Applications

What is it used for?

Applications in stormwater management systems and sewer networks

The Expan Gate is primarily used in stormwater management systems, as well as in hydraulic and sewer systems, to control wastewater flow in tunnels and pipelines. It allows temporary water retention during storm events or high tides to prevent downstream flooding and to regulate water levels in urban drainage networks.

Additionally, it enables the removal of accumulated sediments through controlled discharges and provides a flexible and cost-effective alternative to traditional metal gates. The Expan Gate can also be integrated into coastal infrastructures to manage tidal variations and into temporary storage systems for controlled surcharge management.

When would they be used?

Collecting and conveying wastewater

Expan Gates help manage flow within public sanitary and combined sewer systems, preventing sewer backups and overflows to protect public health and the environment.

Manage stormwater and drainage

Expan Gates regulate stormwater within public drainage systems to reduce flooding, improve receiving-water and sediment quality, and enhance public safety.

Combined Sewer System (CSS) applications

CSS networks use a single set of tunnels to carry domestic wastewater, industrial wastewater, and stormwater runoff, typically in older urban areas. Expan Gates help control flow, increase storage efficiency and improve system performance during wet-weather events.

Combined Sewer Overflow (CSO) applications

During heavy rainfall, combined systems may become overwhelmed, resulting in excess stormwater and untreated sewage being discharged into rivers, lakes or coastal waters. Expan Gates can be used to manage flow, increase storage capacity and reduce overflow events.

Typical Combined Sewer System (CSS) in dry conditions

Typical Combined Sewer System (CSS) under rainy conditions

Expan Gate installed in place of a CSO weir to improve flow control and retention

LEGISLATION, FEDERAL & STATE LAWS (US ONLY)

Wastewater and stormwater management in the United States is governed by a framework of federal and state laws designed to protect public health, water quality and the environment. Compliance with these regulations is essential for municipalities and utilities to prevent pollution, minimize sewer overflows, and ensure rapid response to high-priority drainage issues.

CLEAN WATER ACT (CWA)
Established in 1970; makes it unlawful to discharge any pollutant from a point source into navigable waters without a permit.

NATIONAL POLLUTANT DISCHARGE
Elimination System (NPDES) regulates and controls wastewater and stormwater discharges.

STRICT STATE REGULATIONS
Many states enforce additional, stringent requirements for wastewater and stormwater management.

LIMITING SEWER OVERFLOWS
Some states limit sewer overflows to as few as 4 per 100 miles of pipe, averaged over 2 years.

RAPID RESPONSE REQUIREMENTS
High-priority drainage and wastewater issues must be addressed within a short response period.

LIMIT CSO EVENTS
Combined Sewer Overflow (CSO) events are restricted to no more than 1 untreated discharge per outfall per year.

SOLUTIONS

Rebuild the Combined Sewer
System Converting to a separate system is possible but extremely costly.

Expand Treatment Plant
Capacity Upgrading the plant to handle combined stormwater and wastewater for a 10-year storm event is also expensive.

Storage Tank Approach
Constructing storage tanks to hold stormwater during peak events, then treating it later when the plant has available capacity, is the most cost-effective option. Expan Gates can be used to efficiently manage the storage, controlling flow and reducing overflows.

CHALLENGES

Aging Infrastructures
Many sewer systems are reaching the end of their design life due to past delays in renewal and replacement.

Climate Change
Increasingly heavy and frequent storm events put additional stress on existing systems.

How can they help?

Optimizing Stormwater Management with Expan Gates

Efficient stormwater control is critical for protecting infrastructure and the environment. Expan Gates offer versatile solutions for modern drainage systems, providing everything from maximized storage capacity to reliable backflow prevention. By integrating these adaptive gates, municipalities can enhance system resilience, improve hydraulic performance and ensure safer maintenance operations. Explore the key applications below to see how Expan Gates can transform your management strategy.

Outfall Control and Protection

Installed at the junction of the outfall and trunk tunnels, the Expan Gate keeps the outfall closed during high-flow conditions (up to 10-year storm levels). This prevents unwanted discharge while maintaining control over system hydraulics.

Tunnel Storage Utilization

For tunnels with sufficient length, an Expan Gate can be positioned at the downstream end to capture and temporarily store stormwater or wastewater. The system allows for controlled dewatering once the storm event subsides.

Trunk Tunnel Storage

Expan Gates allow operators to leverage the massive capacity of trunk tunnels as temporary storage reservoirs. The system utilizes advanced control logic to maximize storage volume without risking upstream hydraulic surcharging.

Outfall Management (Tidal / Surge Conditions)

Functioning as a robust closure gate, the Expan Gate prevents tidal backflow and storm-surge intrusion. This protects the drainage network from external water sources and enhances infrastructure resilience in coastal areas.

Flow Regulation

Expan Gate can modulate the discharge rate of stormwater into receiving waters, such as canals, rivers or reservoirs. This is critical during intense rainfall to manage flow and protect downstream capacity.

Sediment Flushing Enhancement

By controlling surges within the system, Expan Gates facilitate periodic flushing cycles. This removes accumulated sediment and debris, ensuring consistent, long-term hydraulic performance.

Maintenance Isolation

The Expan Gates provide a practical solution for isolating tunnel sections. This creates dry, safe working conditions for maintenance crews, eliminating the need for temporary bulkheads or heavy steel gates.