An underwater support device and an installation method for initiating the buckling of a section of rigid underwater pipe (16) deployed on a seabed (14). The device has a longitudinal support (22) capable of being installed between the seabed and the section of rigid underwater pipe (16) in a transverse direction, in such a way as to be able to locally detach the section of rigid underwater pipe (16) from the seabed (14) and allow the rigid underwater pipe (16) to be moved relative to said longitudinal support (22) in the direction of the longitudinal support. The device also has a link member (36) to secure the rigid underwater pipe (16) and the longitudinal support (22) in such a way as to be able to install said longitudinal support (22) on the seabed (14) by deploying the section of rigid pipe (26) on the seabed (14).