The Fast High Volume Infiltration (FHVI) technique uses infiltration wells to infiltrate rainwater into the aquifer. FHVI infiltration wells form a good alternative for cities and companies that disconnect rainwater from the sewers.
How does the FHVI technique work?
The depth of an FHVI rain well can be approximately 12 to 20 metres deep. The depths depend on the location of the aquifer. Water enters the well via one or more street-level drains. The bulk of the street litter, such as leaves, cannot enter the drains. At the top of the rain well, a filter purifies the rainwater to a high quality level. A nozzle is attached at the base of the discharge tube and together with the pressure from the water column above, it increases the velocity of the water. The water is then discharged into the aquifer.
Preliminary test results for rainwater infiltration
The technique was tested under conditions of extreme rainfall in Germany and the Netherlands. This is a so-called T10 rain shower. This shower corresponds with a peak intensity of 5.25 l/sec. for an area of 250 m²: a total volume of 36 mm/hr. The FHVI technique passed the tests well, so the step toward a more extensive pilot phase can now be taken.
The theory underlying FHVI
The FHVI technique was first used for caisson pumping . Caisson pumping is used for work activities that take place below groundwater level, such as drilling tunnels. Huge quantities of groundwater are pumped up from the construction site and then pumped back into the ground in the adjacent area so that work activities can be realised in a dry construction area and to ensure that water of the same quality is returned to the groundwater supply.
The German geohydrologist Werner Wils performed intensive research into the processes in an aquifer during caisson pumping. He discovered that large quantities of water can be discharged quickly if a specific water-discharging layer, or aquifer, is tapped. So when drilling a rain well, it is important to locate the correct infiltration point.