What drainage rate really means

Drainage rate is how fast water moves through the turf system, typically expressed in inches per hour. A turf system is only as fast as its slowest part. Backing permeability, any pad or panel, the stone base, underlying soil, slope, and outlet drains all work together.

  • Backing and tuft bind: Perforations or flow-through backings let water pass quickly.
  • Drainage pad or panel: Creates air channels that move water laterally toward an outlet.
  • Infill: Keeps fibers upright and can influence surface porosity.
  • Base and subgrade: Clean, open-graded stone drains fast. Dense fines and clay slow flow.
  • Slope and outlets: A slight grade plus a place for water to go prevents ponding.

Typical drainage specs by component

Turf backing

Quality perforated backings commonly deliver 30 inches per hour or more. Some flow-through backings and hybrid systems test in the hundreds of inches per hour. Backing speed is rarely the limiting factor once the base is designed correctly.

Drainage pads and panels

Modern pads and underlayment panels often support very high equivalent flow, frequently hundreds to over 1,000 inches per hour. Their job is to move water laterally to a drain when soil or slabs are slow.

Base, soil, and outlets

Open-graded aggregate offers high flow capacity. The typical bottlenecks are clay subgrades and undersized outlet paths. If native soil is slow, route water to French drains, daylight, or tied-in storm lines.

How turf drainage compares to real storms

Even intense cloudbursts are usually below 8 inches per hour and last minutes. A well-built turf system with a 60 inches per hour capacity has a wide safety margin.

Example: A 1,000 square foot area in a 4 inches per hour storm sees about 2,492 gallons per hour. A permeable base with proper outlets clears that load quickly.

Design moves that make turf drain fast

  • Use permeable backing: Choose products with proven flow rates.
  • Build an open-graded base: Clean, angular stone, compacted in lifts. Avoid fines that clog.
  • Add a separator fabric: Geotextile between soil and base prevents migration and fouling.
  • Dial in slope: Aim for 1 to 2 percent toward a defined outlet where feasible.
  • Provide outlets: French drains, daylighted edges, channel drains, scuppers, or floor drains on slab.
  • Consider pads or panels: Use them over concrete, rooftops, or slow soils to speed lateral flow.

Installation scenarios

Over native soil

Excavate organics, stabilize weak spots, install separator fabric, place open-graded base, compact, and set a slight slope. Tie the edge to daylight or a French drain if soils are slow.

Over concrete, pavers, or rooftops

Use a drainage pad or panel under permeable turf. Channel water to scuppers, trench drains, or floor drains. Add weep paths at edges so water exits cleanly.

Pet areas

Choose flow-through backing, fast-draining base or panel, antimicrobial infill, and a clear rinse path. Routine hose-downs keep everything fresh and free flowing.

Maintenance that preserves high flow

  • Brush and decompact infill periodically to keep pores open.
  • Remove leaves and debris so they do not mat the surface.
  • Rinse high-use zones and pet areas.
  • Inspect low spots after big storms and top up base if needed.

Troubleshooting puddles

  • Test: Time how fast 1 inch of water infiltrates within a small ring.
  • Fix surface: Add infill and groom to remove minor birdbaths.
  • Fix base: Core out soft areas, rebuild with clean stone, and reconnect to drains.
  • Improve outlets: Add a French drain, channel drain, or daylight path to move water off the area.

How to estimate your drainage rate

  1. Press a bottomless cylinder or large cup into the turf to seal a small area.
  2. Pour a measured 1 inch of water and start timing.
  3. When it disappears, convert seconds to inches per hour. Example: 1 inch in 30 seconds equals 120 inches per hour.

Specs to ask your installer

  • Backing flow rate and whether it is perforated or flow-through.
  • Full system drainage rate demonstrated on the proposed base.
  • Base type, thickness, and separator fabric.
  • Planned slope percentage and outlet locations.
  • Whether a panel or pad is recommended for your soil or slab.
  • Warranty coverage for workmanship and drainage performance.

When to add a drainage panel system

Use panels or pads over concrete, on rooftops, in dog runs, and on clay-heavy sites. They create reliable pathways that move water to the outlet even when soil infiltration is slow.