A Comprehensive Guide to Permeable Paving Systems: Design, Function, and Technical Implementation

Introduction

Permeable paving represents a crucial advancement in sustainable drainage systems (SuDS), offering an innovative solution to urban water management challenges. As regulations and environmental concerns continue to shape construction practices, understanding these systems becomes increasingly important for developers, architects, and property owners.

How Permeable Paving Works

The Layer System

Surface Layer: Consists of permeable blocks or materials with specifically designed gaps
Laying Course: A level bed of clean stone
Voided Sub-base: A deep layer of clean, crushed stone with approximately 30% void space
Specialist Hydrocarbon Trapping Geotextile Layer - Features a proprietary blend of polyester fibres with properties such as :

Hydrophilic (water-attracting and oil repellent)

Hydrophobic (oil attracting and water repellent)

Captures 6 litres of oil per 10 square metres

Self-maintaining through natural biodegradation

Effectively manages both daily drips and catastrophic oil spills100% recyclable material

Standard Geotextile/Membrane: For additional filtration or water containment

Storage Capabilities

Voided Sub-base Performance

Standard Storage: Up to 150 litres per square metre in a 500mm deep layer
Enhanced Storage: Increases to 247 litres per square metre with plastic modular units
Filtration Efficiency: Removes 60-95% of suspended solids and 70-90% of hydrocarbons
Structural Integrity: Maintains load-bearing capacity for vehicle traffic

Understanding Checkdam Systems

What Are Checkdams?

Checkdams are engineered barriers strategically installed within the sub-base layer of permeable paving systems. Think of them as underwater dams beneath the surface, dividing the sub-base into separate compartments. These structures are essential for managing water flow, particularly on sloping sites where gravity affects water distribution.

Why Are Checkdams Essential?

Water Management on Slopes

Without checkdams, water naturally flows to the lowest point due to gravity
Uncontrolled flow results in only 75% storage capacity utilisation
Lower areas become overwhelmed with water
Upper areas remain underutilised for storage

Storage Optimisation

Creates level storage zones within the slope
Increases storage utilisation to 90-100% capacity
Enables even water distribution throughout the system
Prevents water accumulation at lowest points

Technical Implementation

Construction Specifications

Maximum installation depth: 600mm from finished ground level
Minimum installation depth: 325mm
Standard connections: 110mm and 160mm diameter pipework
Multiple inlet capacity: Three 110mm diameter stubs

Flow Control Features

Minimum orifice size: 15mm diameter (CIRIA C753 compliant)
Customisable sizing for micro-catchments
Protected by integrated filter screens
Removable components for maintenance

Performance Features

Standard diffuser units (710x710x150mm) handle:100m² catchment area inflow3 l/s outflow rates
Removable filters for maintenance
Silt collection sumps
Level invert design for efficient gravity flow

Key Benefits

Environmental Impact

Natural pollutant filtration
Groundwater recharge
Ecosystem support
Sustainable drainage solution

Practical Advantages

Dual-purpose functionality
Reduced downstream infrastructure
Simplified drainage design
Lower maintenance requirements

Cost Benefits

Minimised traditional drainage needs
Reduced excavation requirements
Long-term maintenance savings
Efficient space utilisation

Maintenance Considerations

Self-cleansing functionality
Accessible filters for cleaning
Integrated silt collection
Regular inspection points
Biodegradation of trapped pollutants

Conclusion

Permeable paving systems represent a sophisticated approach to sustainable drainage, combining effective water management with practical functionality. Through careful design and implementation of features like checkdams and hydrocarbon trapping layers, these systems offer a robust solution for modern construction projects while meeting environmental requirements and reducing long-term maintenance costs.