Inconsistency in flow simulation with pond in soil columns

A discussion forum for Hydrus-1D users.
Post Reply
Flavio Azevedo
Posts: 2
Joined: Sun May 17, 2020 1:24 pm
Location: Brazil

Inconsistency in flow simulation with pond in soil columns

Post by Flavio Azevedo » Mon May 18, 2020 1:26 am

Hello,
I am simulating a one-dimensional flow of water in columns for the study of bioretention with a single layer and varying heights, as well as ponds on the surface. However, for some cases the simulation has shown inconsistencies as the infiltration is abruptly interrupted at the end of the rain event period and the accumulation in the pond decreases abruptly as well. The rates of atmospheric precipitation (inflow) in the period of 60 min are higher than the hydraulic conductivity Ks. I noticed that the problem occurs when there is saturation of the profile in the interval of 60 min and the base and top flow are processed with the same rate.

Any ideas how to resolve this situation? Help!!

The input data are:
Single layer 130cm
Rain event 60 minutes
Simulation time 300 minutes
Atmospheric BC wich surface layer
Free drainage
Initial conditions - In water contents = 0.15
Attachments
bioretention flux h_130_surface layer_30.rar
project
(31.66 KiB) Downloaded 7 times

Jirka
Posts: 4922
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: Inconsistency in flow simulation with pond in soil columns

Post by Jirka » Mon May 18, 2020 3:50 pm

When you consider the surface layers, you need to have a higher precision in terms of the pressure head (e.g., 0.1 cm). See the attached modified project. J.
Attachments
00bioretention 130 , surface layer 30.zip
(49.12 KiB) Downloaded 4 times

Flavio Azevedo
Posts: 2
Joined: Sun May 17, 2020 1:24 pm
Location: Brazil

Re: Inconsistency in flow simulation with pond in soil columns

Post by Flavio Azevedo » Tue May 19, 2020 2:27 am

Thanks Jirka for your answer

But I do not understand what really happens ... Even if I copy the file you sent and try to run the program, in the processing it is unable to converge to solution as shown in the attachment. Did you change another parameter in the project besides “Pressure Head Tolerance”?
* I reinstalled the software but it is still in the same situation.
I appreciate the great help.
Flávio.
The attachment run program.jpg is no longer available
run program.jpg
run program.jpg (348.71 KiB) Viewed 130 times

Jirka
Posts: 4922
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: Inconsistency in flow simulation with pond in soil columns

Post by Jirka » Tue May 19, 2020 5:56 pm

The problem with your project is that the entire soil column gets fully saturated and the free drainage BC is not appropriate BC for such conditions. See our description of this BC in the help:
"A zero-gradient boundary condition can be used to simulate a freely draining soil profile. Such a situation often occurs in field studies of water flow and drainage in the vadose zone. This lower boundary condition is most appropriate for a situation where the water table lies far below the domain of interest."

You should either extend the profile so that you avoid the full saturation of the entire profile or use a different bottom BC (perhaps a seepage face).

J.

PS. I was using my own computational module rather the one that is in the HYDRUS installation file.

Post Reply