The Hydrological parameters of RAINFALL.pdf

the presentation contains the details about hydrological parameters of rainfall including tests procedures.

1. HYDROLOGICAL
PARAMETER
Rainfall

2. RAINGAUGE
•ARaingaugeisameteorologicaltoolwhichhasbeendesignedto
measuretheamountofrainfallreachingtheground.
•Theraingaugeismadeupofacollectioncontainer,aretaining
container,ameasuringcylinderandislocatedinanopenspace,
whererainfallisunobstructedbysurfaceeffects.
•Rainfallisrecordedastheheightoftheprecipitatedwaterwhich
hasaccumulatedintheretainingcontainer.Thisvalueis
expressedinmm.
•1mmofmeasuredprecipitationisequivalentto1Lofprecipitated
rainwatervolumepermetresquare.
For information about EFFECTIVE RAINFALL:
http://www.fao.org/3/X5560E/x5560e02.htm

3. TYPES OF RAINGAUGES

4. TYPES OF RAINGAUGES
•NON-RECORDINGRAINGAUGE
•Manuallyoperated–dailymeasurementsaretaken
•TippingBucketRaingauge
•Atippingbucketraingaugeconsistsofapairofrainwatercollectingbuckets.Itiscoveredbyafunnel,withan
opencollectorareaatthetopwhereAistheareaofcollection.Thetippingbucketraingaugeisanautomated
rainmeterthatusesa"tippingbucket"mechanismtomeasurerainfall.Itisusedbyprofessionalweathers
services'remoteweatherstations,andisalsopopularandwidelyusedinhomeweatherstations.
https://www.sciencedirect.com/topics/engineering/rain-gauge

5. TYPES OF RAINGAUGES
•Manuallyoperated–dailymeasurementsaretaken
•WeighingPrecipitationGauge
•Aweighingprecipitationgaugeconsistsofreceivingbucket
mountedonaweighingdevice,usuallyamechanical
mechanismsuchasaspring.Therainaccumulatesinthe
container,andtheincreasedweightcompressesthesprings.
Theamountofcompressiongetsmeasuredandusedto
calculatetheweightofthewater.Themeasurementcanbe
recordedmanuallywithapenonadrum,orelectronically
withadata-logger,andsendtothebaseweatherstationvia
landlineorwirelessconnection.Mostmodernsystemsare
alsoself-emptying,reducingtheamountof
maintenancerequiredonthistypeofraingauge.
https://ownyourweather.com/what-is-a-rain-gauge/

6. TYPES OF RAINGAUGES
•RECORDINGRAINGAUGE
•Automaticallyoperated–hourly
(attimesevery15minutes)
measurementsaretaken

7. RAINGAUGES

8. RAINGAUGES

9. FACTORS TO BE CONSIDERED WHILE SITING A
RAINGAUGE

10. GOVERNING FACTORS
•Accessibilitytothesite–(Nonrecording/dailymeasurement)
•Nonrecordingraingauge–wheneasytotakedailymeasurements,humanresources
mobilization
•Recordingraingauge–Siteisnoteasilyaccessible,butregularmeasurements
needed.
•Obstructions
•Obstructionsdeflectrainwater–buildings,trees,shadedplaces,corridorscreatedby
presenceofmanyhighrisebuildings
•Potentialuseoftherainfalldata
•Forfloodanalysis–needrainfalldataevery15minutes
•Forwaterdemandofcrops–needrainfalldataeveryhouratleast
•Forwaterresourcesdevelopment–needweeklyormonthlyrainfalldata

11. GOVERNING FACTORS
•HigherAccuracy
•Dailymeasurementsreliesonhumanresources–onemaymisscollectingthe
data
•Onecanmakeerrorwhilerecordingthedata(nonrecordingraingauge)
•Nearbydisturbingactivities:
•People–temptationtotamperwiththeraingauge
•IrrigationSystemsnearby
•Topography&Landusewithinthestudyarea
•Rainfallpatternsinfluencedbytopography
•Rainfallpatternsalsoinfluencedbylanduseactivities–winddirection

12. ESTIMATING AVERAGE RAINFALL
https://file.scirp.org/Html/5-9402024_43175.htm

13. ARITHMETIC MEAN

14. Limitations of the Arithmetic Mean
•Iftheareaunderstudyhasaflattopographyandlanduseisuniformoverthe
studyarea,thenwecansafelyexpectthattherecordedrainfallvalueswillfal
withinacloserange.

15. Weightage Average –Thiessen Polygon methods
(Graphical)
•WeightageAverage:Byarea
•Thismethodappliestostudyareas
characterizedbychangesintopography&
landuse.
•Itrequiresadensenetworkofraingauge
•Eachraingaugereflectstherainfallpatterns
aroundit,notfortheentirecatchment.

16. Weightage Average –The Method of Isohyets (Graphical)
•Alsoweightedbyarea
•Thismethodappliestostudyareascharacterizedby
changesintopography&landuse.
•Itrequiresadensenetworkofraingauge
•Therainfallrecordedbyeachraingaugeare
interpolatedoverthewholestudyarea.Insodoinga
seriesofisohyets–rainfallofequalintensityare
drawn.Thestudyareaisthensubdividedinto
subareasundertheinfluenceofrespectiveisohyets.
https://www.biologydiscussion.com/hydrology/estimation-of-
the-average-depth-of-rainfall/73328
https://www.yourarticlelibrary.com/water/precipitation/calcula
ting-average-depth-of-precipitation-3-methods/60452

17. GENERATION OF MISSING DATA

18. PRE RAINFALL DATA ANALYSIS
•Priortousingtherainfalldataatagivenstation,thedatahavetobecheckedfor
ContinuityandConsistency.Simplestatisticssuchaslongtermmean,dailymean,long
termmonthly/annualmean(normalprecipitation)arecalculated.
•Anymissingdatacanbegeneratedusingrainfalldatafromnearbyrainfallstations.
•N=Normalannualprecipitation.(Meanof30yearsofannualprecipitationdata)
•Ifthenormalprecipitationsatthedifferentrainfallstationsarewithin10%ofthe
normalprecipitationatthesuspectstation,thesimpleaverage-methodofNormal
Ratiocanbeusedtogeneratethemissingdata,elsetheweightedaveragewillbe
used:

19. NORMAL RATIO METHOD

20. NORMAL RATIO METHOD -Example

21. CHECKING THE RELIABILITY OF A SUSPECT
STATION

22. SUSPECT STATION
•Arainfallstationcanforsomereasonsrecordwrongrainfalldata.
•Thiscanbedetectedwhenanalysisthestatisticalparametersofnearby
otherstations.
•Datafromothernearbystationscanbeusedtocheckwhetherthe
consistency/validityoftherecordedrainfalldatafromthe‘suspect’
station.
•ThemethodisreferredtoastheDoubleMassCurveMethod.

23. The Double Mass Curve Method

24. POTENTIAL REASONS FOR INCONSISTENCY OF RAINFALL DATA RECORDED
•Therainfallstationisdamaged.
•Thereareinterferencesnearby(irrigationsystems,abuildinghas
beenconstructed,oratreeisshadingthestation)
•Otherreasonsmaybeduetoachangeinthelandusepatternofthe
surroundingphysicalenvironment.
•Someonemayhavemovedthestationfromitsoriginalposition.

25. ADDITIONAL READING MATERIALS
•MeasurementofPrecipitation:[http://www.jma.go.jp/jma/jma-eng/jma-
center/ric/Our%20activities/International/CP6-Precipitation.pdf]
•PrecipitationSensors: [https://observator.com/instruments/meteo-and-
hydro/meteorological-products/rain-gauges-precipitation-sensors/]
•Generation of Spatial Variation of Rainfall:
[https://ewater.org.au/archive/crcch/overview/archive/pdfs/working200201.pdf]