Does artificial grass improve garden drainage?

How effective is artificial grass at improving garden drainage?

So you’re getting sick of your doggy lawn and want to replace it with something which will be dry and green all year. No more mud, no more puddles.

lots of people opt for artificial grass for this very reason. It can’t get muddy, it’s permeable and it’s easy to clean. Poor drainage will be a thing of the past… or will it?

Artificial grass can help improve drainage but only in certain situations. Artificial grass as a surface layer is permeable and will not hold water for long so water can pass right through it. If it’s installed correctly it will have a layer of coarse sand or granite dust underneath it which is also permeable and will let water flow through it quickly.  

So far so good.

Seems like a no brainer, so why not just got for it? Well… as with almost everything, its not that simple.

Most drainage issues are only partly related to the surface layer of the garden. The bigger issue will be below the surface down at 150mm depth and below. 

At their most basic level, drainage issues are caused by water not being able to move through the ground fast enough. This causes a build-up which results in boggy ground, waterlogging and flooding. 

Based on this, improving drainage is almost always about improving the speed water can travel through the ground. Artificial grass improves the speed that water will travel through the top 100 – 150mm of ground but does nothing to improve the speed below that. This means that you could see no improvement in drainage whatsoever. 

Illustration of ground composition and how this effects drainage speed

The images above show ground before and after artificial grass. The bottom layer could be clay heavy soil which allows water through it at 5mm per hour. As you can see on the right, switching the top 150mm of clay soil for a sand and hardcore base under some artifical grass will increase the speed to 90mm per hour which is considered good drainage speed. 

The issue you run into then is that once it has passed through that later it hits the lower layer where it can only travel 5mm per hour. This effectively means that when the top layers are saturated the speed water can travel through them will be equal to the rate it can drain through the bottom layer. 

Is artificial grass a good investment to improve drainage?

On its own, no. As you can see from the example above it will still be limited by whatever is underneath it. However, when used in combination with other types of drainage it can be very effective. 

For example, a French drain underneath the artificial grass base will allow water to freely flow away indefinitely. This will mean that water within a certain radius of the French drain will drain at 90mm per hour and will never become saturated. 

This same idea would work with other types of drainage too.

Conclusion

Artificial grass improves drainage when the base it is set on is more permeable than the surface which it replaced. The effectiveness is limited by the layers of soil below the base so in most situations there will be little noticeable change after artificial grass is installed. 

Where artificial grass becomes very useful is in combination with other types of drainage which catch water coming through the permeable artificial grass base and redirect it.

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