Excess water within any garden can cause many problems.
The presence of excess surface and subsurface water can reduce the amenity of an area significantly, therefore drainage is one of the most critical aspects of a garden. But if it's not correctly designed and installed, drainage can cause considerable grief and damage.
A well-designed drainage system will divert either surface and sub-surface water or both, away from areas such as building foundations, behind retaining walls, turf areas and garden beds.
Soils are like a sponge, they are made up of pore spaces which, depending on the texture class and structure of the soil, will hold water in greater or lesser quantities.
The soil's characteristics will determine how well the soil drains and give some indication as to the need for surface or sub-surface drainage.
A coarse textured soil, such as a sandy loam, will have larger pore spaces and therefore drain more readily than a fine textured clay soil - the latter being renowned for its poor drainage. When a soil is saturated during a rain event, the larger pore spaces are filled with water and there are no forces holding the water to the solid surface of soil particles.
Water will move downwards under the force of gravity. In a saturated soil, surface puddling will occur and if not drained properly runoff will result and lead to soil erosion or garden damage.
The installation of drainage systems provides a suitable solution to move excess water from a garden. A major consideration of drainage is to determine where the excess water is to go and what method will be the most efficient in getting it there.
In many residential situations the slope of the land will divert surface water towards the front of the property and into the street drain, however in many circumstances the grade of land is insufficient, or the characteristics of the area and soil type require a more efficient system to divert surface water.
Installing surface or sub-surface drains can rectify many problems. Prior to any drainage installations it is essential the cause of the drainage problem is correctly determined.
Thorough investigation of an area and analysis of soil conditions is crucial to good drainage system design. The best time for this is when the rains arrive. Water finds its own level so follow the flow to gain some idea of where a drainage system may be most effective.