Aquaculture Engineering (2+1)

Booking and Reducing Levels - Rise and Fall method

Unit 1- Surveying

Find out the elevation of points using different methods

Booking and Reducing Levels

Rise and Fall method
In this method the height of instrument is not at all calculated but the difference of level between consecutive points is found out by comparing the staff reading on the two points for the same setting of the instrument. The difference between their staff readings a rise or fall according as the staff reading at the point is smaller or greater than that at the proceeding point. The figures for rise and fall worked out thus for all the points give the vertical distance of each point above or below the preceding one, and if the level of any one point is known the level of the next will be obtained by adding its rise or subtracting its fall as the case may be.

Check
The difference between the sum of back sight and sum of the fore sights should be equal to the difference between the sum of rise and sum of fall and should also be equal to the difference between the first R.L. and Last R.L.
∑ BS - ∑FS = ∑Rise - ∑Fall = First R.L.- Last R.L.

2. The following staff readings were observed successively with a level, the instrument having been moved after second, fifth and seventh readings.
0.865, 2.105, 1.025, 1.580, 1.865, 2.230, 2.835, 2.355, 1.760
Enter the above readings in a page of a level book and calculate the R.L. of points if the first reading was taken with a staff held on a B.M. of 560.500 (Use rise and fall method)

Check = ∑BS - ∑FS = ∑rise - ∑Fall = Frits RL – Last RL
= 6.475 – 8.565= 0.595-2.685 = 558.41-560.500
= 2.09 = 2.09 = 2.09