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.
Resin Bound System
Resin bound aggregate systems are becoming increasingly popular as a driveway surface for a number of reasons. In this system, the gravel (also known as aggregate) is mixed with a special resin before being spread evenly over the surface.
A resin bound system is porous, allowing water to pass through the small gaps between aggregates and resin.
Resin bound systems also bring other practical benefits:
- A smooth, flat finish
- Low maintenance
- No loose gravel means it cannot be redistributed and made uneven
- Weed and frost resistant
By combining aggregates of varying colours and sizes, a resin bound system can be a very attractive and highly versatile permeable surface.
A resin bound system contrasts with a resin bonded system which is another resin based aggregate system, except resin bonded consists of a solid layer of resin with aggregates spread on top. The result of this is an impermeable surface, which is therefore not a SUDS compliant solution.
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.
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.
Why we recommend a Resin Bound System
The solutions listed above each bring their own advantages; however, we at Derbyshire Specialist Aggregates strongly recommend a resin bound system for installing a permeable and SUDS compliant driveway.
This is simply because a resin bound surface is the only solution which offers all of the benefits listed above, with none of the compromises.
The surface is attractive and natural looking, just like loose gravel and grass, but requires less maintenance and will not diminish over time. It is strong and sturdy, unlike loose gravel, and you will not need to top it up. It also offers the neatness of a plastic grid gravel system without the unsightly plastic webbing.
Most importantly, it is an excellent long-term solution to modern drainage concerns; its growing popularity is evidence of this.