Posted Thu, 28 Jan 2021 16:24:03 GMT by Virgile Laurent Ingénieur hydrogéologue
I do a model for aquifer drawdown and I don't understand why the pumping rate is more important with wells than with seepage face. In fact seepage face permits to have the water level wanted on the site of excavation while wells are going to do a drawdown more important in the center of the excavation. For example if I want a drawdown of -2 meters, with seepage face a drawdown of -2 will be in the excavation while with the wells there will have a drawdown of -3 meters in the center of the excavation and -2 meters on the borders. So seepage face should extract less water than wells so I don't why it's the inverse in my simulations.
Thank you in advance for your answers.
Posted Fri, 29 Jan 2021 07:48:52 GMT by Peter Schätzl Grundwassermodellierer
Indeed with a seepage face you would expect to get less abstraction than with wells. Why this is the opposite in your model can only be found out by analyzing the model.
Posted Fri, 29 Jan 2021 09:39:39 GMT by Virgile Laurent Ingénieur hydrogéologue
Thanks for answering.
As an attachement there is a description of my model with a scenario with seepage face and a scenario with wells. You notice that pump rate is very different : 5900 m3/d with seepage face and 1370 m3/d with wells. I don't understand why extract with seepage face is so important in comparison with wells...
Thanks in advance if you take time to watch.

Posted Sun, 31 Jan 2021 06:48:43 GMT by Igor Pavlovskii Dalhousie University Post-Doctoral Fellow
Given the K distribution and saturated thickness, most of the inflow would be expected to occur upwards from 1.4E-3 aquifer (as opposed to seepage from the sides). I am wondering if wells actually fail to lower head for the entire excavation floor (slice 3).
I  also doubt that wells in the centre actually reach their target drawdown of 34 m (if I understand correctly). Given that they terminate at 34 m (slice 4), they wouldn't have any saturated thickness left limiting their efficiency.

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