1、PD CEN/TR15996:2010ICS 07.060NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWPUBLISHED DOCUMENTHydrometry Measurement of snowwater equivalent usingsnow mass registrationdevicesThis Published Documentwas published under theauthority of the StandardsPolicy and StrategyCommittee o
2、n 31 March2010 BSI 2010ISBN 978 0 580 68499 9Amendments/corrigenda issued since publicationDate CommentsPD CEN/TR 15996:2010National forewordThis Published Document is the UK implementation of CEN/TR15996:2010.The UK participation in its preparation was entrusted to TechnicalCommittee CPI/113, Hydro
3、metry.A list of organizations represented on this committee can be obtained onrequest to its secretary.This publication does not purport to include all the necessary provisionsof a contract. Users are responsible for its correct application.Compliance with a British Standard cannot confer immunityfr
4、om 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 en eau de la neige au moyen
5、 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 Committee CEN/TC 318. CEN members ar
6、e 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, Slovakia, Slovenia, Spain, Swede
7、n, 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 for CEN national Members. R
8、ef. No. CEN/TR 15996:2010: EPD CEN/TR 15996:2010CEN/TR 15996:2010 (E) 2 Contents Page Foreword 3Introduction .41 Scope 52 Normative references 53 Terms and definitions .54 Symbols and abbreviated terms 55 Purpose of method 66 Principle 67 Operational requirements .68 Monitoring by hydrostatic pressu
9、re measurements 89 Monitoring by weight measurements . 1010 Data collection, transfer and processing . 1011 Factors affecting accuracy of stationary point measurements of SWE . 1012 Factors affecting accuracy of snow mass monitoring specifically . 1113 Evaluation of method . 12Annex A (informative)
10、List of methods for determination of SWE in total snowpack 13Annex B (informative) Snow mass registration stations networks 14Annex C (informative) Manual SWE measurements . 16Annex D (informative) Snow pillow 17Annex E (informative) Snow plate 19Bibliography . 21PD CEN/TR 15996:2010CEN/TR 15996:201
11、0 (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 subject of patent rights. CEN and/or CENELEC shall
12、 not be held responsible for identifying any or all such patent rights. PD CEN/TR 15996:2010CEN/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 melting the snowpack on a corresponding surface area,
13、 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 proportionally represent the total SWE in the studied area. Th
14、e 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 calibration using in-situ measurements. Annex A is a
15、 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 the technique, but improvements in equipment design
16、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 15996:2010CEN/TR 15996:2010 (E) 5 1 Scope This Technical Report defines the requirements for the use of snow mass registration dev
17、ices 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 references, only the edition cited applies. For undated
18、 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 25377:2007) 3 Terms and definitions For the purposes of th
19、is 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/m3V Volume m3A Area m2Table 2 lists the abbreviated terms us
20、ed in this document. Table 2 Abbreviated terms Abbreviation Term SPA Snow Pack Analyzer GPR Ground-penetrating radar PVC Polyvinyl chloride PD CEN/TR 15996:2010CEN/TR 15996:2010 (E) 6 5 Purpose of method The use of snow mass registration devices provides stationary single point measurements of the t
21、otal 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 terrain, the data obtained by this method can be used for the
22、 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 snow on top of a measuring device is equivalent to the mass
23、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 the mass of accumulated snow can be determined. 7 Operationa
24、l 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 m2and 15 m2. The measuring device should be installed horizontally on a stable foundation. The top surface should be at the same l
25、evel 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 similar to that of the surrounding soil (see 12.2). It is recom
26、mended 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 of snow accumulation at the measuring site due the measuring
27、 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 installation could be protected by a fence, but it should not interfere
28、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 height. 7.2 Site selection Detailed site investigations are requi
29、red 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 avoided, as well as pronounced recessions in the terrain. PD
30、 CEN/TR 15996:2010CEN/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 instrument and the nearest obstacle is between 2/3 and three ti
31、mes 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 the installation. The soil should allow good natural drainage. S
32、now 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 with external power an accumulator can be used, recharged by a
33、 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 concentrations along the perimeter of the measuring device (see Clauses 1
34、1 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 measurements of the SWE should be performed with samples being tak
35、en 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 manual measurements. Registration of meteorological parameters suc
36、h 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 based on observations of for example precipitation and air tem
37、perature, 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 measurements can be used to derive an estimate of the snow density
38、(Equation (1): mdmkgSWEmkgsnowsnow23= (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-3, but typical values of a late winter snow pack is often around 250 kgm-3
39、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 inspected for changes. New vegetation and obstacles that could have an affect of the
40、measurements should be removed and drainage of the site may have to be improved. PD CEN/TR 15996:2010CEN/TR 15996:2010 (E) 8 8 Monitoring by hydrostatic pressure measurements 8.1 Description Snow pillows for determination of SWE were developed in the early 1960s. The snow pillow consists of a flat b
41、ag 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, rectangular or hexagonal shaped and made of UV-resistant butyl, neoprene rubber
42、 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 from United States Department of Agriculture (USDA) and Norwegian Water Resources a
43、nd Energy Directorate (NVE) on the minimum area in relation to the maximum expected SWE is shown in Figure 1. Key Y Area (m2) X SWE (mm) USDA steel pillow USDA butyl pillow - NVE butyl pillow Figure 1 Recommendations on the minimum area of snow pillows in relation to the maximum expected SWE A snow
44、pillow with a depth of about 10 cm is recommended. This means that a pillow with an area of 3 m2requires approximately 300 l of fluid. With a good installation, periodical control, and normal use and care, snow pillows should have a working life in excess of ten years. 8.2 Fluids The snow pillow sho
45、uld 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 national environmental regulations should be adhered to. Table 3 shows the most common a
46、nti-freeze mixtures, their freezing point, and their rate of toxicity. PD CEN/TR 15996:2010CEN/TR 15996:2010 (E) 9 Table 3 Anti-freeze solutions used in snow pillows Solution (50:50 by mass) Freezing point Toxicity ethanol : water - 32 C low propylene glycol : water - 34 C low propylene glycol : eth
47、anol lowmethanol : 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 pressure sensor inside the pillow, or in a riser pipe connected to the pillow (see Anne
48、x 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 manual readings on a riser pipe scale. 8.3 Installation In order to allow the surface
49、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 protect the pillow. Local material may be used provided that the material has full contact with the bottom
