Agricultural drainage systems help manage water flow in fields. This study looked at how water moves in fields with both surface and subsurface drainage. They found that surface and subsurface drains remove a significant amount of rainwater. However, a lot of water still goes deep into the soil. When the soil is dry, rainwater goes straight to the subsurface drains. But when the soil is wet, existing soil water is the main source of drainage water. Rainwater can also contribute to subsurface drainage, especially during heavy rain.