Bathymetric mapping in turbid braided mountain streams using SfM-MVS photogrammetry and statistical approaches

2020 ◽  
Author(s):  
Davide Mancini ◽  
Gilles Antoniazza ◽  
Stuart Lane
Keyword(s):  
Braided River ◽  
Differential Gps ◽  
Erosion And Deposition ◽  
Survey Techniques ◽  
Bathymetric Data ◽  
River Bed ◽  
Braided Stream ◽  
Suspended Sediment Concentrations ◽  
Statistical Relationships ◽  
Derived Data

<p>River bathymetric investigation has a long tradition as river-bed morphology is a crucial geomorphological variable that also has implications for river ecology and sediment management. In one sense, this is becoming more straightforward with the development of UAV platforms and SfM-MVS photogrammetry. Mapping inundated and exposed areas simultaneously has proved possible either by adopting two media refraction correction or by using some form of the Beer-Lambert Law. However, both of these approaches rely upon the bed being visible which becomes restricted to progressively shallower zones as stream turbidity increases. Traditional survey techniques to collect bathymetric data for inundated zones (e.g. total station or differential GPS systems) are time consuming and require a trade-off between point density and the spatial extent of survey. In this study we test a simple hypothesis: it is possible to generalize the likely depth of water in a shallow braided stream from basic planimetric information and use such statistical relationships to reconstruct the bathymetry of inundated zones. This is based upon the principle that a suite of planimetric variables (e.g. distance from stream banks, river channel width, local curvature magnitude and direction, streamline convergence and divergence) can be used to model the spatial distribution of water depths. We attempt to do this for a shallow braided river with high suspended sediment concentrations using orthoimages and DEMs derived from application of SfM-MVS photogrammetry to UAV-based imagery. We develop separate calibration and validation relationships to train and to assess the statistical models developed. These are then applied to the stream to produce bathymetric maps of flow depth for integration with SfM-MVS derived data from exposed areas. The method produces a point specific measure of uncertainty and tests suggest that the associated uncertainties are sufficiently low that after propagation into DEMs of difference reliable data on braided river dynamics and erosion and deposition volumes can be obtained.</p>

scholarly journals Grain sorting in the morphological active layer of a braided river physical model

2015 ◽  
Vol 3 (4) ◽  
pp. 577-585 ◽  
Author(s):  
P. Leduc ◽  
P. Ashmore ◽  
J. T. Gardner
Keyword(s):  
Grain Size ◽  
Numerical Modeling ◽  
Active Layer ◽  
Bedload Transport ◽  
Scale Model ◽  
Active Layer Thickness ◽  
Braided River ◽  
River Bed ◽  
Physical Scale ◽  
Bed Material

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.

Spatiotemporal response of an Alpine braided river reach to snow melt and flood events

2020 ◽  
Author(s):  
Maarten Bakker ◽  
Florent Gimbert ◽  
Clément Misset ◽  
Laurent Borgniet ◽  
Alain Recking
Keyword(s):  
Morphological Change ◽  
Return Period ◽  
Temporal Dynamics ◽  
Bedload Transport ◽  
Snow Melt ◽  
Braided River ◽  
Flood Events ◽  
River Bed ◽  
Extreme Flood ◽  
Braided Reach

<p>Alpine environments are responding to accelerated climate warming through the release and mobilization of large amounts of unconsolidated sediment. Sediment fluxes delivered to Alpine streams may be buffered, filtered and/or modulated as they pass through braided river reaches, which play a key role in the downstream transfer and dynamics of bed material. The functioning of these braided reaches is however still poorly understood, particularly during high magnitude events whose effects are very difficult to monitor but play an ever more prominent role in river system evolution.</p><p>In this study, we investigate the transfer of bedload material and river bed morphological change in a braided reach of the Séveraisse River (France), over the course of the melt season and two large flood events with an estimated return period of 5 and 50 years. To quantify braided reach dynamics, a multi-physical approach is employed that combines both temporally and spatially resolved techniques. We use bank-side geophones and locally derived parameters that describe seismic wave propagation in the subsurface to accurately quantify bedload transport and gain a unique insight in its temporal dynamics, particularly during the flood events. River bed elevation changes are determined from intermittent UAV-based LiDAR and photogrammetric acquisition. These are complemented with hourly (daytime) time-lapse images that register planform changes during the flood events.</p><p>Our results show strongly contrasting morphodynamic behavior with different flow conditions. During ‘normal’ bedload transport conditions driven by annual snow-melt, channel aggradation occurs leading to progressively lower bedload export from the reach for a given discharge. During the flood with a 5 year return period, which occurred at the end of the melt season, the braided riverbed morphology is rearranged and net sediment export took place. Most interestingly, in the autumn an extreme flood event led to the development of a single channel, meandering planform with significant outer bend erosion on alternating banks. Although this morphological change may be only temporary, i.e. a braided configuration may be expected to be gradually re-instated, it has important implications on the general functioning and morphological evolution of the reach and the downstream transfer of sediment.</p>

scholarly journals Assessment of a numerical model to reproduce event-scale erosion and deposition distributions in a braided river

2016 ◽  
Vol 52 (8) ◽  
pp. 6621-6642 ◽  
Author(s):  
R. D. Williams ◽  
R. Measures ◽  
D. M. Hicks ◽  
J. Brasington
Keyword(s):  
Numerical Model ◽  
Braided River ◽  
Erosion And Deposition ◽  
Event Scale

scholarly journals Uniform grain-size distribution in the active layer of a shallow, gravel-bed, braided river (the Urumqi River, China) and implications for paleo-hydrology

2018 ◽  
Author(s):  
Laure Guerit ◽  
Laurie Barrier ◽  
Youcun Liu ◽  
Clément Narteau ◽  
Eric Lajeunesse ◽  
...  
Keyword(s):  
Grain Size ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Active Layer ◽  
Size Distributions ◽  
Gravel Bed ◽  
Surface Samples ◽  
River Bed ◽  
Braided Stream ◽  
Grain Size Distributions

Abstract. The grain-size distribution of ancient alluvial systems is commonly determined from surface samples of vertically exposed sections of gravel deposits. This method relies on the hypothesis that the grain-size distribution obtained from a vertical cross-section is equivalent to that of the river bed. We report a field test of this hypothesis on samples collected on an active, gravel-bed, braided stream: the Urumqi River in China. We compare data from volumetric samples of a trench excavated in an active thread and surface counts performed on the trench vertical faces. We show that the grain-size distributions obtained from all samples are similar and that the deposit is uniform at the scale of the river active layer, a layer extending from the surface to a depth of approximately ten times the size of the largest clasts.

scholarly journals 3D numerical modeling of flow and sediment transport in rivers and open channels

2019 ◽  
Vol 3 (1) ◽  
pp. 23-36
Author(s):  
Le Song Giang ◽  
Tran Thi My Hong
Keyword(s):  
Boundary Condition ◽  
Sediment Transport ◽  
Numerical Model ◽  
Differential Equations ◽  
Water Level ◽  
Suspended Sediment ◽  
Three Dimensional ◽  
River Bed ◽  
Suspended Sediment Concentrations ◽  
Flow And Sediment Transport

Numerical model is a useful tool in studying the flow and sediment transport, change in river bed and is built on solving governing differential equations. Numerical model has many different levels and three-dimensional model is the highest level, allowing detailed simulation of flow and sediment transport process in 3D space. The paper presents a method calculating three - dimensional flow and sediment transport in the open channel. Water level and flow velocity are solved from three-dimensional equations with hydrostatic hypothesis. Concentration of suspended sediment, bottom sediment and bottom evolution is solved from transport equations. The governing differential equations in the "sigma" transform coordinate system are solved by finite volume method on unstructured grid of quadrilateral elements. Boundary condition of water level or flow will be imposed on open boundary. For suspended sediment concentrations in the injected phase, suspended sediment concentrations are applied and the outflow phase applies free drainage conditions. This method of calculation was tested with the problem of curved channel sediment transport which was studied experimentally by Odgaard and Bergs. Calculation results are quite consistent with the measured data. In order to test the practical applicability, this method is also tested with the problem of sediment transport in Cu lao Pho islet on Dong Nai river. To solve the matter of hydraulic boundary condition of this problem, the model of Cu lao Pho islet is integrated into the Sai Gon - Dong Nai river system model. Results of the calculation of the river bed evolution of the Cu lao Pho islet on the Dong Nai river also show that this calculation method gives results consistent with the rule and can be used in practical research.  

scholarly journals USE OF NEW TECHNOLOGIES FOR THE SYSTEMATIC NAUTICAL CARTOGRAPHIC MAPPING OF THE PARAGUAY RIVER WATERWAY

GEOGRAFIA ◽  
2018 ◽  
Vol 42 (3) ◽  
pp. 175-183
Author(s):  
Paulo Pereira Oliveira MATOS ◽  
Juarez Cerqueira FERREIRA ◽  
Victor Hugo do Espírito Santo CONCEIÇÃO
Keyword(s):  
New Technologies ◽  
Single Beam ◽  
Bathymetric Data ◽  
Complete Mapping ◽  
Paraguay River ◽  
West Region ◽  
River Bed ◽  
Mapping Process ◽  
Safe Transport ◽  
Modern Technologies

One of the main cargo corridors of the Brazilian West region is the Paraguay River. Currently, the Paraguay River Waterway moves more than seven million tons of cargo, being the second largest waterway for cargo movement in Brazil. However, for the uick and safe transport of goods it is essential to have a proper, systematic and complete mapping of the river bed. This work, in charge of the Brazilian Navy and dating back to the Nautical Cartographic Basic Plan of 1935, is performed with the construction of oficial nautical documents, aiming the navigation safety. These cartographic documents, called Official Nautical Charts, are the result from the mapping process, originated from the collection of bathymetric data on specific spots. This collection used always the most modern technologies available and recently, single beam echo-sounders and accurate positioners. Today new technologies are available, including the multi-beam echo-sounder, equipment with several advantages, allowing, among others, the full coverage of the riverbed. This article describes this paradigm shift for the collection of bathymetric data in Paraguay River basin, presenting the preliminary findings and conclusions from the use of this technology

scholarly journals Grain sorting in the morphological active layer of a braided river physical model

2015 ◽  
Vol 3 (3) ◽  
pp. 577-600
Author(s):  
P. Leduc ◽  
P. Ashmore ◽  
J. T. Gardner
Keyword(s):  
Grain Size ◽  
Numerical Modeling ◽  
Active Layer ◽  
Scale Model ◽  
Bed Load ◽  
Active Layer Thickness ◽  
Braided River ◽  
River Bed ◽  
Physical Scale ◽  
Bed Material

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 morpho-dynamics and for measuring and predicting bed load 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 re-work the river bed. The vertical extent of the active layer was measured using 40 hourly high-resolution DEMs 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. Normalizing active layer thickness and dividing into 10 sub-layers we show that all grain sizes occur with almost equal frequency in all sub-layers. 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 bed load prediction a morphological active layer that is fully mixed with respect to grain size is a reliable approximation.

Adjustment mechanism of the sand bars in the jingjiang reach after the impounding the three gorges

2020 ◽  
Author(s):  
Xuhai Yang
Keyword(s):  
Negative Impact ◽  
Fine Sand ◽  
Deformation Characteristics ◽  
Three Gorges ◽  
Flow Process ◽  
Erosion And Deposition ◽  
Adjustment Mechanism ◽  
Sand Bars ◽  
The Three Gorges ◽  
River Bed

<p>After the application of the large reservoirs, the conditions of discharge and sediment are changed. Based on a large number of measured hydrological and topographic data, this paper studies the deformation characteristics of sandbars micro-geomorphology in sandy reach of jingjiang river after the impounding of the three gorges reservoir(TGD), and discusses the adjustment mechanism of sandbars. The result shows that the sandy bars showed the head scoured and the shrink of area, and the sandbars in the reach with revetment project was relatively stable.The evolution of the sandbars was mainly influenced by riverbed composition, discharge and sediment process and revetment project. The composition of the riverbed determined the scour resistance of the sandbars, while the change of flow process determined the location and property of scour and silting, and the amount of incoming sediment determined the extent of scour and silting, the implementation of revetment project was beneficial to sandbars stability. After the TGD operation, the erosion of the bars in the Jingjiang reach ranked the strongest when the discharges fall in 15000 m³/s~25000 m³/s. The duration of this flow range increased after the TGD operation in 2003, and the bars presented an erosion state. Due to the impacts of river bed armoring and the significantly reduced sediment, there existed certain interactive relationships between the adjustment in the erosion and deposition of bars and the changes in the percentage of the grain size belonging to 0.125<d<0.25mm. The reduction of the fine sand had a negative impact on the sedimentation of bars after erosion. The layout of the revetment project had a certain control effect on the sandy reach, but the unguarded sandy bars presented scour and deposition with the fluctuation of discharge and sediment process between years.</p>

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