What Is Rip Rap?
Rip rap (also written as riprap or rip-rap) is a layer of large, angular stones placed along shorelines, stream banks, bridge abutments, and slopes to protect soil from erosion caused by water flow, wave action, or ice. It is one of the most effective and widely used erosion control methods in civil engineering and landscaping.
The stones interlock to absorb and dissipate the energy of flowing water, preventing it from washing away the underlying soil. Properly sized and placed rip rap can last decades with minimal maintenance, making it a cost-effective long-term solution.
Rip Rap Calculation Formula
Rip Rap Stone Size Guide
| Stone Size | Density (tons/yd³) | Typical Use |
|---|---|---|
| 4-8 inch | 1.2 | Small ditches, mild slope protection |
| 6-12 inch | 1.3 | Stream banks, moderate erosion control |
| 12-18 inch | 1.4 | Shoreline protection, bridge abutments |
| 18-24 inch | 1.5 | Heavy-duty applications, dam spillways |
Recommended Depth Guidelines
- Minimum depth: The rip rap layer should be at least 1.5 times the maximum stone diameter.
- Mild slopes (3:1 or flatter): 12 inches of rip rap is typically sufficient.
- Moderate slopes (2:1): 18-24 inches is recommended.
- Steep slopes (1.5:1): 24-36 inches with geotextile fabric underlayment.
- Always place a geotextile filter fabric beneath the rip rap to prevent soil migration through the stone layer.
Frequently Asked Questions
How much does rip rap cost per ton?
Rip rap typically costs $25-$75 per ton depending on the stone size, type, and delivery distance. Larger stones and longer haul distances increase the cost. Budget an additional $40-$60 per ton for delivery and placement.
Can I use rip rap on a steep slope?
Yes, but slopes steeper than 2:1 (horizontal to vertical) require thicker rip rap layers, larger stones, and often a toe key at the base. For slopes steeper than 1.5:1, consider gabion baskets or concrete alternatives instead.
Do I need geotextile fabric under rip rap?
Yes, in nearly all cases you should place a non-woven geotextile fabric under the rip rap. This prevents the underlying soil from migrating through the stone voids while still allowing water to drain through. Without fabric, the rip rap may eventually sink into the soil.