Dynamic changes in the lower Gállego River (Ebro Basin, NE Spain) and their relationship with anthropic activities and the quaternary substrate

Abstract

The lower Gállego River has been strongly degraded since the 1960s due to human activity (gravel mining, dump accumulation, channeling works), which has produced a deep channel incision. Although these human-driven processes are usually reported in fluvial bibliography, in this case, more complex results are observable. For instance, regarding the depth and incision rates, we observed no relationship between the most anthropically impacted areas and the sections with the deepest incisions; moreover, the deepening process continues 40 years after the human interventions ceased. The reason for this maladjustment is the role played by the exhumation of the underlying Pleistocene substrate, affected by the synsedimentary processes of karstification. The appearance of paleodolines filled with fine sediments on the incision bottom and sides is the main factor conditioning the continuity and magnitude of the process. Besides, these paleodepressions direct the river dynamics and course, thus favoring its widening when they appear and causing the development of a new riverbed (Qt13) while the 1960s floodplain (Qt12) is becoming an old terrace located between 5 and 11 m above the new alluvial bottom. There are no previous records about this kind of consequences in the regional fluvial dynamics.

Impacts of in‐stream aggregate mining on the distributary channels of the alluvial fans of Tafí valley (Northwest Argentina)

“…The greatest impacts are related to changes in sediment connectivity (Poeppl et al, 2017) and channel geometry (Downs et al, 2013), including planform patterns, bedform proportions, channel geometry, and the location of geomorphic features (Calle et al, 2017). Most studies on the geomorphological changes caused by aggregate mining have focused on perennial rivers (Martin-Vide et al, 2010;Peña-Monné et al, 2020, among others), while little is known about the subject on ephemeral streams (i.e. Downs et al, 2013;Kondolf, 1994;Kondolf et al, 2001;Sanchis-Ibor & Segura-Beltrán, 2014).…”