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Guide to Hydrological Practices, 6Th Edition, Volume I Guide to Hydrological Practices Volume I Hydrology – From Measurement to Hydrological Information www.wmo.int WMO-No. 168 Guide to Hydrological Practices Volume I Hydrology – From Measurement to Hydrological Information WMO-No. 168 Sixth edition 2008 WMO-No. 168 © World Meteorological Organization, 2008 The right of publication in print, electronic and any other form and in any language is reserved by WMO. Short extracts from WMO publications may be reproduced without authorization, provided that the complete source is clearly indicated. Editorial correspondence and requests to publish, repro- duce or translate this publication in part or in whole should be addressed to: Chairperson, Publications Board World Meteorological Organization (WMO) 7 bis, avenue de la Paix Tel.: +41 (0) 22 730 84 03 P.O. Box No. 2300 Fax: +41 (0) 22 730 80 40 CH-1211 Geneva 2, Switzerland E-mail: [email protected] ISBN 978-92-63-10168-6 NOTE The designations employed in WMO publications and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of the Secretariat of WMO concerning the legal status of any country, territory, city or area, or of its authorities, or concerning the delimitation of its frontiers or boundaries. Opinions expressed in WMO publications are those of the authors and do not necessarily refl ect those of WMO. The mention of specifi c companies or products does not imply that they are endorsed or recommended by WMO in preference to others of a similar nature which are not mentioned or advertised. VOLUME I TABLE FOR NOTING SUPPLEMENTS RECEIVED Inserted Supplement Dated No. by date 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 CONTENTS Page PREFACE ........................................................................................................................................... xiii ACKNOWLEDGEMENTS ................................................................................................................... xv CHAPTER 1. INTRODUCTION .......................................................................................................... I.1-1 1.1 Background ........................................................................................................................... I.1-1 1.2 Scope .................................................................................................................................... I.1-1 1.3 Contents of the Guide ........................................................................................................... I.1-2 1.4 The Hydrological Operational Multipurpose System .............................................................. I.1-4 References and further reading .......................................................................................................... I.1-4 CHAPTER 2. METHODS OF OBSERVATION ...................................................................................... I.2-1 2.1 Introduction – The hydrological cycle as the subject of observation ....................................... I.2-1 2.2 Water resources information systems ..................................................................................... I.2-2 2.2.1 Need for data and information ............................................................................. I.2-2 2.2.2 Hydrological information systems ......................................................................... I.2-3 2.2.3 Uses of water resources information ...................................................................... I.2-5 2.2.4 Types of water resources information .................................................................... I.2-5 2.3 Hydrological symbols, codes and accuracy of measurements ................................................. I.2-7 2.3.1 Units and symbols ................................................................................................ I.2-7 2.3.2 Hydrological codes ............................................................................................... I.2-7 2.3.3 Accuracy of hydrological measurements ............................................................... I.2-12 2.3.4 Calibration of instruments .................................................................................... I.2-17 2.4 Design and evaluation of hydrological networks .................................................................... I.2-18 2.4.1 General concepts of network design ..................................................................... I.2-18 2.4.2 Density of stations for a network ........................................................................... I.2-24 2.4.3 Specifi c requirements for water quality ................................................................. I.2-28 2.4.4 Operational data acquisition networks .................................................................. I.2-34 2.4.5 Network-strategy options ..................................................................................... I.2-34 2.5 Data collection ...................................................................................................................... I.2-35 2.5.1 Site selection ........................................................................................................ I.2-35 2.5.2 Station identifi cation.............................................................................................. I.2-35 2.5.3 Frequency and timing of station visits ................................................................... I.2-39 2.5.4 Maintenance of sites ............................................................................................. I.2-40 2.5.5 Observation .......................................................................................................... I.2-40 2.5.6 Transmission systems ............................................................................................ I.2-43 2.5.7 Water-quality monitoring ...................................................................................... I.2-44 2.5.8 Special data collection .......................................................................................... I.2-46 2.6 Measurement of physiographic characteristics ....................................................................... I.2-47 2.6.1 General ................................................................................................................ I.2-47 2.6.2 Reference systems and data frameworks ............................................................... I.2-47 2.6.3 Point measurements ............................................................................................. I.2-48 2.6.4 Linear measurements ............................................................................................ I.2-49 2.6.5 Area measurements ............................................................................................... I.2-52 2.6.6 Volumetric measurements ..................................................................................... I.2-55 2.6.7 Geographical Information Systems ....................................................................... I.2-55 2.6.8 Emerging technologies ......................................................................................... I.2-56 2.6.9 Staff training ......................................................................................................... I.2-57 References and further reading .......................................................................................................... I.2-58 vi GUIDE TO HYDROLOGICAL PRACTICES Page CHAPTER 3. PRECIPITATION MEASUREMENT ................................................................................. I.3-1 3.1 General requirements: accuracy and precision ....................................................................... I.3-1 3.2 Raingauge location ................................................................................................................ I.3-1 3.3 Non-recording raingauges .................................................................................................... I.3-3 3.3.1 General ................................................................................................................ I.3-3 3.3.2 Standard raingauges ............................................................................................. I.3-3 3.3.3 Storage raingauges ............................................................................................... I.3-3 3.3.4 Methods of measurement ..................................................................................... I.3-4 3.3.5 Errors and accuracy of readings ............................................................................ I.3-4 3.3.6 Correction of systematic errors .............................................................................. I.3-5 3.4 Recording raingauges ............................................................................................................ I.3-7 3.4.1 Weighing–recording gauge .................................................................................. I.3-7 3.4.2 Float gauge .......................................................................................................... I.3-7 3.4.3 Tipping-bucket gauge .......................................................................................... I.3-8 3.4.4 Rainfall-intensity recorder ....................................................................................
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