Rise and Fall Method Basics

The Rise and Fall method is a technique used in surveying, specifically in leveling, to calculate the Reduced Level (RL) of various points. The primary goal is to determine the elevation difference between consecutive points accurately. This method involves calculating whether the ground has risen or fallen between two points based on the staff readings taken.

Staff Readings Explained

In leveling, two key readings are involved when moving from one point to another:

• Backsight (BS) Reading: This is the first reading taken by the surveyor on a point of known Reduced Level (RL), looking backward towards the previously occupied instrument position.
• Foresight (FS) Reading: This is the last reading taken by the surveyor from an instrument station, looking forward to the point whose RL needs to be determined. It is also referred to as the 'fore reading'.

The 'preceding point' typically refers to the point where the backsight reading was taken.

Interpreting Readings for RL Changes

The change in elevation (rise or fall) between the preceding point and the current point is determined by comparing the backsight (BS) and foresight (FS) readings. The specific statement considered correct is:

If a staff reading (fore reading) is greater than that at the preceding point, then there is a fall and if smaller then there is a rise.

This statement implies the following logic:

• If FS > BS: A fall occurs between the points.
• If FS < BS: A rise occurs between the points.

The relationship can be summarized in the following table:

Analyzing Surveying Options

Let's evaluate the given options based on the principle stated in the correct answer:

• Option 1: "If a staff reading (fore reading) is greater than that at the preceding point, then there is a fall and if smaller then there is a rise." - This statement perfectly matches the logic presented in the correct answer.
• Option 2: "If reading of a preceding point is greater, then there is a fall." - This correctly identifies a fall when BS > FS, but it's incomplete as it doesn't mention the case for a rise.
• Option 3: "If a staff reading (fore reading) is greater than that at the preceding point, then there is a rise." - This contradicts the correct statement, as it claims a rise when FS > BS.
• Option 4: "If a staff reading (fore reading) is smaller than that at the preceding point, then there is a fall and if greater then there is a rise." - This statement claims a fall when FS < BS and a rise when FS > BS, which is the opposite of the logic stated in the correct answer.

Correct Statement Identification

Based on the analysis, Option 1 is the correct statement because it accurately reflects the relationship between foresight and preceding point readings as defined in the context of determining rise and fall for calculating reduced levels.