This thesis is a study of the morphology and sediment transport dynamics of mountain streams in southeast Australia. Mountain streams represent important geomorphological and ecological systems in Australia which have hitherto been poorly studied. The variability of mountain stream reach morphology was investigated at the regional scale using topographical surveys and sediment sampling techniques. Study sites were stratified by slope and local lithology. Eight channel-morphologies including Bedrock, Cascade, Step-pool, Planebed, Pool-Riffle, Cascade-pool, Riffle-step and Infilled, were identified using an objective statistical approach. Overall, channel types were found to correspond to existing reach-scale mountain stream templates. Five morphologies were associated with a specific lithology type which controlled the size and shape of grains supplied to the channels. Differences in coarse sediment transport processes between morphologies were investigated using stream monitoring techniques and Optically Stimulated Luminescence (OSL) dating. Monitoring results from a 3 year period indicated that channel beds are resistant to entrainment with shear stress thresholds for bedload transport ranging between 64 to 74 N/m2. Transport of reach median grain sizes requires floods that exceed bankfull discharge. Existing competence equations were found to over-predict the hydraulic driving force and consequently, a modified entrainment model was used to account for the regional channel characteristics. OSL dating was investigated as a tool to provide data on long-term sediment transport processes. Minimum age model results from the OSL dates show overall agreement with a selected entrainment model, and indicate differences in sediment transport dynamics between some reach morphology types. A regime model was used to quantify the physical domains of different channel morphologies. Limitations of the model were overcome by modifying the sediment supply surrogate to better reflect the dominant transported bedload size. Morphology types were delineated according to different sediment transport capacity-sediment supply domains. The distribution of channel morphology types within a series of catchments in southeast Australia was modelled within a GIS platform using the diagnostics of reach morphology derived from this study. The model provides a conceptual framework to evaluate the potential link between channel form, potential habitat diversity and aquatic biodiversity within the channel network in mountain streams.

This thesis is a study of the morphology and sediment transport dynamics of mountain streams in southeast Australia. Mountain streams represent important geomorphological and ecological systems in Australia which have hitherto been poorly studied. The variability of mountain stream reach morphology was investigated at the regional scale using topographical surveys and sediment sampling techniques. Study sites were stratified by slope and local lithology. Eight channel-morphologies including Bedrock, Cascade, Step-pool, Planebed, Pool-Riffle, Cascade-pool, Riffle-step and Infilled, were identified using an objective statistical approach. Overall, channel types were found to correspond to existing reach-scale mountain stream templates. Five morphologies were associated with a specific lithology type which controlled the size and shape of grains supplied to the channels. Differences in coarse sediment transport processes between morphologies were investigated using stream monitoring techniques and Optically Stimulated Luminescence (OSL) dating. Monitoring results from a 3 year period indicated that channel beds are resistant to entrainment with shear stress thresholds for bedload transport ranging between 64 to 74 N/m2. Transport of reach median grain sizes requires floods that exceed bankfull discharge. Existing competence equations were found to over-predict the hydraulic driving force and consequently, a modified entrainment model was used to account for the regional channel characteristics. OSL dating was investigated as a tool to provide data on long-term sediment transport processes. Minimum age model results from the OSL dates show overall agreement with a selected entrainment model, and indicate differences in sediment transport dynamics between some reach morphology types. A regime model was used to quantify the physical domains of different channel morphologies. Limitations of the model were overcome by modifying the sediment supply surrogate to better reflect the dominant transported bedload size. Morphology types were delineated according to different sediment transport capacity-sediment supply domains. The distribution of channel morphology types within a series of catchments in southeast Australia was modelled within a GIS platform using the diagnostics of reach morphology derived from this study. The model provides a conceptual framework to evaluate the potential link between channel form, potential habitat diversity and aquatic biodiversity within the channel network in mountain streams.

This thesis is a study of the morphology and sediment transport dynamics of mountain streams in southeast Australia. Mountain streams represent important geomorphological and ecological systems in Australia which have hitherto been poorly studied. The variability of mountain stream reach morphology was investigated at the regional scale using topographical surveys and sediment sampling techniques. Study sites were stratified by slope and local lithology. Eight channel-morphologies including Bedrock, Cascade, Step-pool, Planebed, Pool-Riffle, Cascade-pool, Riffle-step and Infilled, were identified using an objective statistical approach. Overall, channel types were found to correspond to existing reach-scale mountain stream templates. Five morphologies were associated with a specific lithology type which controlled the size and shape of grains supplied to the channels. Differences in coarse sediment transport processes between morphologies were investigated using stream monitoring techniques and Optically Stimulated Luminescence (OSL) dating. Monitoring results from a 3 year period indicated that channel beds are resistant to entrainment with shear stress thresholds for bedload transport ranging between 64 to 74 N/m2. Transport of reach median grain sizes requires floods that exceed bankfull discharge. Existing competence equations were found to over-predict the hydraulic driving force and consequently, a modified entrainment model was used to account for the regional channel characteristics. OSL dating was investigated as a tool to provide data on long-term sediment transport processes. Minimum age model results from the OSL dates show overall agreement with a selected entrainment model, and indicate differences in sediment transport dynamics between some reach morphology types. A regime model was used to quantify the physical domains of different channel morphologies. Limitations of the model were overcome by modifying the sediment supply surrogate to better reflect the dominant transported bedload size. Morphology types were delineated according to different sediment transport capacity-sediment supply domains. The distribution of channel morphology types within a series of catchments in southeast Australia was modelled within a GIS platform using the diagnostics of reach morphology derived from this study. The model provides a conceptual framework to evaluate the potential link between channel form, potential habitat diversity and aquatic biodiversity within the channel network in mountain streams.

This thesis is a study of the morphology and sediment transport dynamics of mountain streams in southeast Australia. Mountain streams represent important geomorphological and ecological systems in Australia which have hitherto been poorly studied. The variability of mountain stream reach morphology was investigated at the regional scale using topographical surveys and sediment sampling techniques. Study sites were stratified by slope and local lithology. Eight channel-morphologies including Bedrock, Cascade, Step-pool, Planebed, Pool-Riffle, Cascade-pool, Riffle-step and Infilled, were identified using an objective statistical approach. Overall, channel types were found to correspond to existing reach-scale mountain stream templates. Five morphologies were associated with a specific lithology type which controlled the size and shape of grains supplied to the channels. Differences in coarse sediment transport processes between morphologies were investigated using stream monitoring techniques and Optically Stimulated Luminescence (OSL) dating. Monitoring results from a 3 year period indicated that channel beds are resistant to entrainment with shear stress thresholds for bedload transport ranging between 64 to 74 N/m2. Transport of reach median grain sizes requires floods that exceed bankfull discharge. Existing competence equations were found to over-predict the hydraulic driving force and consequently, a modified entrainment model was used to account for the regional channel characteristics. OSL dating was investigated as a tool to provide data on long-term sediment transport processes. Minimum age model results from the OSL dates show overall agreement with a selected entrainment model, and indicate differences in sediment transport dynamics between some reach morphology types. A regime model was used to quantify the physical domains of different channel morphologies. Limitations of the model were overcome by modifying the sediment supply surrogate to better reflect the dominant transported bedload size. Morphology types were delineated according to different sediment transport capacity-sediment supply domains. The distribution of channel morphology types within a series of catchments in southeast Australia was modelled within a GIS platform using the diagnostics of reach morphology derived from this study. The model provides a conceptual framework to evaluate the potential link between channel form, potential habitat diversity and aquatic biodiversity within the channel network in mountain streams.

This thesis is a study of the morphology and sediment transport dynamics of mountain streams in southeast Australia. Mountain streams represent important geomorphological and ecological systems in Australia which have hitherto been poorly studied. The variability of mountain stream reach morphology was investigated at the regional scale using topographical surveys and sediment sampling techniques. Study sites were stratified by slope and local lithology. Eight channel-morphologies including Bedrock, Cascade, Step-pool, Planebed, Pool-Riffle, Cascade-pool, Riffle-step and Infilled, were identified using an objective statistical approach. Overall, channel types were found to correspond to existing reach-scale mountain stream templates. Five morphologies were associated with a specific lithology type which controlled the size and shape of grains supplied to the channels. Differences in coarse sediment transport processes between morphologies were investigated using stream monitoring techniques and Optically Stimulated Luminescence (OSL) dating. Monitoring results from a 3 year period indicated that channel beds are resistant to entrainment with shear stress thresholds for bedload transport ranging between 64 to 74 N/m2. Transport of reach median grain sizes requires floods that exceed bankfull discharge. Existing competence equations were found to over-predict the hydraulic driving force and consequently, a modified entrainment model was used to account for the regional channel characteristics. OSL dating was investigated as a tool to provide data on long-term sediment transport processes. Minimum age model results from the OSL dates show overall agreement with a selected entrainment model, and indicate differences in sediment transport dynamics between some reach morphology types. A regime model was used to quantify the physical domains of different channel morphologies. Limitations of the model were overcome by modifying the sediment supply surrogate to better reflect the dominant transported bedload size. Morphology types were delineated according to different sediment transport capacity-sediment supply domains. The distribution of channel morphology types within a series of catchments in southeast Australia was modelled within a GIS platform using the diagnostics of reach morphology derived from this study. The model provides a conceptual framework to evaluate the potential link between channel form, potential habitat diversity and aquatic biodiversity within the channel network in mountain streams.

This thesis is a study of the morphology and sediment transport dynamics of mountain streams in southeast Australia. Mountain streams represent important geomorphological and ecological systems in Australia which have hitherto been poorly studied. The variability of mountain stream reach morphology was investigated at the regional scale using topographical surveys and sediment sampling techniques. Study sites were stratified by slope and local lithology. Eight channel-morphologies including Bedrock, Cascade, Step-pool, Planebed, Pool-Riffle, Cascade-pool, Riffle-step and Infilled, were identified using an objective statistical approach. Overall, channel types were found to correspond to existing reach-scale mountain stream templates. Five morphologies were associated with a specific lithology type which controlled the size and shape of grains supplied to the channels. Differences in coarse sediment transport processes between morphologies were investigated using stream monitoring techniques and Optically Stimulated Luminescence (OSL) dating. Monitoring results from a 3 year period indicated that channel beds are resistant to entrainment with shear stress thresholds for bedload transport ranging between 64 to 74 N/m2. Transport of reach median grain sizes requires floods that exceed bankfull discharge. Existing competence equations were found to over-predict the hydraulic driving force and consequently, a modified entrainment model was used to account for the regional channel characteristics. OSL dating was investigated as a tool to provide data on long-term sediment transport processes. Minimum age model results from the OSL dates show overall agreement with a selected entrainment model, and indicate differences in sediment transport dynamics between some reach morphology types. A regime model was used to quantify the physical domains of different channel morphologies. Limitations of the model were overcome by modifying the sediment supply surrogate to better reflect the dominant transported bedload size. Morphology types were delineated according to different sediment transport capacity-sediment supply domains. The distribution of channel morphology types within a series of catchments in southeast Australia was modelled within a GIS platform using the diagnostics of reach morphology derived from this study. The model provides a conceptual framework to evaluate the potential link between channel form, potential habitat diversity and aquatic biodiversity within the channel network in mountain streams.

This thesis is a study of the morphology and sediment transport dynamics of mountain streams in southeast Australia. Mountain streams represent important geomorphological and ecological systems in Australia which have hitherto been poorly studied. The variability of mountain stream reach morphology was investigated at the regional scale using topographical surveys and sediment sampling techniques. Study sites were stratified by slope and local lithology. Eight channel-morphologies including Bedrock, Cascade, Step-pool, Planebed, Pool-Riffle, Cascade-pool, Riffle-step and Infilled, were identified using an objective statistical approach. Overall, channel types were found to correspond to existing reach-scale mountain stream templates. Five morphologies were associated with a specific lithology type which controlled the size and shape of grains supplied to the channels. Differences in coarse sediment transport processes between morphologies were investigated using stream monitoring techniques and Optically Stimulated Luminescence (OSL) dating. Monitoring results from a 3 year period indicated that channel beds are resistant to entrainment with shear stress thresholds for bedload transport ranging between 64 to 74 N/m2. Transport of reach median grain sizes requires floods that exceed bankfull discharge. Existing competence equations were found to over-predict the hydraulic driving force and consequently, a modified entrainment model was used to account for the regional channel characteristics. OSL dating was investigated as a tool to provide data on long-term sediment transport processes. Minimum age model results from the OSL dates show overall agreement with a selected entrainment model, and indicate differences in sediment transport dynamics between some reach morphology types. A regime model was used to quantify the physical domains of different channel morphologies. Limitations of the model were overcome by modifying the sediment supply surrogate to better reflect the dominant transported bedload size. Morphology types were delineated according to different sediment transport capacity-sediment supply domains. The distribution of channel morphology types within a series of catchments in southeast Australia was modelled within a GIS platform using the diagnostics of reach morphology derived from this study. The model provides a conceptual framework to evaluate the potential link between channel form, potential habitat diversity and aquatic biodiversity within the channel network in mountain streams.

La Durance est une large rivière méditerranéenne à charge grossière et à lit divagant. Le fonctionnement hydro-sédimentaire de son bassin versant a été profondément modifié par la mise en place d'aménagements hydro-électriques et par les extractions de graviers, qui ont entraîné une rétraction de sa bande active et une incision marquée de son lit. Ces évolutions morphologiques correspondent à des enjeux majeurs en termes de gestion du territoire en moyenne et basse Durance, du fait de la nécessité du maintien d'une capacité d'écoulement du lit en crue, et de la mobilité latérale du lit, souvent incompatible avec l'occupation de la vallée. Cette thèse, basée sur la collecte de données de terrain, vise à développer un schéma de fonctionnement du transport sédimentaire dans les rivières à charge grossière de grande largeur, en intégrant les différentes échelles spatiales (et donc temporelles). Elle a également pour objectif de donner des clefs de compréhension pour la gestion des flux sédimentaires en Durance. Les mécanismes de la mobilité des particules sédimentaires et des formes fluviales sont étudiés dans une démarche ascendante de reformulation scientifique de questionnements opérationnels. / The Durance River (South-Eastern France) is a large and steep wandering gravel-bed river, deeply impacted by gravel mining and flow diversion in its whole catchment area. The Durance River is characterized by a sediment deficit that led to a reduction of active channel width and river bed degradation. These lateral and vertical dynamics lead to important issues in terms of landscape management, because of (i) maintaining the bed hydraulic capacity to evacuate flood discharges and (ii) planform evolution of the river that conflicts with landscape use. This field-based thesis aims at developing a functioning scheme of bedload transport in large gravel bed rivers at various spatial (and consequently temporal) scales and gives keys to understanding for sediment fluxes management on the Durance River. Particle and bedform mobility mechanisms are studied with a scientific approach closely linked to management issues.

Doctoral thesis in detail and comprehensively deals with mechanic of incipient bedload motion for gravel-bed rivers. This study based on theoretical knowledge, experimental researches, numerical models and field survey extends present knowledge concerning with incipient bedload motion and sediment transport at small relative height and hydraulically rough surface bed for turbulent unaerated free surface flow. Incipient bedload motion and sediment transport have been determined for homogeneous and inhomogeneous bed materials. For homogeneous bed material the velocity profiles have been described by different methods in near the bed. Further, hydraulic flow resistance has been evaluated. In the case of inhomogeneous bed material, static armouring and influence of surface layer sorting on hydraulic roughness have been investigated. The correctness of obtained knowledge has been confirmed on the object of nature-inspired river widening. Results shown, among others, that incipient bedload motion does not depend on relative height or final armouring of surface layer to what extend hydraulic roughness is influenced.

L’objectif global de ce travail est d’étudier une modélisation multi échelle et de développer une méthode adaptée pour la simulation numérique du processus d’érosion à l’échelle du bassin versant. Après avoir passé en revue les différents modèles existants, nous dérivons une solution analytique non triviale pour le système couplé modélisant le transport de sédiments par charriage. Ensuite, nous étudions l’hyperbolicité de ce système avec diverses lois de sédimentation proposées dans la littérature. Concernant le schéma numérique, nous présentons le domaine de validité de la méthode de splitting, pour les équations modélisant l’écoulement et celle décrivant l’évolution du fond. Pour la modélisation du transport en suspension à l’échelle de la parcelle, nous présentons un système d’équations couplant les mécanismes d’infiltration, de ruissellement et le transport de plusieurs classes de sédiments. L’implémentation et des tests de validation d’un schéma d’ordre élevé et de volumes finis bien équilibré sont également présentés. Ensuite, nous discutons sur l’application et la calibration du modèle avec des données expérimentales sur dix parcelles au Niger. Dans le but d’aboutir la simulation à l’échelle du bassin versant, nous développons une modélisation multi échelle dans laquelle nous intégrons le taux d’inondation dans les équations d’évolution afin de prendre en compte l’effet à petite échelle de la microtopographie. Au niveau numérique, nous étudions deux schémas bien équilibrés : le schéma de Roe basé sur un chemin conservatif, et le schéma avec reconstruction hydrostatique généralisée. Enfin, nous présentons une première application du modèle avec les données expérimentales du bassin versant de Ganspoel qui nécessite la parallélisation du code. / The overall objective of this thesis is to study a multiscale modelling and to develop a suitable method for the numerical simulation of soil erosion on catchment scale. After reviewing the various existing models, we derive an analytical solution for the non-trivial coupled system modelling the bedload transport. Next, we study the hyperbolicity of the system with different sedimentation laws found in the literature. Relating to the numerical method, we present the validity domain of the time splitting method, consisting in solving separately the Shallow-Water system (modelling the flow routing) during a first time step for a fixed bed and updating afterward the topography on a second step using the Exner equation. On the modelling of transport in suspension at the plot scale, we present a system coupling the mechanisms of infiltration, runoff and transport of several classes of sediment. Numerical implementation and validation tests of a high order wellbalanced finite volume scheme are also presented. Then, we discuss on the model application and calibration using experimental data on ten 1 m2 plots of crusted soil in Niger. In order to achieve the simulation at the catchment scale, we develop a multiscale modelling in which we integrate the inundation ratio in the evolution equations to take into account the small-scale effect of the microtopography. On the numerical method, we study two well-balanced schemes : the first one is the Roe scheme based on a path conservative, and the second one is the scheme using a generalized hydrostatic reconstruction. Finally, we present a first model application with experimental data of the Ganspoel catchment where the parallel computing is also motived.