What is riprap?

Imagine walking out onto a constructed pier, looking down and seeing a bunch of rocks that have been placed around the base and along the edges. This layer of durable rock is used to protect shorelines and structures against erosion from moving water or waves. The armored layer of rocks is known as riprap.

What is riprap?

Riprap is a human-placed rock that is used for shoreline protection. Riprap comes in many forms and can be made of rock, stone, shale or other materials. It is also known as rip rap, rip-rap, shot rock, rock armor or rubble. Riprap is used for shoreline protection, erosion control, landscaping and flood control.

One of the most common uses for riprap is shoreline protection. The rock is placed along the shore or structures as a first line of defense against waves and currents. Riprap can help prevent the loss of land while protecting infrastructure against coastal erosion and tidal surges.

Riprap has different classifications that vary by state. Typical classifications and designations include Type 1, 2, A and B. The loose stone comes in a variety of sizes typically from 4-inches to 2 feet. Materials include fieldstone, repurposed concrete rubble, granite and limestone.

What are common applications of riprap?

Crashing waves and flowing waters are a common cause of erosion. Riprap is angular and interlocks well together while also allowing for good drainage. Crashing waves are diverted and absorbed by riprap which can help cut down on erosion. Riprap is commonly used for:

• Erosion control
• Sea walls
• Riverbanks
• Bridge abutments
• Slope stability
• Channel flow
• Shoreline protection
• Railroad ballast
• Road linings
• Inlets and outlets for culverts and storm pipes

What is the purpose of riprap?

Riprap is a layer of stones that protects shorelines and structures from erosion. It is useful for armoring areas against waves and water flows. Rirap can be paired with other stormwater control measures to reduce stormwater flow rates.

Riprap can be used to stabilize cut-and-fill slopes, channel side slopes and bottoms, and for inlets and outlets for culverts, bridges, slope drains, grade stabilization structures, storm drains and stream banks.

Why is it called riprap?

Riprap originated as a nautical term in the 19^th century which defined a stretch of rippling water. One of the first known uses of riprap as an erosion control measure was when the Panama Canal was constructed in the early 1800s.

What are the disadvantages of riprap?

The primary goal of rirap is to prevent erosion along coasts and shorelines. The placed rock is meant to protect structures and shorelines against crashing waves by distributing the impact of the water rushing against it. The angular rock distributes the water and even drains it, but riprap comes with a few disadvantages including:

• Permits: Permitting for riprap differs from community to community. Some communities may restrict the use of riprap to protect water bodies.
• Environmental concerns: The use of riprap may disrupt the natural habitats for aquatic animals, birds and other species that are typically found around a coastal environment.
• Cost: Riprap is a material-based solution. It requires a vast amount of material and a specialized nature of installation. It also costs money to ensure the riprap structure is properly engineered and graded.
• Access: The installation of riprap requires heavy machinery to move and grade the rock. Access may be difficult depending on the location of installation. The grade of riprap also makes it difficult to walk on.

Riprap design considerations

The U.S. Environmental Protection Agency (EPA) recommends that for slopes steeper than 2:1, developers should consider using materials other than riprap for erosion protection due to the unstable nature of steep slopes. The agency also highlights the importance of construction sequencing as riprap in high-flow locations can be difficult to remove.

Other considerations include:

• Gradation: Use a well-graded mixture of rock sizes rather than one uniform size.
• Riprap size: The size of the riprap depends on the stress of the flows that it will be subject to.
• Stone quality: The stone should vary in size and be resistant to freeze and thaw cycles.
• Riprap depth: Minimum depths depend on site flow, median riprap size and local design requirements.
• Filter material: Applying a filter, such as fabric or wire, can help prevent erosion of the underlying soil.
• Upper limits: Riprap should be placed so it extends up to the maximum flow depth.
• Curves: Local design standards should be consulted to ensure riprap extends far enough upstream and downstream of any curve.
• Wire enclosures: Using wire mesh or fencing can ensure that installations are secured.