Question

Runoff plots are isolated areas of commonly used size in hectares

• A. 1/100 to 1/50
• B. 1/125 to 1/100
• C. 1/250 to 1/125
• D. 1/500 to 1/250

Hint:

The standard USLE plot size is $5\text{ m}^2$, which is almost exactly $1/250\text{ ha}$. Remembering this value makes it easy to identify the correct range.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Runoff plots are small, bounded outdoor areas used to measure surface runoff and soil loss under natural or simulated rainfall conditions.
These plots are designed to isolate a specific segment of the slope to study soil erosion and water infiltration.

Step 2: Detailed Explanation:
Standard runoff plots are classified based on their dimensions and purposes:
- Micro-plots and small plots are commonly used in agricultural research stations to evaluate different tillage practices and crop covers.
- A standard Universal Soil Loss Equation (USLE) plot, designed by Wischmeier and Smith, has dimensions of $13\text{ m}$ in length and $1.83\text{ m}$ in width.
Let us calculate the area of a standard USLE plot:
\[ \text{Area} = 13\text{ m} \cdot 1.83\text{ m} \approx 5\text{ m}^2 \]
To convert this area into hectares:
\[ \text{Area in ha} = \frac{5}{10000} = 0.00405\text{ ha} \approx \frac{1}{247}\text{ ha} \approx \frac{1}{250}\text{ ha} \]
Smaller micro-plots used for specific infiltration and erosion studies have areas around $20\text{ m}^2$, which corresponds to:
\[ \text{Area} = \frac{20}{10000} = 0.002\text{ ha} = \frac{1}{500}\text{ ha} \]
Therefore, the most commonly used range of sizes for isolated runoff plots is $1/500\text{ to } 1/250\text{ hectares}$.

Step 3: Final Answer:
The commonly used size of runoff plots ranges from 1/500 to 1/250 hectares.