— also known as rip rap
, rubble, shot rock or rock armour — is rock or other material used to armor shorelines, streambeds, bridge abutments, pilings and other shoreline structures against scour, water or ice erosion.
It is made from a variety of rock types, commonly granite, limestone or occasionally concrete rubble from building and paving demolition. It is used to protect coastlines and structures from erosion by the sea, rivers, or streams. It is used on any waterways or water containment where there is potential for water erosion.
works by absorbing and deflecting the impact of a wave before the wave reaches the defended structure. The size and mass of the riprap
material absorbs the impact energy of waves, while the gaps between the riprap
traps and slows the flow of water, lessening its ability to erode soil or structures. The mass of riprap also provides protection against impact damage by ice or debris, which is particularly desirable for bridge supports and pilings.
It is frequently used to protect the base of old Edwardian/Victorian sea walls, which due to the vertical wall, are often undermined. The riprap
absorbs the impact of the waves as they shoot up the wall, and then fall back down.
In the Western United States, riprap
can also refer to a cross between cobblestones and stairs.