Choosing the Right Riprap Size for Your Drainage Project

The wrong riprap size fails just as fast as having none at all. Here's how sizing decisions actually get made. Riprap sizing isn't a guess, it's calculated based on how fast and how forcefully water is expected to move across a given point on your site.

What Drives Sizing Decisions

  • Expected flow velocity at the specific location
  • Channel or slope geometry
  • Duration and frequency of high-flow events
  • Whether the area is a straight run or a bend, which concentrates force differently

General Sizing Categories

Flow Condition

General Rock Size Need

Low velocity, gentle slope

Smaller rock, sometimes combined with vegetation

Moderate velocity, standard ditch

Mid-size rock, engineered per flow calculation

High velocity, outfalls and bends

Larger rock, often heaviest at concentrated points

Frequently Asked Questions

Can I oversize riprap to be safe?

Oversizing avoids washout risk but adds unnecessary cost, correct sizing balances protection and budget.

Does rock shape matter, not just size?

Yes, angular rock interlocks better than rounded rock, which affects overall stability of the installed layer.

The Bottom Line

Sizing riprap correctly is an engineering calculation, not a rule of thumb, and it's the single biggest factor in whether the installation holds up.

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How We Work Differently

Bid Smarter With the Right Tools

We build bids using HeavyBid and AGTEK because the details matter long before the job starts. When the numbers are accurate and the scope is clearly defined, it sets the tone for how the entire project runs. Estimating isn’t just a step in the process, it’s the foundation we build on.

Quality in the
Field

That same mindset carries into the field. Our crew is trained to work with purpose, follow the Civil Engineers’ Plan to the finest detail, and hold the line on quality. When expectations are clear from day one, there’s no need for shortcuts, and no confusion about how the work gets done.

Clear, Complete Bid Packages

Clients trust our bid packages because they’re complete and ready to use. Project managers know what we’re covering, what’s excluded, and how we plan to approach the job. That clarity removes friction and lets teams focus on execution instead of interpretation.

Proactive RFI Process

As part of our review process, we go into the plans before anything hits the site. We ask the questions early, resolve issues before they show up in the field, and keep RFIs moving. This approach prevents delays and protects the timeline.

Referred by the People Who Build

Over time, that consistency builds trust. Many of the people we work with today came through referrals from past projects – engineers, GCs, and superintendents who’ve seen how we operate and want the same experience again.

A New Chapter with Saga Infrastructure Solutions

In 2024, Foshee Construction was acquired by Saga Infrastructure Solutions, a national network of civil construction companies. Saga supports regional contractors by giving them access to better tools, long-term resources, and operational backing, without changing how they run day to day.
Foshee will continue to operate under its name, with the same team and field leadership in place.

“From the very time a project starts, we start that partnership. We try to catch as much as we can with the tools that we have. Not everybody is using the software platforms we are. That’s the differentiator: we’re not just bidding. We’re anticipating, problem-solving, and making sure the job runs right.”


— Don, CEO, Saga Infrastructure Solutions

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Foshee is now part of a broader regional strategy that includes Florida, the Piedmont Atlantic, Texas, Colorado, and the Arizona Sun Corridor. The name, crews, and standards remain. What’s improving is the support behind it.