contouring-180417110533.pdf

map

1. 1
CONTOURING
By
Sachin M. Gunjal
Assistant Professor
Department of Civil Engineering
Sanjivani College of Engineering, Kopargaon

2. •Contours are those lines you can
see on OS maps.
•A contour line is an imaginary
line that joins points of equal
height above sea level.
•Theycanbeusedtolearnabout
theshapeoftheland(therelief).
•Amapwithonlyafewcontour
lineswillbeflat(andoftenlow
lying)
•Ifamaphaslotsofcontoursitis
amountainousorhillyarea.
•Theactualpatternofthelines
willtellyoumoredetailabout
theareatoo.
Steep slopes
Area that is
flatter with only
a gentle slope
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3. CONTOURS
•ContourAnimaginarylineonthegroundsurfacejoiningthepoints
ofequalelevationisknownascontour.
•Inotherwords,contourisalineinwhichthegroundsurfaceis
intersectedbyalevelsurfaceobtainedbyjoiningpointsofequal
elevation.Thislineonthemaprepresentsacontourandiscalled
contourline.
•ContourMap:-AmapshowingcontourlinesisknownasContour
map.
•Acontourmapgivesanideaofthealtitudesofthesurfacefeatures
aswellastheirrelativepositionsinplanservesthepurposeofboth,
aplanandasection.
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4. Contouring
•Theprocessoftracingcontourlinesonthesurfaceoftheearthiscalled
Contouring.
•PURPOSEOFCONTOURING
•Contoursurveyiscarriedoutatthestartingofanyengineering
projectsuchasaroad,arailway,acanal,adam,abuildingetc.
i)Forpreparingcontourmapsinordertoselectthemosteconomical
orsuitablesite.
ii)Tolocatethealignmentofacanalsothatitshouldfollowaridge
line.
iii)Tomarkthealignmentofroadsandrailwayssothatthequantityof
earthworkbothincuttingandfillingshouldbeminimum.
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5. iv)Forgettinginformationaboutthegroundwhetheritisflat,
undulatingormountainous.
v)Tofindthecapacityofareservoirandvolumeofearthwork
especiallyinamountainousregion.
vi)Totraceoutthegivengradeofaparticularroute.
vii)Tolocatethephysicalfeaturesofthegroundsuchasapond
depression,hill,steeporsmallslopes.
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6. METHODS OF CONTOURING
•There are mainly two methods of
locating contours:-
(1)Direct Method and
(2) Indirect Method.
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7. 1] Direct Method:
•Inthismethod,thecontourstobe
locatedaredirectlytracedoutinthe
fieldbylocatingandmarkinga
numberofpointsoneachcontour.
•Thesepointsarethensurveyedand
plottedonplanandthecontours
drawnthroughthem.
•Thismethodismostaccuratebut
veryslowandtediousasalotoftime
iswastedinsearchingpointsofthe
sameelevationforacontour.
•Thisissuitableforsmallareaand
wheregreataccuracyisrequired
DIRECT METHOD OF
CONTOURING
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48
B.M.
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8. Procedure:
•Tostartwith,atemporaryB.Misestablishedneartheareatobe
surveyedwithreferencetoapermanentB.Mbyflylevelling.
•Thelevelisthensetupinsuchapositionsothatthemaximum
numberofpointscanbecommandedfromtheinstrumentstation.
•Theheightofinstrumentisdeterminedbytakingabacksightonthe
B.M.andaddingittotheR.L.ofbenchmark.
•Thestaffreadingrequiredtofixpointsonthevariouscontoursis
determinedbysubtractingtheR.L.ofeachofthecontoursfromthe
heightofinstrument.
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9. •Example:
•Iftheheightofinstrumentis82.48m.,thenthestaffreadings
requiredtolocate82,81and80mcontoursare0.48,1.48and
2.48mrespectively.Thestaffisheldonanapproximatepositionof
pointandthenmovedupanddowntheslopeuntilthedesired
readingisobtained.Thepointismarkedwithapeg.
•Similarlyvariousotherpointsaremarkedoneachcontour.Theline
joiningallthesepointsgivetherequiredcontour.Itmaybenoted
thatonecontourislocatedatatime.Havingfixedthecontours
withintherangeoftheinstrument,thelevelisshiftedandsetupin
anewposition.
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10. Procedure (Contd…..)
•Thenewheightofinstrumentandtherequiredstaffreadingsare
thencalculatedinasimilarmannerandtheprocessrepeatedtillall
thecontoursarelocated.
•Thepositionsofthecontourpointsarelocatedsuitablyeither
simultaneouswithlevellingorafterwards.
•Atheodolite,acompassoraplanetabletraversingisusually
adoptedforlocatingthesepoints.
•Thepointsarethenplottedontheplanandthecontoursdrawnby
joiningthecorrespondingpointsbydottedcurvedlines.
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11. Direct Method By Radial Lines
•Thismethodissuitablefor
smallareas,whereasingle
pointinthecentrecan
commandthewholearea.
Radiallinesarelaidoutfrom
thecommon centreby
theodoliteorcompassand
theirpositionsarefixedupby
horizontalanglesandbearings.
RADIAL LINES METHOD
OF CONTOURING
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60
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12. Direct Method By Radial Lines (contd.):
•Temporarybenchmarksarefirstestablishedatthecentreandnear
theendsoftheradiallines.
•Thecontourpointsarethenlocatedandmarkedontheselinesand
theirpositionsaredeterminedbymeasuringtheirdistancesalong
theradiallines.
•Theyarethenplottedontheplanandthecontoursdrawnby
joiningallthecorrespondingpointswiththehelpofaplanetable
instrument.
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13. 2. INDIRECT METHOD
•Inthismethodthepointslocatedandsurveyedarenotnecessarily
onthecontourlinesbutthespotlevelsaretakenalongtheseriesof
lineslaidoutoverthearea.
•Thespotlevelsoftheseveralrepresentativepointsrepresenting
hills,depressions,ridgeandvalleylinesandthechangesinthe
slopeallovertheareatobecontouredarealsoobserved.
•Theirpositionsarethenplottedontheplanandthecontoursdrawn
byinterpolation.
•Thismethodofcontouringisalsoknownascontouringbyspot
levels.
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14. •Thismethodiscommonlyemployedinallkindsofsurveysasthisis
cheaper,quickerandlesstediousascomparedtodirectmethod.
Therearemainlythreemethodofcontouringinindirectmethod:
•(I)BYSQUARES[SQUAREMETHOD]:-
•Inthismethod,thewholeareaisdividedintonumberofsquares,
thesideofwhichmayvaryfrom5mto30mdependinguponthe
natureofthegroundandthecontourinterval.Thesquareneednot
beofthesamesizethroughout.
•Thecornersofthesquaresarepeggedoutandthereducedlevels
ofthesepointsaredeterminedwithalevel.
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15. SQUARE METHOD
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16. (II) By Cross-Sections:
•This method is most suitable for the survey of long narrow strips
such as a road, railway or canal etc.
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17. •(III) By Tacheometric method:
•Atecheometerisatransittheodolitehavingadiaphragmfittedwith
twostadiawires,oneaboveandotherbelowthecentralwire.
•Thehorizontaldistancebetweentheinstrumentandstaffstation
maybedeterminedbymultiplyingthedifferenceofthestaff
readingsoftheupperandlowerstadiawireswiththestadia
constantoftheinstrument,whichisusually100.
•Thusthetecheometerisusedforboththeverticalaswellas
horizontalmeasurements.
Stadia Wires at Diaphragm
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18. iii) By Tacheometric method (contd…):
•Thismethodismostsuitableinhillyareasasthenumberofstations
whichcanbecommandedbyatecheometerisfarmorethanthose
byalevelandthusthenumberofinstrumentsettingsare
considerablyreduced.Anumberofradiallinesarelaidoutata
knownangularintervalandrepresentativepointsaremarkedby
pegsalongtheseradiallines.Theirelevationsanddistancesare
thencalculatedandplottedontheplanandthecontourlinesare
theninterpolated.
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