If you’re thinking about installing geocellular crates there are two options available for how the system can work. A soakaway, as the name suggests soaks water back into the soil and attenuation, which holds and redirects the water to another place.
In soakaway schemes, the system is wrapped with a permeable membrane. Water is collected and slowly soaks back into the ground through an infiltration process in line with the natural rate. This helps prevent water-logged ground and avoid flooding.
An online system
A soakaway system is an online system whereby all storm water flows into the crate structure and infiltrates into the surrounding ground as and when saturation allows, until the crate structure is completely empty. The design of the crate structure is required to ensure a half empty time of 24 hours or less.
For more information on soakaway schemes check out these articles:
In an attenuation scheme water is stored within the system and with flow controls, is slowly released back into a watercourse or sewer system. Legislation has seen more and more pressure on local planning authorities and specifiers to implement systems to prevent flooding. The objective is to design a system to deal with the flow at the source rather than transferring the problem further down the watercourse.
Basically, attenuation means to temporarily store storm water for a period of time, to then release back into a watercourse or sewer network. The storm water is collected and routed into the sewer the normal way but with the use of flow controls, this allows a controlled volume to flow through into the main system. During a heavy rainfall, the rest of the excess water, which would be backing up at this point, is fed into the crate system where it is held until its ready to re-join the main system. When this happens, it will return back into the water system and exit through the flow control at a regular, predevelopment rate; preventing flooding downstream.
Offline or Online?
An online attenuation system means the total volume of rainwater passes through the crate structure. The inlets/outlets are located in different positions and the crate structure fills when the flow rates exceeds the agreed discharge rate.
An offline attenuation system is where the inlet/outlet is connected to the same manhole/inspection chamber. The inlet pipe to the attenuation crate structure is above the normal dry weather flow level. The crate structure only fills up during periods of heavy rainfall.