Area Drain Trenching: Digging the Lines That Carry Water (Oregon)

Quick Verdict

Area drain trenching in Oregon is the earthwork that carries collected yard water away: cutting clean trenches for solid PVC lines, holding a consistent downhill fall to a daylight outlet, bedding and backfilling so the pipe does not sag, and tying multiple grates together into one line. The dig is straightforward, but two things make or break it, fall and backfill. Lose your fall and water stands in the pipe; backfill carelessly and the line settles into a low spot that traps water. Before any trenching, call 811 to locate utilities across the yard. On flat valley lots, the trick is squeezing every bit of fall out of a small drop.

What This Article Covers (and What It Does Not)

This is the execution piece, the actual digging, bedding, and backfilling of area-drain lines. How big the pipes should be, how the whole drainage system is laid out, and how grates are sized is system design, covered under grading and drainage earthwork. Here the focus is on getting the trench right so the designed system actually works.

Area drains are the grated inlets you see in low spots, patios, and lawns. They collect surface water and pipe it underground to an outlet. The trenching connects those grates and carries the water out, and it is core excavation work.

Call 811 First

Before a shovel or trencher touches the ground, call 811 to have underground utilities located and marked. Area-drain trenches snake across the whole yard, often crossing the paths of water service, gas, electrical, irrigation, and cable lines. A drain trench is exactly the kind of shallow, wandering dig that clips an unmarked line. The locate is free, it is the law, and it is the cheapest insurance on the job. Wait for the marks before digging.

Holding Consistent Fall to a Daylight Outlet

Fall, the steady downhill slope of the pipe, is everything in a drain line. Water moves by gravity, so the line must run continuously downhill from each grate to the outlet. A common target is a minimum slope of about 1 percent, roughly 1/8 inch of drop per foot, with more being better where the grade allows.

• Establish the outlet first. Find where the water can daylight, exit at the surface, into a ditch, swale, or lower part of the yard, and work the fall back uphill from there.
• No bellies. A low spot, or belly, in the line collects water and sediment and eventually clogs. The trench bottom must run smooth and continuously downhill.
• Check it as you go. Use a level or laser to confirm fall along the whole run, not just at the ends.

The outlet usually needs to daylight; a drain that runs to a buried dead end with nowhere to go just fills up.

Bedding and Backfill So Lines Do Not Sag

A drain line is only as good as what it sits on and what goes over it. Get this wrong and the carefully set fall disappears as the pipe settles.

1. Bed the pipe. Lay solid PVC on a smooth, firm bedding, often sand or fine gravel, so it is fully supported along its length, not bridging over rocks or dips.
2. Shade the pipe. Hand-place bedding material around and just over the pipe before heavier backfill, protecting it and locking in the fall.
3. Backfill in lifts and compact. Place backfill in layers and compact so the trench does not settle later. Loose backfill settles, the pipe sags, and you get a belly. This is exactly why compacting a backfilled trench matters as much as the dig itself.
4. Restore the surface. Bring the trench back to grade and reseed or sod the lawn over it.

Solid (not perforated) PVC is used for area-drain conveyance lines so collected water stays in the pipe and is carried to the outlet rather than leaking back into the ground.

Tying Multiple Grates Together

Most yards need several inlets, a grate in each low spot, patio corner, or downspout location, feeding one main line. The trenching ties them together with fittings (wyes and tees) so every grate drains into the shared pipe and out the single outlet. Each branch holds its own fall into the main, and the main holds fall to the outlet. Planning the layout so the lines converge cleanly keeps the system simple and the digging efficient. Where several lines meet or a deeper collection point is needed, a catch basin is added, which ties into catch basin pit digging.

Current Market Reality

Drain-line trenching is usually priced by the linear foot and depth, plus the inlets and outlet. Cost rises with length, depth, hard digging, and how much lawn restoration is included.

Cost Driver	Effect
Trench length	More linear feet, more cost
Depth	Deeper trenches cost more per foot
Soil	Clay smears and slows; rock costs more
Number of grates and fittings	More inlets, more connections
Lawn restoration	Reseeding or sod over trenches

Industry Baseline Range: area-drain trenching commonly runs $8 - $40+ per linear foot for the dig, pipe, bedding, and backfill, with grates, fittings, and the outlet adding to the total; most small jobs carry a minimum callout. These are industry baseline ranges for planning only -- actual pricing depends on site conditions, soil, access, depth, haul-off, and current market conditions. Get a site-specific quote. Costs run higher in rocky ground, where the run is long, or where extensive lawn restoration is needed.

The Oregon Factors

A few local realities shape area-drain trenching here:

• 811 across the yard. Wandering trenches cross many buried lines, so the locate matters more than on a single straight run.
• Clay that smears. Willamette Valley clay smears the trench walls and the pipe bedding, and wet clay can glaze the trench bottom, so bedding and clean fall are extra important.
• Flat valley lots. Many valley properties are nearly level, so squeezing out enough fall over a long run is the real challenge, sometimes requiring a deeper outlet end or a pumped system where gravity simply will not reach.
• Restoring lawn over trenches. Wet-season trenching tears up turf, so plan for reseeding or sod and for the trench to settle before final lawn finish.

The Bottom Line

Area-drain trenching is about fall and backfill. Call 811, set your outlet, dig a smooth trench that runs continuously downhill, bed and shade the pipe, and compact the backfill so the line never sags into a belly. Get those right and the drain quietly carries water away for years. Cojo is CCB licensed and insured and works statewide across Oregon and the I-5 corridor. See our excavation services, read the full Oregon excavation contractor guide, and request a free estimate.