Question

A windbreak 20 m tall will give some protection for ______________ on the upwind side and on the downwind side respectively

• A. 100 m and 500 m
• B. 25 m and 100 m
• C. 25 m and 275 m
• D. 100 m and 375 m

Hint:

The "Rule of Thumb" for leeward protection is $20H$. For windward, it is much smaller, usually $5H$.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
This question relates to the "Shelter effect" of windbreaks in agroforestry. A windbreak provides protection over a distance proportional to its height ($H$).

Step 2: Key Formula or Approach:
1. Protection on the upwind (windward) side typically extends to $2H$ to $5H$.
2. Protection on the downwind (leeward) side extends to $15H$ up to $25H$.

Step 3: Detailed Explanation:

• Height ($H$) = 20 m.

• Upwind Side: Applying the rule ($5H$):
\[ 5 \times 20 = 100 \text{ m} \]

• Downwind Side: Applying the standard practical limit ($15H$ to $20H$):
\[ 15 \times 20 = 300 \text{ m} \]
\[ 20 \times 20 = 400 \text{ m} \]

• The value 375 m falls within the highly effective range ($15H$ - $20H$).

• Thus, for a 20 m tall tree, protection is observed up to 100 m upwind and around 375 m downwind.

Step 4: Final Answer:
The protection is for 100 m and 375 m respectively.