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Conceptual Model -> MODFLOW: Pumping Data

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I'm having some difficulty with the conceptual model translation when using the WEL or MNW packages. I have a transient pumping rate dataset, and my model's stress period setup matches the intervals exactly (e.g., rate specifications at the start of each stress period).

After converting the data from the conceptual model to MODFLOW, I notice the rates have been altered with respect to the inputs to the coverage attribute table. That is, interpolation is being performed (even though I'm not getting a message).

Am I missing something in terms of how GMS interprets transient data in the conceptual model versus a transient MODFLOW stress period setup? Again, this occurs when using either the WEL or MNW packages to represent transient pumping rates.

Any help would be greatly appreciated,


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You may already have done this, but make sure that your conceptual model coverage is set up in a "step" format. For example if you want to pump 5 ft3/d for 10 days and then switch to 3 ft3/d for the next 10 days, you need to set it up as 5 beginning at 0 and ending at 10 days and as 3 beginning at 10 days and ending at 20 days. I haven't done this in a while, but also recall running into some initial problems like you are describing a long time ago. You could probably also set up an example in MODFLOW and export it to see if it is doing something different (e.g., different format) than what you have been doing in the conceptual model.

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The conceptual model pumping coverage has an attribute table constructed as you describe (step format) - the problem is, while the time intervals match the stress periods in the transient MODFLOW model, the pumping data are not converted correctly. For example, if I have a rate specified as 5.0 cfd at time = 10 days, after converting to MODFLOW, I would expect to see a rate of 5.0 cfd corresponding to the transient stress period spanning day 10 to day 11.

Instead, I see a rate that has been adjusted by some form of interpolation.

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