Concept:
Contour bunding is a soil and water conservation measure in which bunds are constructed along contour lines.
Step 1: Contour bunds reduce runoff velocity.
Step 2: They help increase infiltration and reduce soil erosion.
Step 3: However, the land occupied by bunds cannot be used for crop cultivation.
Step 4: The approximate land loss under contour bunding is generally taken as:
\[
10%
\]
\[
\boxed{10%}
\]