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Peter Huggenberger - One of the best experts on this subject based on the ideXlab platform.
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subsurface flow mixing in coarse Braided River deposits
Hydrology and Earth System Sciences, 2016Co-Authors: E Huber, Peter HuggenbergerAbstract:Abstract. Coarse, Braided River deposits show a large hydraulic heterogeneity on the metre scale. One of the main depositional elements found in such deposits is a trough structure filled with layers of bimodal gravel and open-framework gravel, the latter being highly permeable. However, the impact of such trough fills on subsurface flow and advective mixing has not drawn much attention. A geologically realistic model of trough fills is proposed and fitted to a limited number of ground-penetrating radar records surveyed on the River bed of the Tagliamento River (northeast Italy). A steady-state, saturated subsurface flow simulation is performed on the small-scale, high-resolution, synthetic model (size: 75 m × 80 m × 9 m). Advective mixing (i.e. streamline intertwining) is visualised and quantified based on particle tracking. The results indicate strong advective mixing as well as a large flow deviation induced by the asymmetry of the trough fills with regard to the main flow direction. The flow deviation induces a partial, large-scale rotational effect. These findings depict possible advective mixing found in natural environments and can guide the interpretation of ecological processes such as in the hyporheic zone.
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influence of conceptual model uncertainty on contaminant transport forecasting in Braided River aquifers
Journal of Hydrology, 2015Co-Authors: Guillaume Pirot, E Huber, Julien Straubhaar, Philippe Renard, Peter HuggenbergerAbstract:Hydrogeologist are commonly confronted to field data scarcity. An interesting way to compensate this data paucity, is to use analog data. Then the questions of prediction accuracy and uncertainty assessment when using analog data shall be raised. These questions are investigated in the current paper in the case of contaminant transport forecasting in Braided River aquifers. In using analog data from the literature, multiple unconditional geological realizations are produced following different geological conceptual models (Multi-Gaussian, Object-based, Pseudo-Genetic). These petrophysical realizations are tested in a contaminant transport problem based on the MADE-II tracer experiment dataset. The simulations show that reasonable contaminant transport predictions can be achieved using analog data. The initial concentration conditions and location regarding the conductivity heterogeneity field have a stronger influence on the plume behavior than the resulting equivalent permeability. The results also underline the necessity to include a wide variety of geological conceptual models and not to restrain parameter space exploration within each concept as long as no field data allows for conceptual model or parameter value falsification.
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Subsurface flow mixing in coarse, Braided River deposits
Hydrology and Earth System Sciences Discussions, 2015Co-Authors: E Huber, Peter HuggenbergerAbstract:Abstract. Coarse, Braided River deposits show a large hydraulic heterogeneity at the metre scale. One of the main depositional elements found in such deposits is a trough structure filled with open-framework–bimodal gravel couplet cross-beds. Several studies investigated the impact of the highly permeable open-framework gravel texture mainly in terms of concentration breakthrough curves. However, although the trough fills are expected to be significant mixing agents for the subsurface flow, their impact on the three-dimensional flow field has not draw much attention. This study aims to evaluate the subsurface flow mixing caused by overlapping trough fills embedded in a poorly-sorted gravel matrix. Below the River bed of the Tagliamento River (northeast Italy), trough fills were identified with ground-penetrating radar (GPR) probing. Based on field observations of coarse, Braided River deposits, a simple three-dimensional geometrical model with associated hydraulic properties was fitted to the interpreted GPR reflectors. Then, steady-state subsurface flow and advective transport simulations were performed on the small-scale, high-resolution model (size: 45 m × 50 m × 10.26 m). The impact of trough fills on the flow field is visualised by the injection of a conservative tracer at three different depths.
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a sedimentological model to characterize Braided River deposits for hydrogeological applications
2009Co-Authors: Peter Huggenberger, Christian RegliAbstract:Braided River deposits form important aquifers in many parts of the world, and their heterogeneity strongly influences groundwater flow and mass transport processes. To accurately characterize these coarse gravelly aquifers, it is important to understand the erosional and depositional processes that form these sediments. Moreover, it is important to evaluate the relative importance of various parameters that determine the preservation potential of different depositional elements over geological time scales. These objectives may be achieved by developing techniques that allow for the integration of different quality data into quantitative models. Information concerning sedimentary textures and the spatial continuity of sedimentary structures in Braided River deposits, inherent in depositional facies descriptions, allows the spatial variability of hydrogeological properties (e.g. hydraulic conductivity and porosity) to be predicted. Depositional elements in gravel deposits can contain a restricted range of textures, which form a limited number of sedimentary structures. These depositional elements are bounded by erosional and/or lithological surfaces. The frequency, size and shape of different elements in a sedimentary sequence depend on several factors, including aggradation rate, channel belt mobility on the kilometre scale, gravel-sheet/scour activity at the scale of hundreds of metres and topographic position of the different elements within an evolving system. Preserved shape and size of the elements affect the correlation lengths and the standard deviations of the aquifer properties, such as hydraulic conductivity and porosity. Different quality data sets that may be used in characterizing Braided River deposits can be recognized in outcrop, boreholes and on ground-penetrating radar (GPR) sections. This paper proposes a means of integrating outcrop, borehole and GPR data into a stochastic framework of sedimentary structures and the distribution of hydraulic aquifer properties. Data integration results in variable degrees of uncertainty when assigning values to hydraulic properties and characterizing the geometry of sedimentary structures. An application of this approach is illustrated using a data set (400 m × 550 m) from the northeastern part of Switzerland at the confluence of the Rhine and Wiese Rivers. The data set includes drill-core data from five boreholes and 14 GPR sections with a total length of 3040 m. The results of the variogram analysis provide the orientation of sedimentary structure types representing the main flow direction of the River Rhine in the lower part of the aquifer, and of the River Wiese in the upper part. The analysis also results in large ranges of spatial correlation, ranging from a few metres up to tens of metres for the different sedimentary structure types.
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Braided Rivers: Process, Deposits, Ecology and Management - A sedimentological model to characterize Braided River deposits for hydrogeological applications
Braided Rivers, 1Co-Authors: Peter Huggenberger, Christian RegliAbstract:Braided River deposits form important aquifers in many parts of the world, and their heterogeneity strongly influences groundwater flow and mass transport processes. To accurately characterize these coarse gravelly aquifers, it is important to understand the erosional and depositional processes that form these sediments. Moreover, it is important to evaluate the relative importance of various parameters that determine the preservation potential of different depositional elements over geological time scales. These objectives may be achieved by developing techniques that allow for the integration of different quality data into quantitative models. Information concerning sedimentary textures and the spatial continuity of sedimentary structures in Braided River deposits, inherent in depositional facies descriptions, allows the spatial variability of hydrogeological properties (e.g. hydraulic conductivity and porosity) to be predicted. Depositional elements in gravel deposits can contain a restricted range of textures, which form a limited number of sedimentary structures. These depositional elements are bounded by erosional and/or lithological surfaces. The frequency, size and shape of different elements in a sedimentary sequence depend on several factors, including aggradation rate, channel belt mobility on the kilometre scale, gravel-sheet/scour activity at the scale of hundreds of metres and topographic position of the different elements within an evolving system. Preserved shape and size of the elements affect the correlation lengths and the standard deviations of the aquifer properties, such as hydraulic conductivity and porosity. Different quality data sets that may be used in characterizing Braided River deposits can be recognized in outcrop, boreholes and on ground-penetrating radar (GPR) sections. This paper proposes a means of integrating outcrop, borehole and GPR data into a stochastic framework of sedimentary structures and the distribution of hydraulic aquifer properties. Data integration results in variable degrees of uncertainty when assigning values to hydraulic properties and characterizing the geometry of sedimentary structures. An application of this approach is illustrated using a data set (400 m × 550 m) from the northeastern part of Switzerland at the confluence of the Rhine and Wiese Rivers. The data set includes drill-core data from five boreholes and 14 GPR sections with a total length of 3040 m. The results of the variogram analysis provide the orientation of sedimentary structure types representing the main flow direction of the River Rhine in the lower part of the aquifer, and of the River Wiese in the upper part. The analysis also results in large ranges of spatial correlation, ranging from a few metres up to tens of metres for the different sedimentary structure types.
E Huber - One of the best experts on this subject based on the ideXlab platform.
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Reduction of conceptual model uncertainty using ground-penetrating radar profiles: Field-demonstration for a Braided-River aquifer
2018Co-Authors: Guillaume Pirot, E Huber, James Irving, Niklas LindeAbstract:Hydrogeological flow and transport strongly depend on the connectivity of subsurface properties. Uncertainty concerning the underlying geological setting, due to a lack of field data and prior knowledge, calls for an evaluation of alternative geological conceptual models. To reduce the computational costs associated with inversions (parameter estimation for a given conceptual model), it is beneficial to rank and discard unlikely conceptual models prior to inversion. Here, we demonstrate an approach based on a quantitative comparison of ground-penetrating radar (GPR) sections obtained from field data with corresponding simulation results arising from various geological scenarios. The comparison is based on three global distance measures related to wavelet decomposition, multiple-point histograms, and connectivity that capture geometrical characteristics of geophysical reflection images. Using field data from the Tagliamento Braided River system, Italy, we demonstrate that seven out of nine considered geological scenarios can be discarded as they produce GPR sections that are incompatible with those observed in the field. The retained scenarios reproduce important features such as cross-stratified deposits and irregular property interfaces. The most convenient distance measure of those considered is the one based on wavelet-decomposition. Direct analysis of the distances is the most intuitive and fastest way to compare scenarios.
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subsurface flow mixing in coarse Braided River deposits
Hydrology and Earth System Sciences, 2016Co-Authors: E Huber, Peter HuggenbergerAbstract:Abstract. Coarse, Braided River deposits show a large hydraulic heterogeneity on the metre scale. One of the main depositional elements found in such deposits is a trough structure filled with layers of bimodal gravel and open-framework gravel, the latter being highly permeable. However, the impact of such trough fills on subsurface flow and advective mixing has not drawn much attention. A geologically realistic model of trough fills is proposed and fitted to a limited number of ground-penetrating radar records surveyed on the River bed of the Tagliamento River (northeast Italy). A steady-state, saturated subsurface flow simulation is performed on the small-scale, high-resolution, synthetic model (size: 75 m × 80 m × 9 m). Advective mixing (i.e. streamline intertwining) is visualised and quantified based on particle tracking. The results indicate strong advective mixing as well as a large flow deviation induced by the asymmetry of the trough fills with regard to the main flow direction. The flow deviation induces a partial, large-scale rotational effect. These findings depict possible advective mixing found in natural environments and can guide the interpretation of ecological processes such as in the hyporheic zone.
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influence of conceptual model uncertainty on contaminant transport forecasting in Braided River aquifers
Journal of Hydrology, 2015Co-Authors: Guillaume Pirot, E Huber, Julien Straubhaar, Philippe Renard, Peter HuggenbergerAbstract:Hydrogeologist are commonly confronted to field data scarcity. An interesting way to compensate this data paucity, is to use analog data. Then the questions of prediction accuracy and uncertainty assessment when using analog data shall be raised. These questions are investigated in the current paper in the case of contaminant transport forecasting in Braided River aquifers. In using analog data from the literature, multiple unconditional geological realizations are produced following different geological conceptual models (Multi-Gaussian, Object-based, Pseudo-Genetic). These petrophysical realizations are tested in a contaminant transport problem based on the MADE-II tracer experiment dataset. The simulations show that reasonable contaminant transport predictions can be achieved using analog data. The initial concentration conditions and location regarding the conductivity heterogeneity field have a stronger influence on the plume behavior than the resulting equivalent permeability. The results also underline the necessity to include a wide variety of geological conceptual models and not to restrain parameter space exploration within each concept as long as no field data allows for conceptual model or parameter value falsification.
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Subsurface flow mixing in coarse, Braided River deposits
Hydrology and Earth System Sciences Discussions, 2015Co-Authors: E Huber, Peter HuggenbergerAbstract:Abstract. Coarse, Braided River deposits show a large hydraulic heterogeneity at the metre scale. One of the main depositional elements found in such deposits is a trough structure filled with open-framework–bimodal gravel couplet cross-beds. Several studies investigated the impact of the highly permeable open-framework gravel texture mainly in terms of concentration breakthrough curves. However, although the trough fills are expected to be significant mixing agents for the subsurface flow, their impact on the three-dimensional flow field has not draw much attention. This study aims to evaluate the subsurface flow mixing caused by overlapping trough fills embedded in a poorly-sorted gravel matrix. Below the River bed of the Tagliamento River (northeast Italy), trough fills were identified with ground-penetrating radar (GPR) probing. Based on field observations of coarse, Braided River deposits, a simple three-dimensional geometrical model with associated hydraulic properties was fitted to the interpreted GPR reflectors. Then, steady-state subsurface flow and advective transport simulations were performed on the small-scale, high-resolution model (size: 45 m × 50 m × 10.26 m). The impact of trough fills on the flow field is visualised by the injection of a conservative tracer at three different depths.
Stuart N. Lane - One of the best experts on this subject based on the ideXlab platform.
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organic matter processing and soil evolution in a Braided River system
Catena, 2015Co-Authors: Nico Bätz, Eric P. Verrecchia, Stuart N. LaneAbstract:Traditionally, Braided River research has considered flow, sediment transport processes and, recently, vegetation dynamics in relation to River morphodynamics. However, if considering the development of woody vegetated patches over a time scale of decades, we must consider the extent to which soil forming processes, particularly related to soil organic matter, impact the alluvial geomorphic-vegetation system. Here we quantify the soil organic matter processing (humification) that occurs on young alluvial landforms. We sampled different geomorphic units, ranging from the active River channel to established River terraces in a wandering/Braided River system. For each geomorphic unit, soil pits were used to sample sediment/soil layers that were analysed in terms of grain size (< 2 mm) and organic matter quantity and quality (Rock-Eval method). A principal components analysis was used to identify patterns in the dataset. Results suggest that during the succession from bare River gravels to a terrace soil, there is a transition from small amounts of external organic matter supply provided by sedimentation processes (e.g. organic matter transported in suspension and deposited on bars), to large amounts of autogenic in situ organic matter production due to plant colonisation. This appears to change the time scale and pathways of alluvial succession (bio-geomorphic succession). However, this process is complicated by: the ongoing possibility of local sedimentation, which can serve to isolate surface layers via aggradation from the exogenic supply; and erosion which tends to create fresh deposits upon which organic matter processing must re-start. The result is a complex pattern of organic matter states as well as a general lack of any clear chronosequence within the active River corridor. This state reflects the continual battle between deposition events that can isolate organic matter from the surface, erosion events that can destroy accumulating organic matter and the early ecosystem processes necessary to assist the co-evolution of soil and vegetation. A key question emerges over the extent to which the fresh organic matter deposited in the active zone is capable of significantly transforming the local geochemical environment sufficiently to accelerate soil development.
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Organic matter processing and soil evolution in a Braided River system
CATENA, 2015Co-Authors: Nico Bätz, Eric P. Verrecchia, Stuart N. LaneAbstract:Traditionally, Braided River research has considered flow, sediment transport processes and, recently, vegetation dynamics in relation to River morphodynamics. However, if considering the development of woody vegetated patches over a time scale of decades, we must consider the extent to which soil forming processes, particularly related to soil organic matter, impact the alluvial geomorphic-vegetation system. Here we quantify the soil organic matter processing (humification) that occurs on young alluvial landforms. We sampled different geomorphic units, ranging from the active River channel to established River terraces in a wandering/Braided River system. For each geomorphic unit, soil pits were used to sample sediment/soil layers that were analysed in terms of grain size (
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quantification of Braided River channel change using archival digital image analysis
Earth Surface Processes and Landforms, 2010Co-Authors: Stuart N. Lane, P E Widdison, Robert E Thomas, Philip Ashworth, James L Best, Ian A Lunt, G Sambrook H Smith, Christopher J SimpsonAbstract:Historical archives of grey-scale River channel imagery are extensive. Here, we present and test a methodology to extract detailed quantitative topographic date from such imagery of sand-bed Rivers. Extracting elevation information from Rivers is difficult as they are characterized by a low relative relief (less than 4 m); the area of interest may be spatially extensive (e.g. active channel widths > 500 m in large Braided Rivers); the rate of change of surface elevation is generally low except in the vicinity of individual channel banks where the rate of change is very high: there is the complication that comes from innundation: and there may be an added complication caused by blockage of the field of view by vegetation. Here, we couple archival photogrammetric techniques with image processing methods and test these for quantification of sand-bed Braided River dynamics, illustrated for a 500 m wide, 3 km long reach of the Spouth Sasketchewan River, Canada. Digitial photogrammetry was used to quantify dry areas and water edge elevations. A methodology was then used to calibrate the special signature of inundated areas by combining established two media digital photogrammetric methods and image matching. This allowed determination of detailed depth maps for inundated area and, when combined with dry area data, creation of depths detectable from sequential digital elevation models. The result was a series of elevation models that demonstrate the potential for acquiring detailed and precise elevation data from any historical aerial imagery of Rivers without needing associated calibration data, provided that imagery is of the necessary scale to capture the features of interest. We use these data to highlight several aspects of channel change on the South Saskatchewan River, including bar movement, bank erosion and channel infilling.
Frédéric Liébault - One of the best experts on this subject based on the ideXlab platform.
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Gravel replenishment and active-channel widening for Braided-River restoration: The case of the Upper Drac River (France).
Science of The Total Environment, 2020Co-Authors: Guillaume Brousse, Frédéric Liébault, Gilles Arnaud-fassetta, Bertrand Breilh, S. TaconAbstract:Massive gravel replenishment combined with active-channel widening could theoretically improve the morphological recovery of altered Braided Rivers but this restoration strategy was not yet tested in the field. A recent Braided restoration project based on this principle was set up to restore a 4.2 km long reach in the Upper Drac River (French Alps) using 355.000 m3 of gravels to rise the bed level and to design a 100-m wide trapezoidal cross-section. The aim of this paper is to capture the morphological trajectory after restoration in order to evaluate efficiency and sustainability of this strategy. A Before and After Control Impact monitoring design has been used by combining a repetitive topographic survey (using airborne LiDAR data and terrestrial topographic surveys along cross-sections), an assessment of bedload supply to the restored reach using sediment tracing and active-layer surveys, and a systematic analysis of historical aerial photographs. In a particular context of low hydrological forcing after restoration, the restored reach adjusts with local braiding reference that highlights the efficiency of the restoration strategy. Despite this spontaneous braiding recovery, scouring processes are observed locally along the restored reach and the sustainability remains uncertain even if a good connection to sediment sources was observed. Feedbacks make it possible to propose recommendations to River managers who plan to use similar strategy of Braided River restoration. This field study demonstrated for the first time that sediment replenishment combined with channel widening can be an efficient solution for the spontaneous recovery of braiding conditions in altered alpine gravel-bed Rivers.
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Step by step error assessment in Braided River sediment budget using airborne LiDAR data
Geomorphology, 2014Co-Authors: S. Lallias-tacon, Frédéric Liébault, H. PiegayAbstract:Sequential airborne LiDAR surveys were used to reconstruct the sediment budget of a 7-km-long Braided River channel in southeastern France following a 14-year return period flood and to improve its accuracy step by step. Data processing involved (i) surfacematching of the sequential point clouds, (ii) spatially distributed propagation of uncertainty based on surface conditions of the channel, and (iii) water depth subtraction from the digital elevation models based on water depths measured in the field. The respective influence of each processing step on sediment budget computation was systematically documented. This showed that surface matching and water depth subtraction both have a considerable effect on the net sediment budget. Although DEM of difference thresholding based on uncertainty analysis on absolute elevation values had a smaller effect on the sediment budget, this step is crucial for the production of a comprehensive map of channel deformations. A large independent data set of RTK-GPS checkpoints was used to control the quality of the LiDAR altimetry. The results showed that high density (7–9 points/m2) airborne LiDAR surveys can provide a very high level of detection of elevation changes on the exposed surfaces of the channel, with a 95% confidence interval level of detection between 19 and 30 cm. Change detection from LiDAR data revealed that 54% of the pre-flood active channel was reworked by the flood. The Braided channel pattern was highly disturbed by the flood owing to the occurrence of several channel avulsions.
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assessment of intermediate fine sediment storage in a Braided River reach southern french prealps
Hydrological Processes, 2010Co-Authors: O. Navratil, C. Legout, D. Gateuille, M. Esteves, Frédéric LiébaultAbstract:This paper presents a field investigation on River channel storage of fine sediments in an unglaciated Braided River, the Bes River, located in a mountainous region in the southern French Prealps. Braided Rivers transport a very large quantity of bedload and suspended sediment load because they are generally located in the vicinity of highly erosive hillslopes. Consequently, these Rivers play an important role because they supply and control the sediment load of the entire downstream fluvial network. Field measurements and aerial photograph analyses were considered together to evaluate the variability of fine sediment quantity stored in a 2*5-km-long River reach. This study found very large quantities of fine sediment stored in this reach: 1100 t per unit depth (1 dm). Given that this reach accounts for 17% of the Braided channel surface area of the River basin, the quantities of fine sediment stored in the River network were found to be approximately 80% of the mean annual suspended sediment yields (SSYs) (66 200 t year−1), comparable to the SSYs at the flood event scale: from 1000 t to 12 000 t depending on the flood event magnitude. These results could explain the clockwise hysteretic relationships between suspended sediment concentrations and discharges for 80% of floods. This pattern is associated with the rapid availability of the fine sediments stored in the River channel. This study shows the need to focus on not only the mechanisms of fine sediment production from hillslope erosion but also the spatiotemporal dynamics of fine sediment transfer in Braided Rivers. Copyright © 2010 John Wiley & Sons, Ltd.
Peter Ashmore - One of the best experts on this subject based on the ideXlab platform.
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short communication challenges and applications of structure from motion photogrammetry in a physical model of a Braided River
Earth Surface Dynamics, 2019Co-Authors: Pauline Leduc, Sarah Peirce, Peter AshmoreAbstract:Abstract. For extending the applications of structure-from-motion (SfM) photogrammetry in River flumes, we present the main challenges and methods used to collect a large dataset ( >1000 digital elevation models, DEMs) of high-quality topographic data using close-range SfM photogrammetry with a resulting vertical precision of ∼1 mm. Automatic target detection, batch processing, and considerations for image quality were fundamental to the successful implementation of the SfM technique on such a large dataset, which was used primarily for capturing details of gravel-bed Braided River morphodynamics and sedimentology. While the applications of close-range SfM photogrammetry are numerous, we include sample results from DEM differencing, which was used to quantify morphology change and provide estimates of water depth in Braided Rivers, as well as image analysis for mapping bed surface texture. These methods and results contribute to the growing field of SfM applications in geomorphology and close-range experimental settings in general.
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Grain sorting in the morphological active layer of a Braided River physical model
Earth Surface Dynamics, 2015Co-Authors: Pauline Leduc, Peter Ashmore, James T GardnerAbstract:Abstract. A physical scale model of a gravel-bed Braided River was used to measure vertical grain size sorting in the morphological active layer aggregated over the width of the River. This vertical sorting is important for analyzing Braided River sedimentology, for numerical modeling of Braided River morphodynamics, and for measuring and predicting bedload transport rate. We define the morphological active layer as the bed material between the maximum and minimum bed elevations at a point over extended time periods sufficient for braiding processes to rework the River bed. The vertical extent of the active layer was measured using 40 hourly high-resolution DEMs (digital elevation models) of the model River bed. An image texture algorithm was used to map bed material grain size of each DEM. Analysis of the 40 DEMs and texture maps provides data on the geometry of the morphological active layer and variation in grain size in three dimensions. By normalizing active layer thickness and dividing into 10 sublayers, we show that all grain sizes occur with almost equal frequency in all sublayers. Occurrence of patches and strings of coarser (or finer) material relates to preservation of particular morpho-textural features within the active layer. For numerical modeling and bedload prediction, a morphological active layer that is fully mixed with respect to grain size is a reliable approximation.
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Geometry and grain-size characteristics of the basal surface of a Braided River deposit
Geology, 2011Co-Authors: J. Tobias Gardner, Peter AshmoreAbstract:Description of the three-dimensional geometry and grain-size patterns of fluvial deposits and their relationship to the morphodynamics of the River has been an elusive objective in sedimentology, hindered by limited exposure and the time scale of fluvial dynamics. In small-scale physical models the time scales are short enough to map River morphology and sedimentology during significant (and continuous) morphological development of the River and its deposits, especially for Braided Rivers. Using close-range digital photogrammetry, the dynamics of the River morphology, and resulting deposit geometry and sedimentology, were captured using digital elevation model differencing techniques, combined with automated grain-size mapping from image texture analysis. Using these novel methods we show the temporal development and characteristics of Braided River deposit geometry, and, for the first time, map the characteristics and development of the basal surface of Braided River deposits in relation to River morphodynamics and formative processes. The basal surface has considerable relief, wide variation in grain size similar to that of the River as a whole, develops progressively over time by switching of channels producing adjacent patches and ribbons of basal incision of different ages, and is only partially related to bed scour associated with laterally migrating channel confluences.
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Length scale of Braided River morphology
Water Resources Research, 2009Co-Authors: Elizabeth J Hundey, Peter AshmoreAbstract:[1] Pool-bar topography in single-channel Rivers has a length scale proportional to channel width. In Braided Rivers confluence-bifurcation units are analogous to pool-bar morphology and, in some cases, develop from initial alternate bars. Consequently, confluence-bifurcation units are expected to have length that scales with the central anabranch width and that constitutes a basic length scale Braided channel morphology. This idea was tested using measurements from a physical model of a gravel bed Braided River and from aerial photographs of Braided Rivers. Length (distance from confluence to bifurcation), anabranch width, and confluence angle of confluence-bifurcation units were measured. A simple length scaling is evident across the range of scales; confluence-bifurcation length is 4–5 times the channel width. This scaling is a fundamental element of Braided River morphology and suggests that Braided patterns are created by processes, and have morphological regularity, similar to pool-bar units of low-sinuosity single-thread Rivers.