The three ways to store stormwater underground in the Kingdom, compared on the factors that actually decide a project — excavation, programme, plant, heat, ground chemistry and 50-year performance.
Every Saudi drainage design that needs to hold water underground chooses between three methods: a modular geocellular tank (interlocking high-void polypropylene cells), a cast-in-place reinforced-concrete tank, or the traditional gravel-filled trench or pipe soakaway. All three can satisfy Balady; they differ sharply in excavation, time, cost and what they demand of the site.
| Criterion | Geocellular tank | Cast-in-place concrete tank | Gravel / pipe soakaway |
|---|---|---|---|
| Storage per m³ excavated | ~950 L (95%+ void) | ~700–800 L (wall & slab thickness) | ~300 L (30% void) |
| Installation time | Days — 200–400 m³ per day, no curing | Weeks — formwork, rebar, pour, cure | Days, but 3× the excavation |
| Heavy plant required | Minimal — units carried by hand | Cranes, pumps, mixers | Excavators and haulage for aggregate |
| Shape flexibility | Any footprint, shallow or deep, around services | Fixed by formwork | Trench shapes only |
| Inspection & maintenance | Inspection channels, jetting access | Manhole access, confined-space entry | None — silts up over time |
| Design life | 50 years (CIRIA C737) | 50+ years if waterproofed and maintained | 10–20 years before clogging |
| Embodied carbon | Low — recycled polypropylene, light transport | High — cement, steel, concrete trucks | Moderate — quarried aggregate haulage |
Material price per cubic metre is the number everyone compares first, and it is the least important. The cost of a stormwater tank in Saudi Arabia is dominated by excavation and disposal, programme time and plant. A geocellular tank stores three times more water than gravel for the same hole, so the excavation is a third of the size; it needs no curing, so the trench is backfilled in days rather than weeks; and its units are carried by two workers, so the crane and pump stay off the site. On urban plots where land is expensive and programme is tight, the whole-project cost of geocellular is consistently the lowest — which is why the giga-projects specify it.
Concrete tanks remain appropriate where the store doubles as a pumping station or treatment chamber that needs personnel entry, where extreme point loads apply directly above, or where a client standard mandates it. Gravel soakaways still make sense for very small, low-value plots where nothing sits above. For everything in between — car parks, roads, compounds, parks, campuses — geocellular is the engineering default, and NGS supplies it with a 50-year design to CIRIA C737. Size yours in the Design Studio or read the attenuation vs soakaway explainer.
Are geocellular tanks strong enough for roads and car parks?
Yes. FloodFort geocellular units are rated in 30, 45 and 60 tonne load classes and are designed to CIRIA C737 for trafficked areas, including HGV loading, with cover depth and bedding specified per case.
How much cheaper is geocellular than concrete?
Material prices vary by project, but the whole-installed cost is typically lower for geocellular because excavation is smaller, no curing time is needed, and no heavy plant is required. On tight urban programmes the time saving alone is decisive.
Can a geocellular tank be inspected and cleaned?
Yes. Systems are designed with inspection channels and access points for CCTV survey and jetting, unlike gravel soakaways which cannot be maintained.
Is a concrete tank more durable than plastic?
Both achieve 50-year design lives when correctly specified. In sabkha and sulphate-rich Saudi ground, polypropylene has the advantage of being chemically inert, whereas concrete requires protection.
Does Balady accept geocellular tanks?
Yes. NGS geocellular systems have been approved through municipal drainage submissions and prequalified on NEOM, Red Sea Global, Diriyah and RCU projects.