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?

    1. Yes indeed. 3.0 would be my upper end.

  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. ;)