To determine the Staff Readings at different points on the natural ground by Auto Level.

Object: To determine the staff readings at different points on the natural ground by Auto level (with the Rise and Fall Method)

Theory:

Leveling is a branch of surveying that deals with the measurement of relative heights of different points on, above, or below the surface of the earth. Thus, in leveling, the measurements are taken in the vertical plane. Simply, leveling is the process used to determine a difference in elevation between two points.

Some important definitions:

• Station: A point where the leveling staff is kept.
• Datum or Datum surface: It is a level surface with respect to which the levels of points are measured. It may be a standard surface like mean sea level(M.S.L)or an arbitrary surface.
• BenchMark(B.M):A benchmark is a permanent physical mark of known elevation above the mean sea level.
• Height of instrument (H.I): For any setup of the level, the elevation of the line of sight is called the height of the instrument.
• Backsight(S):The back sight is the first staff reading taken after setting up the instrument.
• Foresight (F.S): The foresight is the staff reading either held at the last point whose elevation is required or held at the change point before shifting the instrument.
• Intermediate sight (I.S): It is the staff reading taken between the backsight and foresight.
• Changepoint(C.P):It is the point where both backsight and foresight are taken.

Instrumentsrequired:

1. Rope (100m)
2. 10 Arrows
3. 2 Ranging rods
4. AutoLevel
5. Tripod Stand
6. Staff rod

Procedure:

1. Lay down the rope in a straight line on the irregular ground.
2. Fix the first ranging rod at the zero mark and the other at the 100m mark.
3. Place the arrows at 10m intervals from the zero mark from B to J.
4. Set up the Auto level at the Level position.
5. Hold the staff on the Datum i.e. Bench Mark (A) and take a reading. This will be the Backsight (B.S)because it is the first staff reading after the leveling instrument has been set up.
6. Move the staff to B e. at 10m intervals and take a reading. This will be an intermediate sight (I.S).
7. Repeat step 3 for points C, D, E, F, G, H, I and J. All of these will be the intermediate sights.
8. Move the staff toKand take a reading. This will be a foresight (F.S) because it is the last reading.
9. Note down all the readings for B.S, I.S, and F.S in a table shown below in the field book.

Calculations:

Formulaeforcalculations:

• Rise/Fall = staff reading at previous point – staff reading at new point: If the value is positive, it will be Rise and if negative, it will be Fall.
• ReducedLevel(R.L)= Previous L + Rise OR =Previous R.L – Fall

ApplyingCheck:

∑B.S–∑F.S=∑Rise– ∑Fall=LastR.L –FirstR.L

Observations in the field: