Rip Rap Calculator
Calculate rock size using Isbash equation and determine volume for erosion control
Calculate Rip Rap Requirements
What do you want to calculate?
Water Flow Conditions
Average channel flow velocity
Isbash constant for flow conditions
Material Properties
Typical range: 2.5 - 3.0 for most rocks
Rip Rap Calculation Results
Isbash Equation: D50 = V² ÷ (2 × g × C² × (S - 1))
Recommended depth: At least 2 × D50 for effective protection
Analysis & Recommendations
Example Calculation
Open Channel Protection Example
Channel conditions: Gentle flow at 2.0 m/s average velocity
Flow turbulence: Low turbulence (C = 1.20)
Rock material: Local limestone with specific gravity 2.5
Project requirements: 100 m² channel lining, 30cm depth
Calculation Results
D50 = (2.0)² ÷ (2 × 9.806 × 1.2² × (2.5 - 1))
D50 = 4.0 ÷ (19.612 × 1.44 × 1.5) = 4.0 ÷ 42.31
D50 = 0.0946 m = 9.46 cm
Volume needed = 100 m² × 0.30 m = 30 m³
Weight needed = 30 m³ × 1680 kg/m³ = 50.4 tons
Result: Use 9-10 cm diameter rocks, approximately 50 tons needed
Riprap Size Chart
Installation Tips
Use depth ≥ 2 × D50 for effective protection
Install geotextile fabric underneath
Fill gaps with smaller stones for stability
Extend protection beyond erosion zone
Consider grouted riprap for high velocities
Regular maintenance and inspection required
Understanding Rip Rap and Erosion Control
What is Rip Rap?
Rip rap (or riprap) is a layer of rocks placed to protect shorelines, streambed, bridge abutments, and other structures from erosion caused by flowing water. It acts as armor against the erosive forces of water flow while allowing natural drainage.
Why Size Matters
- •Too small: rocks get washed away by water flow
- •Too large: unnecessarily expensive and difficult to place
- •Correct size: provides effective protection at minimum cost
- •D50 means 50% of rocks are smaller than this diameter
Isbash Equation
D50 = V² ÷ (2 × g × C² × (S - 1))
- V: Water velocity (m/s)
- g: Gravitational acceleration (9.806 m/s²)
- C: Isbash constant (0.86 or 1.20)
- S: Specific gravity of rock (2.5-3.0)
Applications
- Channel lining: Prevent streambed erosion
- Embankment protection: Shore and slope stabilization
- Bridge protection: Scour prevention around piers
- Outlet protection: Energy dissipation structures