This document provides an overview of a hydrometry course covering measurement of various components of the hydrological cycle including precipitation, evaporation, soil moisture, and streamflow. It discusses different types of instruments used to measure these variables such as raingauges, evaporation pans, neutron probes, tensiometers, and current meters. Measurement methods include manual observation as well as automated data recording using devices like data loggers. The goal is to introduce concepts and terminology for quantifying water in the hydrological cycle.

1. Hydrology 220: HydrometryHydrological Measurement, Instrumentation and NetworksMark HoranRoom 341

2. Hydrometry Course 4 Lectures 1 Practical

3. Lecture 1: Basics and Introduction

4. Lecture 2: Measurement of Rainfall

5. Lecture 2:Measurement of Interception and Evaporation

6. Lecture 3: Measurement of Soil Moisture

7. Lecture 3: Measurement of Streamflow

8. Lecture 4: Hydrological Network Design

9. Lecture 4: Hydrological Network Design cont.Hydrologic CycleComponentsPrecipitationEvaporationTranspirationStorage-surfaceInfiltrationStorage - SubsurfaceRunoffWater MovementStreamflowStorage-ReservoirsIntroduce basic terminology and concepts of measurement of the hydrological cycle.

10. What are the sources of water for a watershed?

11. Where does all the water go?Water Balance Equation in a CatchmentP - Q - G - ET - S = 0P = PrecipitationQ = Stream dischargeG = Groundwater DischargeET = Evapo-transpirationS = Change in Storage

12. Why MeasurePredict impacts from prior knowledge or experienceInfer impacts from evidence collectedExperimentally investigate impact of certain activities

13. Observations and variablesVariablecharacteristic measured for each sampling unit, e.g. [P]more than one variable can be measured for each sampling unit, e.g. [P], [T], Wind etc.Observationsvalue of a variable for each sampling unit e.g. [P]

14. Types of variablesContinuous:can take any value between fixed limitslength, weight, concentration etc.Discrete or categorical:can only take certain, usually integer, valuescounts, presence/absence, alive/dead etc.

15. Types of variablesRanked:not measured but ranked (often subjectively) by their magnitudee.g. degree of damage from none to highAttributes:qualitative variables with no magnitude scalee.g. position

16. Derived variablesRatios:relation between two variables expressed as single value, e.g. C / N ratioRates:change in variable per unit time, e.g. m3.s-1Others:species diversity, indices of health/integrity

17. Statistics and parametersSample statistics estimate population parametersCentral (middle) value:mean, median, modeSpread (variability) of values:variance, standard deviationStandardised spread:coefficient of variation

18. Accuracy and precisionAccuracy:closeness of measurements to true valuePrecision:closeness of measurements to each otherHigh precision usually means high accuracyunless measuring device is biasedFocus on precision

19. Sources of uncertaintyMeasurement error:difference between two measurements due to measuring device, human error etc.Sampling error:difference between two measurements due to natural variabilityNeed for replicate measurements

20. Recording of DataPaper ChartsData LoggersTelemetry.

21. Recording of DataPaper ChartsSimplest methodChart moved by spring or electronically driven clock past penPen moves with weight/float etcTwo TypesDrum - rotatesStrip - moves past penCharts then “digitised”

23. Recording of DataData LoggersA data logger is a computer that records and stores data from sensors both analog (voltage) and digital(counts). The data logger can also be used as a controller to turn on and off electricalThe data logger requires a program to tell it what to do. Preloaded computer chip that already has the program in it or create the programData can then be accessed by a computer to monitor current conditions or download stored data.

25. Recording of DataData LoggersProblemsVandalism due to desirability of batteries

26. Recording of DataTelemetryData stored by logger can transferred directly to a base station via some form of telecommunication

27. Hydrology 220: HydrometryLecture 2Measurement of Precipitation

28. Types of PrecipitationRainfallHailSnow and Ice

29. Measurement of Precipitationmagnitude, intensity, location, patterns of precipitationquantity of precipitation as well as, the spatial and temporal distributions of the precipitation have considerable effects on the hydrologic response.Measurement byRaingaugeRADARSatellite

30. RaingaugesThe purpose of a rain gauge is to measure the amount of rainfall at a single pointMeasure What?Depth of water on a flat surfaceDepth is assumed to be same as surrounds

31. Raingauges With What?Container of varying dimensions and heightsSA Standard127mm diameter (5 inches)1.2 m height above ground (4 feet)RequirementsSharp edgeRim falls away verticallyPrevent splashingNarrow neck prevents evaporation

32. Image here

33. RaingaugesNon-recording and recording rain gaugesA non-recording rain gauge is typically a catchment device calibrated to provide visual observation of rainfall amounts. Recording gauges are equipped with paper charts and/or data logger equipment.

34. Non-recording RaingaugesMeasure with calibrated flask or dipstickFlask usually tapered to allow accuracy if little rainIn SA - manual daily observation at 08h00Storage gauges in remote areasEvaporation losses highPrevention byoil filmsmall exposed surface areapoor ventilationlow internal temperature

35. Two types of standard storage raingauge

36. Recording RaingaugesAnalogue DevicesWeighing Bucket Rain GaugeFloat Type Rain GaugeDigital DevicesTipping Bucket Rain GaugeOptical Rain Gauge

37. Analogue Recording RaingaugesWeighing Bucket Rain GaugeStandard instrument used to quantify rainfall. Spring scale beneath the collecting bucket platform that is calibrated to mark the rainfall depth on a paper chart. The chart is rotated by a spring-driven or electric clock at speeds of 1 revolution in 6, 9, 12, 24, or 192 hours. The rain gauge chart is a record of the accumulated of rainfall for the selected time interval.

38. Analogue Recording RaingaugesFloat Type Rain GaugeStandard instrument used to quantify rainfall. Float within collecting bucket rises with levelVertical movement marked by pen and shows rainfall depth on a paper chart.The chart is rotated by a spring-driven or electric clock at speeds of 1 revolution in 6, 9, 12, 24, or 192 hours.The rain gauge chart is a record of the accumulated of rainfall for the selected time interval.

39. Analogue Recording RaingaugesFloat Type Rain Gauge with SiphonStandard instrument used to quantify rainfall. Usually with Float Type Rain GaugesSystem siphons itself at a certain level (typically 25mm) Empties container completelyStores siphoned water in separate (total) containerTotal container as checkPen returns to bottom lineProblems15 seconds to siphonFreezesDigitising

41. Digital Recording RaingaugesTipping Bucket Rain GaugeTwo containers on balance beam form a “tipping bucket”Rain fills one container until it threshold weight reachedBucket then tips over, emptying collected water into total container and continues to collect rainfall in other containerMagnet generates electric pulse which is recordedProblemsEvaporation from bucketsDiscontinuous record in light rainSusceptible to freezing

46. Digital Recording RaingaugesOptical Rain Gauge (ORG)The ORG is mounted on a small poleThe ORG sends a beam of light (which you cannot see) from one of its ends to a detector at the other end. When raindrops fall, they break the beam. The rain rate is measured by the ORG by measuring how often the beam is broken. The rain rate can be used to calculate the total amount of rain that has fallen in any given period ORG measures the rate of rainfall in millimeters per hour (mm/hr).

48. Measured Gauge Accuracy(Un)avoidable ErrorsEquipment failureObserver error Avoidable ErrorsSiteAspect - parallel to groundObstructionsHeight - splashingSurroundsWind

49. Ideally, the gauge should be sited with some shelter, but not over-sheltered. Windshields may reduce the loss due to turbulence (eddies) around the gauge

50. Measured Gauge AccuracyCommon ErrorsEvaporation - 1%Adhesion - 0.5%Inclination - 0.5%Splash +1%Wind -5-8%

51. Measured Gauge AccuracyTwo problems arise in quantifying precipitation input to a given land area: how to measure precipitation at one or more points in space how to extrapolate these point measurements to determine the total amount of water delivered to a particular land area.

52. Rainfall SurfacesIf precipitation gauge data is used, then the MAP's are usually calculated by a weighting scheme. A gauge (or set of gauges) has influence over an area and the amount of rain having been recorded at a particular gauge (or set of gauges) is assigned to an area. Thiessen method and the isohyetal method are two of the more popular methods.

53. ThiessenThiessen methodis a method for areally weighting rainfall through graphical means.IsohyetalIsohyetal methodis a method for areally weighting rainfall using contours of equal rainfall (isohyets).RADAR MeasurementsWeather radar has become an increasingly important tool for estimating the spatial distribution of rainfall

55. RADAR MeasurementsRaindrops in the atmosphere and the characteristics of the reflected signal(Z) can be related to rainfall rates (R). Most common is Marshall-Palmer relationshipRadar is far from an absolutely accurate measurement methodProvides detailed information on the time and space distribution of rain and can be particularly valuable for heavy rainfall.

58. Liebenbergsvlei Hydrometeorological Network

59. EvaporationDirect measurement from large surfaces (land & water) not possible at present

60. can do water budget or use indirect methods

61. evaporation pans

62. lysimetersEvaporation Pansdifferent sections, square, round etc.different positions, on ground, above ground, sunken & floatingMost common types in SAA-PanS-Pan (Symons - British Standard)Pan coefficient used to relate measured evaporation to free water surface as measured evap. often far greater than actuale.g. 0.7 for S-Pan on annual basis

64. Evaporation PansUS Class A-PanStandard instrument used to measure evaporation. Diameter = 1210 mmdepth = 255 mmUsually set on 150 mm high baseallows circulation of airMust be levelWater level maintained 50mm below rimMeasure withpoint gauge & still wellgraduated cylinderstaff

66. Example of A-Pan Setup"US class A" pan is used to measure the rate of evaporation. A hook gauge is used to measure the water level inside the pan and A cup anemometer is placed beside the pan to measure the surface wind movement over it

67. Evaporation PansSymons pan

68. Galvanised iron

69. Square of 1830mm

70. 610mm deep

71. Set in ground

72. rim 100mm above ground

73. level free of obstructions

74. natural vegetation surrounds (not tar etc)

75. no shadows on pan

76. fenced, bur not obstructed..protect from birds & animals - chemical or wire mesh

78. LysimeterA device to measure the quantity or rate of downward water movement through a block of soil usually undisturbed, or to collect such percolated water for analysis as to quality. Defined as:A small unit of soil on which water balance values can be obtained.Lysimeters account for change in water storage

79. i.e. Measure actual evapotranspirationLysimetersLarge block of undisturbed soil + vegetation surrounded by watertight container installed in ground

80. Weighing base to quantify water movement through soil

81. Precipitation controlled and known

82. E=Ppt - percolation through the lysimeterPrinciples of a LysimeterA tank filled with soil is weighted on a scale.The difference in weight between the beginning and the end of the day indicates how much water was lost during the day, or, how much water the crop used.At midnight (or some standard time)water tank below the lysimeter is filled with water that can be used for irrigation during the day. ie no weight change as a result of irrigation during the day.

84. Soil WaterSoil-Water Contentamount of water in the soil (volumetric and gravimetric) - quantativeSoil-Water Potentialthe availability of the water to plants (largely qualitative)Methods of soil water content measurement include direct measurement by gravimetric methods (oven or microwave drying)indirect measurements by neutron probes, capacitance probes, time domain reflectometry (TDR), tensiometers, etc.)

87. Soil WaterTime Domain Reflectometry (TDR)TDR measures the transit time, t, for a pulse to travel between the wave guides; the greater the dielectric constant (Ka) of the surrounding medium, the longer the pulse travels through the guides.

88. In a soil system, Ka is predominantly determined by liquid water. Thus, volumetric water content can be correlated to Ka through some calibration equations:Advantages and disadvantagesEasy to be automated to make continuous observations

89. Does not work well in soils with high clay content and/or EC equipment cost is very high

90. Relatively expensive

91. Soil WaterNeutron ProbeA radioactive source emits fast and slow neutrons

92. The fast neutrons collide with elements and slow down

93. Of all the elements, H (Hydrogen) in water is the most effective in slowing down fast neutrons

94. A detector counts the number of slow neutrons returned to the source

95. A calibration curve or equation relates neutron count to water content

96. Advantages and disadvantages

97. It measures a sphere of about 30 cm in diameter