Complex 2d Hec-ras model

[belis Kal]

Hi, I have a quite complex hydraulic 2d hec-ras model with a lot of basins that interact. The hydrology has been modelled in Hec-hms, so I have hydrographs for every junction of streams The hydrographs in each junction are the result of rooting but there are also available, the hydrographs of each basin discharge.
I try to figure out a proper way to build the model in hecras and I would like some opinions in the following:
• I am thinking of splitting the model in submodels(shaded polygons in attached image) in order to reduce the computational needs, but I cant decide the proper way of splitting. I have figured out
that the sub-models should have a quite big overlap in order to achieve a continuity in flooding and not having interruptions at the edges of the grid. The final result will be a merge of the flood of the submodels. In the overlapping regions the answer of maximun depth of each cell will be kept.
• The hydrogrhaphs will be inserted as a boundary condition inside the streams as shown in the attached image. They will be used the hydrographs of each basin.
• For the next downstream model(red shaded model), the upstream hydrograph will be the rooted hydrograph of hec-hms model up to this point. As moving downstream, hydrographs of each basin will be inserted as internal boundary condition.

I would really appreciate any opinion and experience about constructing such models in hec-ras.

https://drive.google.com/file/d/166cK1n69IOwSuenOn4Ol_IVbAbQmSr-W/view?usp=drive_link

Thanks in advance

[Luis Partida]

No, dont do multiple meshes for each basin as the interconnectivity of them all would not only be a build, but a computational nightmare. Model it as a single subbasin in 1 mesh. In Harris County i believe for their modeling updates, placed hydrographs approximately 20-30% north of the subbasin outlet to not double account for time of concentration. BUT that rule worked well because delineation guidelines required subbasins around the 1-5 sq mile size. These methods were widely tested and documented in a series of white papers.

My suggestion is you go back to delineations and delineate to smaller areas giving you multiple hydrograph output locations then you can go back into a RAS domain, import your subbasin file as a map layer and then place your hydrographs as such.

[belis Kal]

Thanks for your response! The area i have to model is very big, with lots of sub-basin. I have to figure out a way to model this large area, by carefully divide it in hydraulic hec-ras models. If i make one model in each sub-basin, i will come up with 50 models probably… that i am not sure how can i merge them. I try to find one way to solve this problem without sacrificing quality in my results, and most important using correctly, the boundary conditions(hydrographs), i have from hydrological analysis.

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