VDV tech – Eel Passage technology (gravity siphon)

Our system is a passive, no‑electricity HDPE tube placed over a dam or weir. It uses only the natural water level difference (head) to carry silver eels downstream – past turbines, spillways, and other hazards.

How the gravity siphon works

• A sealed HDPE tube is primed (filled with water, no air inside).
• Both ends are submerged – intake in the upstream pool, exit in the downstream pool.
• Water flows from the higher upstream level to the lower downstream level – no pump, no electricity.
• Eels that enter the tube are carried gently with the flow.

Designed specifically for silver eels

• HDPE intake ring – 4.6 m diameter, raised on legs above the riverbed. 60 bottom‑entry holes. Debris cannot enter. Covers 21m² of riverbed.
• HDPE siphon tube – standard 30 cm internal diameter. UV stabilised, smooth interior.
• 316 stainless steel hardware – all bolts, nuts, brackets, hinge pins, and leg fittings. Marine grade – no rust, even in salt or brackish water.
• Adjustable leg height: adjustable 5–15 cm
• Hand vacuum pump – included for priming. Simple, reliable, no electricity required.

No bleed line, no intake cover, no manufacturing secrets. Just clean, honest features.

Attraction flow (optional, improves entry)

Attraction flow (optional – improves entry)

To help eels locate the intake, we can add a passive attraction bleed:

• A small pipe (1–2 cm diameter) taps water from upstream of the tube entrance.
• This creates a gentle, local current that eels naturally follow.
• No moving parts, no electricity, no maintenance.

For sites where a bleed is not possible, we offer custom solutions (e.g., venturi or low‑head siphon).

How eels are guided to the siphon

Each of the 8 outer tubes of the octagon has a gangway tube (radial connector) that leads to the central siphon tube. Once eels enter through any bottom hole, they find themselves inside the octagon ring. From there, the 8 open gangway tubes act like corridors – water flows gently through them, creating a current that eels can feel and follow. They swim naturally toward the centre, where the 30 cm siphon tube carries them safely over the dam.

It is like a building with 60 open doors and 8 hallways all leading to one room – eels are drawn in without bait, without electricity.

Key components (all HDPE and 316 stainless steel, no rust)

• HDPE tube – standard 30 cm internal diameter (custom 20–100 cm). UV stabilised, food‑grade.
• Intake cover – debris‑deflecting, keeps leaves and sticks out. Eels enter from sides or underneath.
• Bleed line – small diameter HDPE pipe for attraction flow (optional).
• 316 stainless steel – all bolts, nuts, brackets, hinge pins. Marine grade – no rust, even in salt water.

Materials – corrosion resistance

• HDPE – unaffected by fresh, brackish or salt water.
• 316 stainless steel – all metal hardware, no rust, no galvanic corrosion.
• Seals – EPDM or Viton (saltwater‑compatible).

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).
• Injury rate: negligible (smooth bore, no moving parts).
• Attraction range: up to 20 m with optimised bleed flow.

Custom options

• Larger diameters (up to 1 m) for high fish numbers or large rivers.
• Modular arrays – multiple tubes side by side to cover wide riverbeds.
• Flatpack tube (zipper closure) for easy transport and on‑site assembly.
• Integrated monitoring (camera window or trap).

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).

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.phon)