Lawn drainage- Solving a Soggy Lawn Problem

 

GardenAdvice.co.uk lawn experts show you how to install a drainage system in your lawn with the minimum of hassle. Most drainage systems are based on agricultural systems, which can be very effective in a garden lawn or a sports ground set up.

The key to designing and installing a drainage system in a lawn is to remember that the water must be able to travel from the surface to the drain, which is installed under the lawn.

Firstly you must consider the fact that all drainage systems work because water will always flow to the lowest point, so you need to design the system so that the drainage water will drain to the lowest point in your garden – into a ditch or a soak away. To achieve this, all the drainage pipes you have must have a fall on them no less than 1 in 200 in the direction you wish the water to flow (ideally 10 mm fall for every metre of pipe laid).

To lay the main pipes you must first mark out the area from a plan that you will have needed to draw up (see demo plan). If you need any help doing this, please feel free to use gardenadvice.co.uk free advisor service who will produce a basic plan for a drainage system for you. Once you have the basic plan worked out, you can start to install the system by using the following basic steps:

 

1. Mark out the drain runs on the grass with some sand and cut the turf out in strips 125 mm wide and place by the side of the drain run.

2. Next dig out the run. This is best done with a trenching spade (these can be obtained from your local builders’ merchant). The depth should start at about 400 mm and slope in the direction of the intended flow of water, ideally at 6 mm fall per metre of trench. To test the fall, run some water from a hosepipe to the higher end of the trench and see if that water flows smoothly down the trench.

 

3. Once you have completed the first trench, you should fill the trench with 20 mm of 10-12 mm clean stone, then place a 75 mm perforated drainage pipe on top of it. This pipe can be purchased from a builders’ merchant and normally comes in 25 metre rolls.

4. Next, back fill the trench on top of the drainage pipe with the clean stone to approximately 75 mm from the top of the trench. Next, fill the remaining space with the soil you dug out of the trench, firm it down and replace the turf. When back filling the trench, it is important not to spill the stone on the grass, as this will damage your lawn mower.

5. The next stage is to make a series of slit trenches at right angles at the drainage pipes across the lawn with a spade at 400 mm centres, about 75 mm deep and fill them with a washed sand. It is important that the slits connect with washed stone over the main pipes – you should be able to feel the stone with the spade as you form the slit.

 

6. The final stage needs to be carried out over a number of months. It involves top dressing the lawn with a washed sand over a number of months to build up a carpet of sand at the base of the grass plants to allow the rainwater to move freely on the surface and down the sand slits into the drain.