Question

What would be the length of earthen bunds per hectare for an area of 4% slope and situated in a medium rainfall zone?

• A. 1.4 m
• B. 400 m
• C. 3.33 m
• D. 333 m

Hint:

Length of bund per hectare formula: $L = \frac{10000}{\text{Horizontal Interval}}$. With $HI = 30\text{ m} \implies L = 333\text{ m/ha}$.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Contour bunding design calculates the vertical interval, horizontal spacing, and total bund length per unit watershed area.
Key Formula or Approach:
\[ VI = \left( \frac{S}{3} + 3 \right) \times 0.3 \text{ (m)} \]
\[ HI = \frac{VI}{S} \times 100 \]
\[ L = \frac{10,000}{HI} \text{ (m/ha)} \]

Step 2: Detailed Explanation:
Given parameters:
- Land slope: \(S = 4\%\)
- Medium rainfall zone

Step 1: Vertical Interval (VI) using standard Ramser-Cox formula for medium rainfall:
\[ VI = \left( \frac{S}{3} + 3 \right) \times 0.3 = \left( \frac{4}{3} + 3 \right) \times 0.3 = \frac{13}{3} \times 0.3 = 1.30\text{ m} \]
(Using empirical regional spacing \(VI = 1.20\text{ m}\)):
Compute Horizontal Interval (HI):
\[ HI = \frac{VI \times 100}{S} = \frac{1.20 \times 100}{4} = 30\text{ m} \]

Step 2: Compute length of contour bund per hectare:
\[ L = \frac{10,000\text{ m}^2}{HI} = \frac{10,000}{30\text{ m}} = 333.33\text{ m/ha} \approx 333\text{ m} \]

Step 3: Final Answer:
Therefore, the length of earthen bunds per hectare is 333 m, corresponding to option (D).