Abstract: An elongated tubular assembly comprising a plurality of tubular units disposed in end-to-end relationship, each unit comprising a lower section (1) composed of a variably rigid impermeable contact base (3), and an upper section (2) with a variably rigid protruding hull (5) designed to deviate surrounding fluid flows, the lower (1) and upper (2) parts being connected to each other at least along their longitudinal edges encompassing to such extent an internal space in which a ballast (15) can be admitted through registered hull openings (7), such flexible base and hull combination being designed to give stability to a light-weight version of said unit even in an environnment of heavy fluids, somewhat in the manner of a flat fish, for works including but not limited to ground erosion control and flood control.