Abstract: In a method of constructing an artificial island wherein an envelope or membrane is filled with sand or other permeable material and during filling water is removed from the body of deposited material by suction, drainage of water from the deposited material is improved by the provision of at least one drainage tube which extends downwardly through the body of material and contains perforations along its length through which water may drain to a drainage layer at the base of the island and in communication with a suction pipe. To prevent water being drawn into the part of the drainage tube above the level of the deposited material the pipe is closed by a closure means which is moved upwardly as the level of deposited material rises. There is also described an artificial island formed by the improved method.