Gullies & Rainwater Channels
The requirement for the removal of water from a site in the most efficient manner is often overlooked when planning a garden. It is preferable to design a landscape project with the essential objective of visualising the likely movement of surface water – either rainfall or existing drainage systems across the site, including water capacity (if known) of any existing soakaways (which will have been designed to cope with the likely amount of water anticipated from a given point e.g. roof down-pipes) and taking into consideration the potential water that will be prevented from penetrating the ground by areas of paving and hard landscaping.
It is important to begin any design by taking into consideration the amount or volume of water that you will need to accommodate either on site or off site (and onwards to a roadway or ditch etc) and start linking your design proposals to cope.
Retaining walls, where hydrostatic pressure will require drainage pipes and shingle drains to be installed to the back of the blockwork, with weep-holes and pipe outlets, should be recognised as being a potential source for a considerable amount of water, which will otherwise become trapped by the wall unless drainage is designed into the scheme.
Areas of paving may have decorative grills to cover below ground channel drains, or slot drains included in the paving plan, each of which will need to pass rainwater onto the next sector of the garden by means of connected pipes.
Much will depend on the nature of the site soil, although it is always sensible to assume that groundwater will need to be dealt with from the outset on any project.
On new build sites, the Planning Permission process will have asked the owner for their chosen method of disposing of water from the site, with a choice of either soakaways or existing water channels i.e. permanent drains linked to the house and main drains. It is advisable to check with the client as to their chosen method as scheduled in their house deeds. If soakaways have been nominated, you may have to obtain further permission if you intend to offer other proposals, as the site requirements may be altered from the original permit by new landscaping works.
Photo credit – Laurence Hebblethwaite.
