Excavation
Area Drain Trenching: Digging the Lines That Carry Water (Oregon)
Cojo
June 19, 2026
6 min read
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.
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.
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.
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.
The outlet usually needs to daylight; a drain that runs to a buried dead end with nowhere to go just fills up.
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.
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.
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.
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 |
A few local realities shape area-drain trenching here:
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.
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