1.15.5.a. Rise and Fall Method

Since the ground is undulating, the Staff reading will be more if kept at a lower point, and less if kept at a higher point. Thus, the staff readings provide information regarding relative rise and fall of ground points.

The rise and fall method in surveying helps us measure the changes in height between points on the ground. When the staff is placed at a low point, it will read higher as the ground rises. Conversely, if the staff is placed on a higher point, the reading will be lower. This difference in readings signals whether the land is sloping upwards (rise) or downwards (fall).

Think of a roller coaster. When you are going up the hill, you feel like you're getting higher, similar to an increased measurement on the staff. When you go down, the feeling of descent is like lower staff readings. Just like how roller coasters go up and down, the rise and fall method tracks the changes in the land's height.

The difference in the staff readings indicates a rise or fall according to if the staff reading is smaller or greater than that at the preceding point, respectively. The difference between consecutive points is calculated by comparing each point after the first with that immediately preceding it.

To find the elevation of each point using the rise and fall method, you compare the current staff reading to the last reading. If the current reading is greater than the previous one, there is a rise. If it’s less, that indicates a fall. These calculations help create a profile of the land's elevations.

Imagine you are climbing stairs. Each step up feels like a rise, while each step down feels like a fall. If you track how many steps you gain versus how many you lose, you can determine how high or low you are compared to where you started. The same principle applies to calculating elevation with staff readings.

The RL of each point is then determined by adding rise or subtracting fall to/from the RL of the preceding point. This is the basic concept behind rise and fall method for finding out the elevations of unknown points.

Once you know if you are rising or falling, you can determine the new Relative Level (RL) of your current point. You take the RL of the last point and either add the rise or subtract the fall to find the RL of the current point. This systematic approach allows for a clear tracking of elevations.

Consider a hiker who starts at a base camp with an elevation of 1000 meters. If they hike up a mountain to a new point that is 30 meters higher, the new elevation would be 1030 meters (1000 + 30). Conversely, if they descend to a point that is 20 meters lower, their elevation would then be 1010 meters (1030 - 20). This consistent approach allows hikers to keep track of how high they are!

At the end of all computations, check is applied as: Σ BS – Σ FS = Σ Rise – Σ fall = First RL – Last RL.

To ensure accuracy, at the conclusion of the elevations calculations, a final check is performed. This involves summing all the back sights (BS) and fore sights (FS) and comparing them to the total rise and fall. This relationship helps confirm whether the calculations were done correctly by ensuring that the total change matches the difference between the first and last RL.

Think of a budget. When you sum up all your expenses (like fore sights) and incomes (like back sights), at the end of the month, they should balance out with what you initially had (your starting budget). If they do not align, it signifies that there may be a mistake in your calculations.

This method is a laborious method as staff reading of each point on the ground after the first is compared with that preceding it, and the difference of level is entered as a rise or fall. It is slow and simple method. But, it is more precise because intermediate sights are also considered in calculations and checking the results.

While the rise and fall method may take longer due to the need for multiple readings and comparisons, it is highly accurate because it accounts for all heights between points. This thorough method is particularly useful in projects where precise measurements are crucial, like construction or land surveying.

It's similar to writing a detailed report. Although it takes longer to gather and compile all the necessary information, by the end, you have a well-rounded, accurate representation of the topic. In contrast, a quick glance might miss important details. In surveying, precision can impact the safety and success of construction projects.

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