Abstract: A movable barrier wall system includes a housing assembly 12 that has an interior chamber 32. A barrier member 14 is made of a buoyant material having a selected density. The barrier member 14 floats vertically within the chamber 32 when a liquid is present. The barrier member 14 may be made from a closed cell foam core 34 that is clad with a fiberglass mesh material then the assembly is infused with a resin material. Alternatively, the core 34 may be made from a plurality of elongated rods 38 that are individually clad and reinforced with a shear layer. The individual barrier member modules 15 may be assembled in an end to end relationship with an elongated vertical seal member therebetween. The barrier member 14 may be selectively raised prior to and in anticipation of a flood situation of a nearby body of water by a pump and control system that may be automatically or manually controlled. At least one passive backup system is provided for filling the chamber when the pump or control system fails.