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Water on building roofs

edited February 2019 in Water

Hi,

How is the rainfall on roofs calculated?

I am building a model in the UK. By default, the resolution of the height map is quite low (2m if I'm not mistaking). However, after creating the 3D world using my own data (I imported buildings etc), I decided to test the rainfall overlay on the model. I noticed there are some building where the waterstress is calculated on the roof.

I'm trying to figure out how and why this happens. Could it have something to do with the low resolution height map? And how is the rainfall calculated, using DTM or DSM? Is it possible that, although the roofs of the buildings are slanting, there is still a height depression on the roof where water accumulates?

Thanks in advance,

Thijs

Comments

  • To explain the issue i added a screenshot of the roof.

    Afbeelding water op dak.PNG
    478 x 401 - 440K
  • Hi Thijs,

    The area you indicate in the screenshot shows a very low area with two buildings in it. If you show the Direction result type, you can see the rainfall from the surrounding areas accumulating in this particular low area.

    The rainfall is calculated using the DTM and DSM. For the buildings the height of the attribute of the Rainfall overlay Design_flood_elevation_m is used (see attached image). This attribute replaces the height of buildings (only buildings, not any other constructions in the Platform such as trees). Currently it is set on 1m. In the particular area at a certain point in the simulation is more than 1m of water and therefore it looks like the whole building is flooded (see the Surface max value result type).

    What you can do is change the Design_flood_elevation_m attribute to 'make' the buildings higher. Change it for example to 3 or 4 and see what happens with the rainfall in this area (see attached image).
    The real building height is also taken into account. If you change the attribute for example to 100, the DSM (average) value for this particular building is used, since very high peaks in the model have an effect on the flow of the water.

    The attributes of the Rainfall Overlay can be found by selecting the overlay in the left panel and clicking on the tab Attributes in the right panel.

    I hope I have explained it well to you and that this answers your question!

    height.JPG
    699 x 252 - 33K
    area.JPG
    555 x 490 - 52K

    Tygron support team

  • edited May 2019

    Just to add for more information, see also the following Wiki pages:
    http://support.tygron.com/wiki/Design_flood_elevation_m_model_attribute_(Water_Overlay)
    http://support.tygron.com/wiki/Surface_water_model_(Water_Overlay)

    Tygron support team

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