Black and white lantern slide of men being carried in hammocks out of the entrance of a tunnel built for a levada - an irrigation channel or aqueduct - Visit to Madeira. Part of Box 125 - Madeira. Boswell Collection. A levada is an irrigation channel or aqueduct specific to the island of Madeira in the Atlantic Ocean. The levadas originated out of the necessity of bringing large amounts of water from the west and northwest of the island to the drier southeast, which is more conducive to habitation and agriculture.