scholarly journals Modelling liquid water transport in snow under rain-on-snow conditions – considering preferential flow

2017 ◽  
Vol 21 (3) ◽  
pp. 1741-1756 ◽  
Author(s):  
Sebastian Würzer ◽  
Nander Wever ◽  
Roman Juras ◽  
Michael Lehning ◽  
Tobias Jonas
Keyword(s):  
Water Transport ◽  
Liquid Water ◽  
Field Experiments ◽  
Preferential Flow ◽  
Richards Equation ◽  
European Alps ◽  
Wet Snow ◽  
Snow Conditions ◽  
Dual Domain ◽  
Grain Properties

Abstract. Rain on snow (ROS) has the potential to generate severe floods. Thus, precisely predicting the effect of an approaching ROS event on runoff formation is very important. Data analyses from past ROS events have shown that a snowpack experiencing ROS can either release runoff immediately or delay it considerably. This delay is a result of refreeze of liquid water and water transport, which in turn is dependent on snow grain properties but also on the presence of structures such as ice layers or capillary barriers. During sprinkling experiments, preferential flow was found to be a process that critically impacted the timing of snowpack runoff. However, current one-dimensional operational snowpack models are not capable of addressing this phenomenon. For this study, the detailed physics-based snowpack model SNOWPACK is extended with a water transport scheme accounting for preferential flow. The implemented Richards equation solver is modified using a dual-domain approach to simulate water transport under preferential flow conditions. To validate the presented approach, we used an extensive dataset of over 100 ROS events from several locations in the European Alps, comprising meteorological and snowpack measurements as well as snow lysimeter runoff data. The model was tested under a variety of initial snowpack conditions, including cold, ripe, stratified and homogeneous snow. Results show that the model accounting for preferential flow demonstrated an improved overall performance, where in particular the onset of snowpack runoff was captured better. While the improvements were ambiguous for experiments on isothermal wet snow, they were pronounced for experiments on cold snowpacks, where field experiments found preferential flow to be especially prevalent.

scholarly journals Modeling liquid water transport in snow under rain-on-snow conditions – considering preferential flow

2016 ◽  
Author(s):  
Sebastian Würzer ◽  
Nander Wever ◽  
Roman Juras ◽  
Michael Lehning ◽  
Tobias Jonas
Keyword(s):  
Water Transport ◽  
Liquid Water ◽  
Field Experiments ◽  
Preferential Flow ◽  
Richards Equation ◽  
European Alps ◽  
Wet Snow ◽  
Snow Conditions ◽  
Dual Domain ◽  
Grain Properties

Abstract. Rain-on-snow (ROS) has the potential to generate severe floods. Thus, precisely predicting the effect of an approaching ROS event on runoff formation is very important. Data analyses from past ROS events have shown that a snowpack experiencing ROS can either release runoff immediately or delay it considerably. This delay is a result of refreeze of liquid water and water transport mechanisms in the snowpack. Water percolation is depending on snow grain properties but also on the presence of structures such as ice layers or capillary barriers. During sprinkling experiments, preferential flow was found to be a process that critically impacted the timing of snowpack runoff. However, current one-dimensional snowpack models are not capable of addressing this phenomenon correctly. For this study, the detailed physics-based snowpack model SNOWPACK is extended with a water transport scheme accounting for preferential flow. The implemented Richards' Equation solver is modified using a dual-domain approach to simulate water transport under preferential flow conditions. To validate the presented approach, we used an extensive dataset of over 100 ROS events from several locations in the European Alps, comprising meteorological and snowpack measurements as well as snow lysimeter runoff data. The model was tested under a variety of initial snowpack conditions, including cold, ripe, stratified and homogeneous snow. Results show that the model accounting for preferential flow (PF) demonstrated an improved overall and in particular more balanced performance. While the improvements were small for experiments on isothermal wet snow, they were pronounced for experiments on cold snowpacks, where field experiments found preferential flow to be especially prevalent.

scholarly journals Rainwater propagation through snowpack during rain-on-snow sprinkling experiments under different snow conditions

2017 ◽  
Vol 21 (9) ◽  
pp. 4973-4987 ◽  
Author(s):  
Roman Juras ◽  
Sebastian Würzer ◽  
Jirka Pavlásek ◽  
Tomáš Vitvar ◽  
Tobias Jonas
Keyword(s):  
Liquid Water ◽  
Field Experiments ◽  
Preferential Flow ◽  
Hydrograph Separation ◽  
Runoff Generation ◽  
Total Runoff ◽  
Artificial Rainfall ◽  
Wet Snow ◽  
Natural Snow ◽  
Snow Conditions

Abstract. The mechanisms of rainwater propagation and runoff generation during rain-on-snow (ROS) events are still insufficiently known. Understanding storage and transport of liquid water in natural snowpacks is crucial, especially for forecasting of natural hazards such as floods and wet snow avalanches. In this study, propagation of rainwater through snow was investigated by sprinkling experiments with deuterium-enriched water and applying an alternative hydrograph separation technique on samples collected from the snowpack runoff. This allowed us to quantify the contribution of rainwater, snowmelt and initial liquid water released from the snowpack. Four field experiments were carried out during winter 2015 in the vicinity of Davos, Switzerland. Blocks of natural snow were isolated from the surrounding snowpack to inhibit lateral exchange of water and were exposed to artificial rainfall using deuterium-enriched water. The experiments were composed of four 30 min periods of sprinkling, separated by three 30 min breaks. The snowpack runoff was continuously gauged and sampled periodically for the deuterium signature. At the onset of each experiment antecedent liquid water was first pushed out by the sprinkling water. Hydrographs showed four pronounced peaks corresponding to the four sprinkling bursts. The contribution of rainwater to snowpack runoff consistently increased over the course of the experiment but never exceeded 86 %. An experiment conducted on a non-ripe snowpack suggested the development of preferential flow paths that allowed rainwater to efficiently propagate through the snowpack limiting the time for mass exchange processes to take effect. In contrast, experiments conducted on ripe isothermal snowpack showed a slower response behaviour and resulted in a total runoff volume which consisted of less than 50 % of the rain input.

scholarly journals Development of physically based liquid water schemes for Greenland firn-densification models

2019 ◽  
Vol 13 (7) ◽  
pp. 1819-1842 ◽  
Author(s):  
Vincent Verjans ◽  
Amber A. Leeson ◽  
C. Max Stevens ◽  
Michael MacFerrin ◽  
Brice Noël ◽  
...  
Keyword(s):  
Water Flow ◽  
Liquid Water ◽  
Preferential Flow ◽  
Greenland Ice Sheet ◽  
Single Domain ◽  
Richards Equation ◽  
Retention Capacity ◽  
Water Percolation ◽  
Physically Based ◽  
Dual Domain

Abstract. As surface melt is increasing on the Greenland Ice Sheet (GrIS), quantifying the retention capacity of the firn layer is critical to linking meltwater production to meltwater runoff. Firn-densification models have so far relied on empirical approaches to account for the percolation–refreezing process, and more physically based representations of liquid water flow might bring improvements to model performance. Here we implement three types of water percolation schemes into the Community Firn Model: the bucket approach, the Richards equation in a single domain and the Richards equation in a dual domain, which accounts for partitioning between matrix and fast preferential flow. We investigate their impact on firn densification at four locations on the GrIS and compare model results with observations. We find that for all of the flow schemes, significant discrepancies remain with respect to observed firn density, particularly the density variability in depth, and that inter-model differences are large (porosity of the upper 15 m firn varies by up to 47 %). The simple bucket scheme is as efficient in replicating observed density profiles as the single-domain Richards equation, and the most physically detailed dual-domain scheme does not necessarily reach best agreement with observed data. However, we find that the implementation of preferential flow simulates ice-layer formation more reliably and allows for deeper percolation. We also find that the firn model is more sensitive to the choice of densification scheme than to the choice of water percolation scheme. The disagreements with observations and the spread in model results demonstrate that progress towards an accurate description of water flow in firn is necessary. The numerous uncertainties about firn structure (e.g. grain size and shape, presence of ice layers) and about its hydraulic properties, as well as the one-dimensionality of firn models, render the implementation of physically based percolation schemes difficult. Additionally, the performance of firn models is still affected by the various effects affecting the densification process such as microstructural effects, wet snow metamorphism and temperature sensitivity when meltwater is present.

scholarly journals Rainwater propagation through snow pack during rain-on-snow events under different snow condition

2016 ◽  
Author(s):  
Roman Juras ◽  
Sebastian Würzer ◽  
Jirka Pavlásek ◽  
Tomáš Vitvar ◽  
Tobias Jonas
Keyword(s):  
Liquid Water ◽  
Field Experiments ◽  
Preferential Flow ◽  
Liquid Water Content ◽  
Hydrograph Separation ◽  
Runoff Generation ◽  
Total Runoff ◽  
Artificial Rainfall ◽  
Snow Condition ◽  
Wet Snow

Abstract. The mechanisms of rainwater propagation and runoff generation during rain-on-snow (ROS) are still insufficiently known. Understanding the behaviour of liquid water within the natural snowpack is crucial especially for forecasting of natural hazards such as floods and wet snow avalanches. In this study, rainwater percolation through snow was investigated by sprinkling deuterium enriched water on snow and applying an advanced hydrograph separation technique on samples collected from the snowpack runoff. This allowed quantifying the contribution of rainwater and snowmelt in the water released from the snowpack. Four field experiments were carried out during the winter 2015 in the vicinity of Davos, Switzerland. For this purpose, large blocks of natural snow were isolated from the surrounding snowpack to inhibit lateral exchange of water. These blocks were exposed to artificial rainfall with 41 mm of deuterium enriched water. The sprinkling was run in four 30 minutes periods separated by three 30 minutes non-sprinkling periods. The runoff from the snow block was continuously gauged and sampled for the deuterium concentration. At the onset of each experiment initially present liquid water content was first pushed out by the sprinkling water. Hydrographs showed four pronounced peaks corresponding to the four sprinkling bursts. The contribution of rainwater to snowpack runoff consistently increased over the course of the experiment but never exceeded 86 %. An experiment conducted on a cold snowpack suggested the development of preferential flow paths that allowed rainwater to efficiently propagate through the snowpack limiting the time for mass exchange processes to take effect. On the contrary, experiments conducted on ripe isothermal snowpack showed a slower response behaviour and resulted in a total runoff volume which consisted of less than 50 % of the rain input.

scholarly journals Development of physically based liquid water schemes for Greenland firn-densification models

2019 ◽  
Author(s):  
Vincent Verjans ◽  
Amber Leeson ◽  
C. Max Stevens ◽  
Michael MacFerrin ◽  
Brice Noël ◽  
...  
Keyword(s):  
Water Flow ◽  
Liquid Water ◽  
Preferential Flow ◽  
Greenland Ice Sheet ◽  
Single Domain ◽  
Richards Equation ◽  
Retention Capacity ◽  
Water Percolation ◽  
Physically Based ◽  
Dual Domain

Abstract. As surface melt is increasing on the Greenland ice sheet (GrIS), quantifying the retention capacity of the firn layer is critical to link meltwater production to meltwater runoff. Firn-densification models have so far relied on empirical approaches to account for the percolation-refreezing process, and more physically based representations of liquid water flow might therefore bring improvements to model performance. Here we implement three types of water percolation schemes into the Community Firn Model: the tipping bucket approach, the Richards Equation in a single-domain and the Richards Equation in a dual-domain, which accounts for partitioning between matrix and fast preferential flow. We investigate their impact on firn densification at four locations on the GrIS and compare model results with observations. We find that for all of the flow schemes, significant discrepancies remain with respect to observed firn density, particularly the density variability in depth, and that inter-model differences are large. The simple bucket scheme is as efficient in replicating observed density profiles as the single-domain Richards Equation. The most physically detailed dual-domain scheme does not necessarily reach best agreement with observed data. However, we find that the implementation of preferential flow does allow for more frequent ice layer formation and for deeper percolation. We also find that the firn model is more sensitive to the choice of densification scheme than to the choice of water percolation scheme. The disagreements with observations and the spread in model results demonstrate that progress towards an accurate description of water flow in firn is necessary. The numerous uncertainties surrounding firn micro- and macro-structure, its hydraulic properties, and the one dimensionality of firn models render the implementation of physically based percolation schemes difficult. An improved understanding of the parameters affecting evolution of polar firn, of the effects of the climatic forcing on the densification process and more accurate treatment of liquid water would benefit further developments.

scholarly journals Liquid water infiltration into a layered snowpack: evaluation of a 3-D water transport model with laboratory experiments

2017 ◽  
Vol 21 (11) ◽  
pp. 5503-5515 ◽  
Author(s):  
Hiroyuki Hirashima ◽  
Francesco Avanzi ◽  
Satoru Yamaguchi
Keyword(s):  
Liquid Water ◽  
Laboratory Experiments ◽  
Preferential Flow ◽  
Transport Model ◽  
Three Dimensional ◽  
Water Infiltration ◽  
Flow Paths ◽  
Preferential Flow Paths ◽  
Capillary Barriers ◽  
Wet Snow

Abstract. The heterogeneous movement of liquid water through the snowpack during precipitation and snowmelt leads to complex liquid water distributions that are important for avalanche and runoff forecasting. We reproduced the formation of capillary barriers and the development of preferential flow through snow using a three-dimensional water transport model, which was then validated using laboratory experiments of liquid water infiltration into layered, initially dry snow. Three-dimensional simulations assumed the same column shape and size, grain size, snow density, and water input rate as the laboratory experiments. Model evaluation focused on the timing of water movement, thickness of the upper layer affected by ponding, water content profiles and wet snow fraction. Simulation results showed that the model reconstructs relevant features of capillary barriers, including ponding in the upper layer, preferential infiltration far from the interface, and the timing of liquid water arrival at the snow base. In contrast, the area of preferential flow paths was usually underestimated and consequently the averaged water content in areas characterized by preferential flow paths was also underestimated. Improving the representation of preferential infiltration into initially dry snow is necessary to reproduce the transition from a dry-snow-dominant condition to a wet-snow-dominant one, especially in long-period simulations.

scholarly journals Observations of capillary barriers and preferential flow in layered snow during cold laboratory experiments

2016 ◽  
Vol 10 (5) ◽  
pp. 2013-2026 ◽  
Author(s):  
Francesco Avanzi ◽  
Hiroyuki Hirashima ◽  
Satoru Yamaguchi ◽  
Takafumi Katsushima ◽  
Carlo De Michele
Keyword(s):  
Grain Size ◽  
Spatial Variability ◽  
Liquid Water ◽  
Laboratory Experiments ◽  
Preferential Flow ◽  
Liquid Water Content ◽  
Water Infiltration ◽  
Richards Equation ◽  
Capillary Barrier ◽  
Capillary Barriers

Abstract. Data of liquid water flow around a capillary barrier in snow are still limited. To gain insight into this process, we carried out observations of dyed water infiltration in layered snow at 0 °C during cold laboratory experiments. We considered three different finer-over-coarser textures and three different water input rates. By means of visual inspection, horizontal sectioning, and measurements of liquid water content (LWC), capillary barriers and associated preferential flow were characterized. The flow dynamics of each sample were also simulated solving the Richards equation within the 1-D multi-layer physically based snow cover model SNOWPACK. Results revealed that capillary barriers and preferential flow are relevant processes ruling the speed of water infiltration in stratified snow. Both are marked by a high degree of spatial variability at centimeter scale and complex 3-D patterns. During unsteady percolation of water, observed peaks in bulk volumetric LWC at the interface reached  ∼ 33–36 vol % when the upper layer was composed by fine snow (grain size smaller than 0.5 mm). However, LWC might locally be greater due to the observed heterogeneity in the process. Spatial variability in water transmission increases with grain size, whereas we did not observe a systematic dependency on water input rate for samples containing fine snow. The comparison between observed and simulated LWC profiles revealed that the implementation of the Richards equation reproduces the existence of a capillary barrier for all observed cases and yields a good agreement with observed peaks in LWC at the interface between layers.

scholarly journals Liquid water infiltration into a layered snowpack: evaluation of a 3D water transport model with laboratory experiments

2017 ◽  
Author(s):  
Hiroyuki Hirashima ◽  
Francesco Avanzi ◽  
Satoru Yamaguchi
Keyword(s):  
Water Content ◽  
Liquid Water ◽  
Laboratory Experiments ◽  
Preferential Flow ◽  
Transport Model ◽  
Water Infiltration ◽  
Flow Paths ◽  
Preferential Flow Paths ◽  
Capillary Barriers ◽  
Wet Snow

Abstract. The heterogeneous movement of liquid water through snowpack during precipitation and snowmelt leads to complex liquid water distributions that are important for avalanche and runoff forecasting. We reproduced the formation of capillary barriers and the development of preferential flow through snow using a multi-dimensional water transport model, which was then validated using laboratory experiments of liquid water infiltration into layered, initially dry snow. Three-dimensional simulations assumed the same column shape and size, grain size, snow density, and water input rate as the laboratory experiments. Model evaluation focused on the timing of water movement, the thickness of the upper layer affected by ponding, and on water content profiles and the wet snow fraction. Simulation results showed that the model reconstructs some relevant features of capillary barriers including ponding in the upper layer, preferential infiltration far from the interface, and the timing of liquid water arrival at the snow base. In contrast, the area of preferential flow paths was usually underestimated and consequently the averaged water content in areas characterized by preferential flow paths was also underestimated. Improving the representation of water preferential infiltration into initially dry snow is necessary to reproduce the transition from a dry-snow-dominant condition to a wet-snow-dominant one, especially in long-period simulations.

Can fill-and-spill subsurface flow be represented by a moisture-dependent anisotropic permeability tensor in Richards equation-based models with coarse spatial resolution?

2021 ◽  
Author(s):  
Esther Xu Fei ◽  
Ciaran Harman
Keyword(s):  
Spatial Resolution ◽  
Field Experiments ◽  
Preferential Flow ◽  
Field Measurements ◽  
Structural Heterogeneity ◽  
Permeability Tensor ◽  
Richards Equation ◽  
Fine Scale ◽  
Catchment Scale ◽  
Coarse Spatial Resolution

<p>Subsurface structural heterogeneity can route soil water through the vadose zone in complex ways that are difficult to observe or model in detail. The fill-and-spill hypothesis, which was developed to explain observations from field experiments at the hillslope scale, suggests that lateral flow at the soil-bedrock interface (or other permeability contrasts) is only activated once depressions in the microtopography of that interface become saturated and connect laterally. To reproduce this fill-and-spill phenomenon, a Richards equation-based numerical model would require a discretization of this morphology at a fine scale. A coarse representation smooths the interface eliminating the essential local storage-excess threshold behavior. However, the accuracy and abundance of field measurements rarely provide the data that would be needed to do this, and the fine discretization creates a high computational burden.</p><p>Here we explore the potential of an upscaled representation of the fill-and-spill mechanism based on parameterization of a permeability tensor with saturation-dependent anisotropy. By increasing empirical lateral hydraulic conductivity as they approach saturation, this anisotropy could reproduce how the fill-and-spill causes saturated patches at the permeability contrast to connect along preferential flow paths. Such a process representation could be incorporated into a Richards equation-based model enabling it to reproduce the fill-and-spill phenomenon even with a coarse spatial resolution.</p><p>We tested this idea using ParFlow to model virtual hillslopes with synthetic rugged internal topography. We then investigated the effective permeability tensor over an averaging volume that encloses the interface. By parameterizing the anisotropy of an interface block under changing moisture variables, we may be able to generate predictions of how the fine-scale fill-and-spill processes integrate to the hillslope and catchment scale.</p>

scholarly journals Verification of the multi-layer SNOWPACK model with different water transport schemes

2015 ◽  
Vol 9 (6) ◽  
pp. 2271-2293 ◽  
Author(s):  
N. Wever ◽  
L. Schmid ◽  
A. Heilig ◽  
O. Eisen ◽  
C. Fierz ◽  
...  
Keyword(s):  
Water Transport ◽  
Preferential Flow ◽  
Snow Water Equivalent ◽  
Temporal Evolution ◽  
Winter Season ◽  
Model Performance ◽  
Water Dynamics ◽  
Richards Equation ◽  
Snow Density ◽  
Data Set

Abstract. The widely used detailed SNOWPACK model has undergone constant development over the years. A notable recent extension is the introduction of a Richards equation (RE) solver as an alternative for the bucket-type approach for describing water transport in the snow and soil layers. In addition, continuous updates of snow settling and new snow density parameterizations have changed model behavior. This study presents a detailed evaluation of model performance against a comprehensive multiyear data set from Weissfluhjoch near Davos, Switzerland. The data set is collected by automatic meteorological and snowpack measurements and manual snow profiles. During the main winter season, snow height (RMSE: < 4.2 cm), snow water equivalent (SWE, RMSE: < 40 mm w.e.), snow temperature distributions (typical deviation with measurements: < 1.0 °C) and snow density (typical deviation with observations: < 50 kg m−3) as well as their temporal evolution are well simulated in the model and the influence of the two water transport schemes is small. The RE approach reproduces internal differences over capillary barriers but fails to predict enough grain growth since the growth routines have been calibrated using the bucket scheme in the original SNOWPACK model. However, the agreement in both density and grain size is sufficient to parameterize the hydraulic properties successfully. In the melt season, a pronounced underestimation of typically 200 mm w.e. in SWE is found. The discrepancies between the simulations and the field data are generally larger than the differences between the two water transport schemes. Nevertheless, the detailed comparison of the internal snowpack structure shows that the timing of internal temperature and water dynamics is adequately and better represented with the new RE approach when compared to the conventional bucket scheme. On the contrary, the progress of the meltwater front in the snowpack as detected by radar and the temporal evolution of the vertical distribution of melt forms in manually observed snow profiles do not support this conclusion. This discrepancy suggests that the implementation of RE partly mimics preferential flow effects.

Sign in / Sign up

Export Citation Format

Share Document