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Simulation convergence


Derek
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I am running a long duration (20 yr) transient simulation with many irrigation wells that are only active for three months. It fails to converge during pumping months, and runs fine when the wells are off. Any ideas? Rewetting is active. Stress periods are months.

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I am running a long duration (20 yr) transient simulation with many irrigation wells that are only active for three months. It fails to converge during pumping months, and runs fine when the wells are off. Any ideas? Rewetting is active. Stress periods are months.

This could be due to many things. First, it should converge with the WEL package turned off. Second, check your units to make sure they make sense. I'm guessing you are using either days or years, in which case, double check your hydraulic conductivities and pump rates so they have the same time dimensions (and that they conceptually make sense, such that you aren't pumping excessively high for certain materials).

If these don't work, try increasing the number of time steps per stress periods, and try modifying the multiplier to something like 1.2 or so. (You may want to change some output control options to reduce the size of files from your simulation, since you may not need to record each time step, and just keep the last time step for the end of month.)

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  • 1 month later...

I can get it to converge now; thanks for the input. I am now having problems with convergence using rewetting. I am using transient specified head cells along the boundaries to simulate groundwater fluctuations over a 20 year period. It is a three layer model with the middle layer the principal aquifer and the upper layer is silt and clay and typically dry. Late in the simulation the groundwater rises above the elevation of the top of layer 2 and the top layer has to be rewetted. But, I cannot get the model to run at all if I allow rewetting. I have tried a number of values for WETFCT and the two equations but nothing is working.

Any ideas?

Thanks,

Derek

This could be due to many things. First, it should converge with the WEL package turned off. Second, check your units to make sure they make sense. I'm guessing you are using either days or years, in which case, double check your hydraulic conductivities and pump rates so they have the same time dimensions (and that they conceptually make sense, such that you aren't pumping excessively high for certain materials).

If these don't work, try increasing the number of time steps per stress periods, and try modifying the multiplier to something like 1.2 or so. (You may want to change some output control options to reduce the size of files from your simulation, since you may not need to record each time step, and just keep the last time step for the end of month.)

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