Why is a permeable driveway so important?

The problems facing urban drainage systems

Climate change and increased urban expansion have put strain on drainage systems that simply were not designed to deal with the increased loads they face today.

Unsustainable drainage can have a number of troubling consequences, including increased flood risk, threatening infrastructure, water quality and personal and public property.

What other problems are urban drainage systems facing?

• Less vegetation alters surface runoff patterns and reduces drainage
• There are lots of natural depressions in the ground, which can hold water as large puddles for
• much longer
• Surface runoff is much quicker due to amount of paving and concrete
• Urban pollutants are more widespread

What is SUDS?

In recent years, there have been a number of developments in Sustainable Urban Drainage Systems, or SUDS. 

SUDS aims to solve the problems listed above by encouraging land developers to decrease flow rates through a number of measures, including re-use of water and allowing the earth to absorb more.

SUDS promotes better management of water flow through urban environments, including the following:

• Source Control: Reduces the amount of water entering the drainage system.
• Retention: Providing better water storage elsewhere, such as in ponds.
• Pre-Treatment: Removes pollutants from the water
• Infiltration: Encouraging more water to soak into the ground

One of the key measures here is the encouraged use of permeable surfaces.

What is a permeable surface?

A permeable surface is porous and allows water to pass through and into the ground beneath. This water can then be absorbed into the Earth.

An impermeable surface, by comparison, prevents any water from passing through. The result is either a buildup of water on the surface, or the flowing of this water to other areas. 

A puddle on an asphalt pavement might not look like much in isolation, but across a larger urban area, this can become a big problem.

Does SUDS include driveways?

Yes. All new driveways now need to comply with SUDS regulations when it comes to tackling surface runoff, especially in built up areas. 

What kinds of permeable driveway are there?

If you are having a new driveway installed, there are a number of SUDS compliant solutions available to ensure adequate permeability. Some of these can be found below. 

Grass surface

A natural grass surface is one of the most absorbent surfaces you will find for rainwater, so its SUDS related benefits are fairly obvious.

There are a few challenges that should be considered if choosing a grass driveway:

• Being a driveway, the surface will be put under a lot of pressure from the weight of vehicles and people walking on it. This can ruin a beautiful grassy surface in no time if precautions aren’t taken.
• Like a lawn, a grass driveway will require maintenance such as cutting and watering if the climate requires it.
• If your vehicle is parked over the grass a lot, sunlight deprivation can discolour the grass quite severely.

One solution to make a grass driveway more practical is to install two strips of paving, brick or other hard material to serve as tyre paths. These may not be absorbent, but your drive will still have sufficient permeability from the grass to make it SUDS compliant.

Loose Gravel

One of the most common and perhaps easiest to install permeable driveway solutions is the use of simple loose gravel, chippings or other aggregates. These are simply spread across a prepared surface, leaving plenty of gaps between aggregates to allow for water absorption.

There are a number of benefits of loose gravel or aggregates:

• Fairly low cost
• Natural, attractive surface
• SUDS compliant
• Long lasting

However, there are some potential maintenance issues you should be aware of:

• Vehicles and pedestrians can move about loose aggregates fairly easily, so regular maintenance will be required to redistribute and keep it nice and tidy.
• Some aggregates may be lost over time by rain, wind, vehicles or footsteps, so you may be required to purchase more and top up every so often.

Plastic Grid Systems

Plastic grid systems are a useful way to keep permeable and loose gravel chippings tidy and in place. These are simply hard plastic webs, which are placed on top of the base surface and then filled with loose chippings.

This solution allows you to take advantage of the porous characteristics of loose gravel and chippings, with a more secure placement, meaning less maintenance and redistribution is required.

The clear disadvantage of this solution is aesthetic. Depending upon personal preference, a plastic webbed grid may be unsightly to some, effectively cancelling out the natural visual appeal of aggregates.

Useful Links

• What’s the difference between resin bound and resin bonded?
• More information on SUDS regulations
• Is resin bonding permeable?
• About Resin Bonded Aggregates