In a busy urban development, almost every square metre of land has a purpose. Roads provide access, parking areas accommodate vehicles, landscaped spaces improve the surroundings, and underground corridors carry essential utilities. Finding additional space for storm water storage can become a challenge, especially when the site is already densely planned.

During heavy rainfall, water runs off roofs, roads and paved surfaces faster than it can naturally enter the ground. If the drainage network cannot accommodate the peak flow, water may accumulate around entrances, parking areas and other low-lying sections of the development.

Traditional storm water storage arrangements can require substantial excavation or dedicated surface space. For projects where land availability is limited, soakaway crates provide an alternative by creating storage capacity beneath usable areas.

At Dutco Tennant LLC, we support urban drainage projects with modular geocellular systems that can be configured for rainwater infiltration, temporary storage or controlled discharge, depending on the site's requirements.

When Surface Development Leaves Little Room for Drainage

Urban construction changes how rainwater moves across a site.

Natural ground allows some rainfall to infiltrate into the soil. Once the same area is covered with concrete, asphalt or other impermeable materials, a larger proportion of the rainfall becomes surface runoff.

That runoff is collected through channels, gullies and underground pipes before entering the drainage network.

The difficulty arises when a large volume of water reaches the system within a short period.

For example, a commercial development may have sufficient drainage capacity for ordinary rainfall but experience temporary water accumulation during a more intense storm. Increasing pipe sizes alone may not solve the problem if the downstream network has limited discharge capacity.

A more effective approach may involve storing part of the runoff temporarily and releasing it at a controlled rate.

This is where underground stormwater storage becomes particularly useful. Instead of reserving valuable land for an open storage basin, the development can accommodate a suitable storage system below selected surface areas.

How Geocellular Systems Create Storage Beneath the Ground

A geocellular drainage system consists of modular structural units that form interconnected void spaces when assembled.

Rainwater enters these voids through the drainage network and occupies the available storage volume.

Unlike a solid underground tank, a geocellular system uses a framework of interconnected cells to create storage capacity while supporting the surrounding ground and specified surface loads.

The modules can be arranged in different lengths, widths and depths to suit the available excavation area.

This flexibility is valuable for developments where underground space is restricted by foundations, utility corridors or other infrastructure.

geo cellular soakaway boxes

More Storage Within a Limited Excavation

Traditional stone-filled soakaways rely on the void spaces between individual stones to store water.

A geocellular system provides a much higher proportion of open storage volume.

Our Geo Cellular Soakaway Boxes portfolio includes Rainsmart Solutions modular systems with a stated void ratio exceeding 95%.

This means that a large proportion of the installed module volume is available for water storage, although the actual usable capacity must be calculated for the selected configuration.

The high void ratio can reduce the excavation volume needed to achieve a particular storage capacity compared with conventional aggregate-filled arrangements.

Infiltration or Attenuation: The Difference Changes the Design

Underground storage does not always mean that rainwater will soak into the surrounding soil.

There are two important ways to manage the collected water, and choosing between them depends on the ground conditions and drainage objectives.

Infiltration: Returning Water to Suitable Ground

An infiltration system collects runoff and allows it to pass gradually into the surrounding soil.

The geocellular modules are typically wrapped in a suitable geotextile that helps separate the storage structure from surrounding soil particles while allowing water movement.

This arrangement may be appropriate where the ground has sufficient permeability and the site meets the required environmental and groundwater separation criteria.

However, infiltration is not suitable everywhere.

Low-permeability soils, high groundwater levels, contaminated ground or nearby structures may restrict its use.

Before selecting an infiltration system, site-specific testing and geotechnical assessment are necessary.

Attenuation: Holding Water Until It Can Be Released

Where infiltration is unsuitable or discharge rates must be controlled, the modules can form a sealed storage system.

An impermeable liner prevents stored water from escaping into the surrounding soil.

Water is then released through an appropriately designed outlet or flow-control arrangement.

This process, known as storm water attenuation, reduces the rate at which runoff enters the downstream drainage network during peak rainfall.

For developments with limited drainage discharge capacity, attenuation can help manage peak flows without requiring a large surface storage area.

The distinction is important: infiltration reduces runoff volume by allowing water to enter the ground, while attenuation primarily delays its discharge.

Finding Suitable Locations Beneath an Urban Development

One of the advantages of modular storage is the ability to consider areas that already serve another purpose at ground level.

Depending on structural and drainage requirements, geocellular modules may be installed beneath:

  • Car parks and paved vehicle circulation areas
  • Landscaped open spaces
  • Roadside verges and selected road corridors
  • Sports fields and recreational grounds
  • Residential and commercial development plots

The surface above the installation remains available for its intended use, provided the underground system is designed for the applicable loads and cover conditions.

Storage Beneath Car Parks

Car parks can provide useful underground space for stormwater storage because they often cover relatively large areas.

Rainwater collected from surrounding paved surfaces can be directed towards an underground modular tank.

However, vehicle loading must be considered carefully.

The module's compressive strength, burial depth, pavement construction, soil support and expected traffic conditions all influence the suitability of the installation.

A product described as suitable for trafficked areas should still be checked against the actual structural loading requirements.

Storage Beneath Landscaped Areas

Landscaped spaces can also accommodate underground drainage infrastructure.

These areas may offer greater flexibility in module positioning, but designers must still consider planting depth, root zones, irrigation infrastructure and maintenance access.

Where infiltration is proposed, the surrounding soil must be capable of accepting the intended water volume.

Choosing the Required Storage Capacity

The number of modules needed for a development should come from the stormwater design calculations, not simply the amount of space available for excavation.

The required storage volume depends on several factors.

  • Catchment area: A larger roof or paved surface generally produces more runoff for the same rainfall event.
  • Surface characteristics: Impermeable surfaces generate more direct runoff than permeable or vegetated areas.
  • Design rainfall: The selected rainfall intensity, duration and return period influence the expected inflow.
  • Permitted discharge rate: A restricted outlet may require more temporary storage during peak rainfall.
  • Infiltration performance: For soakaway applications, soil permeability affects how quickly stored water can disperse.
  • Available underground space: Module dimensions, burial depth and nearby infrastructure determine the practical installation layout.

For attenuation systems, hydraulic calculations should assess inflow and outflow over the design storm event.

A storage tank must be capable of managing the calculated peak volume under the approved design conditions.

Our Geocellular Solutions for Different Project Requirements

Our Rainsmart Solutions portfolio includes modular options for storm water storage and associated subsurface drainage applications.

The geo cellular soakaway boxes range includes STM Tank Modules and Ellipse Tank Modules, together with related drainage cells and wrapping accessories.

STM Tank Modules are intended for underground retention, infiltration and detention applications, including installations beneath suitable trafficked or landscaped surfaces.

Ellipse Tank Modules provide a compact modular option for sites where storage space and layout flexibility are important.

Nero Drainage and Pave Cells address related subsurface drainage and permeable surface applications rather than serving as direct replacements for every bulk storage tank configuration.

Geotextile and impermeable liner accessories allow the storage arrangement to be configured according to whether the project requires infiltration or sealed storage.

The modules use lightweight polypropylene construction, helping simplify handling and assembly compared with heavier conventional storage structures.

For urban infrastructure projects, we consider the available space, storage requirements and structural conditions before identifying a suitable modular arrangement.

Why Inspection and Sediment Control Cannot Be Overlooked

An underground storm water tank may be hidden beneath the finished development, but it still requires a practical maintenance strategy.

Rainwater collected from roads and paved areas can carry sand, silt, leaves and other debris.

If these materials enter the storage modules and accumulate over time, they may reduce available storage volume or restrict water movement.

Pre-treatment measures such as silt traps and suitable sediment collection chambers can help reduce the amount of material entering the system.

Inspection points and accessible maintenance arrangements should also be incorporated where required.

Planning Maintenance Before the Site Is Completed

Maintenance access becomes more difficult once roads, paving and landscaping are finished.

For this reason, access provisions should be considered during design rather than added after installation.

The drainage layout should allow the operator to inspect relevant chambers, monitor sediment accumulation and carry out cleaning in accordance with the manufacturer's instructions.

For geo cellular soakaway boxes, appropriate geotextile protection and upstream sediment management are particularly important in limiting soil and debris intrusion.

A high-capacity storage system is only effective if that capacity remains available throughout its service life.

Planning Underground Drainage for UAE Developments

Urban developments across the UAE often combine extensive paved areas, underground utilities and carefully planned landscaped spaces.

These conditions can make conventional surface storm water storage difficult to accommodate.

Modular geocellular systems provide flexibility, but local site conditions remain important.

For example, a development with low-permeability ground may be better suited to a sealed attenuation arrangement than an infiltration soakaway. Another site may have suitable soil conditions but insufficient clearance from nearby foundations or groundwater.

Project teams must also consider local authority drainage requirements, design storm criteria, structural loading and approved discharge arrangements.

Our approach is to evaluate these factors alongside the product configuration rather than assume that one module arrangement will suit every site.

Making Better Use of the Space Below the Surface

Urban drainage planning is no longer limited to moving rainwater away from paved areas as quickly as possible. Where downstream drainage capacity is constrained, temporary storage can play an important role in managing peak runoff.

Geocellular systems make it possible to place that storage beneath selected parts of a development while retaining valuable surface space for roads, parking or landscaping.

The appropriate design depends on whether the project requires infiltration, controlled discharge or water retention, as well as the site's hydraulic, geotechnical and structural conditions.

By combining modular storage with suitable collection systems, sediment control and maintenance access, we can support more practical storm water management in space-constrained developments.

For urban projects where conventional storage options are difficult to accommodate, soakaway crates offer a flexible approach to managing rainfall beneath the surface without compromising the planned use of the land above.