Manual measurement of snow water equivalent

This Technical Report defines the requirements for manual measurements of SWE over land, see ice and glaciers, under natural environmental conditions, and shows methods for calculating the spatial distribution of the data. It includes measurements with snow tubes, core drills and density cutters.

Manuelle Messung des Schneewasseräquivalents

Dieser Technische Bericht definiert die Anforderungen an manuelle SWE Messungen unter natürlichen Umwelt-bedingungen auf dem Festland, von Meereis und Gletschern und bietet Verfahren für die Berechnung der räumlichen Verteilung der Daten. Er bezieht Messungen mit Schneesonden, Kernbohrern und Dichte-ausstecher ein.

Mesure manuelle de l’équivalent en eau de la neige

Ročno merjenje količine vode v snegu

CEN/TR 16588 določa zahteve za ročno merjenje količine vode v snegu (SWE) na kopnem, morskem ledu in ledenikih pri naravnih okoljskih pogojih ter opisuje načine za izračun prostorske porazdelitve podatkov. Zajema meritve s snežnimi cevmi, jedrnimi vrtalniki in rezalniki gostote.

General Information

Status
Published
Publication Date
18-Mar-2014
Current Stage
6060 - Definitive text made available (DAV) - Publishing
Due Date
19-Mar-2014
Completion Date
19-Mar-2014

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SLOVENSKI STANDARD
SIST-TP CEN/TR 16588:2014
01-junij-2014
5RþQRPHUMHQMHNROLþLQHYRGHYVQHJX
Manual measurement of snow water equivalent
Manuelle Messung des Schneewasseräquivalents
Mesure manuel de l’équivalent en eau de la neige
Ta slovenski standard je istoveten z: CEN/TR 16588:2014
ICS:
07.060 Geologija. Meteorologija. Geology. Meteorology.
Hidrologija Hydrology
SIST-TP CEN/TR 16588:2014 en,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST-TP CEN/TR 16588:2014
TECHNICAL REPORT
CEN/TR 16588
RAPPORT TECHNIQUE
TECHNISCHER BERICHT
March 2014
ICS 07.060
English Version
Manual measurement of snow water equivalent

Mesure manuelle de l'équivalent en eau de la neige Manuelle Messung des Schneewasseräquivalents

This Technical Report was approved by CEN on 3 September 2013. It has been drawn up by the Technical Committee CEN/TC 318.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,

Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,

Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United

Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels

© 2014 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TR 16588:2014 E

worldwide for CEN national Members.
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Contents Page

Foreword ..............................................................................................................................................................4

Introduction .........................................................................................................................................................5

1 Scope ......................................................................................................................................................6

2 Terms and definitions ...........................................................................................................................6

3 Symbols ............................................................................................................................................... 10

4 Objective .............................................................................................................................................. 10

4.1 Spatial estimation of SWE ................................................................................................................. 10

4.2 Snow load assessment ...................................................................................................................... 11

4.3 Snow profile ........................................................................................................................................ 11

4.4 Water content in newly fallen snow .................................................................................................. 11

4.5 Reference to automatic SWE measurements .................................................................................. 12

5 Principle of manual SWE measurements ......................................................................................... 12

6 Measurement sites.............................................................................................................................. 12

6.1 General ................................................................................................................................................. 12

6.2 Manual measurements ....................................................................................................................... 13

7 Measurements ..................................................................................................................................... 14

7.1 General ................................................................................................................................................. 14

7.2 Snow density ....................................................................................................................................... 14

7.3 Snow depth .......................................................................................................................................... 15

7.3.1 Manual probing ................................................................................................................................... 15

7.3.2 Manual readings on fixed snow stakes ............................................................................................ 15

7.3.3 Automatic recording ........................................................................................................................... 15

7.3.4 Remote sensing .................................................................................................................................. 16

8 Manual SWE sampling methods ....................................................................................................... 16

8.1 General ................................................................................................................................................. 16

8.2 Snow tubes .......................................................................................................................................... 16

8.3 Core drills ............................................................................................................................................ 17

8.4 Density cutters .................................................................................................................................... 17

9 Spatial estimation ............................................................................................................................... 18

9.1 General ................................................................................................................................................. 18

9.2 Interpolation methods ........................................................................................................................ 18

9.3 Snow courses ...................................................................................................................................... 19

9.4 Regression modelling ........................................................................................................................ 19

9.5 Hydrologic and land surface modelling ........................................................................................... 20

9.6 Remote sensing systems for snow monitoring ............................................................................... 20

10 Maintenance ........................................................................................................................................ 21

11 Uncertainties ....................................................................................................................................... 21

11.1 Environmental factors ........................................................................................................................ 21

11.2 Technical factors ................................................................................................................................ 21

11.3 Human factors ..................................................................................................................................... 22

12 Assessment of quality ........................................................................................................................ 22

13 Measurement uncertainty .................................................................................................................. 22

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14 Recommendations .............................................................................................................................. 22

Annex A (informative) List of methods for determination of SWE in total snowpack ............................... 24

Annex B (informative) Manual SWE measuring bodies in Europe ............................................................... 25

Annex C (informative) Determination of mass of snow sample ................................................................... 26

Annex D (informative) Determination of water volume in snow sample ..................................................... 27

Annex E (informative) Snow stakes ................................................................................................................ 28

Annex F (informative) List of samplers for detection of SWE ...................................................................... 29

Annex G (informative) Snow tubes ................................................................................................................. 30

Annex H (informative) Core drills .................................................................................................................... 31

Annex I (informative) Density cutters ............................................................................................................ 32

Annex J (informative) On-line glossaries ....................................................................................................... 33

Bibliography ...................................................................................................................................................... 34

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Foreword

This document (CEN/TR 16588:2014) has been prepared by Technical Committee CEN/TC 318

“Hydrometry”, the secretariat of which is held by BSI.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent

rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.

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Introduction
Snow water equivalent (SWE) measurements

Snow water equivalent (SWE), also called “water equivalent of snow”, is the depth of water that would be

obtained by melting the snowpack in a given area, and is normally expressed in millimetres. In other words,

SWE corresponds to the mass of snow over a given area.

Measurements of SWE in snowpack, and new snow, improve the estimation of winter precipitation, especially

in areas with a sparse network of meteorological stations. The measurements are mainly made for the

purpose of estimating the spatial distribution of the total water content in catchment areas, as knowledge of

the SWE in river basins is fundamental for estimating the expected snowmelt runoff.

Information about snow accumulation and daily melt rate is essential in flood forecasting during the snowmelt

season. SWE is also used in avalanche theory and forecasting, as well as for risk assessment of heavy snow

loads. Furthermore, the data is important in glaciological mass balance studies and climate monitoring. The

melt from polar ice sheets is a major factor in sea level rise.

Methods and instruments, which have been developed for determination of SWE, are listed in Annex A.

Manual SWE measurements

The first station networks with manual SWE measurements were established in the early 20th century at

meteorological institutes in North America and Europe. Today the measurements are made routinely at

federal and national meteorological and hydrological institutes, within the hydropower industry, and by

universities, in cold climate countries all over the world. Annex B shows a list of manual SWE measuring

bodies in Europe.

Automized methods have been developed to be used in remote areas, as well as to enable continuous

recording, but manual measurements are still more common, as they can provide high quality data for a

relatively low capital cost. The importance of manual measurements is also reflected in their use as reference

to other SWE measuring methods.
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1 Scope

This Technical Report defines the requirements for manual measurements of SWE over land, see ice and

glaciers, under natural environmental conditions, and shows methods for calculating the spatial distribution of

the data. It includes measurements with snow tubes, core drills and density cutters.

2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

Note 1 to entry Primarily ‘The International Classification for Seasonal Snow on the Ground’ (UNESCO), ‘Cryospheric

Glossary’ (NSIDC) and ‘Glossary of Meteorology’ (AMS) has been used as reference.

2.1
ablation

removal of material from the surface of an object by vaporization, chipping, or other erosive processes. In this

case the opposite of snow accumulation
2.2
blowing snow

an ensemble of snow particles raised by the wind to moderate or great heights above the ground; the

horizontal visibility at eye level is generally very poor
Note 1 to entry See also drifting snow.
2.3
condensation

the change of the physical state of matter from gaseous phase into liquid phase (opposite of evaporation)

2.4
deposition

(1) a process by which water vapour is deposited as ice without first forming liquid water (opposite of

sublimation)

(2) the process by which snow is deposited on the ground either with or without wind action

Note 1 to entry As a result, stationary snow deposits such as snow dunes, snowdrifts, or the snow cover itself may

form.
2.5
drifting snow

snow raised from the snow surface by the wind to a height of less than 2 metres; it does not restrict horizontal

visibility at 2 metres or more above the surface
Note 1 to entry See also blowing snow.
2.6
evaporation

vaporization of a liquid that only occurs on the surface of a liquid, at temperatures below the boiling point

(opposite of condensation)
2.7
firn

well-bonded and compacted snow that has survived the summer season, but has not been transformed to

glacier ice
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Note 1 to entry Typical densities are 400 - 830 kg·m . Thus firn is the intermediate stage between snow and glacial

ice where the pore space is at least partially interconnected. Firn usually results from both melt-freeze cycles and

compaction by overload, or from compaction alone, as in inland Antarctic snow.
2.8
glacier

a mass of land ice formed by the further recrystallization of firn, normally flowing continuously from higher to

lower elevations
2.9
new snow

recently fallen snow in which the original form of the ice crystals can be recognized

Note 1 to entry This is usually the snow which has accumulated on a snow board during the standard observing

period of 24 hours.
2.10
old snow

deposited snow whose transformation into firn is so far advanced that the original form of the ice crystals can

no longer be recognized
2.11
recrystallize
to crystallize again, i.e., to form into new crystals
2.12
redistribution

distribution of previously deposited snow that was eroded and transported by the wind

Note 1 to entry Redistribution features such as snowdrifts are usually formed from densely packed and friable snow.

2.13
perennial snow
snow persisting for an indefinite time longer than one year
Note 1 to entry See also seasonal snow.
2.14
seasonal snow
snow that accumulates during one season and does not last for more than one year
Note 1 to entry See also perennial snow.
2.15
snow accumulation

all processes that add mass to the snow cover, i.e. typically solid and liquid precipitation, ice deposition from

atmospheric water vapour, and snow deposited by wind, avalanches, etc. (opposite of ablation)

2.16
snow avalanche
mass of snow which becomes detached and slides swiftly down a slope

Note 1 to entry Large snow avalanches may contain rocks, soil, vegetation, and/or ice.

2.17
snow board

in this case a specially constructed board used to identify the surface of snow that has been recently covered

by snowfall
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2.18
snow core

a sample of snow, either just the freshly fallen snow or the combined old and new snow on the ground,

obtained by pushing, or drilling, a cylinder down through the snow layer and extracting it

2.19
snow course

an established line, or transect, of measurements of SWE across a snow covered area in a representative

terrain, where appreciable amounts of snow accumulates
2.20
snow cover

in general, the accumulation of snow on the ground surface, and in particular, the areal extent of snow-

covered ground; term to be preferably used in conjunction with the climatologic relevance of snow on the

ground
Note 1 to entry See also snowpack.
2.21
snow creep
a continuous, slow downhill movement of a snow layer
2.22
snow density
the mass per unit volume of snow

Note 1 to entry Sometimes total and dry snow densities are measured separately. Total snow density encompasses

all constituents of snow (ice, liquid water, and air) while dry snow density refers to the ice matrix and air only.

2.23
snow depth

the total height of the snowpack, measured vertically from the base to the snow surface

Note 1 to entry The slope-perpendicular equivalent of snow depth is the snowpack thickness.

2.24
snow distribution

spatial and temporal variability of snow cover affected by snowfall, wind speed, elevation, topography,

vegetation and ablation
2.25
snow erosion

the process by which the surface of the snow cover is worn away, primarily by the action of wind

Note 1 to entry Wind erosion is a very important factor in the redistribution of snow.

2.26
snow height

the vertical distance from a base to a specific level in the snow, or to the snow surface

Note 1 to entry Ground surface is usually taken as the base, but on firn fields and glaciers it refers to the level of

either the firn surface or glacier ice. Height is used to denote the locations of layer boundaries but also of measurements

such as snow temperatures relative to the base. Where only the upper part of the snowpack is of interest, the snow

surface may be taken as the reference. This should be indicated by using negative coordinate values. Snow depth is the

total height of the snowpack.
2.27
snow layer
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a layer of ice crystals with similar size and shape
2.28
snow load

the downward force on an object or structure caused by the weight of accumulated snow

2.29
snow metamorphism

the transformation that the snow undergoes in the period from deposition to either melting or passage to

glacial ice

Note 1 to entry Meteorological conditions as well as mechanical or gravitational stresses are the primary external

factors that affect snow metamorphism.
2.30
snow pit

in this case a pit dug vertically into the snowpack where snowpack stratigraphy and characteristics of the

individual snow layers are observed
Note 1 to entry See also snow profile.
2.31
snow profile

a stratigraphic record of the snowpack including characteristics of individual snow layers, usually performed in

snow pits
2.32
snow sample
in this case a sample of snow with a defined volume extracted from the snowpack
2.33
snow sampler
an instrument used for the collection of snow samples in an undisturbed snowpack
2.34
snow season
the time period when the ground usually is covered by snow
2.35
snow surface
the uppermost part of the snow cover, forming the interface to the atmosphere
2.36
snow survey

the process of determining snow parameters, most often depth and density, at representative points, usually

along a snow course
2.37
snow water equivalent (SWE)

the depth of water that would result if a certain amount of snow melted completely

Note 1 to entry It can represent the snow cover over a given region or a confined snow sample over the

corresponding area. The snow water equivalent is the product of the snow height and the snow density divided by the

density of water. It is typically expressed in millimetres of water equivalent, which is equivalent to kilograms per square

metre or litres of water per square metre.
2.38
snowdrift
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a mound or bank of snow deposited as sloping surfaces and peaks, often behind obstacles, irregularities, and

on lee slopes, due to eddies in the wind field. (See also deposition)
2.39
snowfall
the quantity of snow falling within a given area in a given time
2.40
snowpack

the accumulation of snow on the ground at a given site and time; term to be preferably used in conjunction

with the physical and mechanical properties of the snow
Note 1 to entry See also snow cover.
2.41
snowpack stratigraphy
the definition and description of the stratified, i.e. layered snowpack
Note 1 to entry See also snow profile.
2.42
snowpack thickness

the total height of the snowpack, measured perpendicularly from base to snow surface, i.e. at right angle to

the slope on inclined snow covers

Note 1 to entry When observers report thickness, they should also include the slope angle with respect to either the

snow surface or a layer within the snowpack, e.g., the bed surface of an avalanche. The slope-vertical equivalent of

snowpack thickness is the snow depth.
2.43
sublimation

the change of state of matter from solid phase to gaseous phase without entering liquid phase (opposite of

deposition)
3 Symbols
The symbols used in this technical report are given in Table 1.
Table 1 — Symbols
Most common
Symbol Quantity
units
SWE Snow water equivalent m, mm
D Snow depth m, cm
m Mass kg, g
-3 -3
ρ Density kg·m , g·cm
3 3
V Volume m , cm
2 2
A Area m , cm
4 Objective
4.1 Spatial estimation of SWE
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Measurements of SWE are essential for estimation of the total snow water content in catchment areas.

Manual SWE measurements made by meteorological observers are often used as a complement to

precipitation measurements. In areas where water budget calculations are difficult, due to sparse

meteorological networks, additional snow surveys may be required. This is the case especially in mountainous

regions where precipitation at the measuring stations often badly represents the precipitation in the region.

SWE observations are used as input to and verification of models for calculation of river and ground water

flow, water management, flood warnings, snow load assessment, avalanche prediction and glacier mass

balance calculations.

Data from point measurements of SWE can be used to estimate the spatial distribution by means of a number

of methods. These include the following which are described in more detail in clause 9.

Ground measurements can be spatially distributed by use of:
— mathematical regionalization algorithms;
— mean or weighted values from snow courses.
Ground measurements can be used for calibration, validation and updating of:
— meteorological and hydrological models;
— snow distribution models;
— remote sensing systems for snow monitoring.
4.2 Snow load assessment

Collapse of buildings/structures, due to excessive snow loads, is a serious problem both in terms of economic

loss and public safety. The SWE present on roofs often differs a lot from the mean value in the landscape.

Wind and snow creep together with the presence of taller buildings/structures are factors which can decrease

or increase the weight of the snow on a certain building/structure. Measurement of SWE on roofs as well as

on the ground can potentially be of vital importance.
4.3 Snow profile

Periods of melting and freezing, snow falling at different air temperatures, and wind packing the snow, result in

layers of ice, crust, and snow with different densities. By digging a snow pit with a vertical wall, layers in the

snow can be detected and measured separately.

Knowledge of layers with different density is essential in avalanche risk forecasting. Furthermore, it can be

important for the correct assessment of the functioning of automatic measuring instruments.

4.4 Water content in newly fallen snow

Daily data on new snow measurements are very important for, e.g. military services, emergency and civil

protection services, road and airport maintenance services, avalanche forecasting and tourism. Continuous

registration of newly fallen snow can also be a complement to precipitation monitoring, and for verifying

weather forecasts.

Usually the sampling is carried out by use of a snow measurement board, which is made from a thin board

that will not sink into the snow, yet be heavy enough not to be blown away. The board should be pushed into

the snow surface just far enough so that the top of the board is nearly level or slightly below the top of the old

snow. Samples can be taken with a cylinder either at regular intervals or after each snowfall. After each

observation the board should be cleaned and placed in a new location close to the previous sample points.

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The snow measurement board may need daily observations to assure that the top remains flush with the old

snow. To reduce the risk of heat absorption the board should be painted white.

The measuring site should be sheltered as much as possible from drifting and blowing snow.

4.5 Reference to automatic SWE measurements

A manual point measurement of the total value of SWE is regarded to give a more accurate value than any

other measuring method, as the assessment of the quality of the measurement is made directly on site.

Therefore the manual measurement is considered to be the reference standard method.

Layers in snowpack can act like bridges thus affecting the distribution of the weight of the snow on the site,

which may lower or raise the pressure on weighing sensors detecting the snow mass. Another problem can be

changes in homogeneity in the snowpack within very short distances, which typically occurs at the very end of

the snow season. Furthermore, measurements can fail due to malfunction of the sensors, or failure of

electronic circuits.

To ensure that readings of automatic sensors are as accurate as possible a quality control programme using

manual measurements should be established. It may be appropriate to undertake frequent manual

measurements following the initial installation of recorders to ensure correct performance of the instrument.

When the reliability of the sensor is proven, the quality program can be less frequent.

5 Principle of manual SWE measurements

A manual point measurement of the total SWE is performed by taking a vertical core from the snow surface to

the bottom of the snowpack, using a tube or core drill.

The water content of the snow in the sample is assumed to be the amount of snow that has fallen on the site,

and is still left after occasional melting and blowing periods. Determination of the SWE in the sample is

performed either by weighing (see Annex C) or melting (see Annex D) the snow.

The SWE profile of the snowpack is normally measured from the wall of a snow pit by use of a density cutter,

with samples taken horizontally or vertically, but the principle of determination of density and SWE is the

same.
See clause 8 for further explanation of the methods.
6 Measurement sites
6.1 General

The criteria for selection of SWE measuring sites are independent of the measuring method, and similar to

siting precipitation gauges for measurement of snowfall.

Sites for both single point measurements and snow courses should be chosen to be representative of the area

of interest.

Where the snow is distributed homogeneously over the area, a few single point measurements could be

sufficient. In locations where snow depth and density changes are caused by wind drift, and interception play

an important role, snow courses are recommended.

A totally open area where the distribution of snow is more affected by wind should if possible be avoided, as

well as pronounced recesses and summits of the terrain.
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If the total accumulation of snow mass is of interest, the site should be chosen at elevations and exposures

where there is as little melting as possible prior to the peak accumulation;
Recommended locations of SWE measurement sites are:

— at places where the terrain is horizontal in order to minimize the affect from snow creep;

— at clearings in bush land and open forests sufficiently large so that snow can fall to the ground without

being intercep
...

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