What is the Relative Effect of Space and Time to Explain the Braided River Width and Island Patterns at a Regional Scale?

Abstract

Several decades of human activities have severely impacted braided rivers worldwide. Despite their widespread disappearance, some remnant braided sectors are still held in the French Rhone basin, mainly in the south‐east of France. In this paper, we analyse the evolutionary pattern of 53 braided reaches, focusing on the active channel width and island patterns, by comparing aerial photographs from the 1950s and 2000s (Institut Géographique National). Because different braided patterns exist (e.g. bar versus island‐braided), we tested the relative effect of geographical and temporal factors. The hypothesis is that three main biogeomorphological braided types exist (i.e. defined through the presence, the amount and the relative size of vegetated islands), based on the combined effect of the following: (i) their position along the river network (i.e. river gradient, altitude and sediment regime) and (ii) the temporal effect represented by the time since the last large flood, that is, the recent flood history. Our results show that even if the regional context (climate and sediment regime mainly) plays a key role, the temporal factor, represented by recent flood history, seems to heavily influence the response of the width pattern and vegetation recovery. Local factors (i.e. topography and groundwater) may also have an impact, but their influence has no effect at the regional level. These results support braided river management (conservation and/or restoration actions) in the Rhone basin and provide a better understanding of the range of braided rivers' functioning. Further studies (e.g. multidate retrospective survey) are needed to better understand the role of flood events on braided pattern and vegetation recovery. Copyright © 2013 John Wiley & Sons, Ltd.

Hierarchical Object-Based Mapping of Riverscape Units and in-Stream Mesohabitats Using LiDAR and VHR Imagery

“…It also provides a useful indicator of changes in potential ecosystem productivity [10,17,18]. To date, the concept behind the use of RS for the delineation of the riverscape units has been rather simple: features visible on air photos can be manually traced or digitized and transferred to map coordinates [11,19,20].…”

“…The AC is defined in literature as the low-flow channel plus adjacent exposed sediment bar surfaces between established edges of perennial, terrestrial vegetation, which are generally subjected to erosion or deposition [10][11][12][13]. Exposed bars are characterized by vegetation encroachment, which plays a key role in the evolution of alluvial islands [14], i.e., patches of mature vegetation surrounded by water and bare sediment bars.…”

“…An essential aspect when characterizing river hydromorphology is the delineation of the so-called active channel (AC) and more widely of different riverscape units [10]. The AC is defined in literature as the low-flow channel plus adjacent exposed sediment bar surfaces between established edges of perennial, terrestrial vegetation, which are generally subjected to erosion or deposition [10][11][12][13].…”

Spatial and temporal variations of channel lateral migration rates in the Inner Mongolian reach of the upper Yellow River

“…In such alluvial rivers, the channels change frequently from reach to reach as a result of continuous erosion-accretion processes (Kummu et al 2008). Consequently, these changes can cause a variety of socioeconomic and environmental problems in loss of riparian land and infrastructure, bank stability and flood disasters (e.g., Takagi et al 2007;Belletti et al 2015), and the alteration of aquatic and riparian ecosystems. Therefore, a better understanding on river channel changes, lateral migration in particular, is urgently needed.…”

Validation of observed bedload transport pathways using morphodynamic modeling

“…Processes involved include local scour and fill, channel bars development and migration, as well as bifurcation mechanisms. The phenomena listed above are generated due to high stream power as well as low bed and bank erosion resistance relative to stream energy (Ashmore 2013, Belletti et al 2015.…”