Large River Rock in Wisconsin: 2 to 4 Inch Stone for Swales and Channels

Half the lots in lake country have the same feature: a shallow swale that carries runoff off the neighbors' ground, runs hard for two weeks every thaw, and refuses to grow grass for the rest of the year. On tight lake-plain clay the water has nowhere to soak away while the subsoil is still frozen, so it travels across the surface and takes the topsoil with it. Large river rock is the usual answer, because at 2 to 4 inches a rounded stone is heavy enough to stay where it is put when that water is moving.

The stones are smooth and naturally rounded, in tans, grays and browns. That size and weight is the whole difference between this and the smaller rock most people picture.

Will 2 to 4 inch stone stay put in a swale that runs every thaw?

In a swale carrying sheet flow and snowmelt, yes. A stone that size is not going anywhere under the kind of flow a yard swale produces, and unlike the smaller sizes it does not need an edge restraint to stop it wandering into the lawn. Two things still move it: concentrated discharge from a pipe, and a plow. Keep it out of the path of a plow blade, and where a culvert is scouring a hole at its outlet, that is armor work and belongs to RipRap.

Freeze-thaw does not trouble it. The stone is rounded and open, so water drains between the pieces rather than freezing in a mass and lifting the whole layer.

What goes under it on lake clay and sandy outwash?

• Strip the sod and cut the channel to the finished depth before anything goes down. Stone laid on the lawn surface makes a hump, and a hump diverts water rather than carrying it.
• Woven landscape fabric, overlapped at the seams and pinned. Under stone this heavy the fabric earns its place, because you are not lifting the layer again to weed it.
• On tight lake-plain and Fox Valley clay, check where the water leaves before you cover anything. Stone conceals a wet spot; a graded outlet drains it.
• On Central Sands and other outwash ground the opposite problem applies: sand migrates up through the layer, so the fabric is doing separation work rather than weed control.
• In a steeper Driftless coulee, set a few larger stones as check points across the run to slow the water instead of relying on one continuous fall.
• Where a foundation drain is being covered rather than a swale lined, the pipe, the washed stone and the fabric go in first. This rock is the finish over the top, not the drainage layer itself.

How deep does large river rock go in a channel bottom?

Lay it at 4 to 5 inches through the body of a channel, which works out at roughly a stone and a half deep, so nothing shows fabric and nothing rocks underfoot. Go to 6 inches where flow concentrates or where the channel narrows. A decorative border around a feature can sit at 4 inches.

Every one of those is a loose, placed depth. Large river rock is never compacted, and there is no plate that would do anything useful to it other than chip the faces. It settles a little in its first season as the stones find their seats, and that is the end of the movement.

How many tons for a creek run, a foundation drain cover and a turnaround border?

Length times width times depth in inches divided by 12, then divided by 27, gives cubic yards. This site's calculators list river rock at 1 to 3 inch at about 2,700 lb per cubic yard, which is 1.35 tons per yard. Use it as an approximation here, since a 2 to 4 inch stone stacks a little more openly.

• Example, a low spot turned into a dry creek, 35 ft long and averaging 4 ft wide at 5 inches: 140 square feet x 0.417 = 58 cubic feet, divided by 27 = 2.2 cubic yards, times 1.35 = about 2.9 tons.
• Example, a stone cover over 45 ft of a foundation drain, 2 ft wide at 4 inches: 90 square feet x 0.333 = 30 cubic feet, divided by 27 = 1.1 cubic yards, times 1.35 = about 1.5 tons.
• Example, a 2 ft border band around a 30 ft by 20 ft turnaround. The outer rectangle is 34 x 24 = 816 square feet, less the 600 square feet of turnaround, leaves 216 square feet. At 4 inches that is 72 cubic feet, divided by 27 = 2.7 cubic yards, times 1.35 = about 3.6 tons.

One cubic yard covers about 81 square feet at 4 inches and 65 square feet at 5 inches. Those figures are averages, and a load of large stone is lumpier than a load of sand in every sense. The river rock calculator will convert measurements into tons if you would rather not do it on paper.

Do I need a machine, or can two people set it by hand?

Two people can do a small channel over a weekend, and there is a real argument for hand placing it: at this size you are setting stones rather than spreading a material, and the run looks deliberate or it does not. Past about four or five tons, or where the drop spot is any distance from the work, a tractor bucket or a skid steer stops being a luxury. Ask for the load to be dropped in two or three spots along the run if the truck can reach, which saves more wheelbarrow time than anything else you can arrange.

Where does River Rock stop and RipRap start?

The three overlap on purpose. A dry creek often uses this size in the channel and the smaller River Rock on the shoulders, which reads well and costs less than doing the whole thing in one size.

Measure the run, work out the tonnage, then set a quantity and a delivery date on this page. Delivery is arranged at checkout from your ZIP code, and the truck needs a clear route in and room to reverse out, so pick the dump spot before you book.