Practical 2: Measurement of Rainfall

Practical: Measurement of Rainfall

Objective:

To measure and analyze rainfall using a standard rain gauge and calculate the total precipitation over a given period.

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1. Apparatus Required:

1. Standard Rain Gauge (e.g., Symons Rain Gauge or Tipping Bucket Rain Gauge)
2. Measuring Cylinder (for manual gauges)
3. Data Recording Sheet or Digital Logger
4. Funnel and Storage Bottle (for manual collection)

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2. Theory:

Rainfall is measured as the depth of water (in mm or cm) that would accumulate on a flat, impermeable surface if it did not evaporate, run off, or infiltrate into the ground.

Formula for Rainfall Measurement:

$$\text{Rainfall (mm)} = \frac{\text{Collected Rainwater Volume (ml)}}{\text{Area of Rain Gauge Collector (cm}^2\text{)}} \times 10$$

where:

• Collected rainwater volume is in milliliters (ml).
• Collector area is in square centimeters (cm²).

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3. Procedure:

A. Manual Measurement (Using a Symons Rain Gauge)

1. Setup the Rain Gauge

   • Place the rain gauge in an open area, free from obstructions like trees or buildings.
   • Ensure the gauge is level on the ground.

2. Collect the Rainfall Data

   • After a rainfall event (or daily), carefully remove the funnel and measure the collected water.
   • Use a measuring cylinder to determine the volume in milliliters (ml).

3. Calculate Rainfall Depth

   • Use the formula given above to determine the rainfall depth in mm.

4. Record Observations

   • Note the date, time, and total precipitation in a data sheet.

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B. Automatic Measurement (Using a Tipping Bucket Rain Gauge)

1. Install the Tipping Bucket Rain Gauge

   • Mount the device in an open area and connect it to a data logger.

2. Automatic Recording

   • Each bucket tip corresponds to a fixed amount of rainfall (e.g., 0.2 mm per tip).
   • The sensor records each tip and stores data digitally.

3. Data Analysis

   • Retrieve data and analyze rainfall patterns over time.

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4. Observations & Calculations:

Date	Time	Collected Rainwater (ml)	Collector Area (cm²)	Rainfall (mm)
01-02-2025	10:00 AM	500 ml	100 cm²	50 mm
02-02-2025	10:00 AM	200 ml	100 cm²	20 mm

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5. Conclusion:

• The rainfall measurement technique depends on manual or automatic methods.
• The collected data helps in hydrological analysis, flood forecasting, and water resource management.