Register to enable "Calculate" button in riprap rock sizing calculator.
Units in riprap stone sizing calculator: ft=foot, knots=nautical miles per hour, m=meter, mph=miles per hour.
Riprap in a River
Riprap Sizing
Riprap is used for erosion control, to prevent scour, and to minimize sediment transport in rivers and streams.
A stable riprap rock size is desired.
The Isbash equation computes the smallest diameter stone D having specific gravity S that if dropped in water
flowing at velocity V will settle and remain stationary on the channel bed (Blevins, 2003, p. 218; NCHRP, 2006, p. 14).
Our calculation will also solve the equation in reverse. In that case, riprap rock size D is entered. The computed water velocity V is the maximum water velocity
at which the riprap will remain in place.
The variables in the riprap sizing equation are (units shown in SI, but our calculation allows a variety of units):
C = Isbash constant. Per references below, C=0.86 for highly turbulent conditions or C=1.2 for low turbulence.
D = Median diameter of spherical stone or rock. Also known as D_{50} (m).
g = Acceleration due to gravity, 9.8066 m/s^{2}.
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.
V = Water velocity approaching the riprap (m/s).
References
Blevins, Robert D. 2003. Applied Fluid Dynamics Handbook. Krieger Publishing Co.
National Cooperative Highway Research Program [NCHRP]. 2006. Riprap Design Criteria, Recommended Specifications, and
Quality Control. Report 568. Transportation Research Board. Retrieved from http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_568.pdf
© 2017 LMNO Engineering, Research, and
Software, Ltd. All rights reserved.
Please contact us for consulting or questions about riprap sizing.
LMNO Engineering, Research, and Software, Ltd.
7860 Angel Ridge Rd. Athens, Ohio 45701 USA Phone: (740) 7072614
LMNO@LMNOeng.com https://www.LMNOeng.com
 To:
LMNO Engineering home page (more calculations)
Related open channel flow calculations:
Circular Culvert
Trapezoidal Open Channel
Rectangular Channel Design
Culvert Design using Inlet and Outlet Control
Unit Conversions
Register
