Glaciohydraulic supercooling: a freeze-on mechanism to create stratified, debris-rich basal ice: II. Theory

AbstractSimple theory supports field observations (Lawson and others, 1998 that subGlaciol water flow out of overdeepenings can cause accretion of layered, debris-bearing ice to the bases of glaciers. The large meltwater flux into a temperate glacier at the onset of summer melting can cause rapid water flow through expanded basal cavities or other flow paths. If that flow ascends a sufficiently steep slope out of an overdeepèning, the water will supercool as the pressure-melting point rises, and basal-ice accretion will occur. Diurnal, occasional or annual fluctuations in water discharge will cause variations in accretion rate, debris content of accreted ice or subsequent diagenesis, producing layers. Under appropriate conditions, net accretion of debris-bearing basal ice will allow debris fluxes that are significant in the glacier sediment budget.

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Glaciohydraulic supercooling: a freeze-on mechanism to create stratified, debris-rich basal ice: II. Theory

Journal of Glaciology ◽

10.1017/s0022143000002070 ◽

1998 ◽

Vol 44 (148) ◽

pp. 563-569 ◽

Cited By ~ 101

Author(s):

Richard B. Alley ◽

Daniel E. Lawson ◽

Edward B. Evenson ◽

Jeffrey C. Strasser ◽

Grahame J. Larson

Keyword(s):

Water Flow ◽

Accretion Rate ◽

Water Discharge ◽

Steep Slope ◽

Field Observations ◽

Ice Accretion ◽

Flow Paths ◽

Basal Ice ◽

Flow Through ◽

Pressure Melting

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Computing water flow through complex landscapes – Part 2: Finding hierarchies in depressions and morphological segmentations

Earth Surface Dynamics ◽

10.5194/esurf-8-431-2020 ◽

2020 ◽

Vol 8 (2) ◽

pp. 431-445

Author(s):

Richard Barnes ◽

Kerry L. Callaghan ◽

Andrew D. Wickert

Keyword(s):

Water Flow ◽

Hydrological Modeling ◽

Dynamic Models ◽

Terrain Analysis ◽

Flow Paths ◽

Topographic Complexity ◽

Morphological Segmentation ◽

Surface Water Flow ◽

Digital Elevation ◽

Flow Through

Abstract. Depressions – inwardly draining regions of digital elevation models – present difficulties for terrain analysis and hydrological modeling. Analogous “depressions” also arise in image processing and morphological segmentation, where they may represent noise, features of interest, or both. Here we provide a new data structure – the depression hierarchy – that captures the full topologic and topographic complexity of depressions in a region. We treat depressions as networks in a way that is analogous to surface-water flow paths, in which individual sub-depressions merge together to form meta-depressions in a process that continues until they begin to drain externally. This hierarchy can be used to selectively fill or breach depressions or to accelerate dynamic models of hydrological flow. Complete, well-commented, open-source code and correctness tests are available on GitHub and Zenodo.

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Sliding of temperate basal ice on a rough, hard bed: creep mechanisms, pressure melting, and implications for ice streaming

The Cryosphere ◽

10.5194/tc-10-1915-2016 ◽

2016 ◽

Vol 10 (5) ◽

pp. 1915-1932 ◽

Cited By ~ 8

Author(s):

Maarten Krabbendam

Keyword(s):

Heat Flow ◽

Power Law ◽

Basal Layer ◽

Ice Dynamics ◽

Basal Ice ◽

Basal Sliding ◽

Ductile Flow ◽

Flow Through ◽

Pressure Melting ◽

Power Law Creep

Abstract. Basal ice motion is crucial to ice dynamics of ice sheets. The classic Weertman model for basal sliding over bedrock obstacles proposes that sliding velocity is controlled by pressure melting and/or ductile flow, whichever is the fastest; it further assumes that pressure melting is limited by heat flow through the obstacle and ductile flow is controlled by standard power-law creep. These last two assumptions, however, are not applicable if a substantial basal layer of temperate (T ∼ Tmelt) ice is present. In that case, frictional melting can produce excess basal meltwater and efficient water flow, leading to near-thermal equilibrium. High-temperature ice creep experiments have shown a sharp weakening of a factor 5–10 close to Tmelt, suggesting standard power-law creep does not operate due to a switch to melt-assisted creep with a possible component of grain boundary melting. Pressure melting is controlled by meltwater production, heat advection by flowing meltwater to the next obstacle and heat conduction through ice/rock over half the obstacle height. No heat flow through the obstacle is required. Ice streaming over a rough, hard bed, as possibly in the Northeast Greenland Ice Stream, may be explained by enhanced basal motion in a thick temperate ice layer.

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On the Effects of Water Discharge Through Radial Gates at the Caruachi Dam

ASME 2010 10th Biennial Conference on Engineering Systems Design and Analysis, Volume 4 ◽

10.1115/esda2010-24080 ◽

2010 ◽

Cited By ~ 1

Author(s):

Douglas Sanchez ◽

Juan E. Salazar

Keyword(s):

Water Flow ◽

Water Discharge ◽

Three Dimensional ◽

Flow Induced Vibration ◽

Discharge Flow ◽

Cfd Models ◽

Flow Through ◽

Critical Velocities ◽

Flow Effects

This paper presents numerical simulation of the water flow through the radial gates of the 2,280 MW Caruchi Dam, in southern Venezuela, and its relation to the vibration of the dam’s spillways and adjacent Control Building. The study is conducted as a contribution in determining the source of vibration of the fore mentioned structures in the case of gates opening above the normal values of up to 5 m, which occur when a larger water discharge is required in order to maintain an adequate level of the reservoir during the rainy season. The aim of the study was to find the pressure distribution and velocity profiles of the discharge flow through one of the dam’s radial gates and determine critical (reduced) velocities that may result in flow-induced vibration of the gates, as they were deemed to be the source of vibration of the whole set of structures in the first place. For this purpose, a commercially available FEM code was used. Three-dimensional CFD models were developed to simulate behavior of the flow when being released to the spillways, for opening values of 2, 5, 10 and 14 m, including the effect of the spillways’ deflectors. Modal analyses of the gate were performed, to take into account natural vibration frequencies in the determination of its critical velocities. After comparison of the gate’s critical velocities and velocity values from the CFD simulations, it is fair to say that the discharge flow does not directly induce vibration on the gates but rather on the spillways’ structure. This conclusion disregards flow through the gates as triggering the vibration phenomena which gave origin to this project, and puts the emphasis now on studying water flow effects on vibration in the spillway which, if not corrected on time, may ultimately lead to its catastrophic failure.

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Computing water flow through complex landscapes, Part 2: Finding hierarchies in depressions and morphological segmentations

10.5194/esurf-2019-34 ◽

2019 ◽

Cited By ~ 1

Author(s):

Richard Barnes ◽

Kerry L. Callaghan ◽

Andrew D. Wickert

Keyword(s):

Water Flow ◽

Hydrological Modeling ◽

Dynamic Models ◽

Terrain Analysis ◽

Flow Paths ◽

Topographic Complexity ◽

Morphological Segmentation ◽

Surface Water Flow ◽

Digital Elevation ◽

Flow Through

Abstract. Depressions – inwardly-draining regions of digital elevation models – present difficulties for terrain analysis and hydrological modeling. Analogous depressions also arise in image processing and morphological segmentation where they may represent noise, features of interest, or both. Here we provide a new data structure – the depression hierarchy – that captures the full topologic and topographic complexity of depressions in a region. We treat depressions as networks, in a way that is analogous to surface-water flow paths, in which individual sub-depressions merge together to form meta-depressions in a process that continues until they begin to drain externally. The hierarchy can be used to selectively fill or breach depressions, or to accelerate dynamic models of hydrological flow. Complete, well-commented, open-source code and correctness tests are available on Github and Zenodo.

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Basal sliding of temperate basal ice on a rough, hard bed: pressure melting, creep mechanisms and implications for ice streaming

10.5194/tc-2016-52 ◽

2016 ◽

Cited By ~ 1

Author(s):

Maarten Krabbendam

Keyword(s):

Heat Flow ◽

Power Law ◽

Basal Layer ◽

Ice Dynamics ◽

Basal Ice ◽

Basal Sliding ◽

Ductile Flow ◽

Flow Through ◽

Pressure Melting ◽

Power Law Creep

Abstract. Basal ice motion is crucial to ice dynamics of ice sheets. The Weertman sliding model for basal sliding over bedrock obstacles proposes that sliding velocity is controlled by pressure melting and/or ductile flow, whichever is the fastest; it further assumes that stoss-side melting is limited by heat flow through the obstacle and ductile flow is controlled by Power Law Creep. These last two assumptions, it is argued here, are invalid if a substantial basal layer of temperate (T ~ Tmelt) ice is present. In that case, frictional melting results in excess basal meltwater and efficient water flow, leading to near-thermal equilibrium. Stoss-side melting is controlled by melt water production, heat advection by flowing meltwater to the next obstacle, and heat conduction through ice/rock over half the obstacle height. No heat flow through the obstacle is required. High temperature ice creep experiments have shown a sharp weakening of a factor 5–10 close to Tmelt, implying breakdown of Power Law Creep and probably caused by a deformation-mechanism switch to grain boundary pressure melting. Ice streaming over a rough, hard bed, as likely in the Northeast Greenland Ice Stream, may be explained by enhanced basal motion in a thick temperate ice layer.

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Two-Dimensional Liquid Water Flow through Snow at the Plot Scale in Continental Snowpacks: Simulations and Field Data Comparisons

10.5194/tc-2020-199 ◽

2020 ◽

Author(s):

Ryan W. Webb ◽

Keith S. Jennings ◽

Stefan Finsterle ◽

Steven R. Fassnacht

Keyword(s):

Water Flow ◽

Liquid Water ◽

Water Movement ◽

Ground Surface ◽

Two Dimensional ◽

Flow Paths ◽

Sloping Ground ◽

Spatial And Temporal Scales ◽

Northern Colorado ◽

Flow Through

Abstract. Modelling the multi-dimensional flow of liquid water through snow has been limited in spatial and temporal scales to date. Here we present simulations using the iTOUGH2 model informed by the model SNOWPACK, referred to as SnowTOUGH. We use SnowTOUGH to simulate snow metamorphism, melt/freeze processes, and liquid water movement in two-dimensional snowpacks at the plot scale (20 m) on a sloping ground surface during multi-day observation periods at three field sites in northern Colorado, USA. Model results compare well with subalpine and alpine sites, but not a treeline site. Results show the importance of longitudinal (i.e. parallel to ground surface in the downslope direction) intra-snowpack flow paths, particularly during times when the snow surface (i.e. snow-atmosphere interface) is not actively melting. Simulations show that longitudinal flow can occur at rates orders of magnitude greater than vertically downward percolating water flow (a ratio of > 250 : 1) as a result of hydraulic barriers.

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Investigation of the influence of the flow structure on the accuracy of flow measurement before a hydrometric structure in an open channel

Melioration and Water Management ◽

10.32962/0235-2524-2019-5-41-44 ◽

2020 ◽

pp. 41-44

Author(s):

Anatoly Kusher

Keyword(s):

Velocity Profile ◽

Flow Velocity ◽

Water Flow ◽

Flow Measurement ◽

Water Discharge ◽

Critical Depth ◽

Flow Measurements ◽

Study Results ◽

Flow Velocity Profile ◽

Upstream Flow

The reliability of water flow measurement in irrigational canals depends on the measurement method and design features of the flow-measuring structure and the upstream flow velocity profile. The flow velocity profile is a function of the channel geometry and wall roughness. The article presents the study results of the influence of the upstream flow velocity profile on the discharge measurement accuracy. For this, the physical and numerical modeling of two structures was carried out: a critical depth flume and a hydrometric overfall in a rectangular channel. According to the data of numerical simulation of the critical depth flume with a uniform and parabolic (1/7) velocity profile in the upstream channel, the values of water discharge differ very little from the experimental values in the laboratory model with a similar geometry (δ < 2 %). In contrast to the critical depth flume, a change in the velocity profile only due to an increase in the height of the bottom roughness by 3 mm causes a decrease of the overfall discharge coefficient by 4…5 %. According to the results of the numerical and physical modeling, it was found that an increase of backwater by hydrometric structure reduces the influence of the upstream flow velocity profile and increases the reliability of water flow measurements.

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