PURPOSE: To enhance the natural environment by attaching a porous material to the river side surface of each sheet pile made of steel, and allowing plants to grow there.

CONSTITUTION: To the river side surface of each sheet or pipe pile 1 made of steel, a porous material 2 consisting of rock wool or porous concrete is attached by an adhesive etc. The sheet/pipe pile 1 is driven into the water bottom ground 4, and the river water is soaked in the porous material 2 by means of cappilary phenomenon, and at its surface, plants such as sphagnum are allowed to grow. Nurrishment and/or seeds are included, as applicable, in the porous material 2 so that growth of the plant is accelerated. The sheet pile 1 is provided with an opening for water passage so that the continuity of the flows of subsoil water etc., is assured between the land side and river side. and also roots of the plant are allowed to stretch to the land side via the opening. Thereby plants can be grown on the sheet pile surfaces, and the natural environment and the living environment of vital organisms be enhanced.