Guide to Hydrological Practices, Volume I, Hydrology

296 Pages·2008·3.86 MB·English

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
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VOLUME I
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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 ..................................................................................... I.3-8
3.4.5 Distrometers ......................................................................................................... I.3-8
3.4.6 Acoustic type ........................................................................................................ I.3-9
3.4.7 Methods of recording the data ............................................................................. I.3-9
3.5 Snowfall and hail ................................................................................................................... I.3-9
3.5.1 Depth of snowfall ................................................................................................. I.3-9
3.5.2 Water equivalent of snowfall ................................................................................. I.3-10
3.5.3 Snow cover ........................................................................................................... I.3-10
3.5.4 Hail pads .............................................................................................................. I.3-15
3.6 Rainfall estimation from catchment water balance ................................................................. I.3-15
3.7 Observation of precipitation by radar .................................................................................... I.3-15
3.7.1 Uses of radar in hydrology .................................................................................... I.3-15
3.7.2 The radar–rainfall equation ................................................................................... I.3-15
3.7.3 Factors affecting measurements ............................................................................ I.3-16
3.7.4 Snow and hail ....................................................................................................... I.3-18
3.7.5 Scanning strategy ................................................................................................. I.3-19
3.7.6 Summary of accuracy considerations .................................................................... I.3-19
3.7.7 Doppler radar ....................................................................................................... I.3-19
3.7.8 Multi-parameter radar .......................................................................................... I.3-20
3.8 Ground-based radar and rainfall monitoring techniques ........................................................ I.3-20
3.9 Operational radar networks ................................................................................................... I.3-21
3.10 Dual frequency microwave link attenuation measurements of rainfall .................................... I.3-21
3.11 Observations of rainfall by satellite ........................................................................................ I.3-22
3.11.1 Basics ................................................................................................................... I.3-22
3.11.2 Visible and infra-red .............................................................................................. I.3-22
3.11.3 Passive microwave ................................................................................................ I.3-23
3.11.4 Active microwave (rain radar; Tropical Rainfall Measurement Mission) .................. I.3-24
3.11.5 Summary of accuracy considerations ..................................................................... I.3-25
3.12 Remote-sensing measurements of snow ................................................................................ I.3-25
3.13 Satellite remote-sensing of snow cover .................................................................................. I.3-26
3.14 Operational satellites ............................................................................................................. I.3-27
3.15 Dew ............................................................................................................................. I.3-28
3.16 Sampling for precipitation quality ......................................................................................... I.3-29
3.16.1 Rain and snow collectors ...................................................................................... I.3-29
3.16.2 Dry deposition collection ...................................................................................... I.3-29
3.17 A ssimilation of rainfall into hydrological and hydraulic models: combining and assessing
data from different sources .................................................................................................... I.3-29
3.18 Global Precipitation Climatology Project ............................................................................... I.3-30
References and further reading .......................................................................................................... I.3-30
CONTENTS vii
Page
CHAPTER 4. EVAPORATION, EVAPOTRANSPIRATION AND SOIL MOITURE ................................... I.4-1
4.1 Evaporation, evapotranspiration and interception ................................................................... I.4-1
4.1.1 General ................................................................................................................ I.4-1
4.1.2 Defi nitions ............................................................................................................. I.4-1
4.1.3 Measurement of evaporation ................................................................................ I.4-2
4.1.4 Measurement of evapotranspiration ..................................................................... I.4-6
4.1.5 Remote-sensing measurements of evaporation and evapotranspiration variables .. I.4-7
4.2 Estimating evaporation from free surfaces ............................................................................. I.4-8
4.2.1 General ................................................................................................................ I.4-8
4.2.2 Water budget ....................................................................................................... I.4-8
4.2.3 Energy budget ...................................................................................................... I.4-8
4.2.4 Mass-transfer method ........................................................................................... I.4-10
4.2.5 Combination of aerodynamic and energy-balance methods ................................. I.4-11
4.2.6 Extrapolation from pan measurements ................................................................. I.4-12
4.2.7 Empirical formulae ................................................................................................ I.4-14
4.3 Evapotranspiration from drainage basins ............................................................................... I.4-16
4.3.1 General ................................................................................................................. I.4-16
4.3.2 Water-budget method .......................................................................................... I.4-17
4.3.3 Energy-budget method ........................................................................................ I.4-17
4.3.4 Aerodynamic approach ......................................................................................... I.4-18
4.3.5 Penman–Monteith method ................................................................................... I.4-18
4.3.6 Priestley–Taylor (radiation) method ....................................................................... I.4-19
4.3.7 Complementary method ...................................................................................... I.4-19
4.3.8 Crop coeffi cient and reference evapotranspiration method ................................... I.4-20
4.3.9 Large aperture scintillometer ................................................................................ I.4-20
4.4 Evaporation reduction ........................................................................................................... I.4-20
4.4.1 From free surfaces ................................................................................................ I.4-20
4.4.2 From soil surface ................................................................................................... I.4-21
4.5 Soil moisture measurement ................................................................................................... I.4-21
4.5.1 General ................................................................................................................ I.4-21
4.5.2 Quantitative methods ........................................................................................... I.4-22
4.5.3 Qualitative methods ............................................................................................. I.4-28
4.5.4 Remote-sensing ..................................................................................................... I.4-29
References and further reading .......................................................................................................... I.4-30
CHAPTER 5. SURFACE WATER QUANTITY AND SEDIMENT MEASUREMENT ................................. I.5.1
5.1 Water levels of rivers, lakes and reservoirs .............................................................................. I.5-1
5.1.1 General ................................................................................................................ I.5-1
5.1.2 Gauges for measurement of stage ........................................................................ I.5-1
5.1.3 Procedures for measurement of stage ................................................................... I.5-2
5.1.4 Frequency of stage measurement ......................................................................... I.5-2
5.2 Ice on rivers, lakes and reservoirs ........................................................................................... I.5-3
5.2.1 General ................................................................................................................ I.5-3
5.2.2 Elements of ice regime .......................................................................................... I.5-3
5.2.3 Methods of observation ........................................................................................ I.5-3
5.2.4 Times and frequency of observations .................................................................... I.5-4
5.2.5 Accuracy of measurement .................................................................................... I.5-4
5.3 Discharge measurements and computation ........................................................................... I.5-4
5.3.1 General ................................................................................................................ I.5-4
5.3.2 Measurement of discharge by current meters ....................................................... I.5-4
5.3.3 Measurement of discharge by the fl oat method .................................................... I.5-9
5.3.4 Measurement of discharge by dilution methods ................................................... I.5-10
5.3.5 Computations of discharge by indirect methods ................................................... I.5-12
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5.3.6 Measurement of discharge under diffi cult conditions ............................................ I.5-13
5.3.7 Non-traditional methods of stream gauging ......................................................... I.5-16
5.4 Stream-gauging stations ........................................................................................................ I.5-20
5.4.1 Purpose of stream-gauging stations ...................................................................... I.5-20
5.4.2 Selection of site .................................................................................................... I.5-21
5.4.3 Stage-discharge controls ....................................................................................... I.5-21
5.4.4 Measuring structures ............................................................................................ I.5-21
5.4.5 Stage-discharge relationships ................................................................................ I.5-23
5.4.6 Computation of mean gauge height of a discharge measurement ........................ I.5-24
5.5 Sediment discharge and yield ................................................................................................ I.5-24
5.5.1 General ................................................................................................................ I.5-24
5.5.2 Selection of site .................................................................................................... I.5-25
5.5.3 Measurement of suspended-sediment discharge ................................................... I.5-25
5.5.4 Measurement of bed-material discharge ............................................................... I.5-27
References and further reading .......................................................................................................... I.5-28
CHAPTER 6. GROUNDWATER .......................................................................................................... I.6-1
6.1 General ............................................................................................................................. I.6-1
6.2 Occurrence of groundwater .................................................................................................. I.6-1
6.2.1 Water-bearing geological units ............................................................................. I.6-1
6.2.2 Development of a hydrogeologic framework ........................................................ I.6-2
6.3 Observation wells .................................................................................................................. I.6-5
6.3.1 Installation of observation wells ............................................................................ I.6-5
6.3.2 Testing of observation wells .................................................................................. I.6-11
6.3.3 Sealing and fi lling of abandoned wells .................................................................. I.6-11
6.4 Groundwater-level measurements and observation well networks ......................................... I.6-11
6.4.1 Instruments and methods of observation .............................................................. I.6-11
6.5 Aquifer and confi ning-bed hydraulic properties ..................................................................... I.6-18
6.5.1 Hydraulic parameters ............................................................................................ I.6-18
6.5.2 Overview of common fi eld methods to determine hydraulic parameters ............... I.6-20
6.6 Recharge and discharge, sources and sinks in a groundwater system ..................................... I.6-21
6.6.1 Recharge from precipitation ................................................................................. I.6-22
6.6.2 Groundwater–surface water relationships ............................................................. I.6-22
6.6.3 Well pumpage ...................................................................................................... I.6-23
6.7 Use of data in groundwater models ....................................................................................... I.6-23
6.8 Remote-sensing ..................................................................................................................... I.6-23
References and further reading .......................................................................................................... I.6-24
CHAPTER 7. WATER QUALITY AND AQUATIC ECOSYSTEMS .......................................................... I.7-1
7.1 General ............................................................................................................................. I.7-1
7.2 Specifi c requirements for water-quality monitoring ............................................................... I.7-1
7.2.1 Water-quality parameters ...................................................................................... I.7-1
7.2.2 Surface-water quality ............................................................................................ I.7-1
7.2.3 Precipitation quality .............................................................................................. I.7-3
7.2.4 Groundwater quality ............................................................................................. I.7-4
7.2.5 Sediment quality .................................................................................................. I.7-5
7.3 Sampling methods ................................................................................................................ I.7-5
7.3.1 Types of water samples ......................................................................................... I.7-6
7.3.2 Collecting a representative water sample .............................................................. I.7-6
7.3.3 Sampling for the analysis of water stable isotopes ................................................. I.7-6
7.3.4 Radioactivity measurement ................................................................................... I.7-7
7.3.5 Field sampling equipment and techniques ............................................................. I.7-7