1
$\begingroup$

I am trying to run a catchment model using MIKE-SHE (2020 version, DHI) including an unsaturated zone (UZ) and a saturated zone (SZ) in the set-up. I have specified the ‘Finite Difference’ method for both the overland flow and SZ, and Richards Equation for the UZ. I have entered property data for the UZ and SZ materials (for now the default values for sand were used for the UZ); however, I get the following error, followed by termination:

ERROR: UZ column shorter than the initial water depth in ( 7 146) Depth to groundwater: 0.90 m Length of UZ column: 0.90 m (profile no. 6) Termination…. Calling MIKE 1D with stop request after 0 timesteps… Ok Abnormal termination

It looks like the error is due to a single grid cell (7,146), but I do not know the reason for the error and what I can adjust to resolve it.

$\endgroup$
3
  • $\begingroup$ This may not be appropriate for Earth Science SE, I strongly suggest you to post this on Computational Science SE [scicomp.stackexchange.com} $\endgroup$
    – Tardy
    Aug 16 at 18:12
  • $\begingroup$ Thank you for your opinion @Tardy. If you would like to discuss this further I suggest we move this to a chat. We are making an active effort to get our hydrological modelling community onto stack exchange to try and make solutions more transparent and to support students learning. We did quite a lot of research before settling on this site. It has tags for both "hydrology" and "models" and therefore I do not think that our choice of site is misaligned. Anyway the key thing is that the information is available on the internet for other hydrological modelers. $\endgroup$
    – ecohydrol
    Aug 17 at 11:45
  • $\begingroup$ Ok, I understand, if so you are very welcome here $\endgroup$
    – Tardy
    Aug 19 at 21:53

1 Answer 1

1
$\begingroup$

It looks like the UZ column in your model does not extend deep enough in this set-up in some locations.

In MIKE-SHE, when using the UZ Richard’s equation and SZ Finite Difference coupling, the UZ ‘soil’ profile and the SZ material column in the model need to overlap: have the bottom depth of the UZ profile extend below the top of the SZ. Also, the groundwater table elevation should always be above the bottom of the UZ profile. Although the water table is simulated in the SZ module, if the water table drops to an elevation that is below the bottom of the model's UZ profile then there is effectively an unsaturated layer that is located below the UZ calculation domain of the model. This can cause errors in the pressure head calculation at the bottom of the modelled UZ profile.

The model error you received shows that the groundwater table was at the very bottom of the UZ profile, rather than lying within the UZ profile, at the specified grid cell (7,146) at the beginning of the simulation. This may have been true for other cells as well, but the model terminated after the first case was detected.

The UZ profiles should be defined to extend below the deepest depth that the groundwater table will reach in the simulation.

It is also suggested that the uppermost calculation layer of your SZ column should be defined such that the groundwater table will always be located within this top SZ layer. This is because the model’s exchange of water between the UZ and SZ is calculated for the top SZ layer only. Because of this, to be safe, the UZ profile could be defined to extend down to a depth that is just below the bottom elevation of this top SZ calculation layer.

To fix your problem, try extending your UZ ‘soil’ profile further downwards to cover the full range depths you expect for the water table: adjust both the ‘Soil Profile’ table and calculation cell ‘Vertical Discretization’ table for the relevant soil/material profiles. NB: The MIKE-SHE interface labels this as a ‘Soil Profile’, but it may need to extend beyond what is often defined as ‘soil’, into weathered rock layers that are frequently unsaturated.

You may also need to adjust the thickness (or top and bottom elevations) of your top SZ calculation layer so that the water table also lies within that top layer throughout the simulation. Getting these depths right for the full length of the simulation may be an iterative process if the groundwater table is predicted to move up and down by large amounts.

$\endgroup$
1
  • $\begingroup$ Thank you! This solved it. $\endgroup$
    – ecohydrol
    Aug 17 at 11:40

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.