How to Install a Weir

Weirs are sensitive to installation conditions.  Poor installation is often not correctable, so it is crucial that the following be observed when installing a weir plate.

Installing the Weir

• The crest (flow edge) of the weir must be set 2-3 times H_max above the floor of the channel.
• The crest of the weir must be set at least 2-inches [5.08 cm] above the maximum downstream water level.
• The widest portion of the weir crest at H_max should be at least 2 times H_max from the sidewall of the channel (on each side).
• The weir must be centered in the channel.
• The weir must be level from front-to-back and from side-to-side.
• The crest must be horizontally level.
• If present, the bevel of the weir crest must be set downstream.

• In earthen channel applications, the channel downstream of the weir should be reinforced / armored so that scour does not occur.  Scouring can lead to the weir plate shifting out of position or flow bypassing the weir plate.  

  • Water Measurement with Flumes and Weirs (ISBN 90-70754-55-X) provides details of channel reinforcement, however as a rule of thumb protection should extend at least 4 H_max downstream (and not less than 5-feet [1.5 m].