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International audience; Braiding rivers are multi-channel rivers characterized by large active channel or braid plain areas.They occur in mountain or piedmont regions across the world, most likely where there is an activeupstream connection with sediment sources. But do braiding rivers behave the same across theworld? The hypothesis is that there is a range of conditions determining braiding pattern and braidplain size across the world according with catchment scale and larger scale drivers.To demonstrate our hypothesis, this study is based on the analysis of the relationship between theactive channel width and the upstream catchment area (i.e. the normalized active channel width) of257 braiding river reaches across the world, characterized using satellite images at good resolutionavailable between September 2019 and May 2020. We then assessed the range of values assumedby the normalized active channel width against catchment and large scale drivers (e.g. climatic,hydrological and relief conditions). Our results show in some regions these drivers control extremelylarge and dynamic systems against which to compare the status and behaviour of all the braidingrivers across the world.; Les rivières en tresses sont des rivières à chenaux multiples caractérisées par de larges bandes actives. Elles se trouvent surtout dans les régions de montagne ou de piémont à travers le monde, là où il existe une connexion active en amont avec les sources sédimentaires. Mais est-ce que les rivières en tresses fonctionnent de la même manière à travers le monde ? L'hypothèse est qu'il existe, à l'échelle globale, une gamme de conditions déterminant le patron de tressage et les largeurs des bandes actives en fonction de la taille du bassin versant et de ses caractéristiques hydroclimatiques, géologiques ou orographiques. Cette étude est basée sur l'analyse de la relation entre la largeur de la bande active et certaines caractéristiques des bassins versants amont (c'est-à-dire la largeur de la bande active normalisée) de 257 tronçons de rivière en tresses à travers le monde, caractérisés à l'aide d'images satellites disponibles entre septembre 2019 et mai 2020. Nous avons ensuite comparé la gamme de valeurs de largeur de bande active normalisée à certains caractères des bassins (par ex., les conditions climatiques, hydrologiques et de relief). Nos résultats montrent que ces facteurs contrôlent la taille des tresses et qu'il existe ainsi des conditions plus ou moins favorables pour que des systèmes en tresses se développent sur terre.

Numerical morphological modelling of braided rivers is increasingly used to explore controls on river pattern and for applied environmental management. This article reviews and presents a taxonomy of braided river morphodynamic models and discusses the challenges facing model development and use, illustrating these challenges with a case example. The taxonomy is contextualised by an initial discussion of the physical mechanisms of braiding. The taxonomy differentiates between reach-scale and catchment-scale models. Reach-scale models are usually physics-based, which are further divided based upon the mathematical approach used to solve equations (analytical or numerical) and their dimensionality (1D, 2D or 3D). Cellular automata models are one type of numerical model that replace at least some physical processes with expedient rules. A 2D physics-based approach encapsulates sufficient process complexity to provide behavioural predictions. Predictions from catchment-scale landscape evolution models have potential for providing boundary conditions. Future progress in physics-based modelling needs to address three challenges: (i) representation of flow and sediment transport; (ii) temporal and spatial scaling; and (iii) model calibration, sensitivity, uncertainty and validation. The key problem for addressing these is the dearth of laboratory or natural experiment datasets. To show that progress can be made by comparing reach-scale predictions to high-resolution observations, a case study of monitoring and modelling, conducted in the Rees River, New Zealand, is presented. Hydraulic predictions of cellular automata and shallow water equation (Delft3d) models are compared to observed inundation extent. The efficacy of high-resolution, multi-temporal morphological data for assessing 2D physics-based morphodynamic model predictions is also demonstrated.

A poster detailing a potion of my PhD research that was presented at the 2015 fall meeting of AGU in San Francisco.

A poster documeting five years of geomorphic change on the River Feshie, Scotland. Details the methods for capturing the morphodynamic signatures of several braiding mechansisms from successive annual GPS and lidar surveys of the river.

A poster documented the results of TLS scanning on a 3 km reach of the braided River Feshie, Scotland.

Vegetation roughness, and more specifically forest roughness, is a necessary component in better defining flood dynamics both in the sense of changes in river catchment characteristics and the dynamics of forest changes and management. Extracting roughness parameters from riparian forests can be a complicated process involving different components for different required scales and flow depths. For flow depths that enter a forest canopy, roughness at both the woody branch and foliage level is necessary. This study attempts to extract roughness for this leafy component using a relatively new remote sensing technique in the form of terrestrial laser scanning. Terrestrial laser scanning is used in this study due to its ability to obtain millions of points within relatively small forest stands. This form of lidar can be used to determine the gaps present in foliaged canopies in order to determine the leaf area index. The leaf area index can then be directly input into resistance equations to determine the flow resistance at different flow depths. Leaf area indices created using ground scanning are compared in this study to indices calculated using simple regression equations. The dominant riparian forests investigated in this study are planted and natural poplar forests over a lowland section of the Garonne River in Southern France. Final foliage roughness values were added to woody branch roughness from a previous study, resulting in total planted riparian forest roughness values of around Manning's n = 0.170–0.195 and around n = 0.245–330 for in-canopy flow of 6 and 8 m, respectively, and around n = 0.590 and around n = 0.750 for a natural forest stand at the same flow depths.

International audience; Hydraulic resistance of riparian forests is an unknown but important term in flood conveyance modeling. Lidar has proven to be a very important new data source to physically characterize floodplain vegetation. This research outlines a recent campaign that aims to retrieve vegetation fluid resistance terms from airborne laser scanning to parameterize trunk roughness. Information on crown characteristics and vegetation spacing can be extracted for individual trees to aid in the determining of trunk stem morphology. Airborne lidar data were used to explore the potential to characterize some of the prominent tree morphometric properties from natural and planted riparian poplar zones such as tree position, tree height, trunk location, and tree spacing. Allometric equations of tree characteristics extrapolated from ground measurements were used to infer below-canopy morphometric variables. Results are presented from six riparian-forested zones on the Garonne and Allier rivers in southern and central France. The tree detection and crown segmentation (TDCS) method identified individual trees with 85% accuracy, and the TreeVaW method detected trees with 83% accuracy. Tree heights were overall estimated at both river locations with an RMSE error of around 19% for both methods, but crown diameter at the six sites produced large deviations from ground-measured values of above 40% for both methods. Total height-derived trunk diameters using the TDCS method produced the closest roughness coefficient values to the ground-derived roughness coefficients. The stem roughness values produced from this method fell within guideline values.