Designing seawater intakes that protect marine life — low approach velocity, fine passive screening and careful siting to minimise the entrainment and impingement of fish, larvae and plankton, in line with EPA 316(b) best practice and UK/Scottish consent expectations.
Any seawater intake risks harming marine life in two ways. Impingement is when larger organisms — fish, crabs — are pinned against the screen by the flow. Entrainment is when small organisms — eggs, larvae, plankton — pass through the screen and into the system. Regulators (under the US EPA Clean Water Act §316(b), and equivalently under Scotland’s CAR/SEPA regime and UK marine licensing) expect intakes to minimise both using best available technology. The two defences are a low approach velocity, which lets mobile organisms escape, and fine physical screening or a subsurface intake, which excludes the small ones — and both are designed in from the start.
A through-screen velocity of ≤0.15 m/s (0.5 ft/s) is the long-established 316(b) benchmark at which most juvenile and adult fish can swim away from the screen rather than be impinged. We size screen open area to hold it at peak flow.
Approach VelocityLow velocity comes from generous screen open area, not just a bigger pipe. We calculate the required wetted screen area from the design flow and the 0.15 m/s limit, with margin for partial blinding.
Siting the intake where a natural tidal current sweeps past the screen further reduces local approach velocity and helps carry organisms clear — a siting decision made early.
Cylindrical wedge-wire screens with slots of 0.5–3 mm physically exclude larvae and small organisms while resisting blinding, and present a large open area for low velocity.
Wedge-WirePeriodic air-burst back-flushing clears debris and biofilm from passive screens without chemicals or moving parts — keeping velocity low and the screen effective long-term.
Air-BurstWhere ground conditions allow, a beach well or infiltration gallery draws through the seabed — the sand itself excludes organisms, achieving near-zero entrainment and the strongest environmental case.
SubsurfaceFor a research facility — often a low flow near a sensitive coastal habitat — demonstrating marine-life protection is central to the consent. We provide the screen open-area and velocity calculations, slot-size justification against the species and life-stages present, siting rationale, and the cleaning and monitoring provisions that show the intake is designed to best practice. That engineering evidence supports an abstraction/CAR licence and marine-licence application and pre-empts the regulator’s questions.
Tell us the flow, the site and the species present — we’ll design a low-velocity, fine-screened (or subsurface) intake and provide the calculations your consent needs.
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