Fluvial Corridor Changes Over Time in Regulated and Non‐Regulated Rivers (Upper Esla River, NW Spain)

Abstract

Over the last decades, rivers and fluvial corridors have been noticeably modified from their natural conditions. In general, damming and other in-channel human interventions have been traditionally considered as the main drivers of change. However, recent studies highlight the influence of climate, hillslope and floodplain cover changes over fluvial corridor dynamics. The present study illustrates the channel morphology and riparian vegetation responses observed in three gravel bed rivers located in the Upper Esla River, north-west of Spain. The entire study catchment was exposed to afforestation changes and farmland abandonment during the last decades, and two of the rivers are regulated by large dams. Analysis of historical orthophotos at different periods between 1956 and 2011 allowed quantifying channel narrowing, reduction of braiding index and vegetation encroachment along the three rivers. Field reconnaissance of landforms and vegetation structure along transects showed significant differences in species composition and age structure between the non-regulated reach, where recruitment of Salicacea pioneer species existed, and the regulated reaches where mature and late-seral species were much more abundant. These responses were consistent with reductions in mean annual discharge in all rivers and with flood disturbance decrease and summer minimum flow increase that were observed in the regulated rivers.

Modelling feedbacks between geomorphological and riparian vegetation responses under climate change in a Mediterranean context

“…flow regulation by dams and reservoirs, could also act synergistically with climate change, inducing similar biogeomorphic responses on fluvial landscapes. The extensive literature on damming effects includes multiple examples of channel narrowing and vegetation encroachment (Graf, ; Bejarano et al ., ; González del Tánago et al ., ; Martínez‐Fernández et al ., ) which in many cases could become reinforced by climate change. Hence we argue that river impacts should be assessed at multiple scales, and that persistent long‐term and large‐scale pressures like climate change must be taken into account when diagnosing problems induced by small‐scale pressures, in order to strategically design realistic rehabilitation goals and sustainable mitigation or adaptation measures.…”

Channel forms and vegetation adjustment to damming in a Mediterranean gravel‐bed river (Serpis River, Spain)

“…These vegetation communities were not yet present (or did not have adult form) in the 1994 aerial photograph but appeared clearly consolidated in the 2000 image, after a long period without floods (1993–2001) that could have favoured vegetation development at the flowing channel banks. In another river of the region affected by damming, the Mijares River, Garófano‐Gómez et al () observed a period of the same duration (40 years) between reservoir construction and the completion of the process of encroachment of dense woody vegetation, whereas Martínez‐Fernández et al () have identified a similar stage of stability between 2000 and 2015 in Northwestern Spain.…”

“…According to Braatne et al (), although the combination of the three methods is the best option, the pre‐ versus post‐dam approach provides the most reliable results. This approach is endorsed by several works that have explored historical river channel adjustment processes after damming (Surian, ; Magdaleno, Anastasio Fernández, & Merino, ; Scorpio et al, ; Scorpio & Roskoff, ; Martínez‐Fernández, González del Tánago, Maroto, & García de Jalón, ; Arnaud et al, ).…”

From Microhabitat Ecohydraulics to an Improved Management of River Catchments: Bridging the gap Between Scales

“…The reach‐scale analysis of vegetation changes in regulated and unregulated river reaches shown by Martínez‐Fernández et al (), confirms that a better understanding of sediment‐flow interactions with the riverbed substrate and the riverbanks are crucial to understand large‐scale processes induced by afforestation changes, farmland abandonment and construction of dams. This is clear in their long‐term analysis of ortho‐photos over several decades since the 1950's, from a morphological (e.g.…”