Drainage & Irrigation

Drainage

Many gardens will be perfectly fine without having to install additional drainage but there are several instances where it will be required.

On new housing estates, compacted soil can be formed as a result of builders' lorries and trucks and quite often the sub-soil and topsoil becomes mixed which often leads to a heavy, wet plot.

Where new estates have been built on old arable land, there may be an impervious layer of compact soil just below the maximum ploughing depth, caused by years of polishing by the sole of the plough.
The soil may be clay soil which is water retentive or, if the land is low lying, it may be affected by the natural water table of the area.

Generally, to gain an idea of whether you need drainage or not, it should be assessed in wet winter weather. Patches of water on the surface are the most common signs of problems.

You can check how well the land drains by digging a hole about 600mm (24 inch) deep and half filling it with water. It should drain within 24 hours on well-drained soil. On very wet land, the hole may actually fill.

Drainage Solutions

In some cases, all you may have to do is change the top soil (the top 150mm) if it is very poor but we would recommend that the soil below is double-dug and large amounts of bulky organic materials are incorporated as this will also help.

Where the soil is inherently heavy and waterlogged, some form of drainage will be necessary. The type of drainage used depends on the extent of the problem.

If it is not too sever and there is only excess surface water, it may be possible to overcome the problem by shaping the garden surfaces so that the water flows off to the sides.

Alternatively, creating a soakaway may be the answer. This requires a large hole at the lowest point of the garden filled with rubble or broken bricks, and then covered with 300mm of soil.  The size will depend on the area of the garden but be prepared for it to be quite large to have the desired effect - up to 1.8m (6 ft.) deep and the same across.

It is a good idea to include drainage pipes surrounded with gravel within the problem area laid so that they discharge to the soakaway or ditch. In some instances, these may not be required if the ground slopes naturally to the soakaway.

A system of land drains in a herringbone pattern may be required for particularly wet areas.

Underground pipes should always be laid above the local water table otherwise the pipes will just be moving the groundwater instead of draining the topsoil On level ground, the pipes should be sloped underground to encourage water to drain away quickly and on sloping land, the main drain should run down the slope. Drained water obviously needs somewhere to go so all pipes should terminate in a soakaway or ditch.

For localised areas such as patios and paved areas, we would always recommend using a proper drainage system linked to the storm water drains as this will avoid the area puddling and also potential rising damp into any adjacent property.

The best solution is to use an Aco drainage channel as this can be located along one or more edges, making the patio easier to construct.

An Aco drain is particularly useful where a patio slopes towards a property