GRAF detention cisterns for rain detention and channel relief

To guarantee retention of rainwater, a delayed drain is fitted in the channel with 0.05 to 2.0 l/sec. depending on the customer’s specifications. In the event of heavy rainfall, the water level in the cistern rises above this level and is drained into the channel at delayed speed using a floating drain choke. This relieves the channel and the treatment works.

The water level can rise to the emergency overflow and sinks slowly back down again after the rain to the long-term max. water level.
We also construct and supply individual, special solutions.
Sizes between 2,500 – 100,000 l with corresponding retention volumes are possible. 

  • To retain rainwater and relieve the sewers
  • For frost-proof installation in the ground
  • "USA Patent 7854338"



Volume [l]Length [mm]Width [mm]Height [mm]Weight [kg]Retention volume [l]order no.add to enquiry

calculated size Request for information

Technical details


Earth covering with loading capacity [mm] 800 - 2000
max. axle load [t] 8
max. vehicle weight [t] 12
max. vehicle weight with reinforced concrete slab [t] 60

Groundwater installation

Earth covering with groundwater installation [mm] 800 - 1800


max. earth covering [mm] (without groundwater, vehicle loading) 2000