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Head Elevation in MODFLOW Model


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I have a two layer transient model. The model is for an unconfined aquifer and it is nearly flat or horizontal.

The model is 1000 m thick and each layer is 500m thick; the top of Layer 1 is 1000 m and the bottom elevation of Layer 1 is 500 m and the bottom elevation of Layer 2 is 0 m.

Layer 2 is completely saturated. Layer 1 has a water table at 750 m. Layers 1 and 2 differ in material; Layer 1 is sands and gravels, Layer 2 is primarily gravels.

My questions are thus:

(1) If I have a tightly cased well that is screened only in Layer 2, should the water surface in the well be at 750 m above the bottom of Layer 2 (or obversely, should the water surface in the well be 250 m below the top layer elevation)? This seems reasonable but I want to be sure that I haven't missed something in ground water hydraulics.

(2) Based on the well head information above, should I set the starting head in Layer 1 as 750 m and the starting head in Layer 2 as 500 m (the top elevation of Layer 2)? Or should the starting head be 750 m for both Layers 1 and 2? It seems reasonable that hydraulic head of 750 m should be set the same for both Layers 1 and 2 in this instance, but again, I did not want to miss something unique to MODFLOW 2000.

Thank you in advance for your time and attention.

Kevin J Spelts

Edited by KevinSpelts
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