इंटरनेट मानक Disclosure to Promote the Right To Information Whereas the Parliament of India has set out to provide a practical regime of right to information for citizens to secure access to information under the control of public authorities, in order to promote transparency and accountability in the working of every public authority, and whereas the attached publication of the Bureau of Indian Standards is of particular interest to the public, particularly disadvantaged communities and those engaged in the pursuit of education and knowledge, the attached public safety standard is made available to promote the timely dissemination of this information in an accurate manner to the public. “जान1 का अ+धकार, जी1 का अ+धकार” “प0रा1 को छोड न’ 5 तरफ” Mazdoor Kisan Shakti Sangathan Jawaharlal Nehru “The Right to Information, The Right to Live” “Step Out From the Old to the New” IS 15122 (2002): Measurement of Liquid Flow in Open Channels Under Tidal Conditions [WRD 1: Hydrometry] “!ान $ एक न’ भारत का +नम-ण” Satyanarayan Gangaram Pitroda ““IInnvveenntt aa NNeeww IInnddiiaa UUssiinngg KKnnoowwlleeddggee”” “!ान एक ऐसा खजाना > जो कभी च0राया नहB जा सकता हहहहै””ै” Bhartṛhari—Nītiśatakam “Knowledge is such a treasure which cannot be stolen” IS 15122 : 2002 ISO 2425 : 1999 ~ liFtCf} ~ ~Ei~i -q em MCiI • llTtr=r Indian Standard MEASUREMENT OF LIQUID FLOW IN OPEN CHANNELS UNDER TIDAL CONDITIONS ICS 17.120.20 OBIS 2002 BUREAU OF INDIAN STANDARDS- MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG NEW 'DELHI 110002 April- 2002 IS 1&122: 2002 ISO ~426: 1999 AMENDMENTl Page2,Subclause4.3.1 Add the following textat the end ofthe subclause: "Thisvalue, whenusedin conjunctionwiththe cross-sectional~will pro~deanestimateofthe flow in the channel. Page2,Subclause4.3.2 Replace the last sentence withthe following: "Aftercalibration, measurementsofelectricalparametersand waterdq)th provide a meansofestimating the discharge". PageJ, Subclause5.Jc) In the first line, replace "usually" with "could". Page3, Subclause5.2.1 Replacethe penultimate sentencewith the following: "Under variable or unsteady conditioas, the frequency of measurement, although affecting the operationalcost ofeach gaugingstationand importanteconomically,maynotbecompromised". Page3, Subclause5.2.2a) Replace"tidalrange" with "tidal rangeincludinglevel,flow,and velocity" Page4, Subclause5.2.2f) Replacethis subclause withthe following: "f) change in flow direction duringa tidal cycle includingflowreversalor backwatereffects" Fluid Flow Measurement Sectional Committee, WRD 01 NATIONAL FOREWORD This Indian Standard which is identical with ISO 2425 : 1999 'Measurement of liquid flow in open channels under tidal conditions' issued by the International Organization for Standardization ( ISO ) was adoptedby theBureauof IndianStandardsonthe recommendationsofthe Fluid FlowMeasurement Sectional Committee ( WRD 01 ) and approval"of the Water Resources Division Council. Inthe adoptedstandard,certainconventionsare, however. notidenticaltothose usedin IndianStandards. Attention is especi~lIy drawn to the following: . a) Whereverthe words 'International Standard' appear referring to this standard, they should be read as 'Indian Standard'. b) Comma( ,) has been usedas a decimal markerwhile in IndianStandards,thecurrentpractice is to use a point ( . ) as the decimal marker. Amendment No.1 to the above International Standard has been printed at the end. CROSS REFERENCES In thls adopted standard, the following International Standards have been referred. Read in their respective places, the follOWing Indian Standards: International Standard Corresponding Indian Standard Degree of Equivalence ISO 748 : 1997 Measurement IS 1192 : 1981 Velocity-area Identicalwith elucidation in Indian of liquid flow in open methods for measurement of Standard ( IS 1192: 1981 isunder channels - Velocity-area flow of water in open channels revision basedon ISO 748: 1997 methods ( first revision ) 'Measurementofliquidflowinopen channels Velocity-area metnods' ) ISO 772 : 1996 Hydrometric IS 1191 : 1971 Glo~sary of Technically equivalent ( IS 1191 : determinations - Vocabulary terms and symbols used in 1971 is underrevision based on and symbols connection with the measure ISO 772 : 1996 'Hydrometric ment of liquid flow with a free determinations- Vocabularyand surface ( first revision ) symbols' ) REFERENCES TO ERRORS AND CLARIFICATIONS IN TEXT The TechnicalCommitteewhileadoptingthe textof this InternationalStandard identifiedcertaintextual errors to the following clauses and felt necessary to correct/clarify these in the Indian context: Clause Reference Corrections/Clarification 6.1.1.3.1(I) Where oblique flow is unavoidable, the angle between the direction of flow and the line normal to the cross-section shall be measured and the measured velocitycorrected. Special instrumentsare availableformeasuring b9th angle and velocity at a point simultaneously. IS 15'12-2-: 2002 ISO 2425-: 1999- Indian Standard .MEASUREMENT OF LIQUID FLOW IN OPEN CHANNELS UNDER TIDAL CONDITIONS 1 -Scope This Intemational Standard provides a summary of a selection of recommended methods available for the measurement of liquid flow in tidal channels. special consideration being given to those techniques that are either uniqueto or particularly appropriatefor measurement undertidal conditions, includingtreatmentof errors. Reference is also made, where appropriate, to methods developed for measurement in non-tidal channels, but in such cases attention is drawnto theirlimitationswith respectto practicalityand/oraccuracy. This Intemational Standard does not describe altemative-methods, such as weirs, flumes, dilution gauging, salt velocity and floats, although they may be suitable undercertain conditions, es~iallywhere the effect of tides only impedes and does not stop or reverse the passage of stream flow. These methods are described in detail in other International Standards. The standardcomprisestwo parts: a) techniquesforsingle measurements of tidal flow; b) techniques appropriatefor continuous measurementof tidal flow. The cubature method of measurement, although currently not used, is included in annex A. Annex B presents methods suifable for measurement for tidal conditions, and annex C gives an example of the computation for a single vertical. Similarcomputations may be made for otherverticals. 2 Normative references The following normative documents contain provisions which, through reference in this text, constitute provisions of this International Standard. For dated references, subsequent amendments to, or revisions of. any of these publications do not apply. However,.parties to agreements based on this Intemational Standard are encouraged to investigate the-possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest edition of the normative document referred to applies. Members of ISO and lEe rnai·ntain registers-ofcurrenttyvalid"lntemational Standards. ISO 748:1997, Measurementofliquidflow inopenchannels- Velocity-area methods. ISO 772:1996, Hydrometricdeterminations - Vocabularyandsymbols. 3 Terms_and defin:tions Forthepurpos-es-of!hi.s-InIem-&"·U~J"IC'Il-Standard,etherrtnsand ~;.,;._"._---_::::..~:_-_.:.:: :"':~;-'--".-:":' "';:-;;".::j'. 1 IS.-: ~:t.122 ~" 2002~:~; ISO··.··242&.1;~189~'~ .: -_ '._' ~•. _~._:~~..c•._._r-'.Jo,.......... 4 Principles of methods of.meaurement 4.1 General Tidal-flow rneasur~~ntcan be an instantaneous rate of.flow or a total.volume of flow during a flood or ebb tide. The unsteady natUrJI·arld..~C~ ~iRr~~ioft ~f·ftoW:~.ui1der tidal 'c~difl9"S'~te..pr~· of measurement additional to those ~..~~.~~ ,.measurement 01_ the discha,ge of unidirectional streams. The methods specified in ISO 748,~·lSO'1.100•.ISO;,4S69,ISO 9123;.J8O 9823and ISO .9825 cannot-therefore always be applied to tidal channels. Anychange in waterquality brought aboutby tidal conditions may affect the methods specified in ISO 6416and ISO 9213. . Forvarious reasons, dlr.measurements of velocityin tidal channels are more liableto large errors than are those madeunderconditionsof unidirectionalflow. . The methods of measu'rement included in this International Standard may be grouped into either single or continuousmeasurementS. measurement 4.2 Single methods 4.2.1 Velocltj-a....methOd At a chosen gauging site, the velocity of flow and the area of cross-section of the channel are measured. The productofthese measureme~at·anyinstant is the rate of flow ordischargepastthe gauging site at thatinstant. It is referredto'astheVelocity-Areamethodandincludesthefollowing techniques: a) eurrentmeterfrom a fixed station; b) Current meterfrom a moving station (movingboat). 4.2.2 Cubaturemethod In an areawhich includesa stretchof riverchannel and its flood plain, surfaceareas and rise in waterlevel of stored waterare measured at known time intervals. Volumes of stored waterare computed, and the flow into the upstream stretch of riverisestimated, fromwhichthe average rate of flow is determined (see annexA). 4.3 Continuous measurementmethods 4.3.1 UltrasonicmethOd (ISO6416) Transducers are positioned on each bank of the river channel, such that the flight path is at an oblique angle to the direction of flow. The time taken for a pulse of sound to travel in both directions is measured andcompared. From thesetwotimes, the meanvelocitycan becomput~d. 4.3.2 .~omagnetlc method (ISO 9213) A ~ontal.-coil.is'constructed" above.or.below a riv~r channel. A magnetic fieJd is generated by an alternating curret:'! and··voltages are induced in the fJowi~g water which acts as an'electrical conductor. After. calibration, rne~urementsofelectricalparametersand'waterdepthprovidea meansof measuringthedischarge. 4.3.3 Unateady-flowmodels Unsteady-flow modelsmay be used for computi~g contin.~ou~ recoros of discharge in open c~a~nelsin bot~ tidal and non-tidal conditions. These models, however, are not appncable where'aIongitudiilal density gradient. such as a salt-waterwedge, ispresent. Unsteady...fIow ~ are.·based on the numerical solution ofnon-linear partial differential equation$ that describe one gradually varied unsteady flow in open channels. The available models enlploy or:"moM of·SeVeral·rlumerical computation techniques. Data requirements, which can be substa.ntiaf,·.depend on the..nUmerical techniques employedby the moderseleCted.·It'·is·A8C8$eary-that·t8e~·fOr-the·appticatioA~Qf-unsteady-ftow·modets andthe datarequire~~be.clearty definedandunderstood·f orsuccessfullycomputingdischarges. -~is ---'.15-122 : 2002 ''SO' 2425-: 1999 5 Special considerations and choice of method--- 5.1 Special considerations ·Changes in waterlevel at the mouth of a riverdueto tidal actioncause backwatereffects in thechannel. These may alterwater level only, orboth water level and direction of flow. The whole flow may be reversed in direction, oronly someof theflow maybe reversed dueto differences in density. Most flow-gauging techniques are generally best suited to condinons closely approximating steady flow, but unsteadyflowcauses additional difficulties as follows. a) At anysection, waterlevelscontinuouslychange; b) at anypointon a vertical, velocities continuouslychange eitherwith orwithoutchange in direction; c) in any vertical, the continuously changing velocities usually create greater velocity gradients than in channels with steady uniformflow; d) during the period of transition in flow direction (flood to ebb or ebb to flood), zero velocity occurs at a succession of points oyerthe changing velocity profile; e) high waterand low watermaynottake placeat the sametime as the reversal in flowdirection; f) the change in direction of flow does nottake place at the same time throughoutthewettedcross-section; g) when the direction of flow changes, the characteristics of the approach conditions from the upstream and the downstream maybe differentand may result in divergence (whenthe angle between the flood andthe ebbflow is otherthan 180°) between theflood and ebbflow; h) flow maybe stratified, with liquids of different densities in each layer. While the liquid in the upperstratum may flow in one direction, the more dense liquid in the lower stratum may flow at a different speed in the same or opposite direction. When such density difference due to a salt water wedge occurs, the maximum velocity in each layermayoccurat differenttimes; i) at anysection in a channel, variations in waterlevel maycausechanges in width andcross-section of flow; j) anincrease in the numberof measurements required to make an estimateof discharge; k)' during atidalcyclethere maybe'vananons in salinityleadingtochanges in thespeed of sound andconductivity of thewater, andthese mayadverselyaffect ultrasonic and electromagneticmethods. 5.2 Choice of method 5.2.1 General In channels with steady flow, one of the main factors affecting the choice of gauging method is the frequency of measurements of discharge in the channel. Observations may be repeated over months or years (continual or repeatedmeasurements)-, oroccasionally, often once only--(occasionalmeasurements). Undervariable or unsteady conditions, the frequency of measurement.--afthough affectingthe cost ofeach gauging and importanteconomically, may notbecompromised. Thephysical-conditionsofflowand waterwa·y dominatethe choice. - 5.2.2 Physicalconditions Thephysicalconditions whichaffectthechoice of gauging method are: a) ..~al ~ng_e;, b) -_width of channel; -. ~:.;_~.··1.',a;~;::2102 .-.~.:~ a.2~.:.'~- c) .variationinwidth·aIong.. channelandwith time; . d) depthofchannel; e) shapeofchannel; f) changeinflow directionduringebbtide·orfIood··tide; g) densityofrivertraffic; h) the numberof·experiencedstaffavailable; i) the numberofboatsand gaugingequipmentavailable; j) environmentalconsiderations; k) the intNsion of asalt-waterwedge; I) a temperaturegradientin the water; m) theincidenceofseichesandwind-induced·waves; n) health andsafetyofpersonnel (includingtheavailabilityof lightingduring hoursof darkness); 0) the number of observatio". to be made, e.g. the velocity-area method requires a considerable number of ~tionsatonecross-section; p) flow reversal oronlya backwatereffect. Theprincipal methodsof measurementandthe effectofphysicalconditionson.the selection of the gauging method aresummarizedin annexB,table B.2. 5.2.3 SelectIonanddemarcationofsite 5.2.3.1 General Thesiteshouldcontain all stagesof flowwhichoccurorwhich needto bemeasured. Ideally,sitesshould conformto thefoll.owing requirement•. a) Sites where weeds grow should be avoided or kept free from weeds to ensure there is no obstruction to the gaugingopenltion, unlessthemethodis tolerantto the presenceofweeds, e.g. el!Ctromagnetic method; b) Thereshould beno vortices,deadwaterorstrongcross-currents; c) Siteswhereice accumulatesshould be avoided; d) Thesiteshouldbeaccessibleforstaffandequipmentatall stagesofflow. 6.2.3.2 PreIImInIHyreconni......aurvey. A p,.ait:ni..-ry~surveyofall.~~ sites should be-_~.to eliminate.those which~are ·unsuitable, and to ~ure .f!lat. ~.tIyd~ulic and topog~icf~t~F88of the remainder.conform to the requirements·of the InternationalStandardspertainiogto~ methodof measurement-to·beused.··· Inspectionsunderdifferentflow conditionsmaybe necessaryto ensurethatconditionsunsuitableforthe .~.pf . measurementdo notoccurwhenobservationsarebeingmade. -. A permanent benchmark should be established and reIa~ to·a··standard dat~ in ~ u~ :in the area.All . subeequentlevellingsurveysshould~reducedtothe.standa~·da~. - . 4·