RipRap in Wisconsin: Armor Stone for Banks, Outlets and Lake Edges

Nobody rakes riprap. A load lands as a heap of separate rocks, the smallest of which you can shift with two hands and the largest of which want a bar, a strap or a bucket, and the first thing most people do is stand there sorting them by eye into the ones that will go on the bottom and the ones that will face the water. That sorting is the job. Everything on this page is about getting the right sizes to the right part of a bank before the spring runoff arrives to test your work.

What RipRap looks like in the pile: 4 inches to 12 inches and up

• Size runs from 4 inches to 12 inches and beyond, so a load is a graded heap rather than a single size.
• Large, heavy stone by type. The weight is the working principle: moving water can carry lighter aggregate away and cannot shift this.
• The mix is useful, not a nuisance. Smaller pieces chink the gaps between the large ones and lock the face together.
• Edges and faces are irregular, which is what lets one stone sit against another instead of rolling.
• Plan the layer at least one stone thick, so where the pieces run to 12 inches the layer is around a foot deep. A single scattered course of big rock on a bank is decoration, not armor.

Where heavy stone belongs on a lake or farm property

Two places it does not belong: as a driveway surface and as a base under anything. Rounded loads spread and lock, this does neither. For those jobs use 3/4" Traffic Bond or Breaker Run.

Wave attack on clay bluffs, red clay banks and the spring runoff

• Along the Lake Superior shore the red clay banks erode easily, and waves, groundwater seepage and freeze-thaw work back the face from three directions at once.
• On the Green Bay and eastern lakeshore bluffs, high water and wave attack undercut clay and till, and the bank above fails in slabs once the toe is gone.
• In the Driftless Area, runoff off steep ridge ground cuts gullies and stream banks fast, and the damage arrives in single heavy storms rather than gradually.
• Across the north, the spring thaw is the real test. Meltwater cannot soak into still-frozen ground, so it runs, and it runs at volume.
• Freeze-thaw also shifts stone from behind. Ice building in saturated soil behind an armor layer pushes individual rocks out of line, which is why the layer needs weight and interlock rather than neatness.

Work at a water's edge often needs approval before stone goes in, so check the requirements that apply to your property and water body before you order.

Stone for a fire pit ring, a pole barn drip line and a culvert apron

Length times width times depth in inches divided by 12, then divided by 27 for cubic yards. For a circle, multiply the diameter by itself and then by 0.7854 to get the area.

• Example, a fire pit surround, a 3 ft wide ring of stone around a 5 ft pit, so an 11 ft outer circle: 11 x 11 x 0.7854 = 95 square feet, less the 20 square feet of pit, leaves 75 square feet. At 12 inches deep that is 75 cubic feet, divided by 27 = 2.8 cubic yards.
• Example, the drip line along both long sides of a 40 ft by 60 ft pole barn, a 2 ft wide strip at 12 inches: 2 x 60 x 2 sides = 240 square feet, so 240 cubic feet, divided by 27 = 8.9 cubic yards. The pad and the approach themselves take compacted base; the stone only handles the water coming off the roof.
• Example, aprons at both ends of a culvert under a single-car gravel driveway, each 8 ft by 6 ft at 12 inches: 96 square feet total, so 96 cubic feet, divided by 27 = 3.6 cubic yards.

This site's calculators put riprap and armor stone at about 3,100 lb per cubic yard, roughly 1.55 tons per yard, so the weights are approximate. That makes the fire pit ring 2.8 x 1.55 = about 4.3 tons, the pole barn drip line 8.9 x 1.55 = about 13.8 tons and the two culvert aprons 3.6 x 1.55 = about 5.6 tons.

Round up. Heavy stone gets placed by hand and by eye, and running short halfway along a bank means the face you already built has an unprotected end. The calculator converts these cubic yards into tons for this material.

Clearing a dump spot before the truck turns in

• Delivery is set up at checkout from your ZIP code, so work out in advance where the load can go down and how the truck gets back out.
• Drop the stone as close to the work as the ground allows. Every foot you save is a rock you are not carrying twice.
• A tarp under the pile keeps it out of the lawn and makes the last of it easier to scrape up.
• Have a pry bar, heavy gloves, a wheelbarrow rated for stone and a helper lined up. This is not a rake-and-go material.
• On soft spring ground, think about what a loaded truck does to a wet lane before you pick the spot.

Set your tonnage and a date on this page, or send the bank measurements and a photo through contact if you want the layer thickness talked through before you order.