It is theoretically possible. I think once the surface drops below the upper layer, the well would act as a free surface well with the same depression cone. for further detail consult with Hydrodynamics by Valentine or any other groundwater mechanics text.

Thanks Mr.Sagravani.

As we know, the quantum of water yielded by a confined aquifer is a function of its storativity. If the aquifer becomes unconfined when the potentiometric surface is lowered below the confining layer, the yield should theoretically become a function of the specific yield, which normally will be several orders higher than the storage coefficient. Does it mean that we will be able to extract a much higher quantum of water from the aquifer than before if we lower the p.surface sufficiently ????

Dear Mr. Pullare

I think the energy principle behind the phenomena should not be overshadowed by the equations. The fact is lowering the water level increases the hydraulic gradient, thus the velocity of water entering into the well while it decreases the area of the entrance. for the same pump with the same power, taking the water out of the well from lower elevation is much more than the case of initial condition. That is why we have to be careful in choosing the right pump for aquifer, safe yield, ..

Referring to your comment on the specific yield and the storage coefficient, I would suggest you to have look over EM 1110-2-1421, pages 2-10 and 2-11. specific yield is much smaller (0.0001) than storage coef. (~0.005).

Moench-Prickett (1972) worked out a solution for a pumping test in a confined/unconfined aquifer in which the pumping pulls the potentiometric surface below the overlying confining layer. This is not uncommon, particularly if the confined head is not far above the bottom of the confining unit.

Moench, A.F. and T.A. Prickett, 1972. Radial flow in an infinite aquifer undergoing conversion from artesian to water-table conditions, Water Resources Research, vol. 8, no. 2, pp. 494-499.

Thank you very much

Nandkumar Sir, as you have taught us earlier, if the potentiometric surface of a confined aquifer geos below the bottom of the confining layer, the aquifer no longer remains a confined one but turns and behaves as an unconfined aquifer. We have some experts reporting these kind of phenomena from fast developing urban hotspots, specially from eastern India. In that case I suppose, the aquifer will start behaving like that of a phreatic aquifer and concerned parameters will apply therein. So theoritically it should increase the yield

Thanks, Anirvan.

Actually, this issue has been causing a lot of discussion among us in the recent past, especially in the context of assessment of Total ground water resources. That's why I thought to seek the opinion of researchers world-wide.If u have any literature on such phenomena, pl. let me know.

Sir,

I have a different problem. For a single aquifer system this theory may be applied. But for abstraction structures tapping and extracting water from multiple aquifer system - as we do in CGWB, how this is applicable and particularly so when we have different quality of ground water in those aquifers. There may also be one or two leaky confining strata in between.