Long-term temporal trajectories to enhance restoration efficiency and sustainability on large rivers: an interdisciplinary study

Abstract

Abstract. While the history of a fluvial hydrosystem can provide essential knowledge on present functioning, historical context remains rarely considered in river restoration. Here we show the relevance of an interdisciplinary study for improving restoration within the framework of a European LIFE+ project on the French side of the Upper Rhine (Rohrschollen Island). Investigating the planimetric evolution combined with historical high-flow data enabled us to reconstruct pre-disturbance hydromorphological functioning and major changes that occurred on the reach. A deposition frequency assessment combining vertical evolution of the Rhine thalweg, chronology of deposits in the floodplain, and a hydrological model revealed that the period of incision in the main channel corresponded to high rates of narrowing and lateral channel filling. Analysis of filling processes using Passega diagrams and IRSL dating highlights that periods of engineering works were closely related to fine sediment deposition, which also presents concomitant heavy metal accumulation. In fact, current fluvial forms, processes and sediment chemistry around Rohrschollen Island directly reflect the disturbances that occurred during past correction works, and up to today. Our results underscore the advantage of combining functional restoration with detailed knowledge of the past trajectory to (i) understand the functioning of the hydrosystem prior to anthropogenic disturbances, (ii) characterize the human-driven morphodynamic adjustments during the last 2 centuries, (iii) characterize physico-chemical sediment properties to trace anthropogenic activities and evaluate the potential impact of the restoration on pollutant remobilization, (iv) deduce the post-restoration evolution tendency and (v) evaluate the efficiency and sustainability of the restoration effects. We anticipate our approach will expand the toolbox of decision-makers and help orientate functional restoration actions in the future.

Restoring a glacier‐fed river: Past and present morphodynamics of a degraded channel in the Italian Alps

“…In fact, the Mareit River featured a multi-thread, anabranching planform in the middle of the 19th century (Figure 13). At that time, this pattern was quite common in rivers flowing in wide valleys of the Alps (Comiti, 2012;Campana et al, 2014;Scorpio et al, 2018b), as well as in other European rivers such as the Danube (Hohensinner et al, 2013), the Upper Rhine (Eschbach et al, 2018), the Trent River (Large and Petts, 1996) and the Morávka River (Škarpich et al, 2013). Based on the analysis presented earlier, the disappearance of the anabranching patternassociated with channel narrowing which took place from the 19th century to the early decades of the 20th century is likely largely due to anthropic disturbances, namely the construction of the levees and the flood retention dam in the upper basin by the Austrian Administration in the late 19th century (Figure 13).…”

Targeting lateral connectivity and morphodynamics in a large river‐floodplain system: The upper Rhine River

“…Further research would include the application of a sediment transport model to the proposed scenarios, comparing results with previous morpho‐sedimentary studies on side channel restoration (Eschbach et al, ; Formann et al, ; Riquier, Piégay, & Šulc Michalková, ). Integration of historical fine sediment filling of side channels would also be helpful (Eschbach et al, ). Furthermore, other processes out of the scope of this study, such as interactions with vegetation, can play an important role on how the system will develop (Corenblit et al, ; Gurnell et al, ).…”

“…Due to its inevitable spatial requirements, potential restoration of the dynamic behaviour may also imply high costs and legal challenges to land ownership (Richards, Brasington, & Hughes, ). Therefore, defining direction and goals for river restoration is of key importance because returning the system to a pre disturbance state does not seem viable for most large rivers and only partial river restoration may be feasible (Eschbach et al, ). The challenge for large rivers lies in selecting a restoration target with the aim of recovering, at least partially, some natural dynamics while acknowledging human constraints that restrict restoration potential (Beechie et al, ).…”

Assessing the effect of flood restoration on surface–subsurface interactions in Rohrschollen Island (Upper Rhine river – France) using integrated hydrological modeling and thermal infrared imaging

“…For their part, integrated hydrologic models emerged in the late 1990s, and they are now recognized as suitable tools to investigate streamflow generation processes at the catchment scale (e.g., Paniconi and Putti, 2015;Fatichi et al, 2016). Although most integrated models rely on the solution to the 3-D Richards equation to describe subsurface flow (e.g., Maxwell et al, 2014), alternative low-dimensional approaches that simplify the description of the subsurface compartment (still with some physical meaning) have recently appeared (e.g., Hazenberg et al, 2015Hazenberg et al, , 2016Jeannot et al, 2018).…”