In Plain English
Quick Answer
Large rocks or boulders placed to protect a slope or waterway bank from erosion.
Definition
Definition
A layer of large, loosely placed angular rock or stone used to protect soil surfaces from erosion caused by flowing water, wave action, or surface runoff. Riprap is commonly used at culvert outlets, stream banks, channel slopes, and at the base of retaining walls. Stone size is selected based on the velocity of water flow to prevent displacement.
Context
Why It Matters in Bidding
Riprap is typically bid by the ton or cubic yard, and the gradation (stone size class) called out in the plans drives both material cost and the haul/placement labor an estimator must carry. Underestimating quantities or pricing the wrong stone class against the spec is a common takeoff miss because riprap often requires an underlying filter fabric or bedding stone that must be quantified separately.
Example
Example
An estimator pricing a highway culvert outlet measures the apron dimensions, applies the specified stone gradation and an 18-inch placement thickness, and adds 25 tons of riprap plus geotextile filter fabric to the earthwork line item.
See Also
Related Terms
FAQ
Questions Contractors Ask
Is riprap measured by weight or by area when estimating?
It depends on the spec. Most DOT and public projects pay by the ton based on weighed truck tickets, while some private jobs pay by the cubic yard in place or by square yard of covered surface. Always read the measurement-and-payment section so your unit price matches how the owner will verify quantities.
Do I need to include filter fabric in a riprap bid?
Usually yes. Most specs require geotextile filter fabric or a granular bedding layer beneath the stone to prevent soil migration and undercutting. These are separate pay items or incidental costs, so review the detail carefully; omitting fabric can leave a gap between your bid and the actual scope.
How does stone gradation affect a riprap price?
Larger gradation classes cost more per ton because they require quarrying, sorting, and heavier placement equipment. Hand-placed or grouted riprap carries far higher labor than dumped stone. Match the exact class and placement method in the plans, since substituting a smaller or cheaper stone makes a bid non-responsive.
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