Infiltration basin: the structure

The infiltration basin is one of the easiest ways to infiltrate surface water on your own property. In our article you can find out how an infiltration basin is constructed, how it works technically and what you always have to pay attention to in the case of drainage basins.

How an infiltration basin works

An infiltration basin is nothing more than an artificially created depression in the terrain into which rainwater is discharged. The rainwater is collected there and slowly seeps into the ground in the hollow.

  • Also read - Trench infiltration: the basic structure
  • Also read - Create a drainage basin - you have to pay attention to this
  • Also read - Build your own infiltration system for rainwater - this is how it works

Part of the water also evaporates due to solar radiation. This means that not all of the rainwater has to completely seep into the ground.

Requirements for infiltration basins

In order to be able to create an infiltration basin at all, some requirements must be met:

  • Permissibility of infiltration
  • sufficient infiltration capacity of the soil
  • sufficient space for an infiltration basin of the correct size (dimensioning)

Permissibility of infiltration

In principle, no rainwater may seep into water and spring protection areas. Creating an infiltration basin in such areas is therefore not permitted.

Sufficient infiltration capacity of the soil

The soil must have sufficient seepage capacity to be able to absorb the rainwater channeled into the basin for a relatively short period of time. As a rule, it is assumed that a sufficiently dimensioned trough (see next section) will be emptied again within a day.

The infiltration capacity of a soil depends primarily on the nature of the soil: in a sandy soil the infiltration speed is up to 10 times as high as in a clay soil. Clay soils that are particularly difficult to seep generally do not allow the creation of seepage basins, as the water that is introduced here would only seep away to a minimal extent.

Dimensioning of the trough

Sufficient space must be available to create a hollow. As a rule, it is assumed that in the case of soils with a medium drainage capacity, the hollow takes up an area of 10% - 20% of the total area to be drained.

Example: 300 m² of roof area would require a trough size of 30 - 60 m² so that the trough can be emptied quickly enough. So much space is not available on many properties; other infiltration methods must be used here:

  • Infiltration infiltration
  • Shaft infiltration
  • combined trough and trench systems

However, these systems are usually more complex to manufacture and more expensive than simple trough infiltration.

Construction of drainage basins

A hollow should be a maximum of 30 cm deep, the inside of the hollow can also be planted. In hollows, seepage occurs directly through the topsoil, which also has a certain filter effect.

If necessary, filter fleece and layers of gravel can also be laid below the trough in order to accelerate the seepage into the subsoil and the emptying of the trough.

Tips & Tricks Always make sure that the lower end of the seepage layer (topsoil or gravel layer) is at least 1 m away from the water table. To achieve this, it is often necessary to look for a suitable location for the hollow.