Dumpy Level Survey Practical

 DUMPY LEVEL SURVEY BY INSTRUMENT HEIGHT METHOD

Bodoland University

STATION	POINTS	L. C	ELEVATION			R. L (in m)	DISTANCE
			B.S	I.S	F.S
A	1	50 + 1.42	1.45			49.97	7.1
	2			1.88		49.54	7.25
	3			1.7		49.72	14.28
	4				1.16	50.29	21.5

 

 

 

 

 

 

 

1.      Instrument height (line of collimation)

Given benchmark reduced level (RL) at Station A:  and a back sight on Point 1: .

               So, the line of collimation is the horizontal line .

2.      Steps & calculations (digit-by-digit)

RL (Reduced Level) = LC − staff reading at each point:

·        Point 1: RL = 51.42 − 1.45 = 49.97 m

·        Point 2: RL = 51.42 − 1.88 = 49.54 m

·        Point 3: RL = 51.42 − 1.70 = 49.72 m

·        Point 4: RL = 51.42 − 1.16 = 50.26 m

DUMPY LEVEL SURVEY BY INSTRUMENT HEIGHT Bodoland University

 

Introduction

A Dumpy Level Survey using the Instrument Height (HI) method is a common levelling technique used in surveying to determine the Reduced Levels (RLs) of various points on the ground. In this method, the height of the instrument (also called the line of collimation) is first established using a known Benchmark (BM) or a point of known elevation.
After that, the RLs of other points are calculated by subtracting their staff readings from the instrument height.

This practical helps students understand:

1. How to set up and use a dumpy level
2. How to take back sight (BS), intermediate sight (IS), and fore sight (FS) readings
3. How to compute RLs using the HI method
4. How to ensure accuracy during field observations

It is one of the fundamental exercises in surveying taught at Bodoland University.

Interpretation

From the provided data, the instrument height (line of collimation) was calculated using the benchmark at Station A. The HI was found to be 51.42 m based on the back sight reading.

Using this HI, the Reduced Levels for points 1, 2, 3, and 4 were calculated as:

1. Point 1: RL = 49.97 m
2. Point 2: RL = 49.54 m
3. Point 3: RL = 49.72 m
4. Point 4: RL = 50.26 m

These RL values indicate the relative elevations of the points.

• Point 2 has the lowest elevation, meaning the ground slopes downward slightly from Point 1.
• Point 4 has the highest elevation, showing a rise in ground level.
• The variations in RLs provide a clear profile of the terrain across the survey line.

Overall, the results show a natural undulating ground surface with minor elevation changes, which is typical for many survey sites.