Drainage Swale Installation in Lancaster, PA

A drainage swale is an open, gently sloped channel lined with grass that moves large volumes of rain runoff across a yard without a buried pipe. It suits homeowners and small property owners in and around Lancaster whose lots take in water from a slope, a neighbouring lot or a paved surface and have the room to give that water a path. Lancaster French Drain designs, cuts and finishes swales so the water leaves your lawn and your foundation instead of pooling against them.

What a drainage swale is and when a yard needs one

A swale is a wide, shallow dip in the ground, shaped like a shallow dish rather than a ditch. It carries water on the surface, so it can handle far more flow than a perforated pipe in a trench. Because it is grassed, it also slows the water and lets some of it soak in along the way. It sits among the open-surface tools used in yard drainage, and it is the one to choose when the problem is a lot of water arriving at once.

A swale fits when runoff comes across the yard as a broad sheet: down a hillside, off a neighbour's higher lot, or from a driveway or roof that sheds a large area. It needs width to work, so it is a poor match for a narrow side yard with no room between the house and the fence line.

• Water flows across the lawn in a sheet after heavy rain and leaves a muddy line.
• A low spot stays soft for days, and the grass there thins or dies.
• Runoff from higher ground heads straight for the foundation wall or a window well.
• A pipe-based fix has clogged or overflowed because the volume is simply too high.

Swale shape, slope and size

The geometry is the whole job. A swale that is too steep scours, and one that is too flat holds water and turns into a boggy strip.

Cross-section

Most residential swales have a flat or gently rounded bottom with side slopes mild enough to mow, usually no steeper than about one foot of rise for every three feet of run. Depth is typically measured in inches to a foot or so, and width is set by how much water the swale must carry at its peak. A wider, shallower channel is safer to walk and mow than a narrow, deep one.

Longitudinal slope

Along its length, a grassed swale generally works best with a fall somewhere between about one and five percent. Below that range water lingers. Above it the flow picks up speed and starts to cut into the turf, which is when rock lining or check dams come into the plan.

The outlet

Every swale must end somewhere that can take the water: a street gutter or storm inlet where allowed, a low corner of your own lot, a rain garden, a catch basin, or a stable drainage path off the property. We confirm the outlet before any digging, because a perfect channel that dumps onto a neighbour's land is a new problem, not a fix.

Soil, grass and lining choices

The channel surface decides how well it survives the first big storm. Dense turf grass is the usual lining. A tall fescue or similar mix with deep roots holds soil better than thin lawn grass, and straw or coir erosion blanket pinned over the seed protects the bare soil while the roots take hold.

Where the grade is steeper or the flow concentrates, such as at a downspout discharge point or a bend, we may add a lining of river stone or riprap over filter fabric. Small check dams of stone can step the water down a long slope. Heavy clay soil drains slowly, so a swale cut into it will stay damp between storms. That is normal for a swale, and the grass is chosen to cope with it. In very wet bottoms, a perforated pipe under the swale floor can be added so the channel dries out faster.

How a drainage swale installation goes, step by step

The work is mostly surveying and shaping, and it is done in an order that keeps the finished grades honest.

• Walk the property in or after rain to see where the water actually enters, travels and leaves.
• Mark the centreline and check fall with a level or laser, then confirm the outlet.
• Call before digging so buried utility lines are located and marked.
• Strip and set aside the sod and topsoil.
• Cut the channel to the planned cross-section and slope, using the spoil to build gentle berms where needed.
• Add stone lining or check dams at steep or high-velocity spots.
• Replace topsoil, seed or lay sod, and cover with erosion blanket.
• Water in the new grass and keep traffic off the channel until it has rooted.

Swale versus French drain, channel drain and regrading

A swale moves surface water. A French drain moves water that has already soaked into the ground. If the yard is wet because of a high water table, a buried drain is the right tool, and a swale will not help.

If the surface is the problem but there is no room for an open channel, a channel drain can intercept sheet flow across a patio or driveway edge. And when the whole yard slopes toward the house, the cheapest fix may be grading and regrading so the first ten feet around the foundation fall away from the wall, with a swale picking up the water further out. Often the best answer is a swale paired with one of these.

Swales in Lancaster: rainfall, soil and older lots

Lancaster sits in the Piedmont region and gets about 42 inches of precipitation a year, with September the wettest month. Those late-summer and early-fall storms can drop a lot of water on soil that is already full, which is exactly when a yard without a path for runoff floods. Winter adds snowmelt on top of frozen ground, so water has even fewer places to go.

Much of Lancaster is older housing on small city lots, where there is rarely space for a wide channel. Out in the surrounding townships, larger lots on gentle slopes are a better fit for a swale. Properties near the Conestoga River and its tributaries also tend to have lower ground that collects water from above. On any lot, we check where downspouts discharge, since an unmanaged downspout drainage line can feed a swale more water than it was sized for.

Keeping a swale working

A swale needs very little care, but it does need some. Mow it like the rest of the lawn and leave the grass a bit taller than you would on a play area. Rake out leaves and silt after big storms so the bottom stays open.

Do not plant shrubs or trees in the channel, pile grass clippings or yard waste in it, or run a fence across it without leaving a gap at the bottom. If ruts form from mower wheels or vehicles, fill and reseed them early. Small fixes keep the channel from cutting deeper. If you want a visit to look at a wet yard, Lancaster French Drain can walk the lot with you and tell you plainly whether a swale is the right answer.