Flow from groundwater to surface

Thomas Mittring · February 2019

Hi support,

Another quick question on the groundwater flow overlay that's recently been added to Tygron.

I did a test in which I tried to have a deep valley in my DTM, surrounded by fairly high groundwater tables. What I noticed, after modelling with 10+ m/d Infiltration Speeds and 100 days of calculation, was that the groundwater table in the valley went all the way op to 0 mm beneath ground level... and then stopped rising.

In other words: I got the impression that groundwater can't leave the freatic zone and flow to the ground level. Could you tell me if I am correct in this assumption?

Thanks!

Hansje · February 2019

Hi Thomas,

Thank you for your question.

The distance is relative to the surface of the terrain. The impenetrable layer is a distance of GROUND_BOTTOM_DISTANCE_M below the surface. For every grid cell, the height of the impenetrable layer relative to datum can differ, following the profile of the height of the surface relative to datum.

Currently, the height of the impenetrable layer (relative to the surface) can only be configured as an attribute for the entire project area, and cannot be varied geographically.

Also, on these pages you can find some additional information:
http://support.tygron.com/wiki/Water_Overlay#GROUND_BOTTOM_DISTANCE_M
http://support.tygron.com/wiki/Water_Overlay#Underground_model

Does this clarify enough for you now?

Thomas Mittring · February 2019

Hi Hansje,

It does indeed answer one of my questions... just not the one that this topic is about

I think you meant to answer my other topic, namely 'Ground Bottom Distance'.

Hansje · February 2019

Oeps! You are correct. I will adjust this so it is also available for other users.
Thank you for getting back at me about this!

Hansje · February 2019

Again, This is the correct answer corresponding with this question now.

Most information can be found on these two pages, but this is not entirely corresponding with your question, therefore I give you some additional information as well.

http://support.tygron.com/wiki/Terrain
http://support.tygron.com/wiki/Terrain_height#Waterdepth

On our preview version we are currently working on various enhancements related to water flow models, and one of them is indeed how we create a baseline of water bodies. In the new version, we relate the water depth and the angle of repose for the water bodies to the terrain in that area. Specifically during the generation of a new project area, when a water terrain is found in a project area, the water body is carved into the base terrain. The angle of the sides of the water body is defined by the ANGLE_OF_REPOSE of the underground terrain type, and the maximum depth to which a water body is carved out is WATER_DEPTH_M as defined for the surface terrain type. If the angle of repose is shallow enough and the water body thin enough, the angled sides may meet up before the maximum water depth is reached. In this case the water body will be appropriately shallower.

Thomas Mittring · March 2019

Hi Hansje,

I'm sorry to bother you again with this, but this still doesn't seem to answer my question.

Hansje · March 2019

Hi Thomas,

Thank you for getting back at us about this.
We've looked into your question, and from how you describe it we should indeed see some groundwater leave the freatic zone. We're currently investigating this setup, and we'll provide you with an update when we have more information for you.
Thank you for your patience.

Hansje · March 2019

Hello Thomas,

On our current preview server a build is released that should resolve this problem. You can test this and please let me know if it has been resolved now.

Flow from groundwater to surface

Comments