Enter your Water Velocity, Rock Specific Gravity, Turbulence Level, and Safety Factor into the Rip Rap Calculator, then add Coverage Length, Width, and Layer Thickness to get the Required Rock Size (D₅₀), Rock Weight, Total Volume, and Total Weight Required.
Required Rock Size (D₅₀)
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D₅₀ in Meters
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Individual Rock Weight
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Total Volume Needed
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Total Weight Required
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Rip rap is a layer of rocks or stones placed along embankments, shorelines, or channels to prevent erosion from water flow. It's commonly used for stream bank protection, drainage channels, and coastal defense structures.
Rip rap rock size is calculated using the Isbash equation: D₅₀ = V² / (2 × g × C² × (S-1)), where V is water velocity, g is gravitational acceleration, C is a stability coefficient, and S is specific gravity of the rock.
D₅₀ represents the median rock size where 50% of the rocks by weight are smaller and 50% are larger. This standardized measurement ensures proper gradation and stability of the rip rap protection.
The amount of rip rap needed depends on the area to be protected and the layer thickness. Typically, the layer should be 1.5 to 2 times the D₅₀ diameter thick for adequate protection.
Rock size is critical because undersized rocks will be displaced by water flow, leading to erosion failure. Oversized rocks are unnecessarily expensive and may not provide proper interlocking for stability.
Install rip rap on a prepared base with filter fabric or graded filter. Place rocks to achieve proper thickness, ensure good interlocking between stones, and extend protection above anticipated high water levels.
Key factors include water velocity, turbulence level, rock specific gravity, channel slope, and the presence of debris or ice. Higher velocities and turbulence require larger rock sizes for stability.
Loose rip rap allows water drainage and adjusts to settlement, while grouted rip rap provides additional structural support but may crack under movement. Loose rip rap is more common for most applications.