Channel Drains: How to Prevent Flooding of Hardstanding Areas

Most areas used by vehicles to park, load/unload and manoeuvre have a hard surface such as asphalt or concrete as these are relatively durable. However, they are also largely impermeable to water, so unless they are properly constructed to manage rainfall, they will be prone to flooding. In most situations, the best solution to prevent this and quickly remove surface water is to install channel drains.

What are the nuisances and dangers of flooding?

A car park that is regularly subject to flooding will reduce the number of available parking spaces and standing water will be unpopular with users; for example, shoppers who use a supermarket car park. 

In colder weather conditions, undrained water may freeze and create a slippery surface that is a danger to pedestrians and vehicles. Floods might also conceal surface debris and damage such as potholes or cracked drain covers that can cause damage to vehicles.

If an area is used by vehicles travelling at higher speeds, flooding can also increase the risk of reduced visibility from road spray and aquaplaning.

In the longer term, standing floodwater may seep through small gaps in the asphalt or concrete. If this water then freezes it can weaken the structure of the surface and accelerate its disintegration.

Floodwater that isn’t properly managed can also erode the subsoil beneath the hardstanding, multiplying the risk of subsidence and leaving pipework or cabling unsupported and at risk of damage.

How do channel drains so effectively manage flooding?

Channel drains are not the only method used to drain large areas of asphalt or concrete; on highways, for example, road gullies covered by a grating are more commonly used. However, channel drains are designed and constructed to quickly divert water from a large area.

A channel drain is comprised of a half-pipe channel covered by a removable grating along its whole length. This allows water to enter the drain at any point, rather than solely where there is a gully. The removable grating also makes it easy for the channel to be regularly cleaned of silt and debris that would otherwise restrict drainage.

While a channel drain can be installed retrospectively, the best results are achieved if they are included in the original plans for the hardstanding area. if the location of the channel drain has already been decided, the subbase and top dressing can be applied with a slight camber that prevents low spots and directs rainwater towards the line of the drain.

If incorporated at the design stage, the channel drain can also be located to optimise the gravity flow of water to a holding tank or watercourse.

Channel drain gratings are also designed with safety in mind. Unlike road gullies, the relatively narrow gaps in the grating are too narrow to trap most heels or allow objects to fall through and the flush-fitting covers present no trip hazard.

What channel drain is suitable for my situation?

While the basic principle and design of channel drain vary little, the size of the drain and the materials used to make the channel and the top grating vary according to the weight of traffic it will be expected to bear. The lighter-weight options may be constructed of polymer or galvanised steel, while channels and grates for heavier-duty applications are more likely to be made of concrete and cast iron.

To ensure the correct product is used for the application, all channel drains are given a load rating, with six standardised load ratings set by BS EN 124:2015 covering all requirements. 

Light-duty channel drains

Class A15 channel drains, rated for up to 1.5 tonnes, are designed for pedestrian areas only such as gardens and patios, while the slightly sturdier Class B250 channel drain is suitable for domestic driveways where vehicles won’t exceed a maximum load rating of 12.5 tonnes. Neither of these is suitable for car parks, loading areas or general hardstanding.

Medium-duty channel drains

For private car parks and roadways that only take light traffic (no HGV, up to 25 tonnes), a Class C250 channel drain may be sufficient. However, bear in mind that heavy vehicles such as dustcarts and builder's merchants' trucks do sometimes use these areas. If this is likely, we would recommend upgrading to the heavier Class D400 channel drain, used for highways, motorways and public car parks, as this has a 40-tonne maximum loading weight.

Heavy- and very heavy-duty channel drains

In many industrial areas, heavy forklifts and materials handling equipment place a particularly high load on channel drains. In such situations, we would recommend using a Class E600 channel drain as this will withstand a maximum weight load of 60 tonnes.

The heaviest weight load rating for channel drains is Class F900. Able to cope with weight loads of up to 90 tonnes, this channel drain is normally only seen where extremely heavy vehicles and equipment are in operation, such as airports and dockyards.

Where should rainwater in a channel drain be diverted?

In most circumstances, rainwater runoff from a roadway or car park is directed to a nearby stormwater main drain, but if a main system isn’t available, where should it go?

Generally speaking, rainwater runoff contains such low levels of pollutants that a channel drain can divert it to a nearby watercourse or soakaway. However, this might be a waste of a useful resource.

Rainwater harvesting systems are increasing in popularity as a means of water conservation, as they allow rainwater to be recycled for some domestic requirements such as flushing toilets, and for industrial and agricultural purposes.

The only occasions where particular care should be taken with surface runoff is if it comes into contact with potential sources of pollution. In these instances, which include car washes and fuel station forecourts, some industrial and chemical processes, the water should be connected to a wastewater treatment system.

We hope you have found this information helpful and interesting. If you have any further questions you are always welcome to call our friendly team of experts on 01420 555600 or email [email protected]. 

Also, look out for more articles in our ongoing series of blog posts, bringing you useful information, insights, guides and tips on all things drainage!