Pixels with high water depth

Glenn Morvan

Dear Tygron community,

After exporting waterstress (water depth) results from a digital twin for a neighborhood in Hoorn (NL), we found strange pixels with extremely high water depth of 500mm after a 40mm rainfall event. The part I don't understand is that the ground level does not really change compared to the surrounding pixels but the water depth of surrounding pixels is much lower (negligible). Another funny thing is that most of these pixels are found in small alleys and in between buildings.

Do you have an explanation for these pixels? I have made the project available for support (name: Hoorn Kersenboogerd1).

Keen to hear from you!

Kind regards,

Glenn

Below some screendumps for better understanding:

1: water depth (500mm) and ground level (-0,694) at "strange" pixel in Tygron.

2: water depth (0,9mm) and ground level (-0,692) at nearby polygon in Tygron.

3 & 4: "strange" pixels with deep water in exported result.

vincent.rd

Hello @Glenn Morvan ,

Thank you for opening up the project for support. We will have a look and get back to you.

Best regards,

Vincent

vincent.rd

Hello @Glenn Morvan,

I passed your question on to R&D to have a look. I have an idea what it might be, but I want to be sure. As soon as I know more, I will let you know too of course.

Regards,

Vincent

Glenn Morvan

Hello @vincent.rd,

First of all, happy new year :).

Is there any news on the above matter?

We're quite curious to know what causes these high water depths near buildings.

Kind regards,

Glenn

vincent.rd

Hi @Glenn Morvan ,

Thanks and a happy new year to you too!

We had a look at thje screen shots you provided, and when the used grid size is more then 1/4 of the width between constructions, this can occur, especially when these are diagonal. Water can then end up in pockets. When you have no building storage (on roofs) and no sewer and no infiltration, water can then end up stuck in a local minimum.

The pockets shown in the images are indeed 4 grid cells.

So to remove these spikes, we advise to look into the grid size, water storage and/ or sewer connection.

I hope this helps?

Best, Vincent

Hedi

In addition: the advice would be to work with higher resolution (use 0.25 m grid option) and to use the increased DEM resolution option in the advanced settings page of the Water Wizard.