Use of the NHI GLG/GHG/GVG data

Andy.arcadis

Is the resulting ground water table altered from the original NHI data if I use the NHI ground water data in the Ground Water overlay and don't enter any rainfall/drought/climate parameters?

Or is the result altered for the presence of surface water for example?

RudolfNL

Hi Andy,

please take a peek at our documentation regarding the underground model for the Water Overlay:

https://support.tygron.com/wiki/Underground_model_(Water_Overlay)#Initialization

For any given simulation, at the start the water is initialized (if you opt to use our provided NHI data, or any other geotiff data, then the groundwater level is initialized in accordance with that data and not affected by surface water etc). After initialization, it is free to flow as dictated by the relevant (underground) formulas for the duration of the simulation. If you leave the simulation settings at their defaults, it will be a relatively brief simulation in which not a lot will happen, but the water will experience some minor flow in the underground. At the same time, water from the surface may infiltrate into the underground. In short: a lot can affect the water level, even in a brief period of a simulation.

Does this provide sufficient insight into the observed results?

Kind regards

Andy.arcadis

Hi Rudolf,

thanks for the explanation.

I still have difficulties understanding the ground water modelling. How can it be that the results of the ground water overlay (up to 0,5m) are so much more detailed than the original 250m*250m NHI data? They should be the same when I compare both if I'm not using any rainfall events etc. right?

Hansje

Hello @Andy.arcadis ,

Like Rudolf mentions, a lot can happen with the groundwaterlevels in a short period of time.

The NHI maps are used as a basis (if you have set this up) and subsequently, at cell level, it is examined what happens to the groundwater.

This video explains how the groundwater model works in the LTS (in Dutch): https://www.youtube.com/watch?v=xmdPkYn0YCc&feature=youtu.be

Maybe this can help you understand it better.

If it is still not clear enough after watching the video I would suggest to plan a short meeting in our customer consultancy hour. We are happy to give a more personal explanation if you want to.