Closed stormwater basins

Closed stormwater basins (underground stormwater storage) are underground vaults either cast in concrete or constructed from rainwater soakaway units. Soakaway units have a high load-bearing capacity and are a simple way of creating an invisible attenuation facility (figure 1). A geotextile membrane is normally fitted round the stack of soakaway units to facilitate construction work and prevent soil from getting into the units. While soakaways are best established as infiltration trenches (see below) to produce maximum wall area, basins are given a more cubic shape to get the largest volume out the smallest area. 

Figure 1: Soakaways being used to build a closed stormwater basin (Photo: Wavin)