So, you’ve installed your drainage system and the problem is solved. But once you’ve gotten rid of the surface water, where is it going to go?
This is called the outfall and there are a few different options of where the surface water can go at the end of the drainage system.
Ditch or drywell
A common option is to have the water run off into a ditch or drywell which is essentially a hole in the ground which remains dry most of the time. When water is flowing it can run into the ditch which will hold the water and slowly release it back into the soil to avoid flooding. These can be wrapped in a geotextile fabric to avoid mud and silt build up and this also allows the water to pass through it. Using some gravel in and around the well or ditch will also help the absorption of the water.
If digging a huge hole in your garden isn’t an option, another solution could be to direct the water into a pre-existing watercourse if that’s a possibility depending on location. To do this you would need to use a solid plastic pipe, such as twinwall, and surround the outlet with concrete into the bank of the watercourse so as not to damage the bank below with erosion for the water flow. Environmental agency consent will be required for discharge to open water courses. The flow to a water course must be restricted to the greenfield runn off rate.
Installing a soakaway crate such as RAINBOX®, acts as an underground reservoir to collect the water from persistent rain to prevent flooding. Wrapping the system with a geotextile, water is collected and slowly soaks back into the ground through an infiltration process. For attenuation water can be stored within the crates and with flow controls can be slowly released back into a watercourse or existing sewer network.
WHERE NOT TO DIRECT THE WATER!
It’s not a good idea to have your surface water run off go anywhere near your neighbour’s home or property which could cause flood damage or damp.
Redirecting the water onto the streets in residential areas is just sending the problem elsewhere and can cause further problems for more people.
If you are going to connect the drainage pipe system to a foul drain you will need permission from your local water authority.
Unused wooded area
It is against best practice to direct water into a wooded area as anytime you send large amounts of water near tree roots they tend to grow very quickly and can even grow into the pipework itself, causing blockages and rendering the system useless.