Special case: Ship channel and levees

[Mathilda]

Hi!

I am working on modelling inundation map using HEC-RAS. The study river has many particularities, including a ship channel and a multiple levees allowing agricultural activities on low lands near the river channel. I am planning on using Steady Flow Analysis.

I am wondering in which layer should I digitize the ship channel, and also the levees. My guess would be ship channel would be digitized in Lateral Structures and Storage Areas Layers (the ”levee” between the ship channel and the major river channel would be digitized in Lateral Structures and the ship channel itself would be digitized as StorageAreas) and the multiple agricultural levees would be digitized as Levees Layer. What do you think? Any suggestion?

Thanks a lot!

[dueckrandy]

Hi Mathilda,
This sounds like a fun project
It sounds like you have some idea of how the different elements of your model will interact. However, it is very difficult to make suggestions in your case without seeing the layout of the river, levees, and canal.
My only caution based on the info you gave is to be wary of levees. If a levee overtops, HEC-RAS assumes the same water surface elevation on both sides.

[Mathilda]

Thank you for your response, dueckrandy.

Do you think it would be preferable to digitize the agricultural levees as Lateral Structures instead? I might understand than Lateral Structures should be used to separate the river channel and storage areas. In my case, the agricultural levees are discontinuous, so they do not act as structures that contains water, so there is no storage areas. That is why I thought it was better to digitize those agricultural levees as Levees in HEC GEORAS. What do you think?

Thanks a lot. This forum is a great source of help!

[dueckrandy]

Again, I must say that it is not possible for me to give a definite answer for your case without knowing the details of your project. It really depends on where the water goes when it spills over your levees. For example, does the water travel in a separate path and rejoin the main channel downstream? If so, then you may need to model it as a separate channel with split flow optimization and use lateral structures wherever you suspect water will spill back and forth between the 2 channels.

To be honest, I have never used levees in the final version of a model. In my experience, the main benefit of using levees instead of lateral structures is that they are quick and easy, whereas lateral structures take more time and effort. The other scenario where levees may be preferred is if you are designing a levee that is meant to completely contain flood waters, and you need a quick way to modify your model to try different options.

If you would rather not post some kind of project layout here, perhaps it would be better to discuss via email.

[Author]

Posts