deactivate 2d cell

[Anonymous]

Hello forum
I am asking on how to deactivate 2d cell so (rainfall grid / overland flow) can not active into this site ie: building roof. thanks

David

[cameron]

you cannot turn off cells in HEC-RAS at this time.

[M. L. Harris]

What if you set the Manning’s roughness value to something unreasonably high for the grid cell or region?

Another thing I have done in 2D flow areas is to “superimpose” the buildings themselves onto the terrain so that they act as physical obstructions to flow.

[alister.hood]

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References: <[email protected]> <[email protected]>
In-Reply-To: <[email protected]>
From: Alister Hood
Date: Tue, 11 Jun 2019 23:49:28 +1200
Message-ID:
Subject: Re: deactivate 2d cell
To: “M. L. Harris [via HEC-RAS Help]”
Content-Type: multipart/alternative; boundary=”000000000000685b06058b0ae40b”

–000000000000685b06058b0ae40b
Content-Type: text/plain; charset=”UTF-8″
Content-Transfer-Encoding: quoted-printable

Hi guys,
Personally I don’t like the “high roughness” approach, so I either
rasterize the buildings and merge with the terrain, or if I am lazy
sometimes I can model them satisfactorily just by using weirs.

Also, be aware that:
– Just rasterising buildings and merging them with your terrain won’t make
them act as a barrier to flow unless you use a very small cell size;
typically in HEC-RAS you would use a cell size at least as large as most
buildings, in which case you might need to mess around with refinement
regions and break lines to try to get it right.
– Similarly, the high roughness method would require very small cells as
HEC-RAS just applies a single roughness to each cell.

Regards,
Alister

On Tue, 11 Jun 2019, 5:41 AM M. L. Harris [via HEC-RAS Help], < [email protected]> wrote:

> What if you set the Manning’s roughness value to something unreasonably
> high for the grid cell or region?
>
> Another thing I have done in 2D flow areas is to “superimpose” the
> buildings themselves onto the terrain so that they act as physical
> obstructions to flow.
>
> M. L. Harris, P.E. | Water Resources Engineer
>
>
> ——————————
> If you reply to this email, your message will be added to the discussion
> below:
>
> http://hec-ras-help.1091112.n5.nabble.com/deactivate-2d-cell-tp7629p7637.=
html
> To start a new topic under HEC-RAS Help, email
> [email protected]
> To unsubscribe from HEC-RAS Help, click here
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–000000000000685b06058b0ae40b
Content-Type: text/html; charset=”UTF-8″
Content-Transfer-Encoding: quoted-printable

=
Hi guys,=C2=A0

Personally I don't like the "high roughness" approac=
h, so I either rasterize the buildings and merge with the terrain, or if I =
am=C2=A0lazy sometimes=
=C2=A0I can model them satisfactoril=
y just by using weirs.

Also, be aware that:

– Just rasterising buildings and merging them with your t=
errain won't make them act as a barrier to flow unless you use a very s=
mall cell size; typically in HEC-RAS=C2=A0you would use a cell size=C2=A0at least as large as most buildings, in which case you might=
need to mess around with refinement regions and break lines to try to get =
it right.

– Similarly, the high roughness method would require very small cells a=
s HEC-RAS just applies a single roughness to each cell.

Regards,

Alister

On Tue, 11 Jun 2019, 5:41 AM M. L. Harris [via HEC-RA=
S Help], <ml+s109=
[email protected]> wrote:

il_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-lef= t:1ex">

What if you set the Manning's roughness value to something unreasonabl=
y high for the grid cell or region?

Another thing I have done in 2D flow areas is to "superimpose&=
quot; the buildings themselves onto the terrain so that they act as physica=
l obstructions to flow.

=09
=09

M. L. Harris, P.E. | Water Resources Engineer

---

If you reply to this email, your message =
will be added to the discussion below:

http://hec-ras-help.1=
091112.n5.nabble.com/deactivate-2d-cell-tp7629p7637.html

To start a new topic under HEC-RAS Help, email ml+s1091112n=
[email protected]
To unsubscribe from HEC-RAS Help, click here.
NAML

–000000000000685b06058b0ae40b–

[Anonymous]

Thank you for input. I do the same thing. With buildings terrain, i assumed you build in another gis package . HECRAS does not have the tool to modify z polygon

[Anonymous]

Thanks Alister for input
I do it too before. but if you build a weir (within building perimeter) , rainfall 2d will pour inside building like container, unless you use small a gap (start to end weir line ) facing downstream slope.

[ckatsoulas]

I have a situation where I have a building with roof that covers an open parking area. this area does not get rainfall however it can get flooded. If I delete the roof over the parking then I also allow direct rainfall over it but if I add the building as a blockage then I can’t model the flowpath through the parking. We need to turn off the 2D cells at this location to prevent rainfall but allow it to get flooded

[Author]

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