Protecting Municipal Stormwater Networks: A Guide for Drainage Engineers

The Growing Pressure on Stormwater Infrastructure

Drainage engineers and local authority asset managers are facing a familiar paradox: stormwater networks designed decades ago for a different climate are now expected to handle more intense rainfall events, more impermeable urban surfaces, and increasingly stringent regulatory requirements — all with the same or reduced maintenance budgets.

The result is a growing number of surcharge events, backflow incidents and localised flooding that cause property damage, disrupt communities, and create liability for the responsible authority. Managing these risks requires a combination of network monitoring, targeted infrastructure investment, and the right products in the right locations.

Where Backflow Incidents Happen

Backflow in stormwater and combined sewer networks typically occurs at predictable locations:

• Low points in the network — where surcharge water collects and reverses flow
• Connections between watercourses and sewer systems — where fluvial flood events cause water to enter the network in reverse
• Pump station bypass or overflow connections — where pump failure or capacity exceedance creates reverse flow conditions
• Residential drain connections on low-lying ground — where surcharge pressure forces water back into properties

Once these locations are identified through CCTV survey, flow monitoring or incident records, they become candidates for targeted intervention. In many cases, an inline check valve is the most cost-effective solution available.

How Inline Check Valves Fit Into Network Management

The WaStop® Inline Check Valve from Wapro — distributed in the UK and Ireland by NordSeal — is designed specifically for installation in live drainage networks with minimal disruption. Unlike flap valves, which require headwall mounting or structural works, the WaStop® inserts directly into the pipe barrel and operates automatically without any external power or control system.

Key characteristics that make it suitable for municipal applications:

• Passive operation — no electricity, no control panel, no telemetry required
• Wide size range — DN/OD 100mm to 800mm covers the majority of distribution and collector mains
• Low maintenance — the flexible sleeve design has no moving parts to corrode or seize
• Minimal installation disruption — installation through existing access chambers, no pipe replacement required
• Proven in combined sewer and stormwater applications — with over 75,000 installations worldwide since 1989

Specifying the Right Product

For drainage engineers, correct specification matters. The key parameters when selecting a WaStop® for a network application are:

• Pipe diameter and material — to confirm the correct valve series and seal dimensions
• Flow rate and velocity — to ensure the valve does not create unacceptable head loss under normal flow conditions
• Backflow pressure — the maximum hydraulic head the valve may be required to seal against
• Access configuration — the available access chamber dimensions and orientation for installation

NordSeal's technical team works directly with drainage engineers on specification, and can provide technical datasheets, hydraulic data and installation guidance for submission to approval bodies.

Case Study: Kristinehamn Municipality, Sweden

Kristinehamn Municipality's Water and Wastewater department had been dealing with repeat backflow incidents at several locations in both their sanitary sewer and stormwater networks. Having trialled the WaStop® Inline Check Valve at one problem site, they went on to specify it across multiple locations in the network.

Their assessment after installation was direct: "Easy to install, reliable, and a high quality product."

Critically, the passive operation of the WaStop® meant no additional control infrastructure was needed, and ongoing maintenance requirements were minimal compared to the mechanical valves they had previously used.

Working With NordSeal on Network Projects

NordSeal supplies WaStop® valves and the wider Wapro product range to drainage contractors, local authorities and water companies across the UK and Ireland. We offer:

• Technical specification support from enquiry through to installation
• Trade account pricing for contractors and framework suppliers
• Access to full Wapro technical documentation, installation guides and hydraulic data
• Supply of the complete product range including WaFlap™ flap valves, WaGate® gate valves and WaReg® flow regulators

View the full WaStop® Inline Check Valve range, explore WaFlap™ flap valves for open-channel applications, or contact our technical team to discuss your network requirements directly.