Inlägg:
Hi everyone!
I’m trying to use HEC-RAS (SI-units) to find the design flow of an existing bridge. When all geometry is set up I start running steady-state runs increasing inflow. Everything looks OK as long as the bridge capacity is not exceeded, as long as Q_Total equals Q_Bridge. However, when I reach maximum capacity of the bridge, a dramatic jump occurs, Q_Bridge is dramatically reduced and most of the water overflows the weir. In my case this happens at around 75 m3/s and I get. At 70 m3/s i get everything through the bridge opening, at 80 m3/s i the bridge opening only gets around 20 m3/s.
Somewhere I got the tip to try defining the bridge as a culvert instead, so I tried that. Using a culvert helped with the initial problem, but it still doesn’t add up. At 80 m3/s the culvert lets through 62 m3/s, but when viewing the Culvert Output window i also have a Q_Weir of 46 m3/s, totaling at 108 m3/s although the total input to the model is 80 m3/s.
Since I’m quite new at HEC-RAS it seems unlikely that this is a bug (SI/metric-related?) although you easily lean towards that after trying, trying and trying, still getting strange results…
please help!
best regards
Finn