Dumpy Level Surveying | How to Use a Dumpy Level

A Dumpy level is an essential tool in the field of surveying that enables professionals to achieve precise measurements of elevation differences. This instrument, known for its accuracy and stability, is widely used in construction, engineering projects, and landscaping.

What is a Dumpy Level?

A Dumpy level is a type of optical level used in surveying to establish or verify points in the same horizontal plane. This instrument consists of a telescope fitted with crosshairs, mounted on a tripod with a bubble level for accuracy. It allows users to measure elevation differences by sighting through the telescope at graduated leveling staffs placed at different points on the land.

The term "dumpy" refers to the short, solid nature of the telescope, making it more durable and resistant to knocks compared to more sensitive instruments like the transit level.

Components of a Dumpy Level

To use a dumpy level effectively, it's essential to understand its core components:

• Telescope: The main part of the dumpy level that magnifies the view of the staff for accurate readings.
• Eyepiece: Located at the end of the telescope, it allows users to view the graduated staff.
• Focusing Knob: Adjusts the clarity of the image being viewed through the telescope.
• Horizontal Circle: This part allows the telescope to rotate 360 degrees horizontally.
• Leveling Screws: These screws help to adjust and level the instrument accurately on its tripod.
• Bubble Level (Spirit Level): This is used to ensure the instrument is perfectly level before taking measurements.
• Tripod: A three-legged stand that holds the dumpy level in place and provides a stable base for accurate measurements.

How to Set Up a Dumpy Level

1. Setting Up the Tripod

The first step in using a dumpy level is to set up the tripod on firm ground. Follow these steps to ensure proper setup:

• Extend the tripod legs and position them so that the tripod head is roughly at your eye level.
• Adjust the legs until the tripod is stable and secure on the ground.
• Use the tripod's adjustable clamps to lock the legs into place.

2. Mounting the Dumpy Level on the Tripod

Once the tripod is in place, attach the dumpy level to the tripod by securing it with the mounting screw. Ensure that the instrument is tightly fastened to prevent any unwanted movement during measurements.

3. Leveling the Instrument

To ensure accurate results, the dumpy level must be precisely horizontal. This can be done by adjusting the leveling screws beneath the instrument:

• Begin by looking at the bubble level on the dumpy level.
• Turn the leveling screws in opposite pairs to move the bubble into the center of the marked circle on the level.
• Repeat the process with the other pair of screws until the bubble remains centered, indicating that the instrument is level.

How to Take Measurements with a Dumpy Level

1. Position the Levelling Staff

After setting up the dumpy level, the next step is to position a levelling staff (a graduated staff) at the location where you need to measure elevation. Make sure the staff is held upright and in a vertical position.

2. Sighting Through the Telescope

Look through the eyepiece of the dumpy level and focus on the levelling staff by adjusting the focusing knob. The crosshairs within the telescope should align with the readings on the staff.

3. Taking the First Reading (Backsight)

The first reading you take is called the backsight or benchmark. This is a reference point for the entire leveling process. It is taken from a known point of elevation, such as a previously established benchmark or starting point.

• Align the crosshairs with the staff and take note of the reading where the horizontal crosshair intersects the scale on the staff.
• Record the reading as your backsight.

4. Moving the Levelling Staff to a New Position (Foresight)

Once the backsight is recorded, the staff is moved to a new location where you want to measure the elevation. This reading is called the foresight.

• Adjust the telescope horizontally to aim at the staff in its new position.
• Focus the telescope if needed and record the new reading as the foresight.

5. Calculating Elevation Differences

The key objective of using a dumpy level is to determine the difference in height between two points. To calculate this:

• Subtract the foresight reading from the backsight reading to find the height difference.
• Continue moving the levelling staff to different positions and repeating the process until all necessary points have been measured.

This process helps establish accurate elevations across a site, making it critical for projects involving land grading, foundation setting, or road construction.

Tips for Accurate Dumpy Level Surveying

1. Double-check Your Readings

Surveying often requires a high degree of precision. Make sure to double-check your readings before recording them. Small errors in measurement can have significant effects on the final results.

2. Keep the Staff Vertical

If the leveling staff is not held perfectly vertical, your readings may be inaccurate. Make sure the staff remains upright at all times during the measurement process.

3. Perform Regular Instrument Calibration

To ensure accuracy, it's important to calibrate the dumpy level periodically. Misalignments in the telescope or leveling system can lead to inaccurate measurements if not corrected.

Applications of a Dumpy Level

Dumpy levels are widely used in various fields, including:

• Construction: For establishing building foundations and determining ground levels.
• Civil Engineering: To ensure roadways, bridges, and infrastructure projects are designed on level ground.
• Landscaping: For grading land and ensuring proper drainage and water flow.
• Agriculture: To design irrigation systems and field leveling.

Common Errors in Dumpy Level Surveying

1. Instrumental Errors

Even with careful handling, a dumpy level can suffer from instrumental errors if it's not properly maintained. Dirt on the lens, misaligned components, or uncalibrated settings can all cause issues.

2. Human Errors

Human error is another common cause of inaccurate results in dumpy level surveying. Incorrect readings, improperly leveled instruments, or misinterpreted results can all lead to significant inaccuracies.

3. Parallax Errors

Parallax errors occur when the crosshairs inside the telescope are not properly aligned with the leveling staff. Always ensure that the staff is viewed perpendicularly to avoid this type of error.

Conclusion

Using a dumpy level is crucial for achieving accurate and reliable results in a wide range of surveying tasks. By following the proper setup, calibration, and measurement techniques, you can ensure that the data you gather is both precise and dependable. From construction sites to engineering projects, the dumpy level remains an indispensable tool in the field of surveying.

For more information, please watch the video tutorial