scholarly journals Glacier Outburst Floods From “Hazard Lake”, Yukon Territory, and the Problem of Flood Magnitude Prediction

1982 ◽  
Vol 28 (98) ◽  
pp. 3-21 ◽  
Author(s):  
Garry K. C. Clarke
Keyword(s):  
Yukon Territory ◽  
Peak Discharge ◽  
Dominant Factor ◽  
Tunnel Enlargement ◽  
Dimensionless Numbers ◽  
Flood Magnitude ◽  
Lake Temperature ◽  
Simplifying Assumptions ◽  
Reservoir Geometry ◽  
Manning Roughness

AbstractIn August 1978 “Hazard Lake” released 19.62 × 106m3of water through a subglacial tunnel beneath Steele Glacier, Yukon Territory, Canada. The discharge during the outburst flood was measured by recording lake level changes with time, and a peak discharge of approximately 640 m3s–1was estimated from the data. We have attempted to model the 1978 flood from “Hazard Lake” using an adaptation of Nye’s (1976) theoretical model for jökulhlaups from Grimsvötn. Our aim has been to calibrate the Nye model as a first step toward using it as a peak discharge estimator for other glacier–dammed basins. The agreement between our measured and simulated hydrographs is good, and we find that creep closure, though included in our analysis, appears to play an insignificant role in limiting the discharge of “Hazard Lake”. Release of thermal energy from the relatively warm lake water is the dominant factor contributing to tunnel enlargement.The Manning roughness of outlet channels from glacier–dammed lakes is not known aprioriand must either be assumed or estimated after the fact from the flood hydrograph. For “Hazard Lake” our fit implies Manning roughness in the rangen′ = 0.105 m–1⁄3s, consistent with Nye’s estimate ofn′ = 0.12 ml⁄3s for the 1972 Grimsvötn flood and our estimate ofn′ = 0.12 m1/3s for the 1967 Summit Lake flood. If the Manning roughness for flood conduits can be shown to lie within a narrow range, this would constrain one of the least certain variables of the Nye model.By making several simplifying assumptions, we have succeeded in reducing our adapted version of Nye’s model to a simple mathematical description involving dimensionless numbers characterizing reservoir geometry and the relative magnitudes of creep closure and tunnel enlargement by melting. In this simplified form, the influence of lake temperature, reservoir geometry, and creep closure on the character of flood hydrographs can be conveniently studied.

scholarly journals Glacier Outburst Floods From “Hazard Lake”, Yukon Territory, and the Problem of Flood Magnitude Prediction

1982 ◽  
Vol 28 (98) ◽  
pp. 3-21 ◽  
Author(s):  
Garry K. C. Clarke
Keyword(s):  
Yukon Territory ◽  
Peak Discharge ◽  
Dominant Factor ◽  
Tunnel Enlargement ◽  
Dimensionless Numbers ◽  
Flood Magnitude ◽  
Lake Temperature ◽  
Simplifying Assumptions ◽  
Reservoir Geometry ◽  
Manning Roughness

AbstractIn August 1978 “Hazard Lake” released 19.62 × 106 m3 of water through a subglacial tunnel beneath Steele Glacier, Yukon Territory, Canada. The discharge during the outburst flood was measured by recording lake level changes with time, and a peak discharge of approximately 640 m3 s–1 was estimated from the data. We have attempted to model the 1978 flood from “Hazard Lake” using an adaptation of Nye’s (1976) theoretical model for jökulhlaups from Grimsvötn. Our aim has been to calibrate the Nye model as a first step toward using it as a peak discharge estimator for other glacier–dammed basins. The agreement between our measured and simulated hydrographs is good, and we find that creep closure, though included in our analysis, appears to play an insignificant role in limiting the discharge of “Hazard Lake”. Release of thermal energy from the relatively warm lake water is the dominant factor contributing to tunnel enlargement.The Manning roughness of outlet channels from glacier–dammed lakes is not known a priori and must either be assumed or estimated after the fact from the flood hydrograph. For “Hazard Lake” our fit implies Manning roughness in the range n′ = 0.105 m–1⁄3 s, consistent with Nye’s estimate of n′ = 0.12 ml⁄3s for the 1972 Grimsvötn flood and our estimate of n′ = 0.12 m1/3 s for the 1967 Summit Lake flood. If the Manning roughness for flood conduits can be shown to lie within a narrow range, this would constrain one of the least certain variables of the Nye model.By making several simplifying assumptions, we have succeeded in reducing our adapted version of Nye’s model to a simple mathematical description involving dimensionless numbers characterizing reservoir geometry and the relative magnitudes of creep closure and tunnel enlargement by melting. In this simplified form, the influence of lake temperature, reservoir geometry, and creep closure on the character of flood hydrographs can be conveniently studied.

scholarly journals Jökulhlaups in Iceland: prediction, characteristics and simulation

1992 ◽  
Vol 16 ◽  
pp. 95-106 ◽  
Author(s):  
Helgi Björnsson
Keyword(s):  
Water Pressure ◽  
Volcanic Eruptions ◽  
Peak Discharge ◽  
Reservoir Water ◽  
Overburden Pressure ◽  
Lake Temperature ◽  
Rapid Ascent ◽  
The Difference ◽  
Manning Roughness ◽  
Peak Discharges

Jökulhlaups drain regularly from six subglacial geothermal areas in Iceland. From Grímsvötn in Vatnajökull, jökulhlaups have occurred at 4 to 6 yearly-intervals since the 1940s with peak discharges of 600 to 10000 m3s−1, durations of 2 to 3 weeks and total volumes of 0.5 to 3.0 km3. Prior to that, about one jökulhlaup occurred per decade, with an estimated discharge of 5 km of water and a peak discharge of approximately 30000 m3s−1. Clarke’s (1982) modification of Nye’s (1976) general model of discharge of jökulhlaups gives, in many respects, satisfactory simulations for jökulhlaups from Grímsvötn the best fit being obtained for Manning roughness coefficients n = 0.08 to 0.09 m−1/3s and a constant lake temperature of 0.2°C (which is the present lake temperature). The rapid ascent of the exceptional jökulhlaup of 1938, which accompanied a volcanic eruption, can only be simulated by a lake temperature of the order of 4°C.Jökulhlaups originating at geothermal areas beneath ice cauldrons located 10 to 15 km northwest of Grímsvötn have a peak discharge of 200 to 1500 m3s−1 in 1 to 3 days, with total volume of 50 to 350 × 106m3, and they recede slowly in 1 to 2 weeks. The form of the hydrograph has reversed asymmetry to that of a typical Grímsvötn hydrograph. The reservoir water temperature must be well above the melting point (10 to 20°C) and the flowing water seems not to be confined to a tunnel but to spread out beneath the glacier and later gradually to collect back to conduits.Since the time of the settlement of Iceland (870 AD), at least 80 subglacial volcanic eruptions have been reported, many of them causing tremendous jökulhlaups with dramatic impact on inhabited areas and landforms. The peak discharges of the largest floods (from Katla) have been estimated at the order of 100 000 to 300 000 m3 s−1, with durations of 3 to 5 days and total volume of the order of 1 km3. It is now apparent that the potentially largest and most catastrophic jökulhlaups may be caused by eruptions in the voluminous ice-filled calderas in northern Vatnajökull (of Bárdharbunga and Kverkfjöll). They may be the source of prehistoric jökulhlaups, with estimated peak discharge of 400 000 m3 s−1.At present, jökulhlaups originate from some 15 marginal ice-dammed lakes in Iceland. Typical values for peak discharges are 1000 to 3000 m3s−1, with durations of 2 to 5 days and total volumes of 2000 × 106 m3. Hydrographs for jökulhlaups from marginal lakes have a shape similar to those of the typical Grímsvötn jökulhlaup. Simulations describe reasonably well the ascending phase of the hydrographs assuming a constant lake temperature of about 1°C; but they fail to describe the recession. Some floods from marginal lakes, however, have reached their peaks exceptionally rapidly, in a single day. Such rapid ascent can be simulated by assuming drainage of lake water at 4 to 8°C.An empirical power-law relationship is obtained between peak discharge, Qmax, and total volume Vt of the jökulhlaups from Grímsvötn: Qmax = KVtb, where Qmax is measured in m3s−1, Vt in 106m3, Κ = 4.15 × 10−3s−1 m2 and b = 1.84. In general, the jökulhlaups (excepting those caused by eruptions) occur when the lake has risen to a critical level, but before a lake level required for simple flotation of the ice dam is reached. The difference between the hydrostatic water pressure maintained by the lake and the ice overburden pressure of the ice dam is of the order 2 to 6 bar.

scholarly journals Jökulhlaups in Iceland: prediction, characteristics and simulation

1992 ◽  
Vol 16 ◽  
pp. 95-106 ◽  
Author(s):  
Helgi Björnsson
Keyword(s):  
Water Pressure ◽  
Volcanic Eruptions ◽  
Peak Discharge ◽  
Reservoir Water ◽  
Overburden Pressure ◽  
Lake Temperature ◽  
Rapid Ascent ◽  
The Difference ◽  
Manning Roughness ◽  
Peak Discharges

Jökulhlaups drain regularly from six subglacial geothermal areas in Iceland. From Grímsvötn in Vatnajökull, jökulhlaups have occurred at 4 to 6 yearly-intervals since the 1940s with peak discharges of 600 to 10000 m3s−1, durations of 2 to 3 weeks and total volumes of 0.5 to 3.0 km3. Prior to that, about one jökulhlaup occurred per decade, with an estimated discharge of 5 km of water and a peak discharge of approximately 30000 m3s−1. Clarke’s (1982) modification of Nye’s (1976) general model of discharge of jökulhlaups gives, in many respects, satisfactory simulations for jökulhlaups from Grímsvötn the best fit being obtained for Manning roughness coefficients n = 0.08 to 0.09 m−1/3s and a constant lake temperature of 0.2°C (which is the present lake temperature). The rapid ascent of the exceptional jökulhlaup of 1938, which accompanied a volcanic eruption, can only be simulated by a lake temperature of the order of 4°C.Jökulhlaups originating at geothermal areas beneath ice cauldrons located 10 to 15 km northwest of Grímsvötn have a peak discharge of 200 to 1500 m3s−1in 1 to 3 days, with total volume of 50 to 350 × 106m3, and they recede slowly in 1 to 2 weeks. The form of the hydrograph has reversed asymmetry to that of a typical Grímsvötn hydrograph. The reservoir water temperature must be well above the melting point (10 to 20°C) and the flowing water seems not to be confined to a tunnel but to spread out beneath the glacier and later gradually to collect back to conduits.Since the time of the settlement of Iceland (870 AD), at least 80 subglacial volcanic eruptions have been reported, many of them causing tremendous jökulhlaups with dramatic impact on inhabited areas and landforms. The peak discharges of the largest floods (from Katla) have been estimated at the order of 100 000 to 300 000 m3s−1, with durations of 3 to 5 days and total volume of the order of 1 km3. It is now apparent that the potentially largest and most catastrophic jökulhlaups may be caused by eruptions in the voluminous ice-filled calderas in northern Vatnajökull (of Bárdharbunga and Kverkfjöll). They may be the source of prehistoric jökulhlaups, with estimated peak discharge of 400 000 m3s−1.At present, jökulhlaups originate from some 15 marginal ice-dammed lakes in Iceland. Typical values for peak discharges are 1000 to 3000 m3s−1, with durations of 2 to 5 days and total volumes of 2000 × 106m3. Hydrographs for jökulhlaups from marginal lakes have a shape similar to those of the typical Grímsvötn jökulhlaup. Simulations describe reasonably well the ascending phase of the hydrographs assuming a constant lake temperature of about 1°C; but they fail to describe the recession. Some floods from marginal lakes, however, have reached their peaks exceptionally rapidly, in a single day. Such rapid ascent can be simulated by assuming drainage of lake water at 4 to 8°C.An empirical power-law relationship is obtained between peak discharge,Qmax, and total volumeVtof the jökulhlaups from Grímsvötn:Qmax= KVtb, whereQmaxis measured in m3s−1,Vtin 106m3, Κ = 4.15 × 10−3s−1m2and b = 1.84. In general, the jökulhlaups (excepting those caused by eruptions) occur when the lake has risen to a critical level, but before a lake level required for simple flotation of the ice dam is reached. The difference between the hydrostatic water pressure maintained by the lake and the ice overburden pressure of the ice dam is of the order 2 to 6 bar.

scholarly journals Overland Flow Resistance Law under Sparse Stem Vegetation Coverage

Water ◽  
2021 ◽  
Vol 13 (12) ◽  
pp. 1657
Author(s):  
Jingzhou Zhang ◽  
Shengtang Zhang ◽  
Si Chen ◽  
Ming Liu ◽  
Xuefeng Xu ◽  
...  
Keyword(s):  
Flow Resistance ◽  
Overland Flow ◽  
Vegetation Coverage ◽  
Dominant Factor ◽  
Roughness Coefficient ◽  
Hydraulic Parameters ◽  
Slope Condition ◽  
Manning Roughness ◽  
The Relationship ◽  
Manning Roughness Coefficient

To explore the characteristics of overland flow resistance under the condition of sparse vegetative stem coverage and improve the basic theoretical research of overland flow, the resistance characteristics of overland flow were systematically investigated under four slope gradients (S), seven flow discharges (Q), and six degrees of vegetation coverage (Cr). The results show that the Manning roughness coefficient (n) changes with the ratio of water depth to vegetation height (h/hv) while the Reynolds number (Re), Froude number (Fr), and slope (S) are closely related to vegetation coverage. Meanwhile, h/hv, Re, and Cr have strong positive correlations with n, while Fr and S have strong negative correlations with n. Through data regression analysis, a power function relationship between n and hydraulic parameters was observed and sensitivity analysis was performed. It was concluded that the relationship between n and h/hv, Re, Cr, Q, and S shows the same law; in particular, for sparse stem vegetation coverage, Cr is the dominant factor affecting overland flow resistance under zero slope condition, while Cr is no longer the first dominant factor affecting overland flow resistance under non-zero slope condition. In the relationship between n and Fr, Cr has the least effect on overland flow resistance. This indicates that when Manning roughness coefficient is correlated with different hydraulic parameters, the same vegetation coverage has different effects on overland flow resistance. Therefore, it is necessary to study overland flow resistance under the condition of sparse stalk vegetation coverage.

scholarly journals Hydraulics of subglacial outburst floods: new insights from the Spring–Hutter formulation

2003 ◽  
Vol 49 (165) ◽  
pp. 299-313 ◽  
Author(s):  
Garry K. C. Clarke
Keyword(s):  
Water Temperature ◽  
Water Pressure ◽  
Potential Gradient ◽  
Confining Pressure ◽  
Hydraulic Roughness ◽  
Outburst Floods ◽  
Natural Streams ◽  
Flood Magnitude ◽  
Manning Roughness ◽  
Fluid Potential

AbstractUsing a slightly modified form of the Spring–Hutter equations, glacial outburst floods are simulated from three classic sites, “Hazard Lake”, Yukon, Canada, Summit Lake, British Columbia, Canada, and Grímsvötn, Iceland, in order to calibrate the hydraulic roughness associated with subglacial conduits. Previous work has suggested that the Manning roughness of the conduits is remarkably high, but the new calibration yields substantially lower values that are representative of those for natural streams and rivers. The discrepancy can be traced to a poor assumption about the effectiveness of heat transfer at the conduit walls. The simulations reveal behaviour that cannot be inferred from simplified theories: (1) During flood onset, water pressure over much of the conduit can exceed the confining pressure of surrounding ice. (2) Local values of fluid potential gradient can differ substantially from the value averaged over the length of the conduit, contradicting an assumption of simple theories. (3) As the flood progresses, the location of flow constrictions that effectively control the flood magnitude can jump rapidly over large distances. (4) Predicted water temperature at the conduit outlet exceeds that suggested by measurements of exit water temperature.

Simulation of the August 1979 sudden discharge of glacier-dammed Flood Lake, British Columbia

1984 ◽  
Vol 21 (4) ◽  
pp. 502-504 ◽  
Author(s):  
Garry K. C. Clarke ◽  
David A. Waldron
Keyword(s):  
British Columbia ◽  
Computer Model ◽  
Discharge Rate ◽  
Peak Discharge ◽  
Maximum Discharge ◽  
Flood Magnitude ◽  
Gauging Station

In August 1979 a glacier outburst from Flood Lake, British Columbia, released 150 × 106 m3 of water. The resulting flood was routed through the Stikine River and yielded a maximum discharge rate of 1200 m3 s−1 at a gauging station 90 km downstream from the glacier dam. We have used a computer model to simulate this outburst in order to test the usefulness of the model as a predictor of flood magnitude. The predicted peak discharge is 2160 m3 s−1 at the outlet tunnel of the ice dam and 1700 m3 s−1 at the gauging station.

scholarly journals Long-period variability in ice-dammed glacier outburst floods due to evolving catchment geometry

2021 ◽  
Author(s):  
Amy J. Jenson ◽  
Jason M. Amundson ◽  
Jonathan Kingslake ◽  
Eran Hood
Keyword(s):  
Peak Discharge ◽  
Water Volume ◽  
Flood Hazards ◽  
Outburst Flood ◽  
Ice Shelf ◽  
Outburst Floods ◽  
Flood Magnitude ◽  
Hydrological System ◽  
Basin Geometry ◽  
Glacier Flow

Abstract. We combine a glacier outburst flood model with a glacier flow model to investigate decadal to centennial variations in outburst floods originating from ice-dammed marginal basins. Marginal basins form due to retreat and detachment of tributary glaciers, a process that often results in remnant ice being left behind. The remnant ice, which can act like an ice shelf or break apart into a pack of icebergs, limits the basin storage capacity but also exerts pressure on the underlying water and promotes drainage. We find that during glacier retreat there is a strong, nearly linear relationship between flood water volume and peak discharge for individual basins, despite large changes in glacier and remnant ice volumes that are expected to impact flood hydrographs. Consequently, peak discharge increases over time as long as there is remnant ice remaining in a basin, the peak discharge begins to decrease once a basin becomes ice free, and similar size outburst floods can occur for very different glacier volumes. We also find that the temporal variability in outburst flood magnitude depends on how the floods initiate. Basins that connect to the subglacial hydrological system only after reaching flotation yield greater long-term variability in outburst floods than basins that are continuously connected to the subglacial hydrological system (and therefore release floods that initiate before reaching flotation). Our results highlight the importance of improving our understanding of both changes in basin geometry and outburst flood initiation mechanisms in order to better assess outburst flood hazards and impacts on landscape and ecosystem evolution.

Motion Equations for the Ball and Beam and the Ball and Arc Systems

2019 ◽  
Vol 141 (12) ◽  
Author(s):  
Constance Lare ◽  
Warren N. White ◽  
Sanzida Hossain
Keyword(s):  
Dynamic Models ◽  
Controller Design ◽  
Equations Of Motion ◽  
Dimensionless Form ◽  
Dimensionless Numbers ◽  
Motion Equations ◽  
Systems Model ◽  
Consistent Manner ◽  
Simplifying Assumptions ◽  
The Impact

Abstract Presently, most derivations of the equations of motion for the ball and beam and ball and arc systems model the ball as a point mass. Other derivations apply assumptions related to the ball that lack physical justification. To understand fully the impact the ball has on the equations of motion and controller design, equations of motion are needed that stem from a derivation invoking few assumptions. At that point, simplifying assumptions applied in a consistent manner are possible. This paper derives the equations of motion for each mechanical system using fewer assumptions than what appears in the literature. The development then applies the assumptions needed to convert the derived dynamics to the well-used equations of motion seen in the literature. The presentation shows that some ball and beam models appearing in the literature do not stem from consistent assumptions or correct kinematics. Incorrect kinematics are also present in some of the ball and arc dynamic models. This paper also introduces dimensionless quantities to the dynamic equations of both systems rendering them in dimensionless form. Such formulations allow for comparisons between different systems through the size of the dimensionless quantities. The dimensionless systems are the means used to demonstrate that the equations of motion of each system are the same as the radius of the arc grows without bound. Finally, the paper shows that comparisons between different ball and beam models using these dimensionless numbers are now possible.

scholarly journals 3-D numerical approach to simulate the overtopping volume caused by an impulse wave comparable to avalanche impact in a reservoir

2015 ◽  
Vol 15 (12) ◽  
pp. 2617-2630 ◽  
Author(s):  
R. Gabl ◽  
J. Seibl ◽  
B. Gems ◽  
M. Aufleger
Keyword(s):  
Numerical Approach ◽  
Scale Model ◽  
Model Concept ◽  
Reference Case ◽  
Hill Slope ◽  
Simplifying Assumptions ◽  
Natural Data ◽  
Self Adaptation ◽  
Reservoir Geometry ◽  
The Impact

Abstract. The impact of an avalanche in a reservoir induces impulse waves, which pose a threat to population and infrastructure. For a good approximation of the generated wave height and length as well as the resulting overtopping volume over structures and dams, formulas, which are based on different simplifying assumptions, can be used. Further project-specific investigations by means of a scale model test or numerical simulations are advisable for complex reservoirs as well as the inclusion of hydraulic structures such as spillways. This paper presents a new approach for a 3-D numerical simulation of the avalanche impact in a reservoir. In this model concept the energy and mass of the avalanche are represented by accelerated water on the actual hill slope. Instead of snow, only water and air are used to simulate the moving avalanche with the software FLOW-3D. A significant advantage of this assumption is the self-adaptation of the model avalanche onto the terrain. In order to reach good comparability of the results with existing research at ETH Zürich, a simplified reservoir geometry is investigated. Thus, a reference case has been analysed including a variation of three geometry parameters (still water depth in the reservoir, freeboard of the dam and reservoir width). There was a good agreement of the overtopping volume at the dam between the presented 3-D numerical approach and the literature equations. Nevertheless, an extended parameter variation as well as a comparison with natural data should be considered as further research topics.

scholarly journals Influence of Thomson effect on amorphization in phase-change memory: Dimensional analysis based on Buckingham’s П theorem for Ge2Sb2Te5

2021 ◽  
Author(s):  
Takuya Yamamoto ◽  
Shogo Hatayama ◽  
Yun-Heub Song ◽  
Yuji Sutou
Keyword(s):  
Contact Resistance ◽  
Phase Change ◽  
Temperature Increase ◽  
Random Access ◽  
Dominant Factor ◽  
Thomson Effect ◽  
Dimensionless Numbers ◽  
Increasing Temperature ◽  
Thomson Coefficient ◽  
Change Material

Abstract To evaluate the Thomson effect on the temperature increase in Ge2Sb2Te5 (GST)-based phase-change random access memory (PCRAM), we created new dimensionless numbers based on Buckingham’s П theorem. The influence of the Thomson effect on the temperature increase depends on the dominant factor of electrical resistance in a PCRAM cell. When the effect is dominated by the volumetric resistance of the phase-change material (C=ρcΔx/σ≪O(1)), the dimensionless evaluation number is B=μTσ∆ϕk, where ρc is the contact resistance, Δx is the thickness of PCM, σ and k are the electrical and thermal conductivities, μT is the Thomson coefficient, and Δφ is the voltage. When the contact resistance cannot be ignored, the evaluation number is B/(1 + C). The characteristics of hexagonal-type crystalline GST in a PCRAM cell were numerically investigated using the defined dimensionless parameters. Although the contact resistance of GST exceeded the volumetric resistance across the temperature range, the ratio of contact resistance to the whole resistance reduced with increasing temperature. Moreover, increasing the temperature of GST enhanced the influence of the Thomson effect on the temperature distribution. At high temperatures, the Thomson effect suppressed the temperature increase by approximately 10–20%.

Sign in / Sign up

Export Citation Format

Share Document