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Measuring Height using Dumpy level

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Rural Technology

Dumpy Levels can be used for:

  • Determining the height of a particular point.
  • Determining differences in height between points.
  • Drawing contours on a land.
  • Providing data to calculate volumes for earthworks.
  • Setting out level surfaces for construction.
  • Setting out inclined surfaces for construction.

Intext questions :

  1. To check the level of the surface ………….. instrument is used.
  2. To determine the height between the two points …….. is used.
  3. Water always remains in ------- level.
  4. A meson always use a ……………… for brick construction.

Measuring height using Dumpy Level :

  • The place of which height is to be measured is called Station.
  • Height is always measured with reference to sea level.
  • Survey of India established benchmarks (B.M) at several places.
  • Ideally the distances should be taken from the benchmark.
  • If it is not available then we can select point on the map whose distance from sea level is known as the reference.
  • We can fix any suitable point as Temporary bench mark and all heights can be measured from that point. We can fix any temporary bench mark , but if its MSL( at temporary BM) is not sure , then before starting the surveying permanent BM reading should be clear.
  • • Now we will learn how to take actual readings. Please observe below figure carefully .


HI= BM+BS BACKSIGHT(BS)

  • In the picture Bench mark is setup at a height of 100 ft.
  • As a first step we need to know the height of the place from where instrument is placed. In the picture, a boy is standing on a place from where survey will begin.
  • To know the height of the instrument place a staff or level rod at bench mark location. And from the instrument take the reading on the staff. In this case reading on the staff is 5.5ft . This reading is called as backsight reading (BS).

Height of the instrument = BM + BS = 100 + 5.5 = 105.5 ft.

Now surveyor can go ahead and determine heights of other places. Look at the following figure to take further reading. These readings are called as foresight reading (FS):

HI+FS=ELEVATION FORESIGHT(FS)







Now staff or level rods are put on the point (D) height of which is to be measured. The reading on the staff is recorded through telescope of dumpy level. In present case the reading shows 2.3ft. This reading is called Forward site ( FS) Therefore height of point D is calculated as follows Height of point D = Height of Instrument (HI) – FS = 105.5 – 2.3 = 103.2 ft

Distance between the instrument and the station D can be measured using meter tape or from the difference between upper & lower readings on the telescope.

IN TEXT QUESTIONS

Fill in the blanks.

  1. …………. is the lowest level of the earth.
  2. Dumpy level survey measurements starts from a …………….
  3. HI= BM+BS ( True / False)
  4. Elevation=HI +FS( True / False)
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