Large River Rock in Maryland: The Size Up When Smaller Stone Washes Out

The usual reason a Maryland yard needs large river rock is that something smaller has already failed. A dry creek was laid with a fine decorative grade, or a downspout apron was set with pea gravel, and then the remnants of a tropical storm came through and moved the whole thing across the lawn. Rounded stone at 2 inches to 4 inches is what you step up to when the flow in a channel is stronger than the stone in it, and it still reads as landscape rather than as engineering.

• Size: 2 inches to 4 inches.
• Type: smooth, naturally rounded stones.
• Color: tans, grays and browns.
• Approximate weight: no figure is published for this grade specifically. The 1 to 3 inch river rock on this site's own calculator pages runs about 2,700 lb per cubic yard, or roughly 1.35 tons per cubic yard. Use it as an estimate.

Building the channel between the spring thaw and the summer storms

There is a natural window for this work, and it is not mid-summer. Channels, swales and splash areas want cutting and stoning in early spring, once the ground is workable and before the season that tests them arrives. Maryland's heavy water comes from summer thunderstorms and from tropical systems and nor'easters later in the year, so a channel finished in April has months to settle and prove itself before it is asked to carry anything.

The window shifts with the ground. In Garrett and Allegany, frozen and saturated ground holds earthwork later into spring than anywhere else in the state and the cold closes in earlier in the autumn, so the workable season is genuinely shorter. On the Eastern Shore the limit is saturation rather than frost, and low flat ground can stay too wet to shape for weeks after winter storms. The Piedmont sits between the two, which is why most of this work in the central counties happens between March and November.

The other honest option is autumn. Repairing a channel in October, after the tropical season has shown you where the water actually goes, is a better use of the information than guessing in spring.

Cutting the channel and setting the fall while the ground is workable

• Watch the yard during a real downpour before you dig. The route water takes is rarely the route a plan drawn in the kitchen gives it.
• Excavate the channel deeper and wider than the finished stone line, because the stone occupies space and a channel filled to the brim overtops.
• Set a consistent fall from head to outlet and decide where the water is being delivered to. A beautifully built dry creek that ends at a fence line has only moved the problem.
• Shape the sides so they hold the stone, with the deepest point at the center of the run rather than at the edges.
• Line the bed with a geotextile before stone goes in where soil would otherwise pump up between the pieces.
• Plan the drop spot. Stone this size is placed rather than raked, and a pile that has to be wheelbarrowed 80 feet will cost you a day.

Where large river rock goes: dry creeks, pond edges, a Bay-country ditch

• A dry creek bed through a rolling Piedmont yard, carrying runoff from a slope down to a low point and staying legible as a feature when it is empty.
• The visible lining of a swale or ditch alongside a drive, where 2 to 4 inch stone slows the flow without turning the edge of the yard into a construction site.
• Pond, fountain and water-feature edges, where the rounded shape and earth tones look like part of the ground rather than an imported product.
• A splash apron where a downspout or a drain outlet discharges, at the point where lighter material keeps getting carried off.
• Accent groupings in a bed or at an entrance, where a few pieces give an area a focal point that mulch cannot.

The size is the whole argument. Where wave action on a tidal shoreline or genuine scour at a culvert mouth is taking ground, the job needs weight rather than looks, and RipRap starts at 4 inches and runs up from there. Where the feature is decorative and the water is gentle, the 1 to 3 inch River Rock covers more ground per ton and sits better at a smaller scale.

Yardage for a drain outlet apron, a regraded low spot and a ditch line

Square feet times depth in feet, divided by 27, gives cubic yards. Multiply by roughly 1.35 for an estimated tonnage. These are worked examples rather than real projects.

• Example, a French drain along a foundation. The buried part, 60 feet at 12 inches wide and 24 inches deep, is 60 x 1 x 2 = 120 cubic feet, divided by 27 = 4.44 cubic yards, and that volume is a Drain Rock order, since a buried run needs washed stone. Where it discharges, an apron 8 feet by 4 feet, or 32 square feet, at 5 inches is 32 x 0.4167 = 13.3 cubic feet, 0.49 cubic yards, about 0.7 tons of this grade.
• Example, a low spot regraded. An area 24 feet by 14 feet, or 336 square feet, raised 5 inches takes 336 x 0.4167 = 140 cubic feet, 5.19 cubic yards, roughly 6.2 tons of Fill Dirt at 1.20 tons per cubic yard. Stone is the wrong material for raising a grade. The swale you shape through it, 24 feet by 3 feet at 5 inches, is 72 x 0.4167 = 30 cubic feet, 1.11 cubic yards, about 1.5 tons of large river rock.
• Example, lining a ditch by a drive, 30 feet long and 4 feet across the wetted width, at 6 inches: 120 square feet x 0.5 = 60 cubic feet, divided by 27 = 2.22 cubic yards, about 3.0 tons. If that ditch is already cutting a channel into its own bed, the flow has outgrown this size.

Put your own measurements through the river rock calculator, then pick a quantity and a delivery date on this page. Where a channel, an apron and a drain are going in together, send the three sets of dimensions through contact and get them split across materials before you order.

The season after: leaf litter, sediment and the pieces that moved

Upkeep on a stone channel is seasonal rather than constant. Autumn is the one job that matters: leaves collecting in a dry creek turn it into a dam, and the next storm goes around the channel instead of through it, which is how a working feature undoes a lawn. Clear the run before winter and again in spring.

Sediment is the slower problem. Silt carried off bare ground upslope works down between the stones and, over a few years, soil and weeds take hold in a channel that used to be clean. Fixing the source beats picking weeds out of a creek bed. Beyond that, a rinse with a hose lifts the color after a dusty spell, and any piece that has shifted out of line goes back by hand in a few minutes. The stone itself does not rot, fade or break down, so nothing here is a renewal cycle the way a mulched bed is.