CONTOURS SURVEYING 1 CE 215 CHAPTER -3- Ishik University / Sulaimani Civil Engineering Department 12/7/2017. Ishik University / Sulaimani

Transcription

1 Civil Engineering Department SURVEYING 1 CE 215 CHAPTER -3- CONTOURS 1 2 1

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3 PURPOSE OF CONTOURING Contour survey is carried out at the starting of any engineering project such as a road, a railway, a canal, a dam, a building etc. i) For preparing contour maps in order to select the most economical or suitable site. ii) To locate the alignment of a canal so that it should follow a ridge line. iii) To mark the alignment of roads and railways so that the quantity of earthwork both in cutting and filling should be minimum. 5 PURPOSE OF CONTOURING (contd.) iv) For getting information about the ground whether it is flat, undulating or mountainous. v) To find the capacity of a reservoir and volume of earthwork especially in a mountainous region. vi) To trace out the given grade of a particular route. vii)to locate the physical features of the ground such as a pond depression, hill, steep or small slopes. 6 3

4 FACTORS ON WHICH CONTOUR -INTERVAL DEPENDS The contour interval depends upon the following factors:- i) The Nature of the Ground In flat and uniformly sloping country, the contour interval is small, but in broken and mountainous region the contour interval should be large otherwise the contours will come too close to each other. 7 FACTORS ON WHICH CONTOUR -INTERVAL DEPENDS ii) The Purpose and extent of the survey. Contour interval is small if the area to be surveyed is small and the maps are required to be used for the design work or for determining the quantities of earth work etc. while wider interval shall have to be kept for large areas and comparatively less important works. 8 4

5 FACTORS ON WHICH CONTOUR -INTERVAL DEPENDS iii) The Scale of the Map. The contour interval should be in the inverse ratio to the scale of the map i.e. the smaller the scale, the greater is the contour interval. iv) Time and Expense of Field and Office work. The smaller the interval, the greater is the amount of field-work and plotting work. 9 COMMON VALUES OF THE CONTOUR - INTERVAL The following are the common values of the contour interval adopted for various purposes:- i) For large scale maps of flat country, for building sites, for detailed design work and for calculation of quantities of earth work; 0.2 to 0.5 m. 10 5

6 COMMON VALUES OF THE CONTOUR - INTERVAL ii) For reservoirs and town planning schemes; 0.5 to 2m. iii) For location surveys. 2 to 3m. iv) For small scale maps of broken country and general topographic work; 3m,5m,10m,or 25m. 11 CHARACTERISTICS OF CONTOURS i) All points in a contour line have the same elevation. ii) Flat ground is indicated where the contours are widely separated and steep-slope where they run close together. iii) A uniform slope is indicated when the contour lines are uniformly spaced and iv) A plane surface when they are straight, parallel and equally spaced. 12 6

7 HILL: AN AREA OF HIGH GROUND. FROM A HILLTOP, THE GROUND SLOPES DOWN IN ALL DIRECTIONS. 13 What are the uses of contours? They can be used to learn about the shape of the land (the relief). A map with only a few contour lines will be flat (and often low lying) If a map has lots of contours it is a mountainous or hilly area. The actual pattern of the lines will tell you more detail about the area too. XXX XXX XXX 14 7

8 It is important to remember that the closer together the contour lines the steeper the slope. XXXX Steep slopes XXXX Area that is flatter with only a gentle slope XXXX 15 This is the side view of a hill. 300m 2m 200m 1m 100m Sea level Let s see where this hill reaches these heights Now let s plot those points Now if we plotted those points on paper. See how these lines are closer together on the steeper slope 16 8

9 CHARACTERISTICS OF CONTOURS 80 v) A series of closed contour lines on the map represent a hill, if the higher values are inside HILL A HILL 17 DEPRESSION: A LOW POINT IN THE GROUND OR SINKHOLE. THEY ARE REPRESENTED BY CLOSE CONTOUR LINES THAT HAVE TICK MARKS POINTING TOWARD LOW GROUND. 18 9

10 CHARACTERISTICS OF CONTOURS 80 vi) A series of closed contour lines on the map indicate a depression if the higher values are outside DEPRESSION A DEPRESSION 19 VALLEY: A STRETCHED-OUT GROOVE IN THE LAND, USUALLY FORMED BY STREAMS OR RIVERS

11 RIDGE: A SLOPING LINE OF HIGH GROUND. 21 CHARACTERISTICS OF CONTOURS vii) Contour line cross ridge or valley line at right angles RIDGE LINE If the higher values are inside the bend or loop in the contour, it indicates a Ridge

12 CHARACTERISTICS OF CONTOURS vii) Contour line cross ridge or valley line at right angles. If the higher values are 100 outside the bend, it represents a Valley VALLEY LINE 23 CHARACTERISTICS OF CONTOURS viii) Contours cannot end anywhere but close on themselves either within or outside the limits of the map

13 CHARACTERISTICS OF CONTOURS ix) Contour lines cannot merge or cross one another on map except in the case of an overhanging cliff OVERHANGING CLIFF 25 CHARACTERISTICS OF CONTOURS x) Contour lines never run into one another except in the case of a vertical cliff. In this case, several contours coincide and the horizontal equivalent becomes zero VERTICAL CLIFF OVERHANGING CLIFF 26 13

14 SADDLE: A DIP OR LOW POINT BETWEEN TWO AREAS OF HIGHER GROUND. 27 CHARACTERISTICS OF CONTOURS X) Depressions between summits is called a saddle. It is represented by four sets of contours as shown. It represents a dip in a ridge or the junction of two ridges. And in the case of a mountain range,it takes the form of a pass SADDLE Line passing through the saddles and summits gives water shed line

15 A valley may look like this Often with a river running down through the valley 29 However a spur can look very similar! But here the heights are increasing in the opposite direction always double check which way the contours are increasing or decreasing

16 Valley Spur 31 Now Try your hand at a short test or click on the return button to re-run this presentation

17 A series of V-shapes indicates a valley and the V s point to higher elevation. 33 Contour lines cannot begin or end on the plan. A contour never splits

18 On uniform slopes, the contour lines are spaced uniformly. No two contours can run into one. 35 Contours deflect uphill at valley lines and downhill at ridge line; line crossing are perpendicular: U-shaped for ridge crossings; V-shaped for valley crossings. Valley Ridge 36 18

19 Example 1 Drawing Contour Lines There is no right or wrong starting point. Pick a contour interval, start at one edge and extend the contour across the map. This example starts with the 14 foot contour. In this example even numbered contours will be used

20 Example 2 Drawing Contour Lines m 40 20

21 41 Since the contour interval is 10m, all contour lines should be multiples of

22 Solution: 43 Example 3 Drawing Contour Lines 44 22

23 Example 4 Drawing Contour Lines 45 Example 5 Drawing Contour Lines 46 23