Rise and Fall Method

For the same set up of an instrument, Staff reading is more at a lower point and less for a higher point. Thus, staff readings provide information regarding relative rise and fall of terrain points. This provides the basics behind rise and fall method for finding out elevation of unknown points.

With reference to Figure 13.2, when the instrument is at I₁, the staff reading at A (2.365m) is more than that at S₁ which indicates that there is a rise from station A to S₁ and accordingly the difference between them (1.130m) is entered under the rise column in Table 13.1. To find the elevation of S₁ ( 101.130m), the rise (1.130m) has been added to the elevation of A (100.0m). For instrument set up at I₂ , S₁ has been treated as a point of known elevation and considered for backsight (having reading 0.685m) . Foresight is taken at S₂ and read as 3.570m i.e, S₂ is at lower than S₁ . Thus, there is a fall from S₁ a nd S₂ and there difference (2.885m) is entered under the fall column in Table 13.1. To find the elevation of S₂ ( 98.245m), the fall (2.885m) has been subtracted from the elevation of S₁ (101.130m). In this way, elevation of points are calculated by Rise and Fall method.

Table 13.1 Level book note for Rise and Fall method

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