1、PD CEN/TR 15996:2010 ICS 07.060 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW PUBLISHED DOCUMENT Hydrometry Measurement of snow water equivalent using snow mass registration devicesThis Published Document was published under the authority of the Standards Policy and Strategy
2、 Committee on 31 March 2010 BSI 2010 ISBN 978 0 580 68499 9 Amendments/corrigenda issued since publication Date Comments PD CEN/TR 15996:2010 National foreword This Published Document is the UK implementation of CEN/TR 15996:2010. The UK participation in its preparation was entrusted to Technical Co
3、mmittee CPI/113, Hydrometry. A list of organizations represented on this committee can be obtained on request to its secretary. This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. Compliance with a British Standa
4、rd cannot confer immunity from legal obligations.PD CEN/TR 15996:2010TECHNICAL REPORT RAPPORT TECHNIQUE TECHNISCHER BERICHT CEN/TR 15996 February 2010 ICS 07.060 English Version Hydrometry - Measurement of snow water equivalent using snow mass registration devices Hydromtrie - Mesurage de lquivalent
5、 en eau de la neige au moyen de dispositifs denregistrement de la masse neigeuse Hydrometrie - Messung des Schnee-Wasser-quivalents unter Verwendung eines Gertes zur Erfassung der Schneemenge This Technical Report was approved by CEN on 11 January 2010. It has been drawn up by the Technical Committe
6、e CEN/TC 318. CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slov
7、akia, Slovenia, Spain, Sweden, Switzerland and United Kingdom. EUROPEAN COMMITTEE FOR STANDARDIZATION COMIT EUROPEN DE NORMALISATION EUROPISCHES KOMITEE FR NORMUNG Management Centre: Avenue Marnix 17, B-1000 Brussels 2010 CEN All rights of exploitation in any form and by any means reserved worldwide
8、 for CEN national Members. Ref. No. CEN/TR 15996:2010: EPD CEN/TR 15996:2010 CEN/TR 15996:2010 (E) 2 Contents Page Foreword 3 Introduction .4 1 Scope 5 2 Normative references 5 3 Terms and definitions .5 4 Symbols and abbreviated terms 5 5 Purpose of method 6 6 Principle 6 7 Operational requirements
9、 .6 8 Monitoring by hydrostatic pressure measurements 8 9 Monitoring by weight measurements . 10 10 Data collection, transfer and processing . 10 11 Factors affecting accuracy of stationary point measurements of SWE . 10 12 Factors affecting accuracy of snow mass monitoring specifically . 11 13 Eval
10、uation of method . 12 Annex A (informative) List of methods for determination of SWE in total snowpack 13 Annex B (informative) Snow mass registration stations networks 14 Annex C (informative) Manual SWE measurements . 16 Annex D (informative) Snow pillow 17 Annex E (informative) Snow plate 19 Bibl
11、iography . 21 PD CEN/TR 15996:2010 CEN/TR 15996:2010 (E) 3 Foreword This document (CEN/TR 15996:2010) 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
12、 subject of patent rights. CEN and/or CENELEC shall not be held responsible for identifying any or all such patent rights. PD CEN/TR 15996:2010 CEN/TR 15996:2010 (E) 4 Introduction Snow water equivalent (SWE) measurements Snow water equivalent (SWE) is the height of water that would be obtained by m
13、elting the snowpack on a corresponding surface area, and is normally expressed in millimetres (mm). Knowledge of the SWE is essential for estimation of total runoff and flood forecasting in river basins where snowfall occurs. Independent of the selected method, the SWE measurements should proportion
14、ally represent the total SWE in the studied area. The parameter is predominant in avalanche theory and avalanche danger forecasting as well as for risk assessment of heavy snow loads. Additionally, the development of SWE measurements using satellite sensors has increased the need for validation and
15、calibration using in-situ measurements. Annex A is a list of methods for determination of SWE. Snow mass registration devices Snow mass registration devices are widely used in North America and Europe. Different problems experienced in the use of the equipment have resulted in a slow development of
16、the technique, but improvements in equipment design and data management in recent years have increased interest in the method. Annex B shows a table of station networks running during publication of this report. PD CEN/TR 15996:2010 CEN/TR 15996:2010 (E) 5 1 Scope This Technical Report defines the r
17、equirements for the use of snow mass registration devices for measurement of SWE under natural environmental conditions. It includes weighing and pressure measuring methods. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated re
18、ferences, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. EN ISO 772:2000, Hydrometric determinations Vocabulary and symbols (ISO 772: 1996) CEN ISO/TS 25377, Hydrometric uncertainty guidance (HUG) (ISO/TS 2537
19、7:2007) 3 Terms and definitions For the purposes of this document, the terms and definitions given in EN ISO 772:2000 apply. 4 Symbols and abbreviated terms Table 1 lists the symbols used in this document. Table 1 Symbols Symbol Term Unit SWE Snow water equivalent mm M Snow mass kg Density kg/m 3V V
20、olume m 3A Area m 2Table 2 lists the abbreviated terms used in this document. Table 2 Abbreviated terms Abbreviation Term SPA Snow Pack Analyzer GPR Ground-penetrating radar PVC Polyvinyl chloride PD CEN/TR 15996:2010 CEN/TR 15996:2010 (E) 6 5 Purpose of method The use of snow mass registration devi
21、ces provides stationary single point measurements of the total SWE and recording of the changes that take place due to further accumulation of snowfall or melting of the snowpack. If the equipment is correctly mounted at a location where the snow accumulation is representative of the surrounding ter
22、rain, the data obtained by this method can be used for the prediction of melting water volumes. It can also be used for calculating the effect of heavy snow loads on structures in the area, avalanche prediction or just provide information on snow quantities in general. 6 Principle The mass of the sn
23、ow on top of a measuring device is equivalent to the mass of the water content in the overlying snow. This mass can be obtained by measuring the pressure in a pillow filled with anti-freeze solution, which is the most common method, or by using a flat plate mounted on weight sensors through which th
24、e mass of accumulated snow can be determined. 7 Operational requirements 7.1 General Snow mass registration devices should be as large as possible to optimise the accuracy of the measurement. The most common areas are between 2 m 2and 15 m 2 . The measuring device should be installed horizontally on
25、 a stable foundation. The top surface should be at the same level as the surrounding ground to minimize the effects of shear perimeter stress concentrations. To reduce environmental effects that cause SWE measurement errors the instrument should have low compressibility and a thermal conductivity si
26、milar to that of the surrounding soil (see 12.2). It is recommended to imitate the properties of the surrounding ground using a permanent cover of, for example, camouflage netting or synthetic grass. This may also prevent snow blowing off the instrument following moderate snow falls. The disturbance
27、 of snow accumulation at the measuring site due the measuring equipment should be minimized. The site should be well drained. Water should not be allowed to collect on the device. The equipment should be protected against interference by animals or unauthorized persons. If necessary, the installatio
28、n could be protected by a fence, but it should not interfere with the accumulation and the ablation of the snow. To be able to locate the exact position of the measuring device, it can be marked with reference poles of sufficient height to be seen above the snowpack at the expected maximum snow heig
29、ht. 7.2 Site selection Detailed site investigations are required to select a representative location. To prevent the snow on the ground from being considerably influenced by the wind, a location surrounded by bush vegetation or a clearing in an open forest is preferable. Wind exposed areas should be
30、 avoided, as well as pronounced recessions in the terrain. PD CEN/TR 15996:2010 CEN/TR 15996:2010 (E) 7 The site selected should be a considerable distance from larger trees, rock outcrops and buildings which could disturb natural accumulation and melting of the snow. An ideal distance between the i
31、nstrument and the nearest obstacle is between 2/3 and three times the height of the obstacle. The slope of the surrounding terrain should be such as to minimize the affect of snow creep on the measuring site. Locations should be selected in order to avoid the risk of rising water levels affecting th
32、e installation. The soil should allow good natural drainage. Snow mass registration devices are preferably located at, or close to, a climate station, since meteorological parameters are important for evaluation and validation of SWE measurements. If the equipment on the site has to be supplemented
33、with external power an accumulator can be used, recharged by a solar panel. In this case, sun conditions have to be considered. 7.3 Validation Rapid and unexpected changes in the monitored SWE might be a result of snow metamorphoses, formation or break up of snow bridges, or shear stress concentrati
34、ons along the perimeter of the measuring device (see Clauses 11 and 12). It can also be a result of leakage in the pressure system in the snow pillow, or a defective sensor. To be able to detect measurement errors it is necessary to establish a control programme. Regular checks utilizing manual meas
35、urements of the SWE should be performed with samples being taken within a few metres from the instrument. It may be appropriate to undertake frequent manual measurements following the initial installation to ensure the correct performance of the instrument. Annex C summarizes the techniques for manu
36、al measurements. Registration of meteorological parameters such as precipitation, air temperature, wind speed and the temperature of the snow at the surface and slightly above the ground at the site is valuable for checking the accuracy of the monitoring. By use of simple numerical modelling of SWE
37、based on observations of for example precipitation and air temperature, the registration can be evaluated continuously. Additional measurements of snow depth in connection to the SWE recording system can also assess the performance of the SWE measurements. The combination of SWE and snow depth measu
38、rements can be used to derive an estimate of the snow density (Equation (1): m d m kg SWE m kg snow snow 2 3 = (1) A calculated snow density outside typical values can be used as indication of problems with the measurement system. The maximum range for snow densities is between 50 kgm -3to 450 kgm -
39、3 , but typical values of a late winter snow pack is often around 250 kgm -3 to 350 kgm -3 . 7.4 Maintenance In summertime the equipment including all complementary and protective devices on site, should be cleaned and checked and the zero point checked. In addition, the site itself should be inspec
40、ted for changes. New vegetation and obstacles that could have an affect of the measurements should be removed and drainage of the site may have to be improved. PD CEN/TR 15996:2010 CEN/TR 15996:2010 (E) 8 8 Monitoring by hydrostatic pressure measurements 8.1 Description Snow pillows for determinatio
41、n of SWE were developed in the early 1960s. The snow pillow consists of a flat bag completely filled with an anti-freeze fluid. The pillow should have a valve for filling the pillow and removing air bubbles. It can be in various shapes, sizes and materials. The most common snow pillows are circular,
42、 rectangular or hexagonal shaped and made of UV-resistant butyl, neoprene rubber or stainless steel. The surface area of the snow pillow should be sufficiently large to minimize the affects of shear stress along the edges of the pillow or bridging in the snowpack (see Clause 12). Recommendations fro
43、m United States Department of Agriculture (USDA) and Norwegian Water Resources and Energy Directorate (NVE) on the minimum area in relation to the maximum expected SWE is shown in Figure 1. Key Y Area (m 2 ) X SWE (mm) USDA steel pillow USDA butyl pillow - NVE butyl pillow Figure 1 Recommendations o
44、n the minimum area of snow pillows in relation to the maximum expected SWE A snow pillow with a depth of about 10 cm is recommended. This means that a pillow with an area of 3 m 2requires approximately 300 l of fluid. With a good installation, periodical control, and normal use and care, snow pillow
45、s should have a working life in excess of ten years. 8.2 Fluids The snow pillow should be filled with an anti-freeze solution suitable for the minimum temperature expected. It is recommended to use environmental friendly solutions. NOTE Where anti-freeze is used then the compliance to existing natio
46、nal environmental regulations should be adhered to. Table 3 shows the most common anti-freeze mixtures, their freezing point, and their rate of toxicity. PD CEN/TR 15996:2010 CEN/TR 15996:2010 (E) 9 Table 3 Anti-freeze solutions used in snow pillows Solution (50:50 by mass) Freezing point Toxicity e
47、thanol : water - 32 C low propylene glycol : water - 34 C low propylene glycol : ethanol low methanol : water - 54 C high ethylene glycol : methanol - 40 C high ethylene glycol : water - 34 C high The pressure in the fluid corresponds to the weight of snow lying on the pillow and is measured by a pr
48、essure sensor inside the pillow, or in a riser pipe connected to the pillow (see Annex D). The pressure sensor as well as any other equipment in contact with the anti-freeze fluid should be resistant to its corrosive effects. A tracer in the fluid can be used to detect leaks and also to facilitate m
49、anual readings on a riser pipe scale. 8.3 Installation In order to allow the surface of the pillow to level with to the surrounding area the ground should be excavated, or the site should be aggraded with filling material. Care must be taken to ensure that there is nothing that would damage the underside of the pillow. A padding of sand or crushed rock with a maximum particle size of 3 mm is ideal to prot
