VDV tech Eel Passages – Technical specifications (gravity siphon version)

This page gives you the key technical data for our downstream silver eel passage system. The system is a passive gravity siphon – no pumps, no moving parts, no electricity. All components are manufactured by us from HDPE and marine‑grade 316 stainless steel – no rust, no corrosion, even in salt or brackish water.

Tube

• Material: HDPE (high‑density polyethylene), UV stabilised
• Internal diameter: standard 30 cm (custom 20 cm – 100 cm)
• Wall thickness: SDR 17 (or SDR 11 for higher pressure)
• Length: up to 100 m (longer on request)
• Operating mode: sealed siphon – 100% water‑filled during operation
• Minimum head (height difference upstream to downstream): 0.5 m
• Maximum head: 10 m (higher requires custom engineering – contact us)

Intake (riverbed) – designed for silver eels

• Type: 4 m diameter HDPE ring (patent pending)
• Riverbed coverage: 21 m² – eels find it from any direction
• Intake holes: 60 holes, 10 cm diameter, located on the underside of the ring (facing down)
• Leg height: Adjustable from 5 -m15cm above the riverbed – eels swim freely underneath, debris passes below
• Foot plates: prevents sinking in soft sand or silt
• Connection to siphon: 6 radial tubes (15 cm each) → central hub (30 cm) → main siphon tube
• Clogging: impossible – holes face down, ring is raised. No screens, no covers, no maintenance.

Attraction flow (optional – improves eel entry)

• Passive bleed line – small HDPE pipe (1–2 cm diameter) taps water from upstream of the tube entrance.
• Creates a gentle, local current that eels naturally follow.
• No moving parts, no electricity, no maintenance.
• Attraction flow rate: adjustable from 0.5 – 5 L/s (by valve or by choosing bleed pipe diameter).
• For sites where a bleed is not possible, we offer custom solutions (e.g., venturi or low‑head siphon).

Exit (downstream or sea)

• Diffuse, low‑velocity discharge – eels are not stressed.
• Optional predator guard (stilling basin or perforated pipe).

Installation

• Portable – two people can install in half a day.
• No dam drilling, no concrete, no permanent changes.
• Tube can be rigid HDPE or flexible (reinforced) – customised per site.

Performance (estimated for silver eels)

• Passage success: >90% (site‑dependent, with attraction bleed optimised)
• Injury rate: negligible (smooth bore, no moving parts)
• Attraction range: up to 20 m with optimised bleed flow

Materials – corrosion resistance

Works in fresh, brackish and saltwater – no rust, no corrosion.

• HDPE – unaffected by fresh, brackish or salt water.
• 316 stainless steel – all bolts, nuts, washers, brackets, hinge pins, and any other metal hardware. Marine grade – no rust, no galvanic corrosion, even in full saltwater immersion.
• Seals – EPDM or Viton (saltwater‑compatible).

Manufacturing and quality

• All components designed and built by our own workshop together with a long‑term Dutch HDPE factory partner
• HDPE welding, CNC cutting – in‑house
• Proven since 2005 (algae tube systems, irrigation projects)
• All materials are guaranteed against corrosion and material defects for 5 years. We stand behind our engineering.

Need exact numbers for your silver eel site?

Contact us with your dam height, river flow, water level difference, and eel migration period. We will provide a free technical assessment and a custom system design.