A modular drainage filtration apparatus comprising a filtration container having an open-ended structure with a shape determined by the number of walls used during assembly, each wall being formed from a generally flat sheet of a rigid material and comprising a flat body portion with a plurality of formed tabs and an upper and lower overhanging portion, the walls being assembled to form a filtration container enclose an interior region and having open and opposite upper and lower faces and a plurality of filtration units each comprising a flat filter stage configured to be placed within a filtration container.