Why are drainage channels and subsurface drains installed in reclaimed polders?

In reclaimed polders and other wet areas, drainage channels and subsurface drains are essential for removing excess water that would otherwise render the land unfit for agriculture. By accelerating the removal of water, these systems prevent crops from being drowned and ensure that cultural operations, such as planting, are not delayed.1

The specific design depends on soil permeability:

• Surface Drainage: In soils with low permeability, such as clay, excess water is removed via surface flow. This requires regularly spaced small ditches and land grading to direct water toward field channels.1
• Subsurface Drainage: In permeable soils, tile lines or underground channels are installed beneath the surface. These systems are advantageous because they allow farm equipment to operate across the entire field without the space loss associated with open ditches.1

Additionally, in polders reclaimed from the sea, these systems work in tandem with dikes and pumps to manage water levels, as the land often sits below sea level. Proper drainage also facilitates the leaching of salt from newly reclaimed soils, which is necessary to make the land agriculturally productive.2