Mauro Werder

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Werder

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Mauro

ORCID

0000-0003-0137-9377

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Publications 1 - 10 of 34

SHIMP The subglacial hydrology model intercomparison Project
de Fleurian, Basile; Werder, Mauro; Beyer, Sebastian; et al. (2018)
Journal of Glaciology
Subglacial hydrology plays a key role in many glaciological processes, including ice dynamics via the modulation of basal sliding. Owing to the lack of an overarching theory, however, a variety of model approximations exist to represent the subglacial drainage system. The Subglacial Hydrology Model Intercomparison Project (SHMIP) provides a set of synthetic experiments to compare existing and future models. We present the results from 13 participating models with a focus on effective pressure and discharge. For many applications (e.g. steady states and annual variations, low input scenarios) a simple model, such as an inefficient-system-only model, a flowline or lumped model, or a porous-layer model provides results comparable to those of more complex models. However, when studying short term (e.g. diurnal) variations of the water pressure, the use of a two-dimensional model incorporating physical representations of both efficient and inefficient drainage systems yields results that are significantly different from those of simpler models and should be preferentially applied. The results also emphasise the role of water storage in the response of water pressure to transient recharge. Finally, we find that the localisation of moulins has a limited impact except in regions of sparse moulin density.
Determining ice-sheet uplift surrounding lakes with a viscous plate model
Walker, Ryan T.; Werder, Mauro; Dow, Christine F.; et al. (2017)
Frontiers in Earth Science
We develop a viscous model of plate bending suitable for studying ice-sheet flexure due to subglacial lake filling and draining, and apply this model to determine the area of ice-sheet uplift surrounding a subglacial lake. The choice of a viscous model reflects our interest in Antarctic subglacial lakes, which can fill and drain on time scales of months to decades. Experiments with idealized lake shapes show that the size of the uplift area relative to lake area depends on subglacial water pressure and ice-sheet thickness, with the viscous material parameters scaling the magnitude of uplift rate within this area. The water pressure therefore has a strong control on the evolution of the lake shape and related subglacial hydrological development, but is not yet well constrained by observations. Due to the likelihood that ice flexure will affect subglacial lake filling and draining, we suggest that the insights of this study should be applied to development of a realistic ice sheet-hydrological coupled model.
Influence of increasing surface melt over decadal timescales on land-terminating Greenland-type outlet glaciers
Gagliardini, Olivier; Werder, Mauro (2018)
Journal of Glaciology
Over recent decades, Greenland ice sheet surface melt has shown an increase both in intensity and spatial extent. Part of this water probably reaches the bed and can enhance glacier speed, advecting a larger volume of ice into the ablation area. In the context of a warming climate, this mechanism could contribute to the future rate of thinning and retreat of land-terminating glaciers of Greenland. These changes in ice flow conditions will in turn influence surface crevassing and thus the ability of water to reach the bed at higher elevations. Here, using a coupled basal hydrology and prognostic ice flow model, the evolution of a Greenland-type glacier subject to increasing surface melt is studied over a few decades. For different scenarios of surface melt increase over the next decades, the evolution of crevassed areas and the ability of water to reach the bed is inferred. Our results indicate that the currently observed crevasse distribution is likely to extend further upstream which will allow water to reach the bed at higher elevations. This will lead to an increase in ice flux into the ablation area which, in turn, accelerates the mass loss of land-terminating glaciers.
Improved representation of laminar and turbulent sheet flow in subglacial drainage models
Hill, Tim; Flowers, Gwenn E.; Hoffman, Matthew J.; et al. (2024)
Journal of Glaciology
Subglacial hydrology models struggle to reproduce seasonal drainage patterns that are consistent with observed subglacial water pressures and surface velocities. We modify the standard sheet-flow parameterization within a coupled sheet–channel subglacial drainage model to smoothly transition between laminar and turbulent flow based on the locally computed Reynolds number in a physically consistent way (the “transition” model). We compare the transition model to standard laminar and turbulent models to assess the role of the sheet-flow parameterization in reconciling observed and modelled water pressures under idealized and realistic forcing. Relative to the turbulent model, the laminar and transition models improve seasonal simulations by increasing winter water pressure and producing a more prominent late-summer water pressure minimum. In contrast to the laminar model, the transition model remains consistent with its own internal assumptions across all flow regimes. Based on the internal consistency of the transition model and its improved performance relative to the standard turbulent model, we recommend its use for transient simulations of subglacial drainage.
Dye tracing and modelling jökulhlaups
Werder, Mauro (2009)
VAW-Mitteilungen
Hydraulic Reconstruction of the 1818 Giétro Glacial Lake Outburst Flood
Ancey, Christophe; Bardou, Eric; Funk, Martin; et al. (2019)
Water Resources Research
In the spring of 1818, ice avalanches from the Giétro Glacier created an ice dam, which in turn formed a glacial lake in the Drance Valley (Canton of Valais, Switzerland). Today, its maximum volume is estimated to have been 25×106 m3. Cantonal authorities commissioned an engineer named Ignaz Venetz to mitigate the risk of the ice dam's failure. He supervised the construction of a tunnel through which a large volume of water was drained as the lake rose (9×106 m3 according to his estimates and 11×106 m3 according to our model). After 2.5 days of slow drainage, the ice dam failed on 16 June 1818 and caused major flooding in the Drance Valley up to 40 km downstream, resulting in about 40 deaths. Venetz's lake monitoring notes, numerous testimonies gathered in the disaster's aftermath, and our field survey have made it possible to collect a wealth of information on this event, which is one of the world's major documented glacial lake outburst floods. Reconstructing major outburst floods remains challenging because not only do they involve enormous volumes of water spreading over long distances but they are also associated with additional physical processes such as massive erosion; intense transport of ice, sediment, and debris; and damage to vegetation and buildings. This paper attempts to reconstruct the 1818 Giétro flood by focusing on its water component. We develop a simple model to estimate the initial hydrograph during the slow drainage and failure phases. The flood's features are deduced by solving the shallow‐water equations numerically. The computational framework involves six free parameters, of which five are constrained by physical considerations. Using iterative manual parameter adjustments, we matched the numerical simulations to the historical data. We found that the peak discharge was close to 14,500 m3/s, the flood's front velocity was about 6 m/s, and flow depth varied considerably along the River Drance's bed (from 30 m just downstream of the ice dam to 2 m on the alluvial fan, 24 km west of the dam). To achieve a good agreement between computations and historical data, we had to select a high value for the Manning friction coefficient n (with n as large as 0.08 s/m1/3). As the Drance Valley is narrow, high flow resistance caused the flood's leading edge to behave like a plug, moving at a fairly constant velocity, with little dependence on what happened behind it. This result may explain why a simple flood routing model is able to reproduce the flood's features, because in an Alpine valley, a lateral spreading of the water volume is limited.
Sediment transport capacity response to variations in water discharge in pressurized subglacial channels
Delaney, Ian; Tedstone, Andrew J.; Werder, Mauro; et al. (2025)
The Cryosphere
Sediment transport capacity in both subaerial and subglacial channels depends on the shear stress exerted across the channel bottom, which varies with water velocity and channel width. In fully subaerial channels, water discharge variations are accommodated by flow depth and width changes along with water velocity. However, in subglacial channels, water is pressurized by the ice above, and they grow in response to the frictional heating of the water flowing through them. As a result, rapid changes in water discharge mainly result in velocity variations, as the channel geometry evolves slowly. Here, we present formulations of sediment transport capacity in different channel types and apply subglacial and subaerial hydraulics models to hydrographs from an Alpine glacier and a catchment of the Greenland Ice Sheet. Numerical experiments show that changing channel size results in sediment transport capacity peaking before the maximum water discharge. This hysteresis causes a highly variable relationship between sediment and water discharge in a transport-limited subglacial system. The results also indicate that high subglacial sediment transport capacities can occur across a wide range of water discharges. Reducing water discharge variability by smoothing lessens the hysteresis effects, in some cases to the point where a covarying relationship between water discharge and sediment transport capacity can be approached, similar to subaerial systems. A second set of numerical experiments shows that subglacial sediment transport is highly non-linear with respect to water discharge, creating more variability in sediment transport capacity. Yet, the results and formulations of subglacial sediment transport capacity show that its variability can approach that of subaerial systems when subglacial channel size is in equilibrium with water discharge. The implications of these findings help to evaluate sediment discharge from glaciers with different hydro-climatic forcings and to establish sources of variability in sediment export-water discharge relationships. These findings can improve the interpretation of sediment discharge records in glacierized catchments.
A numerical model for fluvial transport of subglacial sediment
Delaney, Ian A.; Werder, Mauro; Farinotti, Daniel (2019)
Journal of Geophysical Research
Short term variations of tracer transit speed on alpine glaciers
Werder, Mauro; Schuler, Thomas V. (2010)
The Cryosphere
We first present the results of a series of tracer experiments conducted on an alpine glacier (Gornergletscher, Switzerland) over a diurnal discharge cycle. For these injections, a moulin was used into which an ice marginal lake was draining, providing a relatively constant discharge. The measured tracer transit speeds show two diurnal maxima and minima. These findings are qualitatively different to existing observations from two series of injections conducted at Unteraargletscher (Switzerland) using a moulin fed by supraglacial meltwater having a high diurnal variability, which displayed one diurnal maximum and minimum. We then develop and use a simple two-component model of the glacier drainage system, comprising a moulin and a channel element, to simulate the measured transit speeds for all three injection series. The model successfully reproduces all the observations and shows that the same underlying processes can produce the qualitatively different behaviour depending on the different moulin input discharge regimes. Using the model, we assess the relative importance of the different measurement quantities, show that frequent measurements of moulin input discharge are indispensable and propose an experiment design to monitor the development of the drainage system over several weeks.
Regional and annual variability in subglacial sediment transport by water for two glaciers in the Swiss Alps
Delaney, Ian A.; Bauder, Andreas; Werder, Mauro; et al. (2018)
Frontiers in Earth Science

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