thumb|260x260px|Riprap used to protect a streambank from erosion

Riprap (in North American English), also known as rip rap, rip-rap, shot rock, rock armour (in British English) or rubble, is human-placed rock or other hard, heavy, unconsolidated material used to protect shoreline structures against scour and water, wave, or ice erosion. Riprap is used to armor shorelines, streambeds, bridge abutments, foundational infrastructure supports and other shoreline structures against erosion. Rubble from building and paving demolition is sometimes used, as well as specifically designed structures called tetrapods or similar concrete blocks.

Riprap is also used underwater to cap immersed tubes sunken on the seabed to be joined into an undersea tunnel.

Environmental effects

Sediment effects

Riprap causes morphological changes in the riverbeds they surround. One such change is the reduction of sediment settlement in the river channel, which can lead to scouring of the river bed as well as coarser sediment particles. This can be combatted by increasing the distance between the pieces of riprap and using a variety of sizes.

The usage of riprap may not even stop erosion, but simply move it downstream. Additionally, the soil beneath the riprap can be eroded if the rock was just placed on top without any buffer between the layers such as a geotextile fabric or smaller riprap (crushed stone).

Changes in organic material and the ecosystem

Riprap affects the amount of organic material in a waterbody by acting as a filter, catching wood and leaves before they can enter the water. While it can negatively affect some organisms by removing shoreline vegetation, the rock can provide important refuge for invertebrates and small fish. By preventing woody plants from growing and shading the water, riprap can also increase the amount of algae and hydrophytes.

<gallery>

File:11-8-07 riprap photo.jpg|Concrete rubble used as riprap along the San Francisco Bay shoreline

File:Sea defences - geograph.org.uk - 775461.jpg|Modular concrete block riprap, in the form of Dolos

File:Access to Beach is Blocked - geograph.org.uk - 1107949.jpg|Modular concrete block riprap

File:Cape Hinomisaki Izumo04bs3200.jpg|Modular concrete block riprap

File:Riprap.jpg|Riprap lining a lake shore

File:Construction of river channel closing structure in the Mississippi NRRA (7df8f79e-1761-4967-a358-64b4e9a4d1c3).jpg|Riprap closing off a channel on the Mississippi River

File:Corps completes Yolo Bypass levee repairs (6792076725).jpg|Riprap protecting a levee

File:Crews replacing riprap at Seawall.jpg|Crews replacing riprap at Galveston Seawall after a 1915 hurricane

File:Dawlish Warren , Rip Rap and Coastal Scenery - geograph.org.uk - 1345833.jpg|Riprap protecting a concrete retaining wall

</gallery>

See also

  • Dolos
  • Debris
  • Gabion Basket
  • Rubble

References

  • Ciria-CUR (2007) - Rock Manual - The use of rock in hydraulic engineering.
  • N.W.H. Allsop (2002) - Breakwaters, coastal structures and coastlines.
  • US Dept. of Transportation (2004) - Trail Construction and Maintenance Notebook
  • Ohio Dept. of Natural Resources riprap guide
  • US Bureau of Reclamation publication on riprap for dam overtopping
  • Minnesota DNR
  • USGS Minerals Yearbook: Stone, Crushed