Geomorphic changes in river styles in a typical catchment of the Brazilian semiarid region

Abstract

Rivers in drylands behave differently from those in wetlands due to their irregular flow patterns. This study investigated morphological changes in the Brazilian semiarid region to infer the evolutionary trend of the river. Consequently, the focus was on analyzing the fluvial dynamics and the propensity for change in rivers within the Piranhas River basin. River styles were defined based on the typologies of valley configuration, planimetric shape, sets of geomorphic units, and bed material attributes of the rivers under analysis. In total, eight river styles were identified, broadly classified into confined (two styles), partially confined (three styles), and laterally unconfined (three styles). Confined styles are typically associated with areas near the headwaters, characterized by rocky banks and beds with high flow energy. These channels were found to have low sensitivity to changes in geomorphic conditions. In contrast, unconfined styles predominantly displayed high sensitivity in their stretches, primarily due to the presence of a rocky bed. In the case of partially-confined styles, channels with moderate sensitivity were primarily observed. These channels exhibit a strong tendency to adapt based on their geoindicators and geomorphic conditions, rather than external influences. Interestingly, the resistance to change in geomorphic conditions was linked to unexpected river characteristics within the catchment. Lastly, a historical analysis of the flow allowed an understanding of the dynamics of the styles that displayed a higher propensity to change. This unveiled possible high-magnitude events that may have caused morphological alterations in these styles.