What is the rise and fall method in leveling?

Short Answer:

The rise and fall method in leveling is a technique used to determine the difference in elevation between points. It involves comparing successive staff readings to find whether a point has risen or fallen relative to the previous one. The difference between readings is used to calculate the height of each point. This method ensures high accuracy and is commonly used in surveying to measure land elevations for construction and road projects.

Detailed Explanation:

The rise and fall method is a systematic approach used in leveling to determine the elevation difference between multiple points. It provides accurate height measurements by calculating whether each point is higher (rise) or lower (fall) compared to the previous one.

Principle of the Rise and Fall Method:

  • If the next point’s staff reading is lower than the previous one, there is a rise in elevation.
  • If the next point’s staff reading is higher than the previous one, there is a fall in elevation.
  • The difference between the readings gives the rise or fall value, which is then used to calculate the reduced levels (RL) of different points.

Steps to Perform the Rise and Fall Method:

  1. Take Staff Readings:
    • Place a leveling instrument at a central position.
    • Take the first reading (Back Sight – BS) at a known reference point (benchmark).
    • Take additional readings (Intermediate Sight – IS) at different survey points.
    • Take the final reading (Fore Sight – FS) at the last point.
  2. Calculate the Rise or Fall:
    • Rise = Previous Staff Reading – Next Staff Reading (If the new point is at a higher elevation).
    • Fall = Next Staff Reading – Previous Staff Reading (If the new point is at a lower elevation).
  3. Compute Reduced Levels (RL):
    • New RL = Previous RL + Rise (If the point has risen).
    • New RL = Previous RL – Fall (If the point has fallen).
  4. Check for Accuracy:
    • The sum of all rises minus the sum of all falls should equal the difference between the first and last reduced levels.

Advantages of the Rise and Fall Method:

  • Provides high accuracy compared to other leveling methods.
  • Helps in detecting errors easily since calculations can be checked.
  • Useful in road construction, drainage projects, and land surveys.

Disadvantages:

  • Requires more calculations, making it a time-consuming method.
  • Any mistake in intermediate readings can affect the final results.
Conclusion:

The rise and fall method is an effective technique for finding elevation differences in surveying. It ensures precise measurements and is widely used in civil engineering for construction and land development. By carefully computing rises and falls, surveyors can accurately determine the elevation of various points.