Schuyler Heim Bridge — Enclosed Turbidity Control Curtain (ETCC)

Project type: Enclosed Turbidity Control Curtain (ETCC)

Client sector: Public works / infrastructure — bridge demolition

Year: 2016

Location: Cerritos Channel, Long Beach, California

The Challenge

The demolition of the Schuyler Heim Bridge required removing three separate pier structures from the Cerritos Channel — a tidal waterway with a mixed semidiurnal tidal range of 3.2 m (10.5 ft). Active demolition generates fine sediment and associated contaminants. In a tidal channel of this magnitude, containing that material while maintaining tidal water exchange across the work zone demanded a barrier system engineered for the site's specific hydraulic conditions, not a standard off-the-shelf solution.

The project required:

• Full-depth containment of sediment and contaminants at three discrete pier structures

• Tidal water exchange through the barrier (impermeable curtains fail in high-velocity tidal conditions)

• Structural performance against tidal currents up to 1 fps

• Continuous water quality monitoring to demonstrate compliance with Federal Effluent Guidelines

Engineering Approach

Mackworth-Enviro designed and installed an Enclosed Turbidity Control Curtain (ETCC) customized to the Cerritos Channel's tidal dynamics.

Design validation via CFD modeling

Prior to fabrication, computational fluid dynamics (CFD) modeling assessed the barrier's effect on current velocity across the full tidal cycle. This step confirmed that the curtain geometry and mooring configuration would perform under the site's hydraulic loading — and documented the engineering basis for the design.

Full-depth curtain with tidal exchange capability

The ETCC used a non-woven geotextile as its primary permeable component, allowing tidal water to pass through while retaining sediments and contaminants. An impermeable polystyrene-flotation hood sealed the surface; an impermeable heavy bottom skirt, chain-ballasted to the seafloor, eliminated bypass at the sediment interface.

Engineered mooring for a tide-riding system

The curtain was moored to adjacent piles with a tide-riding configuration, supplemented by deadweight anchors and an additional anchoring system. This allowed the barrier to track the tidal surface through the full 10.5 ft range without compromising the seal at top or bottom.

One ETCC was installed around each of the three pier structures.

Water Quality Monitoring

Daily monitoring was conducted throughout construction at four stations positioned 100 ft and 300 ft east and west of the active work area. Each station was sampled at three depths: near-surface, mid-water column, and near-bottom.

Monitoring results:

• Total samples collected during construction: 51

• Samples exceeding Federal Effluent Guideline (25 NTU): 0

• Samples exceeding background threshold (1.0 NTU): 4 (all near-bottom)

• Likely cause of near-bottom exceedances: Sampling instrument error

• Debris escaped ETCCs: None confirmed

Attributable exceedance event — July 18: A single monitoring event recorded elevated turbidity across all 9 stations (29–61 NTU). Investigation attributed the event to container ship activity in the channel, not to demolition operations. Monitors confirmed no debris escaped the enclosed curtains during this event. Turbidity levels returned to 4–14 NTU within two days without intervention.

Outcome

Construction activity remained consistently below the Federal Effluent Guideline (25 NTU) discharge limit throughout the project. No debris escaped the ETCCs at any point during demolition. The attributable exceedance was documented, source-attributed, and resolved by natural channel flushing — a record that held up to regulatory review.

The Cerritos Channel installation demonstrated that an ETCC designed to tidal site conditions — validated by CFD modeling and monitored to the depth of this protocol — can meet regulatory compliance standards in one of the most hydraulically demanding environments in aquatic demolition work.

Why Mackworth-Enviro

Environmental regulators and project specifiers evaluating turbidity control for permitted aquatic work need more than a product description. They need evidence that the system was designed for the site's conditions, installed correctly, and performed against a compliance standard.

This project provides that evidence: a site-specific CFD-modeled design, 51 samples of monitoring data across a full demolition program, zero construction-period exceedances of Federal Effluent Guidelines, and a documented response to an external anomalous event.

Mackworth-Enviro designs, engineers, fabricates, installs, and monitors aquatic barrier systems under one firm. For permitted work in sensitive aquatic environments, that integration — from CFD model to compliance record — is what the permit requires.

Interested in turbidity control for a demolition, dredging, or marine construction project in a tidal or high-current environment? Contact Mackworth-Enviro.