contourlines-130527092046-phpapp02.pdf

1. 1.  A CONTOUR LINE is a line representing an imaginary line on the ground along which all points are at the same elevation.  Contour lines indicate a vertical distance above or below a datum plane. Starting at sea level, normally the zero contour, each contour line represents an elevation above sea level
2. 2.  CONTOUR INTERVAL:- It is the vertical distance between adjacent contour lines.  INDEX CONTOURS :-  The amount of the contour interval is given in the marginal information. On most maps, the contour lines are printed in brown. Starting at zero elevation, every fifth contour line is drawn with a heavier line. These are known as INDEX CONTOURS.
3. 3.  INTERMEDIATE CONTOURS:- Someplace along each index contour, the line is broken and its elevation is given. The contour lines falling between index contours are called INTERMEDIATE CONTOURS
4. 4.  In Topographical map  In Hilly Region for Farming Purpose  To Avoid Soil Erosion on the slope  To Stop the flow of Water from the slope so that it can be infiltrate
5. 5. You can mark contour lines out with a home made A-frame. 1. MAKING AN A-FRAME  2 pieces of wood, approximately 5cm x 2.5cm and 2m long  1 piece of wood, 1m long  3 nails or screws, 5cm long (if not available, you can use string instead)  a short length of string  a weight (for example a stone)
6. 6. 1. Lay the two longer pieces of wood on the ground, with their ends touching and the other ends 2m away from each other. Fasten the 2 pieces together at one end with a nail or screw. If you have not got nails or screws, cut notches and use string to bind the two ends together. Fix them loosely at first.
7. 7. 2. Fix the third piece of wood (1m) at exactly the middle of each of the long pieces. When the3 pieces are in position 3. Hang a string down from the tip of the A frame, and attach a weight to it, so that it swings below the cross-bar
8. 8. 4. Calibrate the A-frame by placing it upright on ground you know is level. When the stone stops swinging, mark the position where the string crosses the crossbar. Turn the A frame around, putting the legs in exactly the opposite position, and measure the centre-point again. If it is in the same place, then it is the level ground marker
9. 9. Start near the top of the slope. Stand on the hillside with the A-frame, adjusting it until you find level ground as indicated when the weighted string hangs at the level ground marker.
10. 10. The distance between contour lines depends on the steepness of the slope. It could be as little as 8 meters or as much as 30 meters. The steeper the slope, the closer the contour barriers have to be to prevent erosion. It also depends upon the amount of rain that falls, and on what you are going to do with the land.
11. 11. Lines are with respect to the Slope
12. 12.  The Major advantage of Contour lines is in the field Agriculture..  It is very necessary to stop the flow of water on the slope so that water can be infiltrate  By this we can stop the soil erosion
13. 13.  Provide water to crops during drought years  Trap nutrients washed away from the field  Can be converted to compost pits  Reduce siltation to river systems down slope  Can be used to grow crops  Can be used for fish-farming