Tyre Bales for SUDS: Sustainable Urban Drainage Using Recycled Tyres

By:     Kieran Donnelly

Expert review by:     Conor Murphy

Tyre Bales for SUDS are proving to be one of the more practical applications of recycled rubber in civil engineering, turning a waste management challenge into a functional drainage material. As urban development continues to expand across land with poor drainage characteristics, the pressure on designers to find cost-effective attenuation and earthworks solutions has grown considerably.

PAS 108-compliant bales contribute to sustainable urban drainage in two distinct ways: as free-draining permeable fill that stores peak runoff within its void space, and as lightweight structural material for the bunds and embankments that define drainage features. This guide covers both roles, along with the water quality, planning, and supply considerations that apply to tyre bale SUDS schemes.

What SUDS Is and Why It Matters for Urban Development

Sustainable urban drainage systems (SUDS) are the drainage philosophy that has replaced the historical approach of draining urban surfaces as fast as possible through pipes to the nearest watercourse. The old approach worked when urban areas were small, and rainfall events were manageable, but in a densely developed urban landscape with a high proportion of impermeable surfaces, rapid drainage to watercourses produces flash flooding, combined sewer overflow (CSO) events, and ecological damage to receiving water bodies.

SUDS takes the opposite approach. Rather than accelerating the movement of surface water off a site, SUDS systems slow it down, store it temporarily, allow it to infiltrate where ground conditions permit, and treat it to remove sediment and pollutants before discharge. The result is a drainage system that more closely mimics the natural hydrological cycle of an undeveloped site, reducing flood risk downstream, protecting water quality, and, in well-designed schemes, creating amenity and ecological value.

Planning policy in England, through the National Planning Policy Framework, and in Scotland through the SUDS regulations under the Water Environment Act, places a strong expectation on new developments to incorporate SUDS. Local authorities and planning authorities require SUDS schemes as a condition of development consent for most significant developments.

Tyre bales contribute to SUDS in two distinct ways: as permeable, free-draining structural fill in attenuation structures, and as a material for constructing the earthworks that define SUDS features such as bunds, berms, and retention basin embankments. Understanding both roles helps tyre recyclers identify supply opportunities and helps SUDS designers understand where this material fits.

Attenuation Storage Using Tyre Bale Fill

The core function of many SUDS components is attenuation: temporarily storing peak runoff from a rainfall event and releasing it at a controlled, lower flow rate after the peak has passed. This prevents the downstream watercourse or sewer from being overwhelmed by the peak flow from the development.

Attenuation is achieved through storage volume. In a conventional system, that storage volume is a tank or pond. In a SUDS system, it can be a pond, a permeable pavement sub-base, an infiltration trench, or an underground geocellular tank. Tyre bale fill provides another option: a permeable fill material with significant void volume that stores water within the fill while allowing it to drain freely to an outlet structure.

A tyre bale attenuation fill structure works as follows. The development’s drainage system routes surface water runoff into the bale fill zone through inlet pipes. The water fills the void space within the bale layer, storing it temporarily. An outlet structure at the base of the fill controls the rate at which water discharges from the zone. The controlled outlet flow rate is designed to match the pre-development runoff rate from the site, so the downstream watercourse sees no increase in flow.

The storage capacity of the bale fill zone depends on the void ratio of the bale layer, which is the proportion of the total volume that is air or water space rather than rubber. A PAS 108 tyre bale layer typically has a void ratio of 30 to 50 per cent, meaning that a bale fill zone with a total volume of 100 cubic metres provides 30 to 50 cubic metres of water storage. This compares favourably with some geocellular tank systems and is substantially higher than the void ratio of granular drainage fill.

The MKII Tyre Baler produces PAS 108-compliant bales with consistent dimensions and density, which allows reliable void ratio calculations for attenuation design. Inconsistent bale dimensions produce unpredictable void ratios and make the attenuation volume calculation unreliable.

Constructing SUDS Earthworks with Tyre Bale Fill

The second role for tyre bales in SUDS is as structural fill in the bunds, embankments, and berms that define the geometry of SUDS features. Retention ponds, detention basins, and swale systems all require earthworks that hold water within the designed feature and prevent it from migrating into areas where it is not wanted.

Conventional earthworks in SUDS construction use on-site or imported granular fill, compacted to a specified density. Where the ground beneath the bund is soft or compressible, the weight of conventional fill causes settlement that can compromise the bund geometry and the drainage performance of the feature over time.

Lightweight tyre bale fill within the body of a SUDS bund or embankment reduces the total load on the soft subgrade, limiting settlement and maintaining the design geometry over the service life of the drainage system. The technique follows the same principles as lightweight embankment fill for roads over soft ground, applied to the SUDS earthworks context.

For SUDS schemes on brownfield sites, where made ground and disturbed fill typically produce poor subgrade conditions, the combination of poor bearing capacity and the soft cohesive soils often present beneath made ground makes lightweight fill a frequent design requirement. Tyre bale fill, as a waste-derived material available from local recyclers, is a cost-effective option for these applications compared to EPS blocks or other specialist lightweight fill materials.

Water Quality Considerations for SUDS Applications

SUDS is about more than flood risk management. Treatment of surface water runoff to remove pollutants before discharge to watercourses is an integral part of the SUDS philosophy. Road runoff contains heavy metals, hydrocarbons, and suspended sediments. Roof runoff carries atmospheric deposition and biological matter. Car park drainage carries oil and fuel spillage. SUDS systems are designed to treat these contaminants through filtration, sedimentation, and biological treatment in vegetated features.

The water quality question for tyre bale SUDS applications is whether rubber leachate from the bale fill adds contaminants to the water passing through the system. This question has been studied as part of the broader assessment of tyre bale civil engineering applications.

The published research position, supported by WRAP-commissioned studies and independent environmental assessment, is that tyre rubber leachate in the quantities produced by a PAS 108 bale fill structure does not represent a significant pollution risk under normal operating conditions. The key compounds of concern from tyre rubber (zinc, polycyclic aromatic hydrocarbons) leach in very small quantities from compressed rubber under field conditions, substantially less than laboratory extraction methods might suggest, and are further diluted in the drainage water passing through the system.

For SUDS applications discharging to ecologically sensitive watercourses, a site-specific environmental assessment of the leachate risk from tyre bale fill should be carried out using the published research data as the basis. This is good practice for any non-standard fill material in proximity to surface water, and the data available for tyre bales is sufficient to support such an assessment for most sites.

The Environment Agency’s guidance on waste-derived materials in engineering, and WRAP’s technical publications on tyre bale use, provide the reference material needed for environmental assessment of tyre bale SUDS applications.

Planning and Regulatory Context for Tyre Bale SUDS

SUDS features incorporating tyre bale fill are likely to be assessed by the drainage authority (typically the Lead Local Flood Authority in England) as part of the planning process. The assessment will consider whether the design meets the applicable SUDS standards, whether the material used in the fill is appropriate, and whether the water quality implications have been assessed.

Demonstrating that bales are PAS 108-compliant, that the environmental assessment of leachate risk has been carried out using appropriate reference data, and that the drainage design meets the Local Lead Flood Authority’s technical standards are the three key elements of a successful approval submission for a tyre bale SUDS scheme.

The regulatory status of tyre bales used in SUDS fill (waste or end-of-waste) also needs to be confirmed. The Environment Agency’s quality protocols and end-of-waste assessment for waste-derived materials in engineering cover this question, and their guidance should be reviewed for each specific supply and installation context.

Supply Logistics for SUDS Construction

SUDS schemes range from small residential development drainage features requiring a few dozen bales to large strategic drainage schemes for commercial or industrial development that may require several thousand bales across multiple features. Understanding the supply logistics from bale production through to installation is important for both recyclers establishing supply capability and contractors procuring material.

Tyre bales are typically delivered to SUDS construction sites on flatbed vehicles and installed by a tracked excavator from the delivery vehicle. The consistent dimensions of PAS 108 bales allow efficient loading of delivery vehicles (maximising bales per load) and predictable installation rates for the excavator operator. Bale supply must be timed to the earthworks programme: delivery too early creates storage requirements; delivery too late creates programme delays.

For tyre recycling operations supplying the SUDS market, a relationship with civil and drainage contractors working on residential and commercial development sites is the route to consistent demand. The pre-processing capability to produce PAS 108-compliant bales from the MKII Tyre Baler is the production baseline, and the associated documentation and quality management system is the commercial differentiator.

The full pre-processing line, from the tyre rim separator through to the truck tyre sidewall cutter and baler, is detailed across Gradeall’s tyre recycling equipment range. Contact Gradeall International to discuss equipment specification for PAS 108 production targeting the civil engineering and SUDS supply market.

Frequently Asked Questions

Tyre bale SUDS applications raise practical questions across drainage design, environmental compliance, and supply logistics. The answers below cover the key considerations for designers, contractors, and recycling operators working with this material.

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