Rotary Drum Screens for hydropower plants, which are widely used for fish protection and debris/moss removal at turbine intakes.

⚙️ Rotary Drum Screens in Hydropower Plants

🔎 What is a Rotary Drum Screen?

A rotary drum screen is a cylindrical drum with fine mesh or wedge-wire panels that rotates slowly in the water intake channel. Water passes through the screen into the intake → fish, moss, and debris are blocked and guided to a bypass → clean water enters the turbine.

 Working Principle

1. Water Flow
   • Water enters the drum’s submerged portion.
   • Screen mesh (slots 1–10 mm depending on target species) allows water through but blocks fish and debris.
2. Fish Guidance
   • Fish encounter the rotating drum surface.
   • Flow and rotation guide them to a bypass channel alongside the drum.
3. Self-Cleaning
   • As the drum rotates upward, spray jets or brushes clean off trapped moss, algae, and debris.
   • Waste is collected in troughs and conveyed away.

📏 Design Features

• Drum Size: Large diameter (2–6 m typical) and width up to several meters.
• Screen Material: Stainless steel wedge-wire or perforated mesh.
• Slot Size: Fine openings (1–2 mm for juveniles, 6–10 mm for larger fish).
• Rotation: Slow (1–5 rpm), powered by water current or motors.
• Bypass Location: Adjacent to drum for easy fish entry.

🐟 Role in Fish Protection

• Prevents fish from being drawn into turbines.
• Guides fish gently to bypass with low stress and high survival (>95%).
• Especially effective for juvenile salmonids, smolts, and eels, which follow surface flows.

🌱 Role in Moss & Debris Removal

• Removes floating moss, algae mats, and leaves before they clog penstocks.
• Continuous cleaning system reduces downtime and labor.
• Maintains hydraulic efficiency of intake flow.

✅ Advantages

• High fish protection efficiency (meets US NOAA / EU WFD standards).
• Automatic self-cleaning → low manual maintenance.
• Handles large debris + fine moss
• Long lifespan (stainless steel construction).
• Works in variable water levels and flows

⚠️ Limitations

• High capital cost compared to fixed bar screens.
• Needs reliable power or flow for drum rotation.
• Requires spray water system for cleaning.
• Performance depends on correct approach velocity design (≤ 0.3 m/s for juveniles).

🌍 Example Applications

• Columbia River (USA): Rotary drum screens protect juvenile salmon downstream of dams.
• UK Small Hydro Plants: Used for eel and trout protection at intakes.
• Norway & Germany: Installed for both fish safety and algae removal in alpine rivers.

✅ In summary:
Rotary drum screens are self-cleaning, rotating fish protection and debris removal systems at hydropower intakes. They ensure safe fish bypass, prevent turbine clogging from moss/algae, and maintain continuous operation with minimal manual cleaning.

Excellent request 👍 Let’s compare Rotary Drum Screens and Traveling Water Screens, since both are widely used in hydropower intakes for fish protection and debris/moss removal.

🔄 Comparison: Rotary Drum Screen vs. Traveling Water Screen