Riprap Rock Size Formula |
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| \( D \;=\; \dfrac{ v^2 }{ 2 \cdot g \cdot c^2 \cdot (s - 1) }\) |
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| Symbol | English | Metric |
| \( D \) = Median Diameter of Spherical Stone or Rock | \(in\) | \(mm\) |
| \( v \) = Water Velocity Approaching the Riprap | \(ft\;/\;sec\) | \(m\;/\;s\) |
| \( g \) = Gravitational Acceleration | \(ft\;/\;sec^2\) | \(m\;/\;s^2\) |
| \( c \) = Isbash Constant (c = 0.86 for Highly Turbulent Conditions or c = 1.2 for Low Turbulence) | \(dimensionless\) | \(dimensionless\) |
| \( s \) = Specific Gravity of Stone or Rock (Typically Varies from 2.56 to 2.92 Depending on the Rock Material. A Commonly Used Value is 2.65.) | \(dimensionless\) | \(dimensionless\) |
Riprap rock size refers to the dimensions of the stones used in riprap, which is a layer of large, angular rocks placed along shorelines, riverbanks, bridge abutments, and other erosion-prone areas to prevent soil loss due to water or wind. The size of riprap varies based on the application and site conditions. Larger sizes are used for high-energy environments such as coastal protection, while smaller sizes work well for drainage channels and embankments.
Common Riprap Rock Sizes (by Class and Diameter)
- Class 1 - 2" - 12" (50 - 300 mm)
- Class 2 - 4" - 18" (100 - 450 mm)
- Class 3 - 6" - 24" (150 - 600 mm)
- Class 4 - 12" - 36" (300 - 900 mm)
- Class 5 - 18" - 48" (450 - 1200 mm)
