Drain Rock in New York: The Washed Load That Keeps Water Moving

The wall that starts leaning in its third spring was almost always backfilled with the material that came out of the hole. On the silty valley floors along the Hudson and the Mohawk, and on the flat lake clays behind Buffalo and Oswego, that spoil holds water like a sponge, freezes, expands and pushes. Drain Rock is what should have gone against the back of that wall: washed to take the fines and dust out, 3/4 inch to 1-1/2 inch, supplied in rounded or angular form depending on what the job asks for.

It is bought to fix water that has nowhere to go. It is not bought to hold anything up, and most of the disappointment with it traces back to that line being crossed.

What separates a washed load from the graded sizes next to it

Four materials on this site's order form all look like drainage stone in a photograph. They are not interchangeable.

The wider size range is the point of the washed load. A bed with a spread of sizes in it holds a larger open volume than a single graded size, which is why it suits a drywell or a broad backfill zone rather than a 12 inch trench where a smaller stone places more neatly.

Rounded or angular is a second choice. Where soil or wall backfill will bear down on the stone, the angular form interlocks and keeps its voids under that load. The rounded form is the one to ask for where the stone stays visible in a landscape drainage feature and the look matters.

Rounded or angular drain rock behind a Hudson Valley retaining wall

A wall on a slope is holding back saturated ground every March. The drainage column goes against the back face, running the full height from the drain line at the base up to within a few inches of the surface, then capped with soil or a compacted layer so surface water does not pour straight down into it. The drain at the bottom has to daylight somewhere, or the column just fills.

Take the angular form here. The backfill above and behind is pressing on this stone all year, and rounded pieces roll and repack under that pressure while angular ones wedge and hold their gaps open.

A foundation perimeter is the same idea turned sideways, and so is a downspout run carried away from the house instead of dropped at the corner.

A pond edge and a construction entrance ask for weight this stone has not got

Two of the jobs people bring to this product need something heavier.

At a pond or shoreline edge, on Lake Ontario, the Sound or a tidal stretch of the Hudson, the stone is being hit by waves, ice and storm surge. Washed 1-1/2 inch stone is moved by all three. That edge wants RipRap, which New York yards and the state specification also grade as light, medium or heavy stone fill, with Large River Rock where a rounded look is wanted above the waterline.

A construction entrance exists to shake mud off tires before they reach the road, and it takes loaded truck weight all day. That is coarse, heavy stone: #4 Crushed Stone or Railroad Ballast.

Trench depth, pipe cover and the fabric wrap on Finger Lakes hillsides

Depth is set by what the water has to get past, not by a standard figure. A backfill column runs the height of the wall. A drywell is sized to hold a roof's worth of runoff. A perimeter drain is cut to a fall, which matters more than its depth.

Wrap it. Non-woven filter fabric under, up the sides and folded over the top is the difference between a drainage bed and a buried silt trap. On hill ground in the Finger Lakes and the Southern Tier, where silty till washes downslope with every heavy rain, the wrap is doing more work than the stone.

Frost sits around 4 feet down across most of the state, with the local building department setting the exact footing depth. Drainage work rarely goes that deep, and the goal is the opposite anyway: move the water out so there is less of it to freeze.

Working out 48 feet of wall backfill behind a sloped lot

A worked example with invented dimensions.

Drainage column, 48 ft of wall, 12 in wide, 3 ft tall

• 12 in is 1 ft, so the cross section is 1 x 3 = 3 sq ft
• 48 x 3 = 144 cu ft
• 144 / 27 = 5.3 cu yd

There is no published weight for this exact material on the site, so use the nearest listed family, the washed 3/4 inch crushed stones at roughly 2,800 lb per cubic yard, about 1.40 tons per yard. That puts 5.3 cubic yards near 7.4 tons, and the figure should be read as approximate.

Order the whole column in one delivery if you can. A backfill zone filled in two sessions two weeks apart usually ends up with a layer of washed-in soil through the middle of it.

Run your own wall or trench through the river rock calculator, which this site pairs with the material, then choose the tonnage and a delivery date on the Drain Rock page. Delivery is arranged at checkout by ZIP code and the truck needs firm, clear ground to tip on.