putting in a bend in HEC-RAS

[poopencholie]

Hello. I am new to HEC-RAS. I have been given a project in which I am to analyse a existing storm water culvert which changes as one goes down the stream. So far everything seems to be pretty self-explanatory with regards to setting up cross-sections and culvert shapes and what not. But I would like to know just how exactly I am meant to place the existing bend in the culvert? Do I put in a junction? In which case how am I meant to put the kind of bend into the junction editor?

Thanks

Derryck

 

[chicopee]

I have not done this for a couple of years but from what I remember I added extra sections at start, end and within the bend. The values of distances for the right and left banks should reflect a bend.

 

[poopencholie]

Thanks...

But can you elaborate on "the values of distances for the right and left banks should reflect a bend"

 

[poopencholie]

Isn't it just better to make two reaches at the relevant angles accommodating the bend and then to select the momentum principle in order to calculate head losses?

 

[Ryb01]

poopencholie,

If there is a concern about looking into losses associated with bends in a culvert, HEC-Ras is probably not the best tool to use. To my knowledge you cannot account for these types of losses in HEC-Ras. I would recommend using SWMM. You can account for the bend losses directly in the attribute editor. Hope this helps.

 

[francesca]

Is the bend in the culvert or in the channel leading up to the culvert? If it's in the culvert, is the culvert flowing full?

 

[chicopee]

If I remember correctly, lets say that the river bends to the left and since distances between cross sections are needed, the distances on the left hand side will be slightly less than the distances on the right hand side.

 

[gbam]

to elaborate on francesca's questions: If the bend is within the culvert and it is under outlet control it will be necessary to account for the additional head losses due to the bend. This can be achieved by evaluating the culvert hydraulics external of HECRAS and coding a rating curve at the inlet to reestablish the water surface elevation. If the bend is not within the culvert, then the curve is decribed by the different overbank lengths (shorter for inside bend and longer for outside bend).