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“Invent a New India Using Knowledge”

है”ह”ह

IS 5497 (2008): Guide for topographical surveys for rivervalley projects [WRD 5: Gelogical Investigation andSubsurface Exploration]

IS 5497 : 2008

~ tntT ~31T cf>~~~afU1TetT~

( 'ifl'<l gryttorur )

Indian Standard

GUIDE TO TOPOGRAPHICAL SURVEYS FORRIVER VALLEY PROJECTS

( Second Revision)

res 07.060

OBIS 2008

BUREAU OF INDIAN STANDARDSMANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG

NEW DELHI 110002

November 2008 Price Group 4

Geological Investigations and Subsurface Exploration Sectional Committee, WRD 05

FOREWORD

This Indian Standard (Second Revision) was adopted by the Bureau of Indian Standards, after the draftfinalized by the Geological Investigations and Subsurface Exploration Sectional Committee, had beenapproved by the Water Resources Division Council.

This standard was first published in 1969 and revised in 1983. In the first revision, specifications regardingscale ofmaps for different surveys had been modified to reflect current practice. Provisions regarding riversurvey, flood survey and command area development survey had been added. In this revision contourintervals for different types of surveys have been incorporated and modified where needed. Subjectivedetails about the individual surveying methods have been deleted as they are readily available in all standardtext-books on surveying, Geodesy, Photogrammetry and Cartography or departmental handbooks of theSurvey of India.

Topographical survey forms a very important and vital activity for river valley projects. Any river valleyproject to be planned and constructed is to be based on certain basic facts and figures. The process ofcollection of these facts and figures is termed as investigation in general. The first requisite of investigationis to carry out topographical survey and prepare maps which are graphical representation of land.Topographical survey enables presentation of a picture of the terrain in the form of maps, which provideimportant and accurate data about topography and other characteristics of the area. These accurate dataassist in formulation ofcorrect plans for development of river valley projects for harnessing and utilizing thecountry's water resources. The cost of surveying and mapping is only a minor fraction of the total cost of theproject and when undertaken at initial stage will save a lot of infructuous expenditure arising out of incompleteor faulty data.

It hasbeen assumed in the formulation of this Indian Standard that the execution of its provisions is entrustedto appropriately qualified and experienced people, for whose guidance it has been formulated.

For the purpose ofdeciding whether a particular requirement of this standard is complied with, the final value,observed or calculated, expressing the result of a test, shall be rounded off in accordance with IS 2 : 1960'Rules for rounding offnumerical values (revised)'. The number ofsignificant places retained in the roundedotTvalue should be the same as that of the specified value in this standard.

IS 5497 : 1008

Indian Standard

GUIDE TO TOPOGRAPHICAL SURVEYS FORRIVER VALLEY PROJECTS

( Second Revision)

I SCOPE

This standard lays down the general principles andguidelines for topographical surveys connected witha river valley project.

2 REFERENCES

The standards listed below contain provisions whichthrough reference in this text constitute provisionsof this standard. At the time of publication, theeditions indicated were valid . All standards aresubject to revision and parties to agreements basedon these standards are encouraged to investigatethe possibility of applying the most recent editionsof the standards indicated below:

distance. These are further divided into two groups,namely M.D.M. (Microwave distance measuringinstruments) and E.O.D.M. (Electro-optical distancemeasuring instruments). M.D.M . instruments usemicro waves as carrier while E.O.D.M. instrumentsuse light or infra-red rays.

3.5 Height - The height ofa point above mean sea­level is the length of the vertical between the meansea-level surface and the point.

3.6 Latitude - The latitude of a place is the anglebetween the direction of a plumb line at the placeand the plane of the equator. It is marked N or Saccording to the place being north or south of theequator.

IS No.

5510: 1969

15686: 2006

Title

Guide for soil survey for rivervalley projects

Recommendations forpreparation of geological andgeotechnical maps for river valleyprojects

NOTE - If earth is assumed a perfect sphere ofhomogenous density the plumb line shall pass throughthe centre of sphere.

3.7 Longitude - The longitude of a place is theangle between a fixed reference meridian called theprime or first meridian and the meridian ofthe place.Longitude is measured from 00 to 1800 eastward orwestward and is marked °E or oW .

3 TERMINOLOGY

For the purpose of this standard the followingdefinitions shall apply.

3.1 Absolute Orientation - The process by whichan adjoining pair of relatively oriented aerialphotographs are brought to correct horizontal scaleand vertical datum.

3.2 Azimuth - The azimuth of a body is the anglebetween the observer's meridian and the great circle(vertical circle) through the body and the zenith ofthe observer.

NOTE - The meridian of an observer is the greatcircle passing through the poles. the zenith and thenadir.

3.3 Diapositive - A positive print ofa photographprepared on film or glass transparency.

3.4 Electromagnetic Distance Measuring (E.D.M.)Instruments - These are the instruments based onelectro-magnetic waves for precise measurement of

3.8 Mean Sea-Level- Mean sea-level is the averageelevation of the sea water level which is determinedby continuous observation of the varying level ofthe sea for as long a time as poss ible.

3.9 Pbotogrammetry -The science and art ofobtaining reliable measurements by means ofphotography.

3.10 Photographic Interpretation - The art ofexamining photographic images for the purpose ofidentifying objects and judging their significance.

3.11 Relative Orientation - The process by whichtwo successive aerial photographs having commonoverlap is brought to mutual geometrical relationshipbetween themselves, which existed at the time oftheirexposure.

3.12 Stereopair - Two photographs with sufficientoverlap and consequent duplication ofdetail to makepossible stereoscopic examination ofan object or anarea common to both.

IS 5497 : 2008

4 CLASSIFICATION

4.1 Typesof Survey

Topographical surveys required for river valleyprojects may be broadly classified under seve.nimportant types, namely, river survey, reservoirsurvey, site survey, command area survey,communication survey, flood control and commandarea development survey. These surveys are requiredin different stages of investigation of a river valleyproject. Methods of topographical survey .varydepending on the degree of accuracy to be attained,extent of the project and topography of the projectarea (see IS 15686 and IS 55 I0).

4.1.1 River Surveys

River surveys cover longitudinal section (L-Section)and cross-section (X-Section) of the river upstreamand downstream of the proposed structure.

4.1.2 The L-Section on the upstream side shallextend from the axis of the structure to the point upto which the back water effect is likely to extend orup to the maximum water level (MWL) + 5 mwhichever is more . If any headworks is situatedwithin the reach, the L-Section shall be taken up tothe headworks. On the downstream side , theL-Section shall extend for 10 krnfrom the axis ofthestructure or up to the nearest headworks, whicheveris less. The levelling of the L-Section shall be doneat 50 m or less intervals along the fair weather deepchannel. The folIowing items shalI also be indicatedin the L-Section:

a) Date of survey of the particular reach andaverage water level on that day;

b) Deep pools and rapids, rock outcrops, etc ;and

c) Maximum historical observed highest floodlevel (H.F.L.).

4.1.3 The X-Section on the upstream side shall betaken at 200 m intervals up to MWL + 5 m or I km oneither side of the firm bank, whichever is less, for adistance of 2 km from the axis of structure andthereafter at 1 km intervals corresponding to thelength of the L-Section. On the downstream side,X-Section shalI be at 200 m intervals and taken up tohistorical highest flood level + 5 m on either side offirmbank for a distance of2 krnto 5 km from the axisof the structure depending upon the meanderingnature of the river. A X-Section shalI also be takenalong the axis ofthe structure. The levelling shalI bedone at 50 m or less intervals. The following itemsshall also be indicated in the X-Section:

a) Date of survey and the water level on thatday;

2

b) Maximum and minimum historical/observedwater level; and

c) Rapids and rock outcrops, etc.

4.1.4 The longitudinal section shalI be plotted to ascale of I: 10000 horizontal and I: 100 vertical. Cross­sections shall be plotted to a scale of I: 2 000horizontal and I: 100 vertical.

4.2 Reservoir Survey

A reservoir survey is necessary to prov ide the basicdata for calculation of water storage capacity of areservoir, for indicating the limit of submergenceareas and for locating the topographic depressionsor saddles in the reservoir rim which may causespiIling or leakage of the reservoir. The scale andcontour interval for topographical survey forreservoir surve y depend on the extent of the areaand the topography of the site. The reservoir surveyis made with a view to examining all possiblealternatives for its locations and to eliminate such ofthe proposals which become unsuitable fromconsiderations of technical feasibility, economy andpracticability. The reservoir survey enablespreparation of a fairly dependable project reportsupported by cost estimates and economic studies .Reservoir survey maps shall be made on scalesranging from 1:2000 to 1:10 000 with contour intervalof I or 2 or 5 m corresponding to natural groundslopes less than 10°, 10°_30° and more than 30°respectively.

4.3 Site Survey

A site survey is carried out to investigate thesuitability of a site for a particular structure, such asdam site , power house or tunnel site. A dam sitesurvey should cover a sufficiently large area toinclude all possible locations ofthe main dam, cofferdams, spillways, separate outlet structures, and otherappurtenances. The scale of dam site survey mapsmay range from I : 500 to I : 1 000 , with contourinterval of Im to 2m. Power house site survey shouldinclude an area for possible construction of plantsites, stockpile areas, warehouse, switchyard areasand camp sites. The scale of maps may normally befrom 1 : 250 to I : 1 000. Tunnel site survey mapsshould be made along possible tunnel alignmentson scale I : I 000 to 1 : 10 000 , with contour intervalof2 m to 5 m and contour plan ofarea shall cover thelength of the tunnel and minimum 300 m on eitherside of the centre of the tunnel. The levelling shouldbe done at regular intervals into a regular mesh of50m or even closer depending upon the terrain and thecontour interval should be I or 2 or 5 mcorresponding to natural ground slopes less than10°, 10°_30°and more than 30° respectively.

4.4 Command Area Survey

The command area is the area , which is likely to bebenefited from the river valley project. The commandarea survey is very important in order to knowbeforehand the capability of the command area tomake maximum use of the benefits ofthe river valleyproject. Sometimes the command area survey is alsonecessary to assist in designing the layout of maincanals and distributaries for irrigation purposes. Thescale of command area survey maps should rangefrom I : 10 000 to I : 15 000 and contour interval of0.5 m or I m depending upon the steepness of thecountry. Block levelling on 50 m or less grid -basisshall be done.

4.5 Communication Survey

The movement of construction equipment andmaterial to a project construction site will normallyrequire the construction of access roads, as mostproject sites are not accessible from existinghighways . Sometimes branch lines from the existingrailway routes will be required . Existing railways andhighways running through the reservoir area mayhave to be relocated where these are liable to beinundated or submerged by a reservoir. The surveysare required for this purpose and for deciding thealignment and grades of railways and highways. Thesurveys for the location or relocation of railways andhighways are normally performed in consultationwith the field survey parties of the railway orhighways authorities who should be entrusted withthe determination of specification and surveyinstructions.

4.6 Flood Control Survey

These surveys are required in some project areas forflood control work, that is, for the planning andexecution of flood protection works . These maps areprepared on I : 10000 or I : 15000 scale with contourinterval of I or 2 or 5 m corresponding to naturalground slopes less than 10°, 10°_30° and more than30° respectively.

4.7 Command Area Development Survey

These are carried out for shaping topography toconserve water resources and for an integrateddevelopment to optimise productivity of the area .Scale for such survey maps varies between I : I 000to I : 5 000 with contour interval of0.5 m or I m.

5 PROVISION OF CONTROL

5.1 Control Survey

First of all, the whole area should be covered with anumber ofcarefully determined ground control pointswhich will form a network on which the ensuing detail

3

IS 5497 : 2008

survey of the area can be based upon. The accuracyof a detail survey depends on the accuracy of itsnetwork of ground control points and hence thedesired accuracy of control survey has to be decidedin advance keep ing in view the scale, purpose andtopography of area . It is also essential to ensure thatthe control in adjoining river valley projects isconsistent. For this purpose, the control surveys areinvariably linked to the national control networkprovided by the Survey of India .

5.1.1 Two types of ground control points arerequired for survey, namely, horizontal and verticalcontrol points. The horizontal control provides theplanimetric position of a control point . The verticalcontrol provides the altitude or height of a controlpoint above the mean sea-level.

5.2 Horizontal Control

The co-ordinates ofhorizontal control points shouldbe fixed either in terms of lat itude and longitudeexpressed in degrees, minutes and seconds or inrectangular terms in grid metres in northings andeastings relating to predetermined origin and typeof projection.

5.2.1 Horizontal control points may be fixed by oneor a combination of the following method :

a) Doppler satellite control,

b) Triangulation/E.D .M. trilateration,

c) Theodolite/E.D.M. traverse: and

d) Resection.

Of these , the best method for topographicaloperations is a system of accurate triangulation,whereby undue accumulation of error is precludedin the extension of the network, and at the same timelimits are set to the intrusion oferror, in the internaldetails to be surveyed.

5.2.2 Triangulation/E.D.M. Trilateration orTraverse

The electronic distance measuring (E.D .M .)instruments in control surveys operations are useful.In view of the accuracy and speed of operations ofthese instruments, their use is recommended to avoidthe laborious and time consuming methods of linearmeasurements by chains. Since these instrumentsmeasure distances, they may be used for measuringthree sides of a triangle which is known astrilateration. They may also be used for traversing tomeasure traverse legs in conjunction with theodolitefor measuring angles. E.D.M. trilateration oftraverseis carried out by the Survey of India.

5.2.2.1 According to the procedure of observations,instruments used and quality of triangulation results,

IS 5497 : 2008

a triangulation is classified as primary, secondaryand tertiary. There are a variety ofelectronic distancemeasuring instruments available today which arevery useful in control survey operat ions . Th isclassification may also be called as first-order,second-order and third-order triangulation. Theprimary and secondary triangulations are termed asgeodetic. The tert iary triangu lation is calledtopographic. All geodetic data which form the basisof topograph ical survey are published intriangulation and levelling pamphlets . Thesepamphlets may be obtained from the Survey of India .

5.2.2.2 Primary triangulation is the highest grade oftriangulation and is employed for the determinationof the shape and figure of the earth and othergeodetic investigations. It also constitutes the basicprecise framework for mapping and for power orderof triangulation. As it is independent of externalchecks, all possible precautions and refinementsshould be taken in the observations and theirreduction . The length of a base-line in primarytriangulation may be about 8 km to 12 Ian on theaverage and the sides ofthe triangles may range from16 km to 50 km. The average triangulation error (orthe discrepancy between the sum of the measuredangles in a triangle and 180" plus the spherical excessof the triangle) should not be in excess of I s. Theprobable error of computed distance should liebetween I in 50 000 to I in 250000.

5.2.2.3 Secondary triangulation is des igned toconnect two primary series and thus furnish pointscloser together than those of primary triangulation.The average triangular error in secondarytriangulation should not exceed 3 s. The probableerror of computed sides should lie between 1 in 20000 to I in 50 000.

5.2.2.4 Tertiary triangulation is run between thestations of the primary and secondary series andforms the immediate control for topographicalsurveys. The average triangular error may range from3 s to 15 s and the probable error ofcomputed sidesmay lie between 1 in 5 000 to I in 20 000 .

5.2.2.5 The initial data required for commencingtopographical triangulation in an area of which adetail survey is contemplated, is a base of knownlength, an azimuth, latitude, longitude and heightabove mean sealevel ofone station. The triangulationchain starts from this known base and closes onanother known base.

5.2.3 Theodolite Traverse

In some stretches of flat country, primarytriangulation series may lie over 150 Ian apart, andeven where a secondary series might have been runto connect them, many of the secondary control

4

points might have been destroyed. Owing to theflatness of the country the expense of triangulatingthe intermediate area ma y be greater andtriangulation may take several seasons to carry out.In such cases theodol ite travers ing is a moreexpedient and economical method of control survey.Traversing is a more laborious and at the same time aless accurate method of fixing control poin ts thantriangulation and , therefore, may only be resorted toin flat ground where buildings, trees, high grass orhaze prevent distant vision.

5.2.3.1 The length of traverse legs are measured bychains (Crinoline chains, see Note I ) or steel bands[Hunter short base (see Note 2)] or subtense bars orinvar wires or E.D.M . instruments according to theaccuracy aimed at.

NOTES

I Crinoline cha in is a riband of steel about 3 to S mmwide and about 1/2 mm thick. obta inable in lengths of100 m to 110 m. II is calibrated for its length understandard cond it ions of temperature and pressure. It isused for direct measurement of distances where theaccuracy desired is of higher standard . The tensionappl ied during field measurements should normally bethe same as that applied dur ing calibration .

2 Hunter short base is a short measured base, inventedby Hunter, cons isting of calibrated steel tapes hung incatenary, for commencement or carrying forward ofcontrol work by triangulat ion or traverse. Normally itcons ists of four tapes cal ibrated under standardcond it ions of temperat ure and pressure . The tapestogether with other accessories are eas ily portable andform a conven ient base to commence and carry forwardcontrol operat ions in any type of terrain, particularlybushy and undulating, with meagre exist ing controlpo ints.

5.2.3.2 The angles between consecutive traverselegs should be measured by a theodolite set up ateach station in turn. Vertical angles should beobserved by theodolite from one station to anotherwhen heights are required. If the position of onestation and the bearing of a traverse line connectedto it are known, then the position of the next and allsucceeding stations may be computed.

5.2.3.3 The rate ofaccumulation oferrors in traverseaffects the accuracy and shall be kept under controlby closing traverses on well fixed points at both endsand also by introducing bases and azimuths .Topographical or tertiary traverse may have anaccuracy of I in 5 000 provided more precise angularand linear measurement devices are used.

5.2.3.4 The observation ofazimuths, either from sunor stars, at frequent intervals, provides a direct checkagainst accumulation of errors of angularmeasurements. These azimuths, as well as thebearings from one station to another, should becomputed in the field . Ifcomparison reveals an error

larger than I~ minutes in 12 stations in main traverse

lines the line shall be reobserved.5.2.3.5 Th e most important field check in linearmeasurements is the established custom of measuringeach line twice and comparing the values. Each lineshould be measured once with a long chain 30 m inlength and a second time with a short chain 20 m inlength. These two measurements should agree withinI in 500 for cha ins and I in I 000 for steel bands . Themeasurements of the length obtained by the longerchain shall be accepted. In E.D.M . instruments fieldcheck is obtained by repeat observations. However,the time taken is much less than surface taping andaccuracy achieved is of high order.

5.2.3.6 Traverse should be computed in rectangularco-ordinates and referred to an origin.

5.2.4 Resection

This method may be adopted to determine thegeographical position of a point on the groundoccupied by surveyor, by making observations toother stations or points of known co-ordinateswithout visiting them. This method obviates thenecessity of visiting or making observations fromother existing control points and stations. When theobservations are made with theodolite, it is termedas 'trigonometrical resection' or 'theodoliteresection' . In topographical triangulation, stationsmay occasionally be fixed by this method when it isnot convenient to visit other stations for makingobservations. A judicious selection of the controlpoints is essential while adopting this method. It alsoinvolves complicated computations. However,occasionally, it may be necessary to resort to thismethod in exploratory or active service work.

5.3 Vertical Control

5.3.1 Vertical control points are essential to knowthe altitude ofthe area. The heights of vertical controlpoints above mean sea-level may be determined byone or combination of the following methods oflevelling:

a) Trigonometric levelling, andb) Levelling ( spirit levelling ).

5.3.2 Trigonometric Levelling

The elevations of triangulation stations may beestablished by observing the vertical angles betweenstations and computing the differences in elevationtrigonometrically. The angles are taken at the timethe station is occupied for the purpose ofmeasuringthe horizontal angles. The trigonometricallevellingshould start from and close on certain point ofknownelevation. From the known elevation of these pointsthe elevations of the triangulation stations and

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IS 5497 : 2008

intersected points may be computed by means ofthe differences in height derived from the verticalangles and the lengths of the triangle sides. Inmeasuring the vertical angles the theodolite shouldbe placed over the centre mark of the station and itsheight above the station should be measured. Thetriangulation stations should have definite signalswhich should be observed for sighting the cross­hair when measuring the vertical angle. From theknown height of the distant signal above the ground ,the height of the triangulation station sighted maybe computed.

5.3.2.1 The main difficulty in obtaining accurateresults in this kind ofwork arises from the uncertaintyof the atmospheric refraction. It may be nearlyeliminated by taking reciprocal observations betweentwo stations when the refraction is steady. The besttime to observe vertical angles is during the middleof the day, from 1300 h to 1600 h as the refraction isthen much less variable than in the morning or lateafternoon.

5.3.2.2 Trignometric levelling may be used for fixingvertical control points where the terrain is steep andundulating and the contour interval aimed at is 5 mor more.

5.3.3 Levelling

Levelling or the determination of the relative altitudeof points on the earth's surface, is an importantoperation; both in acqu iring data for the design ofall classes of works and during construction. Liketriangulation, depending on its quality, levelling isclassified as high precision, secondary, doubletertiary or tertiary.

5.3.3.1 High precison levelling is carried out toprovide the main vertical framework of the countryand for the detemination of the shape and figure ofthe earth and other geodetic investigations. It alsoconstitutes the basic precise framework for lessprecise levelling. Secondary and double tertiarylevelling may beused for estabilishing the elevationsofthe controlling bench marks in the project area forall subsequent levelling. Tertiary levelling may beused for providing a dense network ofvertical controlpoints in the project area.

5.3.3.2 The simplest operation for levelling consistsin determination of the difference of level betweentwo points so situated that, from one position of theinstrument, readings may be obtained on a staffheldsuccessively on the two points. The precise locationof the instrument is immaterial, but to eliminate theeffects ofpossible instrumental error, refraction andcurvature effects the two sights should be nearlyequal in length as may bejudged. Precision levellingalso requires observations for the values of gravity

IS 5497 : 2008

along the path of levelling, for accuratecomputations.

5.3.3.3 The closing error for the different classes oflevelling shall not exceed those given below:

SI No. Classes 0/ Levelling Error ofClosuremm

(I) (2) (3)

i) High precision + 45

ii) Secondary + 65

iii) Double tertiary + 125

iv) Tertiary + 245

where K is the distance, in Ion.

5.4 Field Observations

For achieving good results, the records should bemaintained in a systematic way in order to facilitatecomputations and reduction of results. All fieldobservations should be recorded neatly in ink in theobservation forms provided for the purpose. Therequired number ofmeasures laid down for the order ofaccuracy to be aimed at should be observed. Oncompletion ofobservations at a station the mean shouldbe calculated and compared for agreement. Oncompleting this, the observer should scrutinize theresults, and when large differences appear, a repeat setof observations of the stations, which gave doubtfulresults, should be taken before doing other works. Ifthis important precaution is omitted, errors willaccumulate subsequently and there will beno means ofrectifying them. Measures which do not comply withthe prescribed cr iterion should be repeated beforeleaving the station of observation.

5.4.1 For triangulation stations, all threeangles ofeachtriangle must be observed and the observer should keepup a record ofcompletely observed triangles, to enablehim to note his triangular error, that is, the difference ofthe sum of the three observed angles of a triangle from1800

, spherical excess being considered as necessary,and to see that it is within the specified limits.Any repeatobservations of triangles, if necessary, should becompleted before leaving the area of work.

5.5 Field Control Charts

Field control charts should be maintained both forhorizontal and vertical control points for showing theirlocation and also for assisting in computations. Fortriangulation , a field triangulation chart should beprepared either on a smaller scale existing map or evenon blank paper with the existing triangulat ion stations

I Ishown on it. A scale of 4to 2of that of the detailed

survey will generally be found suitable. For levelling.

6

a field levelling chart should be maintained on anexisting large scale map of the area.

5.5.1 AIIgreat trignometrical (G T.) stations or otherstations or well defined intersected points of oldtopographical triangulation falling in the area ofworkshould be plotted and inked on the field triangulationchart in a distinctive colour. When one series oftriangulat ion is joined to another, two adjacentstations common to both the series should beobserved and clearly indicated in the triangulationchart for facilitating computation s All new stationsand their connecting rays should be inked clearly onthe chart.

5.5.1. J All high precision and secondary level linesand bench-marks should be clearly marked on thefield) levelling chart in a distinctive colour. All newlevel lines and the ir alignments along with theposition of benchmarks should be inked clearly onthe chart.

5.6 Survey Marks and Stations

Whenever possible, stations should be placed onrock in-situ with a mark which should consist of ahole of about 5 mm diameter drilled into the rockabout 20 mm deep with a circle engraved around it.For more precise work with E.D.M . instruments thehole drilled in the centre may be of I mm to 2 mmdiameter, 3 em to 4 em deep with a copper or brasswire of the same diameter plugged into it and madeflush with the top surface.

5.6 .1 When rock is not available. a large stoneshould be embedded about I m underground. with acircle and dot cut on it, with a second mark-stonesimilarly treated, and hav ing its dot vertically abovethe dot of the lower mark . placed flush with the topsurface of the platform. or , if the triangulator mayobtain some old 2.5 em piping. about I m length, itmay be driven vertically into the ground. the centreof this being taken as the actual mark .

5.6.2 Surrounding the mark. a platform should bebuilt of earth and stones. at least 0 .5 m high andabout 3 m square. The sides of the platform shouldbe revetted with big stones or gently sloped.

5.6.3 For traversing wooden pegs 8 em ~ 8 em squarein section and 30 em long may be used . A circle anddot shall be engraved on top of each peg which aredr iven vert icall y into the ground with the top flushwith the ground . Traverse stations may also be madeby a circle and dot on parapets of culverts. wells orve ra nda hs of public buildings. like inspectionbungalows. dak bungalows. etc .

5.6.4 In levelling. the levelling staves are generallyplaced on iron crow-foots firmly placed on theground so that there is no sinking of the levelling

staff during observations. In precise levelling,wooden pegs are driven in ground in place of ironcrow-foots for stability ofstaves during the levellingoperation. However, for a bench-mark a circle with Band M written on either side may be used for semi­permanent and permanent bench-marks engraved onparapets or culverts, well or verandahs or steps ofpublic buildings like inspection bungalows, dakbungalows, etc.

5.6.5 The descriptions of G.T. stations and highprecision bench marks are given in the G.T. pamphletsand levelling pamphlets (published by Survey ofIndia). These pamphlets covering the area of projectshould be obtained from the Survey of India duringinvestigations.

5.6.6 All the permanent stations and bench-marksestablished by the Survey ofIndia are required to beprotected, maintained and periodically inspected bythe local authorities in collaboration with the Surveyof India . Any of these marks disturbed, damaged ormissing must be reported to the Survey of Indiaimmediately.

5.6.7 For river valley surveys, certain referencecontrol points may be required to be established forcontrolling subsequent surveys and constructionprogrammes. The actual specifications of thesecontrol points will depend on their importance andtype ofsoil on which to be constructed. These shouldbe finalized in consultation with the Survey of Indiaand constructed at least one season in advance tomake allowances for settling down .

5.7 Survey Computations

Apart from carrying out good field work and

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IS 5497 : 2008

computing them correctly, it is also important tomaintain the records in the most systematic manner.All computations should be carried out in duplicateand independently. The duplicate computationsshould be compared to check any grossdisagreement. Both sets of computations should besigned and dated . The completed computationsshould be scrutinized by a responsible officer. Useof electronic scientific pocket calculator in the fieldhelps to expedite survey computations. Computationscan also be carried out with the help of micro andlarge computers. To guard against computer failure,computer programmes should be used with checkdata and results.

5.7.1 On completion ofcomputations the followingrecords of control survey should be prepared:

a) History sheet of control surveys,

b) Description of stations/bench-marks,

c) List of co-ordinates/heights, and

d) Traces of triangulation/traverse levelling

charts.

5.7.1.1 A short narrative account of the controlsurvey, ment ioning the object of the control survey,the instruments and signals used and other facts ofinterest should be included in the history sheet .

5.7.1.2 All basic data collected during the surveyand all computations made as a part thereof shouldbe preserved and filled in such a manner as to bereadily available and easily understood. The recordsshould be classified job-wise and kept safe. Alloriginal records and computations should bepreserved carefully.

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BIS is a statutory institutionestablished under the Bureau ofIndian Standards Act, 1986 to promote harmoniousdevelopment of the activities of standardization, marking and quality certification of goods and attending toconnected matters in the country.

Copyright

BIS has the copyright ofall its publications. No part of these publications may be reproduced in any form withoutthe prior permission in writingofBIS. This does not preclude the free use, in course ofimplementingthe standard,of necessary details, such as symbols and sizes, type or grade designations. Enquiries relating to copyright beaddressed to the Director (Publications), BIS.

Review oflndian Standards

Amendmentsare issued to standards as the need arises on the basis of comments. Standards are also reviewedperiodically; a standard along with amendments is reaffirmed when such review indicates that no changes areneeded; if the review indicates that changes are needed, it is taken up for revision. Users of Indian Standardsshould ~ertain that they are in possession of the latest amendments or edition by referring to the latest issue of'BIS Catalogue' and 'Standards: Monthly Additions'.

This IndianStandard has been developed from Doc: No. WRD 05 (449).

Amendments Issued Since Publication

AmendmentNo. Date of Issue

BUREAUOF INDIAN STANDARDS

TextAffected

Haldquarten:

ManakBhavan,9 BahadurShah lafar Marg,New Delhi 110002Telephones: 23230131,2323 3375,2323 9402 Website:www.bis.org.in

Regiona. Offaces:

Central: Manak Bhavan, 9 Bahadur Shah Zafar MargNEWDELHI 110002

Eastern: 1/14,C.I.T.SchemeVII M, V.I.P. Road,KankurgachiKOLKATA700054

Northern: sea 335-336,Sector34-A,CHANDIGARH 160022

Southern: C.I.T. Campus, IVCrossRoad.CHENNAI 600113

Western: Manakalaya, E9 MIDC, Marol, Andheri(East)MUMBAl400093

Telegrams: Manaksanstha(Common to all offices)

Telephones

{23237617

. 23233841

{23378499,2337856123378626,23379120

{26038432609285

{2254 1216,2254144222542519,22542315

{2832 9295, 2832785828327891,28327892

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