Analysis of a 2-D bed topography model for rivers

1989 ◽  
pp. 153-180 ◽  
Author(s):  
Nico Struiksma ◽  
Alessandra Crosato
Keyword(s):  
Bed Topography ◽  
Topography Model

scholarly journals Bed topography and subglacial landforms in the onset region of the Northeast Greenland Ice Stream

2020 ◽  
Vol 61 (81) ◽  
pp. 143-153 ◽  
Author(s):  
Steven Franke ◽  
Daniela Jansen ◽  
Tobias Binder ◽  
Nils Dörr ◽  
Veit Helm ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ultra Wideband ◽  
Ice Flow ◽  
Detailed Model ◽  
Dynamic Component ◽  
Bed Topography ◽  
Ice Stream ◽  
Topography Model

AbstractThe Northeast Greenland Ice Stream (NEGIS) is an important dynamic component for the total mass balance of the Greenland ice sheet, as it reaches up to the central divide and drains 12% of the ice sheet. The geometric boundary conditions and in particular the nature of the subglacial bed of the NEGIS are essential to understand its ice flow dynamics. We present a record of more than 8000 km of radar survey lines of multi-channel, ultra-wideband radio echo sounding data covering an area of 24 000 km2, centered on the drill site for the East Greenland Ice-core Project (EGRIP), in the upper part of the NEGIS catchment. Our data yield a new detailed model of ice-thickness distribution and basal topography in the region. The enhanced resolution of our bed topography model shows features which we interpret to be caused by erosional activity, potentially over several glacial–interglacial cycles. Off-nadir reflections from the ice–bed interface in the center of the ice stream indicate a streamlined bed with elongated subglacial landforms. Our new bed topography model will help to improve the basal boundary conditions of NEGIS prescribed for ice flow models and thus foster an improved understanding of the ice-dynamic setting.

scholarly journals HIGH-RESOLUTION SURFACE AND BED TOPOGRAPHY MAPPING OF RUSSELL GLACIER (SW GREENLAND) USING UAV AND GPR

2020 ◽  
Vol V-2-2020 ◽  
pp. 757-763
Author(s):  
K. Lamsters ◽  
J. Karušs ◽  
M. Krievāns ◽  
J. Ješkins
Keyword(s):  
Low Frequency ◽  
Climatic Conditions ◽  
Cold Wave ◽  
Glacier Surface ◽  
Warm Up ◽  
Bed Topography ◽  
Marginal Part ◽  
Subglacial Topography ◽  
Topography Model ◽  
Elevation Model

Abstract. This study presents the detailed survey of the northern marginal part of Russell Glacier, SW Greenland using the combination of unmanned aerial vehicle (UAV) photogrammetry and low-frequency ground penetrating radar (GPR) measurements. Obtained digital elevation model (DEM) and ice thickness data from GPR data allowed the generation of high precision subglacial topography model. We report uncertainties arising from GPR, GPS, and DEM suggesting sufficient accuracy for the reconstruction of glacier bed topography. GPR data and generated subglacial topography model does not reveal any possible Nye channel that could be incised into the bedrock, however, we were able to detect englacial tunnel that runs approximately parallel to the ice margin and possibly is a remnant of a tunnel that provided passage for ice-dammed lake waters during the latest jökulhlaups (2007, 2008). We also observe a radar-transparent layer up to 20 m from the glacier surface suggesting the boundary of cold/temperate ice or piezometric surface. The latter one is preferred due to the warm climatic conditions which are supposed to warm up possible winter cold wave.

scholarly journals Modelling glacier-bed overdeepenings and possible future lakes for the glaciers in the Himalaya—Karakoram region

2016 ◽  
Vol 57 (71) ◽  
pp. 119-130 ◽  
Author(s):  
A. Linsbauer ◽  
H. Frey ◽  
W. Haeberli ◽  
H. Machguth ◽  
M.F. Azam ◽  
...  
Keyword(s):  
Ice Thickness ◽  
Surface Slope ◽  
Bed Topography ◽  
Bed Elevation ◽  
Digital Elevation ◽  
Surface Slopes ◽  
Lake Formation ◽  
Topography Model ◽  
Basal Shear ◽  
The Himalaya

AbstractSurface digital elevation models (DEMs) and slope-related estimates of glacier thickness enable modelling of glacier-bed topographies over large ice-covered areas. Due to the erosive power of glaciers, such bed topographies can contain numerous overdeepenings, which when exposed following glacier retreat may fill with water and form new lakes. In this study, the bed overdeepenings for ~28 000 glaciers (40 775 km2) of the Himalaya-Karakoram region are modelled using GlabTop2 (Glacier Bed Topography model version 2), in which ice thickness is inferred from surface slope by parameterizing basal shear stress as a function of elevation range for each glacier. The modelled ice thicknesses are uncertain (±30%), but spatial patterns of ice thickness and bed elevation primarily depend on surface slopes as derived from the DEM and, hence, are more robust. About 16 000 overdeepenings larger than 104m2 were detected in the modelled glacier beds, covering an area of ~2200 km2 and having a volume of ~120km3 (3-4% of present-day glacier volume). About 5000 of these overdeepenings (1800 km2) have a volume larger than 106m3. The results presented here are useful for anticipating landscape evolution and potential future lake formation with associated opportunities (tourism, hydropower) and risks (lake outbursts).

scholarly journals Short-term Variations in Strain and Surface Tilt on Storglaciären, Kebnekaise, Northern Sweden

1989 ◽  
Vol 35 (120) ◽  
pp. 201-208 ◽  
Author(s):  
Peter Jansson ◽  
Roger LeB. Hooke
Keyword(s):  
Water Pressure ◽  
High Water ◽  
Ice Thickness ◽  
Gradual Change ◽  
Short Term ◽  
Glacier Surface ◽  
Vertical Movements ◽  
Bed Topography ◽  
The Waves ◽  
Local Uplift

AbstractTiltmeters that can detect changes in slope of a glacier surface as small as 0.1 μ rad have been used on Storglaciären. The records obtained to date have been from the upper part of the ablation area, where the bed of the glacier is overdeepened. A total of 82 d of records has been obtained for various time periods between early June and early September.There is generally a gradual change in inclination of the glacier surface over periods of several days, but these changes do not appear to be systematic. In particular, they are not consistent with vertical movements of stakes located 2–3 ice thicknesses away from the tiltmeters. This suggests that the tiltmeters are sensing disturbances over areas with diameters comparable to the local ice thickness.Superimposed on these trends are diurnal signals suggesting rises and falls of the surface just up-glacier from the riegel that bounds the overdeepening on its down-glacier end. These may be due to waves of high water pressure originating in a crevassed area near the equilibrium line. If this interpretation is correct, the waves apparently move down-glacier at speeds of 20–60 m h−1and become sufficiently focused, either by the bed topography or by conduit constrictions, to result in local uplift of the surface. Also observed are abrupt tilts towards the glacier center line shortly after the beginning of heavy rainstorms. These appear to be due to longitudinal stretching as the part of the glacier below the riegel accelerates faster than that above. Water entering the glacier by way of a series of crevasses over the riegel is believed to be responsible for this differential acceleration. In June 1987, a dramatic event was registered, probably reflecting the initial summer acceleration of the glacier.

scholarly journals Ice thickness distribution of all Swiss glaciers based on extended ground-penetrating radar data and glaciological modeling

2021 ◽  
pp. 1-19
Author(s):  
Melchior Grab ◽  
Enrico Mattea ◽  
Andreas Bauder ◽  
Matthias Huss ◽  
Lasse Rabenstein ◽  
...  
Keyword(s):  
Ground Penetrating Radar ◽  
Thickness Distribution ◽  
Radar Data ◽  
Tourism Industry ◽  
Swiss Alps ◽  
Ice Thickness ◽  
Hazard Management ◽  
Bed Topography ◽  
Ice Volume ◽  
Ground Penetrating

Abstract Accurate knowledge of the ice thickness distribution and glacier bed topography is essential for predicting dynamic glacier changes and the future developments of downstream hydrology, which are impacting the energy sector, tourism industry and natural hazard management. Using AIR-ETH, a new helicopter-borne ground-penetrating radar (GPR) platform, we measured the ice thickness of all large and most medium-sized glaciers in the Swiss Alps during the years 2016–20. Most of these had either never or only partially been surveyed before. With this new dataset, 251 glaciers – making up 81% of the glacierized area – are now covered by GPR surveys. For obtaining a comprehensive estimate of the overall glacier ice volume, ice thickness distribution and glacier bed topography, we combined this large amount of data with two independent modeling algorithms. This resulted in new maps of the glacier bed topography with unprecedented accuracy. The total glacier volume in the Swiss Alps was determined to be 58.7 ± 2.5 km3 in the year 2016. By projecting these results based on mass-balance data, we estimated a total ice volume of 52.9 ± 2.7 km3 for the year 2020. Data and modeling results are accessible in the form of the SwissGlacierThickness-R2020 data package.

scholarly journals Effect of Mean Velocity-to-Critical Velocity Ratios on Bed Topography and Incipient Motion in a Meandering Channel: Experimental Investigation

Water ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 883
Author(s):  
Nargess Moghaddassi ◽  
Seyed Habib Musavi-Jahromi ◽  
Mohammad Vaghefi ◽  
Amir Khosrojerdi
Keyword(s):  
Experimental Investigation ◽  
Critical Velocity ◽  
Velocity Ratio ◽  
Scour Depth ◽  
Incipient Motion ◽  
Mean Velocity ◽  
Straight Path ◽  
Meandering Channel ◽  
Bed Topography ◽  
The Mean

As 180-degree meanders are observed in abundance in nature, a meandering channel with two consecutive 180-degree bends was designed and constructed to investigate bed topography variations. These two 180-degree mild bends are located between two upstream and downstream straight paths. In this study, different mean velocity-to-critical velocity ratios have been tested at the upstream straight path to determine the meander’s incipient motion. To this end, bed topography variations along the meander and the downstream straight path were addressed for different mean velocity-to-critical velocity ratios. In addition, the upstream bend’s effect on the downstream bend was investigated. Results indicated that the maximum scour depth at the downstream bend increased as a result of changing the mean velocity-to-critical velocity ratio from 0.8 to 0.84, 0.86, 0.89, 0.92, 0.95, and 0.98 by, respectively, 1.5, 2.5, 5, 10, 12, and 26 times. Moreover, increasing the ratio increased the maximum sedimentary height by 3, 10, 23, 48, 49, and 56 times. The upstream bend’s incipient motion was observed for the mean velocity-to-critical velocity ratio of 0.89, while the downstream bend’s incipient motion occurred for the ratio of 0.78.

Dune-scale cross-strata across the fluvial-deltaic backwater regime: Preservation potential of an autogenic stratigraphic signature

Geology ◽  
2020 ◽  
Vol 48 (12) ◽  
pp. 1144-1148
Author(s):  
Chenliang Wu ◽  
Jeffrey A. Nittrouer ◽  
Travis Swanson ◽  
Hongbo Ma ◽  
Eric Barefoot ◽  
...  
Keyword(s):  
Spatial Variability ◽  
Mississippi River ◽  
Nonuniform Flow ◽  
Hydrodynamic Conditions ◽  
Flow Conditions ◽  
Bed Topography ◽  
Fundamental Building Block ◽  
Bed Form ◽  
Spatially Varying ◽  
Topography Data

Abstract Dune-scale cross-beds are a fundamental building block of fluvial-deltaic stratigraphy and have been recognized on Earth and other terrestrial planets. The architecture of these stratal elements reflects bed-form dynamics that are dependent on river hydrodynamic conditions, and previous work has documented a multitude of scaling relationships to describe the morphodynamic interactions between dunes and fluid flow. However, these relationships are predicated on normal flow conditions for river systems and thus may be unsuitable for application in fluvial-deltaic settings that are impacted by nonuniform flow. The ways in which dune dimensions vary systematically due to the influence of reach-averaged, nonuniform flow, and how such changes may be encoded in dune cross-strata, have not been investigated. Herein, we explored the influence of backwater flow on dune geometry in a large modern fluvial channel and its implications for interpretation of systematic variability in dune cross-strata in outcrop-scale stratigraphy. This was accomplished by analyzing high-resolution channel-bed topography data for the lowermost 410 km of the Mississippi River, which revealed that dune size increases to a maximum before decreasing toward the river outlet. This spatial variability coincides with enhanced channel-bed aggradation and decreasing dune celerity, which arise due to backwater hydrodynamics. An analytical model of bed-form stratification, identifying spatial variability of cross-set thickness, indicates a prominent downstream decrease over the backwater region. These findings can be used to inform studies of ancient fluvial-deltaic settings, by bolstering assessments of proximity to the marine terminus and associated spatially varying paleohydraulics.

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