How to Move Water Through Your Landscape: Swales, Subdrainage, and Smart Design

Drainage challenges are common for homeowners, often stemming from original site development and worsening over time due to neighborhood topography changes. Opinions vary on best practices, so understanding your options is crucial when hiring professionals for grading and site work. Water movement in the landscape is also a significant design opportunity—the relationship between water and ground can take many forms, from surface swales to underground pipes to hybrid systems.

Terra Ferma Landscapes

Three Approaches to Water Movement

Swales

Swales are shallow, elongated depressions that collect and move water visibly across the landscape. Their material choices and layout highlight water's journey. Beyond conveyance, they slow water and allow percolation back into the ground, improving water quality.

Subdrainage

Subdrainage uses buried constructed systems—drainpipes, drain inlets—to collect and move water invisibly. It's fast and efficient but hidden from view.

Hybrid Systems

Samuel H. Williamson Associates

Swales and subdrainage often work together—for example, a swale moving water from a roof downspout across the landscape to a drain inlet.

Why Swales Are Gaining Favor

SURROUNDS Landscape Architecture + Construction

For decades, buried drainage was considered most effective due to speed and efficiency. Today, best practices have shifted toward "daylighting" water—bringing it to the surface for sunlight exposure (which improves water quality) and visibility. We've also learned that moving water too quickly causes downstream flooding. Cities now seek ways to reduce sewer system loads; Seattle, for instance, offers guidance on disconnecting downspouts to handle roof runoff with swales and rain gardens instead.

The rock swale shown here is nestled along a terraced planting. Its low point is in the foreground, so rain flows parallel to the slope toward the viewer—a smart solution for steep, rocky terrain that channels water away from outdoor living areas.

Swale Functions: Matching Design to Soil

Falon Land Studio LLC

Swales are environmentally friendly and adaptable. Infiltration rate—how fast water moves through soil—depends on soil texture, incoming water volume, and existing saturation.

• Conveyance swales work in poor-infiltration soils or are lined with impervious layers (engineered clay, geotextile fabric) to prevent infiltration and move water efficiently.
• Infiltration swales suit high-infiltration soils. With gradual slopes, they move water while allowing ground absorption, reducing overall property runoff.
• Swale-pipe combos pair a surface swale with a perforated drainpipe at the bottom. Water collects on the surface, flows to the pipe, then moves along the sloped drain. Common in high-rainfall areas with large runoff volumes.

Swale Materials: Where Design Meets Function

Falon Land Studio LLC

Material selection defines the swale's appearance and the landscape's overall style. Four main styles exist:

• Lawn: Basic, mowable, sloped for water movement.
• Wetland plants: Native species tolerating periodic inundation and drought—streamside and pond-edge plants are ideal. Local advocacy groups often publish regional plant lists.
• Stones: Rock-filled, often called dry streambeds, dry creek beds, arroyos, washes, wadis, or vernal streams when curving.
• Mixed stones and plants: Naturalistic garden swales blending both elements.

Swale Layout: Straight vs. Curvy

Falon Land Studio LLC

Swales can follow any layout fitting the grading plan. Key parameters: they must be sloped and sized for local rainfall. Straight swales work best for gradual slopes and infiltration. Curvy swales are preferable for conveyance—curves break up water energy, allowing meandering flow.

When to Go Underground

Arrow. Land + Structures

Subdrainage is preferred when space is insufficient for swales—tight urban courtyards, for instance, where buried pipes carry roof runoff from large homes. Subdrains use concrete catch basins and PVC pipes, hidden underground. They've become less popular as swales gained favor.

Swales often pair with drain inlets or buried drains when infiltration area is inadequate. Drain inlets also serve as rain garden backups—designed for typical storms, with overflow capacity for 100-year events connecting to city systems.

Anthony Wilder Design/Build, Inc.

Perforated drains work as hidden structures in poorly draining soils, pulling moisture from foundation walls and moving water away from structures. Site slope relates to yard size—a swale needs more space to meander with check dams and terracing on steep sites.

Choosing Your Best Method

Select based on site conditions with a landscape architect's guidance. Ideally, they'll design a system optimizing the overall site. Costs depend on grading and hardscape requirements. Contractors experienced with swales and major grading typically offer competitive pricing. Get multiple opinions. Your yard size and runoff volume are the biggest factors in determining the best approach.