Three words that every drainage submission in the Kingdom turns on. This guide explains what each one means, why the same geocellular tank can be either, and how the ground beneath your site makes the decision for you.
The confusion is understandable: the same modular geocellular tank — high-void plastic cells stacked underground — is used for both. What changes is what wraps it and where the water goes. Wrap the tank in permeable geotextile and it becomes a soakaway: water infiltrates into the ground. Wrap it in an impermeable geomembrane and add a flow-control outlet and it becomes an attenuation tank: water is held back and released at a rate the downstream drain can accept. "Infiltration" and "soakaway" describe the same strategy; "attenuation" is the other one.
| Question about your site | Soakaway (infiltration) | Attenuation (controlled release) |
|---|---|---|
| What happens to the water? | Soaks into the surrounding ground | Stored, then released slowly to a drain or wadi |
| Ground it needs | Permeable sand or gravel, infiltration rate proven by test | Any — including clay, rock, sabkha or high groundwater |
| Needs an outlet? | No (overflow only) | Yes — flow-control chamber to a network |
| Geocellular tank wrap | Permeable geotextile | Impermeable geomembrane |
| Typical Saudi use | Villas, compounds, parks on sandy ground | Car parks, roads, dense urban plots, coastal cities |
| Approval path | Balady drainage report with percolation test | Balady drainage report with discharge-rate calculation |
In Saudi Arabia the choice is rarely a matter of preference — it is dictated by the site. Riyadh's sandy and gravelly plateaus often infiltrate well and suit soakaways. Jeddah and the coastal cities frequently combine high groundwater, sabkha and low-permeability soils, where infiltration is unreliable and attenuation is the correct answer. Dense urban plots with a municipal storm drain nearby are usually designed for attenuation regardless of soil, because the network has a maximum discharge rate to respect. The deciding evidence is the BRE 365 percolation test: if the measured infiltration rate is adequate and groundwater is at least a metre below the tank base, a soakaway is viable; if not, attenuation.
Many NGS designs in the Kingdom combine both. The tank is sized for attenuation with a controlled outlet, but the base is left permeable so that whatever the ground can absorb, it does — reducing discharge and recharging groundwater. Passive-irrigation variants take this further, routing stored stormwater to tree pits and landscape, which is why FloodFort X cells appear beneath so many Riyadh streetscapes.
The NGS Design Studio runs both calculations and produces an engineering summary you can attach to a Balady submission. See also the step-by-step soakaway design guide and the approval guide.
Is a soakaway the same as an infiltration tank?
Yes. Both terms describe an underground store that lets stormwater soak into the surrounding ground. "Soakaway" is the common UK-influenced term used in Saudi specifications; "infiltration tank" or "infiltration system" is the technical equivalent.
What is the difference between an attenuation tank and a soakaway?
A soakaway releases water into the ground through a permeable geotextile wrap. An attenuation tank is wrapped in an impermeable geomembrane and releases water slowly through a flow-control outlet to a drain. Same geocellular modules, different wrap and different destination.
Which is better for Saudi Arabia?
Neither is better in the abstract. Sandy, well-draining ground with low groundwater (common around Riyadh) suits soakaways; coastal, sabkha or high-groundwater sites (common in Jeddah and the Eastern Province) need attenuation. A percolation test decides it.
Can one geocellular tank do both?
Yes. A hybrid design uses a controlled outlet for attenuation while leaving the base permeable so the ground absorbs what it can. NGS designs many Saudi systems this way.
Does Balady require one or the other?
Balady requires a drainage report showing how runoff is managed. For soakaways this includes the percolation test; for attenuation it includes the permitted discharge rate. NGS prepares both.