Potential avalanche release in windthrow areas: the effect of snow height and terrain roughness

2020 ◽  
Author(s):  
Natalie Brožová ◽  
Tommaso Baggio ◽  
Michaela Teich ◽  
Alexander Bast ◽  
Peter Bebi
Keyword(s):  
Surface Roughness ◽  
Snow Accumulation ◽  
Critical Conditions ◽  
Continuous Increase ◽  
Snow Stratigraphy ◽  
Roughness Elements ◽  
Close Range ◽  
Undisturbed Forest ◽  
Local Release ◽  
Avalanche Formation

<p>Windthrow is an important disturbance agent in forest ecosystems and is expected to become more frequent and severe under climate change. Windthrow creates large amounts of surface roughness from downed trees, root plates and stumps. In mountain forests, these elements increase the surface roughness and provide a considerable protective effect against snow avalanches during the first years following a disturbance event. However, if large volumes of snow covers the surface roughness elements, a windthrow area may become prone to avalanche release. Snow accumulation produces terrain smoothing, which is an important factor in avalanche formation.</p><p>To assess the effect of snow accumulation on surface roughness in windthrow areas, we quantified terrain smoothing using a vector ruggedness measure and corresponding snow heights, based on digital surface models from summer and winter terrain produced from repetitive UAV flights. Additionally, the snowpack structure was examined using a digital snow micro penetrometer (SMP) to quantify the heterogeneity of snow stratigraphy and to monitor a possible development of weak snow layers over distances greater than 10-20 m, which may contribute to slab avalanche formation. Four study plots were selected to characterize different conditions: i) undisturbed forest, windthrow area with ii) high and iii) low surface roughness, and iv) an open meadow control plot. We then quantified how surface roughness is smoothed depending on the snow height, and at the same time characterized the snowpack structure and the extent of potential weak layers.</p><p>We found that increasing snow height leads to decreasing surface roughness, which can produce local release areas. We expect that with continuous increase of snow height, these release areas expand in size; however, further analyses of the snowpack structure will provide deeper insights in potential weak layer formation. Critical conditions for avalanche releases in windthrow areas may thus be defined based on scenarios for snow height and close-range sensing-based roughness data.</p>

scholarly journals Estimating snow water equivalent over long mountain transects using snowmobile-mounted ground-penetrating radar

Geophysics ◽  
2016 ◽  
Vol 81 (1) ◽  
pp. WA183-WA193 ◽  
Author(s):  
W. Steven Holbrook ◽  
Scott N. Miller ◽  
Matthew A. Provart
Keyword(s):  
Ground Penetrating Radar ◽  
Snow Water Equivalent ◽  
Ground Surface ◽  
Snow Accumulation ◽  
Accurate Estimation ◽  
Snow Density ◽  
Snow Stratigraphy ◽  
Flood Estimation ◽  
Snow Water ◽  
Ground Penetrating

The water balance in alpine watersheds is dominated by snowmelt, which provides infiltration, recharges aquifers, controls peak runoff, and is responsible for most of the annual water flow downstream. Accurate estimation of snow water equivalent (SWE) is necessary for runoff and flood estimation, but acquiring enough measurements is challenging due to the variability of snow accumulation, ablation, and redistribution at a range of scales in mountainous terrain. We have developed a method for imaging snow stratigraphy and estimating SWE over large distances from a ground-penetrating radar (GPR) system mounted on a snowmobile. We mounted commercial GPR systems (500 and 800 MHz) to the front of the snowmobile to provide maximum mobility and ensure that measurements were taken on pristine snow. Images showed detailed snow stratigraphy down to the ground surface over snow depths up to at least 8 m, enabling the elucidation of snow accumulation and redistribution processes. We estimated snow density (and thus SWE, assuming no liquid water) by measuring radar velocity of the snowpack through migration focusing analysis. Results from the Medicine Bow Mountains of southeast Wyoming showed that estimates of snow density from GPR ([Formula: see text]) were in good agreement with those from coincident snow cores ([Formula: see text]). Using this method, snow thickness, snow density, and SWE can be measured over large areas solely from rapidly acquired common-offset GPR profiles, without the need for common-midpoint acquisition or snow cores.

scholarly journals Photogrammetry-based Texture Analysis of a Volcaniclastic Outcrop-peel: Low-cost Alternative to TLS and Automation Potentialities using Haar Wavelet and Spatial-Analysis Algorithms

2017 ◽  
Vol 31 (1) ◽  
pp. 16-27 ◽  
Author(s):  
Christopher Gomez ◽  
Kyoko Kataoka ◽  
Aditya Saputra ◽  
Patrick Wassmer ◽  
Atsushi Urabe ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Wavelet Decomposition ◽  
Low Cost ◽  
Decomposition Analysis ◽  
Haar Wavelet ◽  
Present Contribution ◽  
Close Range Photogrammetry ◽  
Original Goal ◽  
Close Range ◽  
Made In

Numerous progress has been made in the field of applied photogrammetry in the last decade, including the usage of close-range photogrammetry as a mean of conservation and record of outcrops. In the present contribution, we use the SfM-MVS method combined with a wavelet decomposition analysis of the surface, in order to relate it to morphological and surface roughness data. The results demonstrated that wavelet decomposition and RMS could provide a rapid insight on the location of coarser materials and individual outliers, while arithmetic surface roughness were more useful to detect units or layers that are similar on the outcrop. The method also emphasizes the fact that the automation of the process does not allows clear distinction between any artefact crack or surface change and that human supervision is still essential despite the original goal of automating the outcrop surface analysis.

scholarly journals Hydraulic physical model production with Computer Numerically Controlled (CNC) manufacturing techniques

2018 ◽  
Vol 40 ◽  
pp. 05065 ◽  
Author(s):  
Pierre-Yves Henry ◽  
Jochen Aberle ◽  
Christy Ushanth Navaratnam ◽  
Nils Ruther
Keyword(s):  
Surface Roughness ◽  
Physical Models ◽  
Roughness Effects ◽  
Scaled Model ◽  
Construction Methods ◽  
Roughness Elements ◽  
Computer Numerically Controlled ◽  
Complex Boundary ◽  
Manufacturing Techniques ◽  
Scaled Models

Physical models are a well-accepted tool in hydraulic engineering, allowing for the detailed characterisation of flow processes and the validation of structure designs with complex boundary conditions. The methods used to construct physical models typically produce a surface roughness which does not necessarily scale with the surface roughness of the prototype. In this context, this paper discusses novel construction methods allowing a detailed reproduction of roughness elements in scaled models, such as Computer Numerically Controlled (CNC) manufacturing techniques and bed casting techniques. In particular, the present paper details the protocols developed to mill out a correct representation of the complex rock-fractured geometry of a closed channel which was obtained from Terrestrial Laser Scanners. The novelty of this scaled model production is the implementation of optical accesses in a closed (pressurized) hydraulic model, to allow for Particle Image Velocimetry measurements with a minimum impact on the reproduced roughness elements. The effectiveness of this production protocol is discussed in the context of modelling the roughness effects on the flow regime.

Use of close-range photogrammetry to characterize fracture surfaces

2004 ◽  
Vol 175 (5) ◽  
pp. 481-490 ◽  
Author(s):  
Frédéric Filipe ◽  
Judith Sausse
Keyword(s):  
Surface Roughness ◽  
Natural Fracture ◽  
Fracture Plane ◽  
Natural Fractures ◽  
Fracture Surfaces ◽  
Close Range Photogrammetry ◽  
Contact Points ◽  
Close Range ◽  
Void Geometry ◽  
Non Destructive

Abstract Natural fractures are characterized by rough surfaces and complex fluid flows. A large distribution of apertures (residual voids) within their walls and the presence of contact points produce heterogeneous flows (channelling). The resulting permeabilities, porosities or fluid-rock exchange surfaces cannot be realistically modelled by parallel and smooth plate models. It is therefore very important to better constrain models of the fracture planes : asperity heights and aperture distribution to be able to fix specific models of permeability in specific fracture void geometry. In this approach, a precise description of the fracture surface planes is given by providing some new quantitative data of surface roughness in the case of natural fractures. Studied fractures are sampled in a granite and a sandstone in the deep basement of the Hot Dry Rock site of Soultzsous-Forêts (Bas-Rhin, France). An original use of close-range photogrammetry is performed to quantify XYZ data on fracture walls. This methodology is presented as a non destructive, precise and accurate technology to quantify some digital terrain models (DTM) of the fracture plane topography. XYZ results are statistically treated in terms of surface roughness and tortuosity and are compared for different rocks to previous data obtained by mechanical profilometry. The results shows that the photogrammetric approach gives same order of asperity heights magnitudes as profilometry despite a shift towards more important values of roughness when close range photogrammetry uses relative autocorrelation models. The advantage of photogrammetry is that this technique gives very quick results and is non destructive when thin alteration or pulverulent deposits are present within fracture walls or in the rock matrix. The disadvantage is that a slight smoothing of data is inherent to an absolute model calibration. Finally only relative 300*300 DTM are finally chosen to match profilometry data because of their higher precision in terms of micro roughness description to compare natural fracture surfaces. In the objective of a classification of fracture roughness in specific geological contexts, the photogrammetric approach gives a good estimation of different classes of roughness in function of rock alteration and type.

Wind Shear Fluctuations Downwind of Large Surface Roughness Elements

1978 ◽  
Vol 17 (4) ◽  
pp. 436-443 ◽  
Author(s):  
J. V. Ramsdell
Keyword(s):  
Surface Roughness ◽  
Wind Shear ◽  
Roughness Elements

Predicting Skin Friction and Heat Transfer for Turbulent Flow Over Real Gas-Turbine Surface Roughness Using the Discrete-Element Method

2003 ◽  
Author(s):  
Stephen T. McClain ◽  
B. Keith Hodge ◽  
Jeffrey P. Bons
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Wind Tunnel ◽  
Discrete Element Method ◽  
Skin Friction ◽  
Gas Turbine ◽  
Discrete Element ◽  
Real Gas ◽  
Roughness Elements ◽  
Element Method

The discrete-element method considers the total aerodynamic drag on a rough surface to be the sum of shear drag on the flat part of the surface and the form drag on the individual roughness elements. The total heat transfer from a rough surface is the sum of convection through the fluid on the flat part of the surface and the convection from each of the roughness elements. The discrete-element method has been widely used and validated for predicting heat transfer and skin friction for rough surfaces composed of sparse, ordered, and deterministic elements. Real gas-turbine surface roughness is different from surfaces with sparse, ordered, and deterministic roughness elements. Modifications made to the discrete-element roughness method to extend the validation to real gas-turbine surface roughness are detailed. Two rough surfaces found on high-hour gas-turbine blades were characterized using a Taylor-Hobson Form Talysurf Series 2 profilometer. Two rough surfaces and two elliptical-analog surfaces were generated for wind-tunnel testing using a three-dimensional printer. The printed surfaces were scaled to maintain similar boundary-layer thickness to roughness height ratio in the wind tunnel as found in gas-turbine operation. The results of the wind tunnel skin friction and Stanton number measurements and the discrete-element method predictions for each of the four surfaces are presented and discussed. The discrete-element predictions made considering the gas-turbine roughness modifications are within 7% of the experimentally-measured skin friction coefficients and are within 16% of the experimentally-measured Stanton numbers.

Roughness Effects on the Mixing Properties in Open Channel Turbulent Boundary Layers

2004 ◽  
Vol 126 (6) ◽  
pp. 1025-1032 ◽  
Author(s):  
Mark F. Tachie ◽  
Donald J. Bergstrom ◽  
Ram Balachandar
Keyword(s):  
Surface Roughness ◽  
Boundary Layers ◽  
Open Channel ◽  
Turbulent Boundary Layers ◽  
Turbulence Structure ◽  
Roughness Effects ◽  
Mixing Properties ◽  
Roughness Elements ◽  
Specific Geometry ◽  
Transport And Mixing

This paper investigates the effects of surface roughness on the transport and mixing properties in turbulent boundary layers created in an open channel. The measurements were obtained on a smooth and two different types of rough surfaces using a laser Doppler anemometer. The results show that surface roughness enhances the levels of the turbulence kinetic energy, turbulence production, and diffusion over most of the boundary layer. The distributions of the eddy viscosity and mixing length are also strongly modified by surface roughness. Furthermore, the extent to which surface roughness modifies the turbulence structure depends on the specific geometry of the roughness elements.

MEASUREMENT OF SURFACE ROUGHNESS IN DESERT TERRAIN BY CLOSE RANGE PHOTOGRAMMETRY

2006 ◽  
Vol 13 (78) ◽  
pp. 855-875 ◽  
Author(s):  
R. P. Kirby
Keyword(s):  
Surface Roughness ◽  
Close Range Photogrammetry ◽  
Close Range
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