Practical 1 To determine rate of infiltration and infiltration capacity using double ring infiltrometer

Practical to Determine Rate of Infiltration and Infiltration Capacity Using Double Ring Infiltrometer

Objective:

To determine the rate of infiltration and infiltration capacity of soil using a double-ring infiltrometer.

Equipment Needed:

1. Double-ring infiltrometer – consists of two concentric metal rings (inner and outer).
2. Measuring cylinder or container for water.
3. Stopwatch or timer.
4. Ruler or measuring tape.
5. Bucket for water supply.
6. Calculator for calculating infiltration rates.
7. Soil auger or hand tool to remove soil for setting up the rings.
8. Leveling device (e.g., spirit level) for ensuring rings are set properly.

Theory:

• Infiltration refers to the process by which water enters the soil. The rate of infiltration is the amount of water that enters the soil per unit of time (e.g., cm/hr).
• Infiltration capacity refers to the maximum rate at which soil can absorb water. It is typically determined at the start of the test when the infiltration rate is highest.

Procedure:

1. Site Selection:

   • Choose a flat, undisturbed area where you intend to measure the infiltration.
   • Ensure the soil is homogeneous and free from plant cover or disturbances.

2. Setup of Double Ring Infiltrometer:

   • Place the double ring infiltrometer on the soil surface. The inner ring (smaller diameter) should be positioned centrally within the outer ring (larger diameter).
   • The rings should be pressed into the soil to a depth of approximately 10 cm to minimize water seepage from the sides.
   • Use a level to ensure that the rings are placed evenly on the soil surface.

3. Water Filling:

   • Fill the inner and outer rings with water to a specific level (e.g., 5 cm above the soil surface).
   • The outer ring serves to minimize lateral flow of water, ensuring that the water in the inner ring infiltrates vertically into the soil.

4. Start the Experiment:

   • Start the timer as soon as the water is filled.
   • Measure the water level in the inner ring at regular intervals (e.g., every 5 minutes) using a graduated scale or a marked measuring cylinder. Record the drop in water level (in cm) for each time interval.
   • Ensure that you refill the inner ring as needed to maintain a constant water level. The outer ring should not need refilling if the test is done correctly.

5. Data Collection:

   • Continue to record the water level at regular intervals (e.g., every 5 minutes) for at least 30 minutes or until the infiltration rate stabilizes.
   • The rate of infiltration is generally faster at the beginning of the test and then decreases as the soil becomes saturated.

6. Calculation of Infiltration Rate:

   • Use the following formula to calculate the infiltration rate at each time interval: $$\text{Infiltration Rate} = \frac{\text{Volume of water infiltrated (cm}^3)}{\text{Area of inner ring (cm}^2) \times \text{Time (hours)}}$$
   • The volume of water infiltrated can be determined by measuring the water added to the inner ring.
   • Infiltration Capacity can be considered as the rate of infiltration when the rate becomes constant (after the initial fast infiltration phase).

7. Plotting the Data:

   • Plot the infiltration rate (y-axis) versus time (x-axis) on a graph. Initially, the rate will be high, but it will decrease over time as the soil becomes saturated.
   • The slope of the curve can give an idea of how quickly the soil absorbs water.
   • The point where the curve flattens out corresponds to the infiltration capacity, which is typically the maximum infiltration rate that the soil can handle at a given time.

8. Conclusion:

   • The rate of infiltration is the change in the water level over time.
   • The infiltration capacity can be determined from the data as the point at which the water level in the inner ring stabilizes, indicating the maximum rate at which the soil can absorb water.

Calculations:

• Infiltration rate at any time $t$:

  $$I_t = \frac{\Delta h}{t \times A}$$

  Where:

  • $I_t$ is the infiltration rate at time $t$ (cm/hr).
  • $\Delta h$ is the change in water level in the inner ring (cm).
  • $A$ is the area of the inner ring ($\pi \times r^2$).

• Infiltration capacity: The point at which the rate becomes constant or the water infiltrates the soil at a uniform rate.

Observations:

• Take note of the soil type (e.g., sandy, loamy, clayey), which significantly influences the infiltration rate.
• Compare infiltration rates at different times (beginning, middle, and end) to observe the change over time.

Safety Considerations:

• Be cautious when handling tools and equipment.
• Ensure that the test site is free from obstacles and that the equipment is handled carefully to avoid damage.

References:

• Soil Physics and Hydrology Textbooks
• Relevant Soil Science Research Papers
• https://www.youtube.com/watch?v=PYvfTxQhbOQ