How to Choose The Right Drainage System for Paved Areas
Paved areas need their own type of drainage system as they’re generally impermeable to water. This means rainfall or other water will flow on their surface and this can easily lead to nasty build ups and flooding.
With that in mind, the first step to creating a strong drainage system begins before the paving has even been placed. Creating a gradient to the paving (it only has to be slight) will ensure that water runoff goes exactly where you want it. Which is to say, away from the walls of your house. Ideal gradients for your paving is between 1/60 and 1/40.
In an ideal world, all your paving would have a gradient that leads to an area such as grassland that can absorb up all that excess rainwater. This technique is often known as freedraining and is employed so long as the soakage capacity of the ground has been judged to be capable of handling the runoff. Ensure the permeable ground that will be absorbing your water isn’t next to a building. If it is, then the draining water could severely damage the building’s foundations.
Not all paving is an impermeable barrier to water drainage. It is possible to obtain paving slabs that allow water to pass through. These are often designed to be multi-layered for maximum control of water drainage; the lower layer will be granular to act as an intermediate storage reservoir. This helps to ensure water influx in the underlying soil is more gradual and lower the chances of flooding.
Some models of paving even have a third impermeable layer beneath the granular. This allows flow discharged from the granular to be controlled further. This can be particularly handy when avoiding bulding foundations is a challenge or on steep slopes.
Pervious paving does have its disadvantages though.
- The fine pores in the upper layer of the paving slabs are easily blocked, rendering them impermeable and a barrier to water.
- Pollutants such as oil should also not be used with pervious paving.
Finally, a more conventional drainage system can be used as a last resort when it is not possible to have a graded, free draining system or pervious paving.
- A system of gullies and channels should be created to drive flow of water away from buildings and to a sewer opening or an area such as a grassland where the excess water can be absorbed.
- Gratings should be placed over gullies 5 mm lower than the paved areas to ensure water settles into the gullies.
- Gully pots or catchpits should be installed to catch sediment such as silt and grit.