What is a Network

In the context of drainage and sewerage infrastructure, a network refers to the entire system of interconnected components that transport wastewater, stormwater or both from their sources to treatment facilities or discharge points. This structure includes pipes, links, manholes, inspection chambers, gullies, pumping stations and outfalls, all working together to collect, convey and manage water in both urban and rural environments.

A well-designed and maintained drainage network is critical for public health, environmental protection, and the prevention of flooding and pollution. Networks range from small, privately owned systems serving individual properties to extensive municipal or regional systems covering entire towns and cities.

Components of a drainage network

A drainage or sewer network is composed of a variety of physical elements, each with a specific function. These include:

  • Pipes
    The primary conduits that carry water or waste from one point to another. They vary in diameter, material and purpose depending on flow volume and type (foul, surface water or combined).

  • Manholes
    Access points to the pipe network used for inspection, cleaning, and maintenance. They allow engineers to monitor flow and respond to blockages or defects.

  • Junctions and nodes
    Points where two or more pipes connect. These include T-junctions, Y-junctions and crossings that direct flow within the network.

  • Pumping stations
    Used to move wastewater uphill or through low-gradient areas where gravity flow is not sufficient.

  • Flow control devices
    Elements such as orifices, valves or weirs that regulate flow within the system to prevent surcharge or manage peak volumes.

  • Outfalls
    The points where the network discharges into watercourses, treatment works or soakaways.

  • Gullies and inlets
    Structures that collect surface water from roads, roofs and paved areas, channelling it into the network.

Each component is connected, either directly or via chambers and bends, to ensure continuous and efficient flow throughout the system.

Types of drainage networks

There are several types of drainage networks depending on the nature of the water being transported and the design philosophy:

  1. Foul water networks
    Designed to carry wastewater from toilets, sinks, showers and other appliances to a sewage treatment facility.

  2. Surface water networks
    Handle rainwater and runoff from roofs, roads and paved surfaces. These are usually directed to rivers, soakaways or stormwater attenuation systems.

  3. Combined sewer networks
    Transport both foul and surface water in the same pipe. Common in older urban areas, though now largely replaced by separate systems in new developments.

  4. Private networks
    Serve individual properties or small developments. Typically connect to a public network at a defined boundary.

  5. Public networks
    Operated and maintained by water authorities or local councils. These are larger and regulated under statutory frameworks.

Each type has its own design criteria, maintenance responsibilities and operational risks.

Functions of a drainage network

A properly functioning drainage network must be able to:

  • Collect water and waste from all relevant sources

  • Convey flow efficiently without causing surcharge or stagnation

  • Allow inspection and maintenance access at key locations

  • Respond to peak flow conditions through storage, attenuation or diversion

  • Prevent pollution and cross-contamination between water types

  • Operate reliably under varied weather conditions

Achieving these goals requires both effective engineering design and ongoing maintenance and asset management.

Network design principles

When designing a drainage network, engineers consider a range of factors to ensure system efficiency and longevity:

  • Topography and gradients
    Systems are designed to follow natural land slopes where possible to support gravity flow.

  • Hydraulic capacity
    Pipes and chambers are sized to accommodate expected peak flows from rainfall or usage.

  • Connectivity and redundancy
    Networks should allow for rerouting of flows in the event of blockage or failure.

  • Access and inspection
    Manholes and chambers are placed at suitable intervals for operational access.

  • Separation of flows
    Separate networks are preferred for foul and stormwater to improve treatment efficiency and reduce environmental risk.

  • Sustainability
    Modern networks may include green infrastructure such as swales, rain gardens and permeable surfaces to reduce loading on hard infrastructure.

Maintenance and monitoring

Maintaining a drainage network is critical for public safety and system performance. Tasks include:

  • Regular CCTV inspections to identify defects or blockages

  • Jetting and cleaning of pipes and gullies

  • Repair or replacement of damaged pipes and manholes

  • Monitoring flow rates, surcharge levels and overflow events

  • Managing root intrusion, sediment build-up or pipe misalignment

Asset management systems and GIS mapping are often used by operators to track network performance and schedule interventions.

Integration with treatment and discharge

The drainage network is only one part of a broader water management system. It must be integrated with:

  • Sewage treatment works, which process foul water before environmental discharge

  • Stormwater attenuation systems, which delay and store rainwater

  • Rivers, estuaries or the sea, which receive treated or overflow discharges

  • Sustainable drainage features that manage runoff at source

The network must also be designed to interact safely with upstream and downstream systems under both normal and extreme weather conditions.

Challenges in network management

Several challenges can affect the performance and sustainability of a drainage network:

  • Ageing infrastructure in older urban areas

  • Misconnections and illegal discharges

  • Infiltration and inflow during storms

  • Blockages from inappropriate waste disposal

  • Climate change impacts such as more intense rainfall

  • Urban expansion and increased impermeable surfaces

Addressing these challenges requires investment in upgrades, public education, and innovative design solutions such as real-time control and adaptive infrastructure.

Conclusion

A drainage or sewer network is a complex system of interconnected pipes, manholes and associated structures designed to safely transport water from its source to a point of treatment or discharge. Its effectiveness depends on good design, coordinated maintenance, and responsiveness to environmental conditions.

As urban environments evolve and the demands on infrastructure increase, the design and management of drainage networks will remain a central concern for engineers, planners and local authorities.