Step 1: Understanding the Concept:
Contour bunding is a soil and water conservation practice where small earthen embankments (bunds) are constructed along the contours of the land. These bunds intercept runoff and promote infiltration. However, the land occupied by the bunds themselves cannot be used for cultivation. The question asks for the typical percentage of the total area that is lost to cultivation due to the construction of these bunds.
Step 2: Detailed Explanation:
1. The area lost to cultivation depends on the design of the bunds (their cross-sectional area) and the spacing between them.
2. The spacing between bunds, known as the Horizontal Interval (HI) or Vertical Interval (VI), depends on the slope of the land. On steeper slopes, bunds need to be closer together, so a larger percentage of the area is lost.
3. The cross-section of a bund is typically trapezoidal, with a certain base width, top width, and height.
4. To calculate the percentage area lost, one would calculate the area occupied by one bund over a length L (Area = Base Width $\times$ L) and divide it by the total area between two bunds over that same length (Area = Horizontal Interval $\times$ L).
\[ % \text{Area Lost} = \frac{\text{Base Width of Bund}}{\text{Horizontal Interval}} \times 100 \]
5. While this can be calculated for specific designs, there are generally accepted average values based on typical field conditions for which contour bunding is recommended (usually on slopes from 1% to 6%).
6. For this range of slopes, the area lost to cultivation due to contour bunds is generally estimated to be in the range of 3% to 5%.
7. Let's analyze the options given this standard range:
- 2% is a bit low.
- 5% is a very common and representative figure for the upper end of the typical range.
- 7% and 10% are generally considered too high for contour bunding; such high area loss might be associated with more intensive structures like bench terraces on very steep slopes.
Step 3: Final Answer:
The typical percentage of area lost to cultivation under a contour bunding system is around 5%. Therefore, option (B) is the correct answer.