7/30/2019 3140-FS-DEP2058 (1)

1/2

TRASH RACKS ON DAMS AND RESERVOIR OUTLETS

What is a Trash Rack?

A trash rack is designed to provide protection against clogging of outlet works or principal spillways under anyoperating level of water in the reservoir. Trash rack structures may take on varied shapes, depending on how theyare mounted or arranged on the intake structure. A trash rack for a drop inlet intake is generally formed as a cagesurrounding the entrance. It may be arranged as an open box placed in front of a vertical entrance, or it may bepositioned along the front side of a tower structure.

If there is no danger of clogging or damage from small trash, a trash rack may consist simply of struts and beamsplaced to exclude only larger trees and floating debris.

The rack arrangement also depends on accessibility for removing accumulated trash. For instance, a submergedrack in a dam that will seldom be drained must be more substantial than one that is at or near the surface.Similarly, an outlet with controls at the entrance where the gates can be jammed by trash protruding through theopenings in the trash rack must have a more substantial arrangement.

Trash Rack Design

Trash racks usually consist of steel bars that are spaced at roughly one-quarter the diameter or minimumdimension of the outlet conduit being protected. Frequently, the trash rack is assembled in sections. The required

area of the trash rack is fixed by a limiting velocity through the rack, which inturn depends on the nature of the trash to be excluded. Where a trash rack isnot accessible for cleaning, the velocity through it should not exceed 2.0 feetper second. A velocity of up to 5.0 feet per second may be tolerated for a trashrack that is accessible for cleaning. The velocity is to be computed on the basisof the net area of opening through the trash rack.

The design of trash racks on outlet works depends on:

the size of the sluice or conduit,

the type of control device used,

the nature of the trash burden in the reservoir,

the utilization of the water,

the need for excluding small trash from the outflow and other factors.

These factors will determine the type of trash rack and the size of the openings.Where an outlet consists of a small conduit with valve controls, closely spacedbars will be needed to exclude small trash. Where an outlet involves a largeconduit with large slide gate controls, the bars can be more widely spaced.

Special Considerations

If a reservoir outlet with a trash rack or a ported concrete riser is used to keep the sediment pool drained, thetrash rack or riser should extend above the anticipated sediment elevation to provide for full design flow through

the outlet during the design life of the dam.It is critical to provide resistance against the lifting forces of winter ice that can lock onto a trash rack, and be liftedby the rising reservoir level in the spring. A movable trash rack that can move with these forces should beconsidered.

The design and drawings for a proposed trash rack must be submitted to the Department of EnvironmentalProtection (DEP) for approval prior to installation. Mail submittals to PA DEP, Bureau of Waterways Engineeringand Wetlands, Division of Dam Safety; P.O. Box 8460, Harrisburg, PA 17105-8460.

7/30/2019 3140-FS-DEP2058 (1)

2/2

Commonwealth of Pennsylvania Department of Environmental Protectionwww.d ep.state.pa.us 3140-FS-DEP2058 Rev. 4/2012

DEPs Watershed Management ProgramRegional Offices

Northwest Region230 Chestnut St.Meadville, PA 16335-3481814-332-6984

Counties: Butler, Clarion,

Crawford, Elk, Erie, Forest,J efferson, Lawrence, McKean,Mercer, Venango and Warren

Northcentral Region208 W. Third St., Suite 101Williamsport, PA 17701-6448570-327-3574

Counties: Bradford, Cameron,

Clearfield, Centre, Clinton,Columbia, Lycoming, Montour,Northumberland, Potter, Snyder,Sullivan, Tioga and Union

Northeast Region2 Public SquareWilkes-Barre, PA 18701-1915570-830-3093

Counties: Carbon, Lackawanna,

Lehigh, Luzerne, Monroe,Northampton, Pike, Schuylkill,Susquehanna, Wayne andWyoming

Southwest Region400 Waterfront Dr.Pittsburgh, PA 15222-4745412-442-4000

Counties:Allegheny, Armstrong,Beaver, Cambria, Fayette, Greene,Indiana, Somerset, Washington andWestmoreland

Southcentral Region909 Elmerton Ave.Harrisburg, PA 17110-8200717-705-4707

Counties: Adams, Bedford, Berks,Blair, Cumberland, Dauphin,Franklin, Fulton, Huntingdon,Juniata, Lancaster, Lebanon,Mifflin, Perry and York

Southeast Region2 East Main StreetNorristown, PA 19401-4915484-250-5970

Counties: Bucks, Chester,Delaware, Montgomery andPhiladelphia

For more information, visitwww.dep.state.pa.us, keyword: Dam Safety.

http://www.dep.state.pa.us/http://www.dep.state.pa.us/http://www.dep.state.pa.us/http://www.dep.state.pa.us/