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Types of Positive Barrier Screens. Rotary Drum Fixed Vertical Plate Vertical Traveling – belt and panel Non-Vertical Fixed Plate Horizontal Fixed Plate Eicher Screen Modular Inclined Screens End-Of-Pipe (Pump) Intake Screens. Acceptance of Existing Screens.
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Types of Positive Barrier Screens • Rotary Drum • Fixed Vertical Plate • Vertical Traveling – belt and panel • Non-Vertical Fixed Plate • Horizontal Fixed Plate • Eicher Screen • Modular Inclined Screens • End-Of-Pipe (Pump) Intake Screens
Acceptance of Existing Screens • If constructed prior to 1989, approval of existing screen considered based on: • must function as designed and in good working condition. • upon replacement, mesh must be replaced with current criterion. • provides safe timely and effective passage. • no emergent fry at site • access allowed for NMFS inspection.
Rotating Drum Screens - Advantages Proven fish protection Self-cleaning by rotation Passes debris downstream
Rotating Drum Screens - Disadvantages Susceptible to direct hits from large debris Large civil works are required. Seals require much maintenance. Susceptible to abrasions by sand - mesh requires periodic replacement. Need control to maintain submergence between 65% and 85% - easy step usually.
Vertical Fixed Plate Screens - Advantages Easy to seal Mechanically simple Can be installed on river’s edge - small screens No bypass required Can use profile wire (very strong) Mechanical/brush cleaning usually effective Air burst cleaning system is on back side of screen. Cleaning is started by timer or head loss.
Vertical Fixed Plate Screens - Disadvantages Must be cleaned mechanically Large bypass flows required Brush arms can be damaged by large debris. Circular air burst cleaners do not clean entire screen.
Traveling Screens - Advantages Small screens can be installed on riverbank. Compact civil works Self cleaned by rotation Jet sprays provide additional cleaning.
Traveling Screens - Disadvantages Mechanically complex Seals can be a problem. Make sure meets all NMFS criteria (old styles may not)
Non-Vertical Fixed Plate Screens - Advantages No moving parts No bypass required if built in-river
Non-Vertical Fixed Plate Screens - Disadvantages Self-cleaning may not be reliable Risk of injury/mortality on screen during low flow Must raise and control water surface Tricky, unreliable flow rate control Adult upstream passage concerns Potential issues with hydraulic gradients
Fixed Cylinder Screens Source: Johnson Screens, Inc..
Fixed Cylindrical Screens - Advantages Good option for deep intakes Air burst cleaning system can be made to be effective Some off-the-shelf models with water backwash systems meet NMFS criteria for active screens.
Fixed Cylindrical Screens - Disadvantages Out of sight, out of mind Need sweep velocity to transport debris from screen site. Air burst systems on large installations don’t always clean entire screen - especially the bottom. Long, stringy vegetation is a problem on small pump screens.
Passive Screens (not self-cleaned) Selection Criteria : • Only considered for use when site is not suitable for an active screen. • Uniform approach velocity must be apparent from the conceptual screen design. • Approach velocity not to exceed 0.2 ft/s. • The combined rate of flow at the diversion site must be less than 3 cfs.
Passive Screens (not self-cleaned) Maintenance and debris management: • A maintenance program must be approved by NMFS and implemented by the water user. • The screen must be frequently inspected with debris accumulations removed, as site conditions dictate. • Sufficient stream depth must exist at the screen site to provide for a water column of at least one screen radius around the screen face. • The screen must be designed to allow easy removal for maintenance, and to protect from flooding.
Passive Screens (not self-cleaned) Maintenance and debris management: • The debris load must be low. • Sufficient ambient river velocity must exist to carry debris away from the screen face.
Passive Screens • A maintenance program must be approved by NMFS and implemented by the water user. • The screen must be frequently inspected with debris accumulations removed, as site conditions dictate. • Sufficient stream depth must exist at the screen site to provide for a water column of at least one screen radius around the screen face. • The screen must be designed to allow easy removal for maintenance, and to protect from flooding.
