What Is Geocellular Storage? From Plastic Cells to a Working Drainage System

Updated October 2026

Geocellular storage consists of a connected, modular network of hollow plastic cells that contain rainwater within their internal voids. What’s geocellular storage? It provides space for infiltration into appropriate subsoil, or temporary storage, prior to water removal via a controlled outlet. The cells create the reservoir; the surrounding drainage components dictate how the reservoir is filled and emptied.

What Is Geocellular Storage and What Is Inside It?

A geocellular system stores stormwater in a buried lattice of structural plastic units, similar to stackable bottle crate units with the bottles removed: the lattice carries the load while connected, empty spaces hold water. Unlike a pile of loose boxes, the installed assembly needs a firm base, continuous water pathways and suitable access.

The modular geocellular structure can follow a long, shallow footprint or form a deeper tank. Parts of each unit, such as plastic columns and plates, take up space, so the unit’s external volume exceeds its water storage capacity. CIRIA’s Susdrain component guidance describes these systems as modular or honeycomb structures used for storage or infiltration.

Geocellular plastic products are typically made of polypropylene, and various models may differ in internal structure. Each geocellular module contributes connected space to the reservoir. The complete stormwater management system collects runoff, keeps damaging sediment out and delivers water to its intended destination, so the plastic structure is only one part of the water path.

An infiltration installation uses the permeable route, while a lined tank uses the containment route. Protective geotextiles may be placed outside a membrane. Buying every item in the table as a separate product is unnecessary when functions are combined, but each function still needs an owner.

Geocellular Infiltration and Attenuation: Follow the Water

Infiltration sends stored water into suitable surrounding soil; attenuation holds it temporarily and slows its discharge elsewhere. The same family of geocellular units may be used for either route. Wrapping changes containment, while soil permeability, groundwater, inlets and outlets determine whether the chosen arrangement works on the site.

Water in a geocellular soakaway travels through permeable geotextile and seeps into the ground, while water in a geocellular attenuation tank is contained by an impervious geomembrane and directed to a designed outlet. England’s national standards for sustainable drainage systems place water destinations and site suitability ahead of product selection.

A permeable site may suit soakaway crates. Where the design calls for contained storage, attenuation tank systems need a continuous liner and coordinated connections. Choosing attenuation or infiltration starts with the receiving soil or outlet, before the wrapping is selected. A combined layout intentionally shares water between the routes.

Does an open geocellular crate guarantee infiltration?

No. An open geocellular crate provides storage space; the surrounding ground controls infiltration. Water can infiltrate into the surrounding ground only if soil conditions, groundwater levels, and the available infiltration area permit. A crate installed in poorly draining ground can remain full even though its plastic sides are mostly open.

A rainwater harvesting system provides another water option: storage for later use. Pumps, treatment and distribution must suit that use. Stored runoff isn’t automatically clean water suitable for reuse. Roof runoff and runoff from traffic areas may require different treatment.

Void Ratio, Gross Volume and Usable Storage

The published specifications for a Storm Manage H500 module give dimensions of 1,000 × 500 × 500 mm and a nominal water capacity of 237.5 L at 95% void. The outer box takes up more space than the water it stores. Available storage for stormwater management may be smaller still if retained water or other hydraulic exclusions occupy part of the assembly.

Suppliers often call the water-filled fraction a void ratio. In this case, the denominator is the outside volume of the module. The excavation for the modules also includes bedding, surrounds, protection and cover, so multiplying the entire excavation volume by the module void percentage overstates storage.

3-Volume Storage Ladder

The 3-Volume Storage Ladder separates outside module volume, nominal water capacity, and storage volume available to accept the next storm.

The ladder should be used in this order. Begin with the catalog dimensions, and convert to nominal water volume. Apply hydraulic exclusions in the design. The published H400 alternative provides 190 L of storage in a shorter unit. Catalog capacities describe modules; the rainfall requirement still comes from the site design.

Storm Manage’s published H400 and H500 module data give the following comparison. Gross volume is calculated from the outside dimensions; water capacity is the manufacturer’s nominal figure.

Example inputs: use 20 H500 modules, arranged as two layers of ten. Assume the hydraulic layout leaves 1.00 m³ permanently occupied or otherwise unavailable. That unavailable volume is a separate teaching assumption and isn’t calculated from an assumed water depth for this product.

A stormwater attenuation design specifies a stage-storage relationship, outlet levels, and the rainfall basis that show how much water a system can accept and how quickly the space becomes available after it rains. Unwanted groundwater and sediment can also occupy space. Air needs to be able to escape.

The Philadelphia Water Department’s subsurface detention guidance says permanent pools should be excluded from storage estimates. Design criteria for Philadelphia remain Philadelphia criteria. For another storage medium and the footprint it needs, see infiltration trenches versus geocellular crates.

Where Geocellular Systems Fit, and Where They Do Not

Geocellular stormwater storage suits constrained sites where a buried modular block can achieve the required water volume, structural loading and maintenance access. Parking, landscaped areas and development sites with limited surface space are common locations. The layout also requires a working outlet or suitable receiving soil.

Long-term structural performance of geocellular assemblies depends on the foundation and surrounding soil. CIRIA’s C737 structural and geotechnical design guide covers testing, deformation, assemblages and installation. Its publisher states that it supersedes C680. A short-duration compression test on one cell addresses a different issue from long-term structural performance under sustained earth and traffic loads, particularly in deeper applications where the overlying ground contributes to the load.

What is a shallow geocellular drainage system?

A geocellular drainage system spreads storage across a relatively wide, low-height layer where excavation depth is constrained. It can be placed within a coordinated pavement or landscape build-up. Reducing module height reduces the storage depth available, so the design may need more plan area to accommodate the same water volume.

A reported example is the Counters Creek scheme in west London. New Civil Engineer’s 2020 project report describes Polypipe Permavoid storage beneath permeable paving, combined with rain gardens, tree pits and flow controls. Approximately 700 mm excavation helped the team work around utilities. Construction ran from June 2019 to March 2020. That depth belongs to this project’s whole build-up, rather than a universal cover requirement. The mix of surface and underground measures also provided functions that empty cells alone can’t provide. The report attributes the project to Thames Water and its partners, including Polypipe; it’s separate from Storm Manage’s products.

The wider surface water management scheme must also manage flood risk when runoff exceeds the buried store’s capacity.

Where storage is lost or a layout stops working

For infiltration in England, standard 1.15 specifies at least 1 m of unsaturated ground between the infiltration system’s base and the maximum likely groundwater level. This is a mode-specific ground condition and not a burial depth for every tank. Further constraints are introduced by the nearby structures and the receiving drainage network.

During construction, there’s potential to compromise an otherwise satisfactory design. Construction runoff carries fines into unprotected cells; backfilling can damage a membrane or move connections. Recording dimensions and invert levels before burial, protecting liners and keeping construction sediment out are quality control checks during design and installation.

Geocellular Crates, Chambers or Concrete: Compare the Boundary

Compare crates, arch chambers and concrete storage at the same usable water volume and site conditions. A high module void percentage describes one product boundary. The total comparison includes excavation, stone or structural surrounds, access, protection of groundwater and the means to install and maintain the system.

Crates allow adaptable modular layouts. The arch chambers create different spaces and surrounding stone arrangements. A concrete vault stores water inside a structural vessel. Replacing one structure with another changes the water-storage architecture and the construction around it.

Philadelphia’s manual distinguishes vault, pipe, stone and grid storage and requires manufacturer values for proprietary void space. Its stone porosity assumption is not the total storage efficiency of an arch-chamber installation. The existing stormwater chambers versus modular crates comparison compares the two plastic architectures in more detail.

A smaller stormwater storage package can still require more excavation or more difficult maintenance. Keeping identical hydraulic requirements on both layouts lets procurement compare those differences without awarding either material an automatic cost advantage.

Inspection and Maintenance: Sediment, Access and the Crate’s Limits

Geocellular storage needs sediment control, inspectable flow paths and a practical way to remove accumulated material. A storage system may be inspected to determine condition; the system may not be cleanable and the space may not be recoverable. Each product and layout is different, so a camera opening doesn’t necessarily mean the entire storage space is cleanable.

University of Minnesota guidance on infiltration maintenance identifies sediment and organic debris as common causes of clogging in infiltration practices. Sediment within a buried store will also take up the water-holding space. An upstream catchpit or silt trap will only offer protection to the system while the captured material is removed.

“Regular inspection of silt traps, manholes, pipework and pre-treatment devices, with removal of sediment and debris as required.”

Sediment and pollutant treatment have different roles. England’s standard 4 calls for a water quality risk assessment and appropriate treatment. A clear inspection channel helps during maintenance and doesn’t transform the storage cells into a verified pollutant-removal device.

Pay attention to product names. Polypipe calls Polystorm Inspect a dedicated inspection and access module. Wavin’s own guide says AquaCell Plus-R is for inspection and Q-Bic Plus for access. The supplier’s channel layout and equipment reach define the serviceable area.

Consider a maintenance scenario in a car park where water is found to be above normal levels after it has rained. The cause could be a blocked inlet, a restricted flow control, sediment inside storage, a surcharged downstream pipe or slower infiltration into the soil. The operator first checks accessible traps and controls, then compares water levels with the expected drawdown before deciding whether camera inspection or cleaning can reach the suspected blockage through the installed access route. Follow the water path to locate the cause of excess water before arranging repairs.

How long does an attenuation system last?

The required service life is the development’s design life. England’s standard 7.24 allows for planned replacement or rehabilitation of components that have shorter lives. A liner, flow control and accessible sediment devices may require different interventions from buried cells. Therefore, one advertised module life can’t represent the entire system’s maintenance or replacement schedule.

England’s standard 7.24 sets out that design-life approach. Ground conditions and loading as well as the way the system is constructed would impact the long-term performance of the system. Maintained inlets and outlets would also help to retain useful storage between storms. The maintenance plan should identify who inspects the system, what triggers sediment removal, and how the work is done to reach the affected parts of the system.

Relevant operating tasks are described in detail in the attenuation tank maintenance guide. For product family comparisons, see the soakaway crate manufacturers overview.

What a Geocellular Tank Costs in the UK

RAINCATCHER attenuation packages were listed at £1,817.04 – £3,109.02 on 29 October 2026, with prices varying by capacity and pipe fittings. Prices shown are net prices with VAT added. This gives a dated reference for a supply package cost, and a project budget must also account for the installation scope and the actual usable water capacity.

The RainCatcher package listing provides capacities of 3,200, 4,800 and 7,200 liters with fitting options. Packages include crates, prefabricated liners, butyl tape and geotextile fleece. Instructions are also included. Optional extras include Vortex controls, Orifice Plates, Silt Traps and Chambers. The seller’s pricing and delivery terms also address VAT, unloading and potential delivery surcharges.

At module level, that package listing differentiates 200L nominal from 190L actual water capacity. The package label and the project’s usable water volume should be shown on separate quote lines. Dividing a headline package price by an unqualified liter label can produce a misleading cost per cubic meter.

The Environment Agency’s 2015 study of sustainable drainage costs separates materials from investigation, design, management, site preparation and construction. The costs include inspection, maintenance and future replacement as well as disposal.

For layouts meeting the same project requirements, compare excavation, disposal, surface reinstatement and maintenance work to determine which is cost-effective. The attenuation tank cost discussion covers the wider purchasing scope.

Specifying a Complete Geocellular Drainage System

A complete geocellular storage specification connects the water destination, required live volume, structural conditions and maintenance arrangement. Start with those inputs before selecting module quantity. A supplier can then coordinate the product layout and accessories, while the project team retains clear responsibility for hydraulic design, installation quality and long-term operation.

Defra’s national drainage standards, published in June 2025, are non-statutory and apply to England. Standard 7 covers whole-system construction, operation and structural integrity. Requirement 7.2 calls for a management and maintenance plan, while 7.25 addresses imposed design loadings and safety factors. The project’s approval route and relevant guidance must reflect the project location.

Use of geocellular storage works best when the designer and supplier share one coordinated brief:

1. Set the water route. State infiltration, controlled discharge or reuse and the intended receiving point.
2. Define the storage. Give the required live volume, rainfall basis, inlet and outlet levels, and exceedance route.
3. Describe the ground and loads. Include soil permeability, groundwater, traffic loads, construction loads and nearby structures.
4. Map the serviceable parts. Locate pretreatment, controls and inspection access, with the maintenance method and responsible owner.
5. Coordinate the supply scope. Match the module arrangement, wrap, connections and access components to the design and technical support required.

Request the dimension of the models of interest together with declared water capacity, test method and structural evidence. Agree who will record installed levels and check protected interfaces before backfilling. This gives the construction industry’s different project teams the same physical layout to price, install and maintain.

Frequently Asked Questions

Related Articles

• Choosing an infiltration trench or crate store
• Comparing chamber and modular storage layouts
• Planning access and attenuation maintenance