Question 1

What's the difference between a French drain, a dry well, and a swale?

Accepted Answer

A French drain is a gravel-filled trench with a perforated pipe that collects water along its length and carries it, by gravity, to an outlet point away from the problem area — it's a linear collection-and-conveyance system. A dry well is a buried chamber (or gravel-filled pit) that collects water from one point, typically a downspout or French drain outlet, and lets it slowly infiltrate into the surrounding soil rather than carrying it elsewhere — it's a point-source storage-and-infiltration system. A swale is a shallow, graded surface channel that directs water across the top of the ground toward an outlet using slope alone, with no buried pipe or gravel at all — it's a surface conveyance system. All three move water away from a problem area, but by very different mechanisms.

Question 2

Which is cheapest to install?

Accepted Answer

A swale is generally the cheapest since it's essentially a graded surface feature requiring earthwork and sometimes sod or erosion-control planting, without buried pipe, gravel, or fabric — DIY swale grading for a modest slope can cost very little beyond labor and equipment rental. A dry well's cost depends heavily on size, ranging from a simple gravel-filled pit (relatively cheap) to a manufactured plastic infiltration chamber (more expensive but higher capacity and longer-lasting). A French drain is typically the most expensive of the three per linear foot because of the excavation depth, pipe, gravel, and geotextile fabric involved, though its per-foot cost is offset by solving problems the other two can't (subsurface water interception, not just surface flow).

Question 3

Can these three methods be combined?

Accepted Answer

Yes, and combining them is common and often the correct solution — a French drain frequently discharges into a dry well when there's no suitable gravity outlet point downhill, and a swale is often used on the surface directly above or alongside a French drain to handle surface sheet flow while the French drain handles subsurface water. Treating these as three separate, mutually exclusive options rather than complementary tools is a common planning mistake for anything beyond the simplest single-symptom drainage problem.

Question 4

Does my yard have room for a dry well, or does it need specific soil conditions?

Accepted Answer

Dry wells depend on soil infiltration rate to work — they're a poor fit for dense clay soil that drains very slowly, since water can back up and overflow the dry well faster than the soil absorbs it. A percolation test (digging a test hole, filling it with water, and timing the drop rate) before installation tells you whether the soil can actually accept the water a dry well would deliver to it; in poorly draining clay soil, a French drain routed to a distant gravity outlet, or a swale directing water off the property entirely, is usually the more reliable choice over a dry well.

Question 5

Will a swale work if my yard is flat?

Accepted Answer

Swales need a minimum slope to function since they rely entirely on gravity to move surface water — a typical minimum working grade is around 1-2% (roughly 1-2 ft of drop per 100 ft of length), and less than that risks the swale holding standing water instead of conveying it. On a genuinely flat lot, a French drain (which can be laid with a controlled, precise fall even where the natural grade doesn't provide one) or a dry well is usually the more reliable option, since a swale on flat ground just becomes another wet ditch.

Question 6

Which solution is best for a wet basement or foundation problem?

Accepted Answer

A French drain, specifically installed as perimeter/exterior footing drainage around the foundation (or as a curtain drain intercepting water before it reaches the foundation on the uphill side), is the standard, most direct solution for a foundation moisture problem caused by groundwater or surface water reaching the foundation. A swale can help by redirecting surface runoff away from the foundation before it ever gets there, and is often used together with a French drain rather than instead of one. A dry well alone doesn't address foundation water directly unless it's specifically receiving the outflow from a foundation drain system.

Question 7

Do I need a permit for a French drain, dry well, or swale?

Accepted Answer

It depends on your municipality and the scope of the work — many jurisdictions don't require a permit for a simple French drain or swale entirely within a single property that doesn't alter drainage onto a neighboring lot or into a public right-of-way, but larger dry wells, any drainage work discharging toward a property line or street, and anything affecting stormwater management in a regulated area can require a permit or engineering review. Check local requirements before starting, especially if the solution involves directing water toward a neighbor's property, which can create liability regardless of permitting.

Question 8

Can I dump downspout water directly into a French drain?

Accepted Answer

It's possible but often not ideal without a settling or catch basin first, since downspout water carries roof debris (leaves, grit, shingle particles) that can clog the French drain's gravel and geotextile fabric faster than groundwater alone would. A common and more durable setup routes the downspout to a solid (non-perforated) pipe or a small catch basin first, then either to a dry well or into the French drain's outlet end, keeping debris out of the perforated collection section.

Question 9

How do I know which one my yard actually needs?

Accepted Answer

Match the solution to the water's source and behavior: if water is seeping up from wet, saturated subsurface soil along a line (a persistently soggy strip, water at the base of a slope), that's a French drain problem. If water needs somewhere to go after being collected at one point (the end of a downspout or the outlet of a French drain) and there's no gravity path to daylight, that's a dry well problem. If water is simply running across the surface in the wrong direction (sheeting toward the house, pooling in a low spot after rain) and there's enough slope to work with, that's a swale problem. Many real yards have more than one of these symptoms and need more than one solution.

Factor	French Drain	Dry Well	Swale
What it solves	Subsurface/groundwater seepage along a line	Point-source water needing somewhere to infiltrate	Surface sheet flow across open ground
Mechanism	Buried perforated pipe in gravel, gravity-fed to an outlet	Buried chamber/pit allowing slow soil infiltration	Graded surface channel, gravity conveyance only
Relative install cost	Highest per linear ft (excavation, pipe, gravel, fabric)	Moderate, scales with chamber size	Lowest — mostly earthwork
Needs a gravity outlet or absorbent soil	Needs a downhill outlet point	Needs soil with adequate infiltration rate	Needs at least ~1–2% slope
Works on flat ground	Yes — pipe fall can be built in regardless of surface grade	Yes, if soil infiltrates well	No — needs surface slope to function
Best for foundation/basement water	Yes — standard perimeter/curtain drain solution	Supporting role — receives outflow	Supporting role — redirects surface water away first
Maintenance	Low, but can clog over many years without proper fabric	Can silt up if it receives debris-laden water untreated	Occasional regrading/resodding if erosion occurs

What You're Seeing	Best Fit	Why
Persistent soggy strip or seepage along a slope base	French drain	Intercepts subsurface water moving through the soil
Downspout water with nowhere to drain on a flat lot	Dry well (after a French drain or solid pipe run)	Gives collected water a place to slowly infiltrate
Surface water sheeting toward the house after rain	Swale	Redirects surface flow using grade alone, no excavation needed beyond shaping
Wet or damp basement/foundation	French drain (perimeter/curtain drain), often paired with a swale	Standard direct solution; swale helps by keeping surface water away in the first place
Flat yard with no natural outlet downhill	French drain to a dry well	Combines controlled pipe fall with a soil-infiltration endpoint
Heavy clay soil that won't easily absorb water	French drain routed to a distant outlet, not a dry well	Dry wells depend on soil infiltration rate, which clay doesn't provide
Low-cost first attempt at redirecting minor runoff	Swale	Cheapest option if there's enough natural slope to work with

French Drain vs Dry Well vs Swale: Which Drainage Solution Fits

Head-to-Head Comparison

Which to Choose — By Symptom

When to Combine Solutions

Common Mistakes

Installing a Dry Well in Poorly Draining Clay Soil

Building a Swale With Too Little Slope

Skipping Geotextile Fabric on a French Drain

Routing Downspout Debris Directly Into a French Drain's Perforated Section

Directing Any of These Solutions Onto a Neighbor's Property

Final Verdict

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