The drainage system is the most important part of any riding arena/manege construction. There is no point having an expensive surface if corners have been cut with the drainage. A wet surface will mean the arena/manege is susceptible to freezing during the winter months and may be un-rideable after heavy downpours.
A typical riding arena/manege drainage system consists of a series of trenches containing perforated pipe. The trenches are then backfilled with gravel to prevent fines entering the drainage system and blocking pipework.