What is the primary direction that drainage flows in relation to contour lines?

The primary direction that drainage flows in relation to contour lines is perpendicular. Contour lines represent elevation on a topographic map, and they show areas of equal elevation. Water naturally flows from higher elevations to lower elevations due to gravity. Therefore, when observing contour lines, drainage will typically flow downhill, which is at an angle that intersects these lines. This intersection produces a perpendicular relationship, as water moves directly away from the elevated areas represented by the contour lines.

Understanding the relationship between drainage and contour lines is essential for effective erosion and sediment control practices, as proper management of water flow helps to prevent soil erosion and maintain stability in both agricultural and construction settings. The other options, while they may suggest relationships between lines and flow, do not accurately describe the natural movement of water in a landscape defined by elevation changes.