I have read up multiple articles and talked to different folks and they all seem to have slightly different opinions regarding drainage. Some say to backfill with 6" wide of gravel, but others said to also have drainage pipes in addition to gravel.

My question: are drainage pipes really necessary? If I only have gravel with no pipes, what happens to all the water after it sinks down to the bottom of the gravel?

The wall will not be over 2.5 ft at its highest point and will be only .5 ft high at its lowest point. The wall curves and "wraps" around two sides of the patio and it will be about 30-40 ft in total length. Also, since the patio is attached to the house foundation, one end of the wall will be touching the foundation.

Thanks for any advice you can give me.