Multi Domain 2D Model Using Effective Precipitation

[Mark]

Hello.

I would like to develop a multi-domain 2D model for various sites with various types of surfaces (paved, grass, wooded etc.) that provides a high level estimate of potential surface water flooding based on precipitation only.

In trying to go this route I would need to use SA/2D Area Connectors to join the different 2D domains but I have previously had an issue with this approaching giving me errors which I assume is related to issues with HWs, TWs and weir elevations resulting from having not divided the 2D area based on hydraulics (i.e. a high area draining to a low area) but on land-cover resulting in a variation in the boundary edge which is actually the HW and TW (Lonnie A also adds that the weir needs to be higher than the HW and TW in a related post).

Is there a way to develop a multi-domain 2D model divided according to land-cover and therefore not obeying HW, TW and weir rules as mentioned above?

Thanks for any feedback.

[Anonymous]

Just a small correction. The lateral weir connecting the 2 areas does NOT have to be higher it just cannot be lower, i.e. it can be the same height as the cell elevation. Since runoff will be expected to transfer from one area to the next, the weir will be fully submerged so a weir coefficient of 0.2-0.5 should be used.

There are absolutely ways to model multiple domains in one model however i have found that it is not very efficient. Run times can be high, i have had some run as long as 4 days to obtain stability as well as an acceptable mass balance output. What i suggest is modeling one area at a time which has outflow weirs acting as free outfalls. These outfall hydrographs will then be input into the adjacent model as inflow hydrographs.

[Mark]

Thanks for that input Luis

Is the conclusion then that you cannot create a multi domain (distributed) 2D model using land-cover/soils as your domain (mesh) divider and that you HAVE to go the hydraulic route where your outflow boundary for an upslope 2d area is higher or the same as the inflow boundary of the downslope 2d area across the full length of the SA/2D Area Connector?

If so, this will be problematic in modelling precipitation derived surface water flooding of a large site since hydrologically homogeneous areas which would have the same effective infiltration (total rain less infiltration and depression storage) would either need to be lumped into ‘hydraulic areas’ thereby losing spatial detail or otherwise broken down into much smaller units.

[Anonymous]

Well currently Mark, the grid you create within RAS does not account for infiltration but does account for surface storage because the mesh builds cross sections from the terrain its associated with. If you adjust your hydrological model and have a varying land use/mannings value grid also, then you should have no problem modeling multiple areas with different basin characteristics

[Lonnie A]

The next version of RAS (v5.0.4) I believe will have the capability of applying varied precipitation across a single mesh….I’m not certain losses make it into the next version yet though. If not you’ll just have to apply the excess precip value from HMS letting HMS take care of the soil losses.

[froni]

Can you tell when v5.0.4. will be released? I am also struggeling applying various precipitation across the mesh.

[Lonnie A]

Looks like varied precipitation is not making it into v5.0.4. I suspect we’ll see v5.0.4 sometime late spring or summer 2018.

[Anonymous]

I need some help regarding adding the precipitation in the HEC-RAS.

1- What does the actual mean of time series of precipitation? Is it mean the accumulated rainfall?
for example

Date Simulation time Precipitation (mm)
11-01-2019 07:00 00:00 30
11-01-2019 08:00 01:00 30
11-01-2019 09:00 02:00 30

Does it mean the total rainfall added on the 2D flow area during the whole simulation time is 90 mm? Please elaborate?

Thanks

[cameron]

yes. It is the effective precipitation hyetograph.

[Author]

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