Tuesday, December 8, 2015

Pressure and Weir Flow

Here’s a video of pressure and weir flow yesterday at a bridge near my house.  This was brought on by some very intense rainfall over a short period of time.  What do you think the weir coefficient would be?

‘Tis the season in many parts of the world for heavy rains and high water.  This is a good reminder to always try to get out and view your rivers and streams when they are flooding.  There is nothing like a first-hand view of a flood to understand how water interacts around our infrastructure.  This is invaluable information for setting up and calibrating your HEC-RAS models. 


  1. 3.0?? Is there a hydraulic jump at the downstream side of the bridge?

  2. did you happen to measure the velocity or depth? when the water goes down, a crude survey of the elevation drop between the upstream and downstream sides would also be a great value.

  3. I'd say between 2.5 and 3.0 for the weir coefficient. The flow looks pretty smooth and I didn't see a lot of impediment to flow over the weir. I'd be hesitant to use anything over 3.0 as well. I know the theoretical value, but that is realized only in the lab, in general. ;)