Obstructions in 2D area

[Anonymous]

Dear 2D HEC-RAS users,

I am running a dam break in a HEC-RAS model with only a 2D mesh. The dam is a small flood retention dam and only about 5 m (about 16 ft) tall. The storage volume is only 47’000 m3 (38 ac-ft). The breach affects only the local areas close to the small river (2m/6ft wide) and I need to model the houses in that area.
I have two GeoTIFF terrain models that I can work with. One is a DTM and the other a DSM with all trees and houses. I do however not want to model the trees as those distort the flow paths.
In the 1D cross sections it is possible to create obstructions to permenantly block out areas. I was wondering if it is possible to do something similar in 2D. Does anyone know if there is a way to block flow through certain areas? There are two many houses to lift the surface at each one of them, so I’m trying to find another way. Or should I try to lift the surface of the DTM in GIS and then import this into RAS Mapper?

Thank you for your help
Regards,
Stephanie

[Lonnie A]

You can define a landuse layer and set the N=1 for the building footprint areas. I believe RAS takes the majority of the landuse in the cell as it’s n-value for that cell.

[Robert]

Hi Stephanie,

HecRas 5.0 (2D) hasn’t ability to define the obstacles by Obstructions. I hink, the best option is use dtm with buildings.

I think, that increase n-values isn’t well solution, Lonnie. Because you change only properties of flow, but the houses will be flooded.

regards
Robert

[Chris G.]

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Subject: Re: Obstructions in 2D area
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Lifting the terrain is one option. But you could also use 2D area connection=
s to block flow. Another option is to draw n value areas around the building=
s to block and assign very high n values (say about 10). N values effectivel=
y block the flow but also account for the storage of water inside the buildi=
ngs.=20

Sent from my iPhone

> On Aug 10, 2015, at 02:11, Stephanie Morach [via HEC-RAS Help] wrote:
>=20
> Dear 2D HEC-RAS users,=20
>=20
> I am running a dam break in a HEC-RAS model with only a 2D mesh. The dam i=
s a small flood retention dam and only about 5 m (about 16 ft) tall. The sto=
rage volume is only 47’000 m3 (38 ac-ft). The breach affects only the local a=
reas close to the small river (2m/6ft wide) and I need to model the houses i=
n that area.=20
> I have two GeoTIFF terrain models that I can work with. One is a DTM and t=
he other a DSM with all trees and houses. I do however not want to model the=
trees as those distort the flow paths.=20
> In the 1D cross sections it is possible to create obstructions to permenan=
tly block out areas. I was wondering if it is possible to do something simil=
ar in 2D. Does anyone know if there is a way to block flow through certain a=
reas? There are two many houses to lift the surface at each one of them, so I=
‘m trying to find another way. Or should I try to lift the surface of the DT=
M in GIS and then import this into RAS Mapper?=20
>=20
> Thank you for your help=20
> Regards,=20
> Stephanie=20
>=20
> If you reply to this email, your message will be added to the discussion b=
elow:
> http://hec-ras-help.1091112.n5.nabble.com/Obstructions-in-2D-area-tp1896.h=
tml
> To unsubscribe from HEC-RAS Help, click here.
> NAML

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Lifting the terrain is one option. But you could also use 2D area connections to block flow. Another option is to draw n value areas around the buildings to block and assign very high n values (say about 10). N values effectively block the flow but also account for the storage of water inside the buildings. 

Sent from my iPhone

On Aug 10, 2015, at 02:11, Stephanie Morach [via HEC-RAS Help] <[email protected]> wrote:

Dear 2D HEC-RAS users,

I am running a dam break in a HEC-RAS model with only a 2D mesh. The dam is a small flood retention dam and only about 5 m (about 16 ft) tall. The storage volume is only 47’000 m3 (38 ac-ft). The breach affects only the local areas close to the small river (2m/6ft wide) and I need to model the houses in that area.

I have two GeoTIFF terrain models that I can work with. One is a DTM and the other a DSM with all trees and houses. I do however not want to model the trees as those distort the flow paths.

In the 1D cross sections it is possible to create obstructions to permenantly block out areas. I was wondering if it is possible to do something similar in 2D. Does anyone know if there is a way to block flow through certain areas? There are two many houses to lift the surface at each one of them, so I’m trying to find another way. Or should I try to lift the surface of the DTM in GIS and then import this into RAS Mapper?

Thank you for your help

Regards,

Stephanie

---

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NAML

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