluvial systems carve the Earth's surface under the influence of climate and tectonics. This process tends towards dynamic equilibrium conditions, in which rivers respond by regularizing their longitudinal profiles to a graded form. However, external forcings frequently interrupt this trend displacing the system to a transient state from which the system will evolve again with a tendency towards a graded form. In bedrock incising rivers, the longitudinal profile shape provides information on transient states, and quantifying the regularization level makes it possible to establish inferences about a river's evolutionary trend and its relationship with the influencing external forcings. This work presents a procedure for quantifying the regularization level of streams from the analysis of the shape of the longitudinal profiles. This procedure involves quantifying of the departure of the current shape of the longitudinal profile from that representing the graded long profile under dynamic equilibrium conditions. This comparison is quantified by two indices: ‘stream regularization index_G’, calculated for the entire long profile, and ‘regularization index_g’, calculated discretely along the long profile. To illustrate the usefulness of the indices and how they respond in different fluvial contexts and evolutionary stages, the longitudinal profiles of 14 streams from the central area of the Iberian Peninsula were analyzed. The results are interpreted together with the area-slope graph and the Ksn index, which corroborated the usefulness of this technique as a morphometric tool for quantifying the river maturity and identify tectonic regime transitions.