Wetland modeling

[Anonymous]

Hello everyone. I’m writing from Brazil… I would like to ask if you think it is possible to represent a region composed by 2 lakes connected and a wetland in the middle of them. There is no river in the study area, that’s why I am asking this question.

Thank you so much.

[Anonymous]

I would think that you should be able to do that in RAS using 2D flow.

[Anonymous]

The problem is the information available for the area. The 1st lake is connected to the wetland by something that can be represented as a weir and a culvert and the information available is just the long therm serie of
water level measured on the interface of the lake with the wetland. I need also to input precipitation in the Wetland area, and the other lake connect to the wetland has also a long therm observed serie of water level.
I can obtain elevation vs volume of the first lake as well.

Any ideias?

[Anonymous]

If all you have for the lakes are elevation vs volume curves, then you will have to model them as 1D storage areas.

You could use a 2D area for the wetlands and connect the wetland to each 1D lake with a storage area connector.

You cannot use 2D without terrain data. So you would need terrain data for the wetlands for 2D.

[Anonymous]

I do have elevation volume for the lakes and 2D terrain for the wetland, but when I try to model them with connections it seems that the water doesn’t flow from the lake to the wetland using a stage hydrograph. Can I use measured water level over time as a condition to the lake? I don’t know if I should add as a BC or something else..

Thank you so much.

[Anonymous]

There is not a way to directly add a stage boundary to a 1D storage area. (If the lake was modeled as a 2D area, you could add a stage boundary condition.)

You could do it indirectly.

You could add a fake 1D reach where the downstream end of the reach is directly connected to the lake (the 1D storage area). At the upstream end of the reach, use a stage time series where the stage is the measured lake levels. The reach only needs two or three cross sections. Make the cross sections really large so that the velocity in the cross sections are really small and the lake and the cross sections should all have the same water surface within the computation tolerance.

[Anonymous]

I see… But in case I try to use a 2D storage area for the Lake with a stage hydrograph as a BC, does it matter the shape of the lake or just the water level measured on the interface wetland/lake?

[Anonymous]

For what you are trying to do, I don’t think the shape of the lake would matter.

[Anonymous]

The connection between the lake and the wetland I will represent by a weir, but the stage measurements that I have are on the interface. Hec does not allow me to add a BC and a connection in the same place… Also, it seems that the stage hydrograph that I am adding is not forcing the water level to be that number in the lake. What can I do?

Thank you again.

[Anonymous]

Add an elevation in the unsteady flow editor. then check keep initial elevations constant during warmup, and see how this interacts with your table you manually entered

[Anonymous]

If you have a lake represented by a 2D area and also have a stage boundary, RAS doesn’t “force” the lake to have that stage boundary. Instead, it will compute an inflow (or outflow) along that boundary.

So if you want the stage in the lake to match the stage along the boundary, you want there to be a large flow area along the boundary. So draw the 2D lake boundary polygon so that there is deep water along part of the boundary and attach the stage boundary there.

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