Rain water is drained from a golf course sand bunker or like structure by a drainage system which comprises a conduit having a solid top and perforations in the sidewall. A conduit which is a chamber having an arch shape cross section is contained within a sand filled trench running along the bottom of a bunker. Water flows downwardly from the bunker into the trench, passing through opposing side trapezoid cross section spaces which are defined between the outwardly angled chamber sidewalls and the essentially vertical trench sidewalls. The water then flows horizontally into the conduit. Geotextile, in combination with downward sloping louvers which define slot perforations in the chamber sidewalls, hinders flow of sand into the interior of the chamber. The arch shape of the preferred conduit frees the trench bottom of vertical soil-compressive load and enables it to be fully exposed for water penetration. An endplate at the end of a string of chambers has an elevated outlet that causes water which flows into the chamber to be retained until it reaches a predetermined level.