There are 2 key aspects of creating our lawn drainage system, firstly creating a soakaway that will receive the water from the drainage pipes and then laying the drainage pipes underneath the lawn. This system is widely regarded as the best drainage system for a waterlogged lawn that is the result of a heavy clay sub soil.
Creating a soakaway
A soakaway will collect the water from the drainage pipes and should be located at the lowest point of your garden. The soakaway should be about 1m square and dug to a depth of around 4-6 feet. Fill the soakaway with rubble and hardcore (large stones / broken bricks etc) up to around 1 foot from the surface. Add 6 inches of small stones / coarse gravel and then add a 6 inch layer of top soil to top up the soakaway to its original level.
If you can’t create a soakaway then see if you are able to create a ditch where the soakaway would be located that leads away (downhill) from the garden. Whether or not this is possible may depend on the land surrounding your garden and your neighbours (if you have any).
Laying the drainage pipes
A lawn drainage system is considerably easier to install today than it used to be due to the lightweight, flexible, lengthy plastic drainage pipes that are now available. Before these were available heavy, cumbersome, interlocking clay pipes had to be used to drain the lawn. The lawn drainage pipe system consists of a main pipe and a series of narrow ‘slit’ side pipes.
Main lawn drainage pipe
Mark out the proposed line of the drainage pipes on the lawn surface with a thin line of sand. Dig up a width of turf (around 5 inches) along the main drainage pipe line and place the turf next to the line. Now dig the trench out to a depth or around 15 inches making sure that there is a slight downward slope from the top end of the trench to the bottom end of the trench (which meets the soakaway). You should have a slope of 1cm to every 1m of pipe that is to be laid.
Once you have dug the trench you can test whether it will function correctly by adding water from a hosepipe at the top of the trench and seeing if it flows down the entire length of the trench without stopping due to a poor slope / barriers.
After testing the water flow down the trench add a 1 inch layer of small stones / shingle. Now lay the 3 inch land drainage pipe on top of the shingle (this type of pipe normally comes in rolls that should be long enough for most lawns).
Now continue to add shingle into the trench so that it comes around the sides of the pipe and over the top of it until the trench is about 8cm deep. The next stage is adding the topsoil that you dug out of the trench until the trench is the depth of the turf layer. Now simply replace the turf that is lying next to the main drainage channel.
Now you can dig the ‘side’ slit drainage channels for the narrow slit drainage pipes. These drainage channels are shallower than the main channel (around 4 inches) and end above the main drainage pipe. The water can then pass out of the side channels and drain into the main drainage channel shingle and down into the main drainage pipe where it then flows into the soakaway.
Again it is important to note that there must be at least 1cm downward slope to every 1m of side drainage channel with the lower end being at the point where the side channel meets the main drainage channel.
Lay slit pipes on coarse sand / find shingle and back fill round the pipe sides, recover with a fine layer of top soil and turf.
Now that your lawn drainage system is complete you can continue to top dress the lawn at regular intervals to help aid drainage into the drainage channels.