Booking and reducing of levels
Booking and reducing levels is an essential part of land surveying and construction projects. It involves the process of measuring and recording elevations or heights of points on the ground relative to a reference point or benchmark. This information is crucial for various applications in civil engineering, including site design, construction, and drainage planning. Here's a step-by-step guide on how to book and reduce levels:
**Booking Levels:**
1. **Setup and Instrument Calibration:**
- Begin by setting up your leveling instrument, such as a dumpy level or automatic level, on a stable tripod.
- Make sure the instrument is correctly leveled, and the crosshairs are focused for accurate measurements.
- Check and adjust the instrument's calibration if necessary.
2. **Select Benchmark:**
- Identify a known benchmark or reference point with a known elevation. Benchmarks are typically permanent markers placed by surveyors or government agencies.
3. **Establish a Level Line:**
- Set up the leveling instrument at a convenient location, ensuring it has a clear line of sight to the benchmark and the points you want to measure.
4. **Take Backsights and Foresights:**
- Start by taking a backsight reading on the benchmark. Record this reading along with the height of the instrument (HI).
- Next, take foresight readings on the points whose elevations you want to determine. These points are typically stakes, ground features, or objects.
5. **Recording Data:**
- Create a field book or digital record for data entry.
- Record the following information for each foresight:
- Point description or identifier.
- The reading on the leveling staff (RL or Reduced Level).
- The height of the instrument (HI).
- Calculate the height of collimation (HC) for each foresight, which is the sum of HI and RL.
- Calculate the rise (R) or fall (F) by comparing the foresight reading with the backsight reading.
**Reducing Levels:**
1. **Calculate Reduced Levels:**
- Subtract the backsight reading from each foresight reading to determine the rise or fall in elevation. Use the formula:
- RL (Reduced Level) = HI (Height of Instrument) + Rise or - Fall
2. **Record Reduced Levels:**
- Enter the calculated RL values in your field book or digital record next to the corresponding point descriptions.
3. **Check for Errors:**
- Review your recorded data for any errors or inconsistencies.
- Ensure that the rises and falls are correctly calculated.
- Double-check the math to avoid mistakes.
4. **Apply Corrections (if necessary):**
- Apply any necessary corrections for instrument or atmospheric effects, such as refraction and curvature corrections, to improve the accuracy of your elevation measurements.
5. **Final Documentation:**
- Prepare a final leveling report or elevation plan that includes all recorded RL values and descriptions of the surveyed points.
- Present the data in a clear and organized manner for use in engineering and construction projects.
Booking and reducing levels accurately is essential for creating elevation profiles, contour maps, and ensuring precise vertical measurements in civil engineering and construction applications. It forms the foundation for various design and planning activities in the field.
Using Rise / Fall Method
In this method booking is done in the following manner,
| B.S | I.S | F.S | Rise | Fall | R.L | Remarks |
|---|---|---|---|---|---|---|
| 2.570 | – | – | – | – | 100.00 | A |
| 3.750 | – | 1.200 | 1.370 | – | 101.37 | C.P |
| – | – | 3.750 | – | 0.70 | 100.67 | B |
| 5.620 | – | 4.950 | 1.370 | 0.70 | – | – |
- On any page of book the first reading is always a B.S and last reading is always a F.S. If you are not getting F.S as last reading on each page then it means you have done mistake while booking readings.
- From the B.S next F.S is subtracted. If the answer is +ve it will be Rise and if the answer is -ve it be Fall and put that reading in respective box.
- In the above table, I have assumed that Reduce Level (R.L) of point A is 100.0 and you can see R.L of point B is 100.67, which shows that point B is .67 units higher than point A.
In case of numerous readings the check should be applied at the end of each page while booking reading,
∑ (B.S) – ∑ (F.S) = ∑ Rise – ∑ Fall = R.L of last point – R.L of first point 5.620 – 4.950 = 1.37 – 0.70 = 100.67 – 100 0.67 = 0.67 = 0.67
Using Height of collimation Method (H.O.C)
For this method use the following formulas,
R.L + B.S = H.O.C and H.O.C – F.S = R.L
| B.S | I.S | F.S | H.O.C | R.L | Remarks |
|---|---|---|---|---|---|
| 2.50 | – | – | 102.50 | 100.00 | – |
| 1.75 | 1 | 1.95 | 102.30 | 100.55 | – |
| – | 2.55 | – | – | 99.75 | – |
| – | 2.70 | – | – | 99.60 | – |
| 2.95 | – | 3.10 | – | 99.20 | – |
| – | – | 2.75 | – | 99.40 | – |
| 7.20 | – | 7.80 | – | – | – |
All other considerations are same as Rise/ Fall method. Below check have applied,
∑ (B.S) – ∑ (F.S) = R.L of last point – R.L of first point = 7.2 – 7.8 = 99.4 – 100 = -0.6 = -0.6
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