Waterlogged Lawn? How to Fix Drainage Before You Returf

Poor lawn drainage in South East Queensland has five common causes: compacted soil, sodic clay, builder’s fill with no fall, a high water table, or neighbour and roof runoff. Test first: dig a 300 mm hole and fill it with water. If it still holds water after 24 hours, aerating won’t fix it. Fix the drainage, then returf.

Key facts

Signs your lawn has a drainage problem

Any lawn is soft for a day after a big storm. A drainage problem is the same patch, storm after storm, still wet when the rest of the yard has dried. Look for:

• puddles that are still there 24 hours or more after rain
• ground that squelches underfoot, or footprints that fill with water
• thin, yellowing grass and shallow roots that lift out easily
• moss, algae or sedges moving in
• a sour, rotten-egg smell when you dig

Waterlogged or just overwatered?

Turn the irrigation off for a dry week. If the patch dries out, cut back your run times. If it stays wet with no rain and no sprinklers, water is getting in from elsewhere (a leaking pipe, a neighbour or groundwater) or has nowhere to go.

Do the 24-hour drainage test

This tells you whether the problem is at the surface or deeper. Do it in the worst spot, and in a good spot to compare.

1. Dig a hole about 300 mm deep and 300 mm wide.
2. Fill it with water and let it drain away completely. This wets the surrounding soil.
3. Fill it again to the top and note the time.
4. Check it after 1 hour, after 4 hours and the next morning.

Two more checks: push a long screwdriver into the lawn (if it stops hard at 50 to 100 mm, you have compaction or a clay layer), and next time it pours, watch where the water comes from and where it goes.

What’s causing it? Brisbane and Sunshine Coast soils

Reactive and sodic clay

Much of Brisbane, Ipswich and Logan sits on heavy clay, and some of it is sodic. The Queensland Government explains that soil sodicity causes surface crusting and sealing and slows water moving through the soil.

Builder’s fill on new estates

On new estates such as North Lakes, Ripley, Yarrabilba and Palmview, yards are often compacted clay fill with a skim of topsoil and little fall. Service trenches settle, and water ends up against the slab or along the fence.

Coastal sand over clay

Sandy Sunshine Coast soils usually drain fast. Where sand sits over clay, or the water table is high in low-lying areas, the sand fills like a sponge and stays wet.

Quick fixes for mild waterlogging

If your test hole emptied by the next day, start here.

• Stay off it while it’s wet. Traffic on saturated soil compacts it further.
• Core aerate, then top-dress. Hollow tines pull out plugs of soil; brush washed sand or sandy loam into the holes so they stay open. Do it while the grass is growing, spring to early autumn in SEQ.
• Gypsum for sodic clay. Gypsum helps only dispersive clay, not compaction or low spots. Drop a dry soil crumb into rainwater: if a cloudy halo forms, try gypsum at the rate on the bag.
• Fill shallow low spots. Top-dress dips a little at a time, keeping leaf tips showing.

Does sand help lawn drainage?

Yes, but only when it gets into the soil. Sand brushed into aeration holes creates drainage channels. A layer spread over clay without aerating does little and can hold water on top of the clay. Avoid brickies’ sand, which contains clay.

Permanent lawn drainage solutions

If water was still in the hole after 24 hours, change the shape of the ground or give the water somewhere to go.

• Regrade to a fall. Shape the subsoil so water runs away from the house. We work to about 1% (10 mm per metre) on sports fields, a sensible target for a backyard too. Keep the fall running away from the slab, and check it against your builder’s or council’s approved levels.
• Ag pipe or French drains. This is what most people mean by drainage under lawn. A simple lawn drainage system of slotted pipe in a socked, gravel-filled trench carries water away, provided the trench has a fall and discharges somewhere lawful.
• Spoon drains and swales. A shallow turfed dish along a boundary or slope catches surface water, handy where runoff comes from next door.
• Soakwells in clay: usually not. In heavy clay a soakwell just fills up and stays full.

Plumber or turf team?

Shaping, decompacting, subsurface drains within the lawn and returfing are landscape work. Connecting to a stormwater pit, kerb outlet or downpipes is not. In Queensland, drainage work other than unregulated work needs a licensed plumber or drainer, and your water must go to a lawful point of discharge. Your council can tell you where that is. Sunshine Coast Council notes it may get involved if water is concentrated onto a neighbouring property, so don’t push your problem over the fence.

We use the same principles on sports fields. At Genesis College, Bray Park, we built swale drains with subsurface drains along their toe. At Clive Berghofer Stadium, Toowoomba, we reused the red clay site soil, ripped it, added gypsum and lime, and laser-graded it to a 1% fall to swale drains. At Sheldon College, subsurface drains sit on a 1% fall, with gravel bands connecting them to the surface. Our commercial and sports turf construction page has more of that work.

Fix drainage first, then returf

New turf on the same bad base fails the same way, usually in its first wet summer. Work in this order:

1. Find the cause with the 24-hour test and a storm check.
2. Remove the old lawn and any weeds.
3. Rip or cultivate compacted subsoil, and work in gypsum if the clay is sodic.
4. Shape the subgrade to a fall, away from the house.
5. Install ag drains or swales, and have a licensed plumber make any stormwater connections.
6. Spread 100 to 150 mm of sandy loam underlay, following the same fall.
7. Level, lightly firm, then lay and water in the turf, or have our team handle the turf installation.

This is what our site and soil preparation service covers: levelling, drainage correction such as subsurface drainage and contouring, and soil conditioning before the turf goes down.

Best turf for wet or poorly drained SEQ yards

No lawn grass likes sitting in water, and no variety rescues a yard that floods. Once drainage is fixed, match the grass to the light and use. Our turf varieties page compares every lawn we grow.

All three are cut to order at our Woodford farm and delivered across Brisbane and the Sunshine Coast. Once you have measured your lawn, the turf calculator gives you the square metres and the price.

What drives the cost of fixing drainage

We price drainage work after seeing the site. The main drivers are:

• the area, and how much soil must be moved or imported to create a fall
• machinery access
• the length of drain, and how far it is to a lawful discharge point
• any plumbing connections, which are a separate licensed trade
• underlay volume, and the turf variety you choose

Doing drainage, soil and turf as one job beats returfing twice. For a whole yard, a front and backyard turf package bundles the site assessment, turf and installation.

Timing around the Queensland wet season

SEQ’s heaviest rain usually falls from December to March. August to October is usually the driest time, and storms tend to arrive from late spring, so that is the best window for drainage work: the ground is workable and new turf has a head start before the wet. Wait for summer and you’re working wet clay that smears, with new turf that can wash out. For the turf itself, see the best time to lay turf in South East Queensland.

A note on artificial grass

Artificial grass still needs a free-draining base and a fall, because water drains through the backing into whatever is underneath. We grow and lay natural turf only, but the basics (find the cause, create a fall, discharge lawfully) apply to both.

Frequently asked questions

Fix it once

If your lawn floods every wet season, returfing alone won’t fix it. We’ve grown turf at Woodford since 1994, and we can assess your drainage, rebuild the soil profile and lay fresh, farm-grown turf in one job. Read about our site and soil preparation, see our lawn care services for ongoing care, or ask for a free quote.

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