Weirs

[mweng]

Does anyone know of a reference which discusses the use of weirs in outlet control structures for detention basins? I am looking for a practical explanation of when to use different types of weirs, dos and don'ts, etc.

 

[jgailla]

You should be able to check the DOT site for your state. They have lots of information on drainage control.

 

[uncivilized]

Use weirs for situations where you need moderate to high flows with low head requirements. Use orifices for smaller flows. Very small weirs tend to get clogged. I would read Debo's "Municipal Stormwater Mgt."

 

[bltseattle]

Open-Channel Hydraulics by Chow is a classic reference on weirs (and other hydraulic design elements). The fact that it's in a pond means your approach velocities will be essentially zero.

Uncivilized hit it dead-on regarding when to use weirs vs orifices. You cannot obtain precise low-flow control with a weir, but can accomodate high flow with low head.

Also note that an overflow riser operates as a weir under low stage conditions, but starts to operate as an orifice as the stage increases.

Check your DOT or Drainage Utility's manuals for guidance first, if what you need is not in there consider checking out Chow.

 

[mweng]

What about sharp-crested v. broad v. v-notch in detention basins? Any practical experience?

 

[bltseattle]

Generally, overflow spillways are modeled as broad-crested whereas an overflow riser, weir plate or other "structural" weir (wood, metal, conc) less than say 12"/300mm would be sharp-crested.