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Analysis of Steady-State Flow To Multiscreened Wells Under Natural Vertical Flow Conditions |
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| Authors: | F J Samper M R Llamas G Galarza J Cruces de Abia |
| Institution: | Departamento de Ingeniería del Terreno, E.T.S. de Ingenieros de Caminos, Canales y Puertos Universidad Politécnica de Catalu?a, C/Gran Capitán s/n, 08034-Barcelona, Spain, ES Departamento de Geodinámica, Facultad de Ciencias Geológicas, Universidad Complutense de Madrid, Ciudad Universitaria s/n, 28040-Madrid, Spain, ES Departamento de Física Aplicada, E.T.S. de Ingenieros de Caminos, Canales y Puertos Universidad de Santander, Avda. de los Castros, s/n, 39005-Santander, Spain, ES |
| Abstract: | Water levels measured at multiscreened wells in unconfined aquifers may not coincide, in general, with the elevation of the
water table. The presence of vertical gradients (as often is the case in recharge areas) or the existence of confining layers
may cause the water levels to differ from local hydraulic heads in the aquifer. In these cases, a misinterpretation of water
levels may lead to the erroneous conclusion that observed drawdowns are provoked by overpumping. In this paper, we analyze
the effect that a natural vertical gradient has on water levels in wells screened over their entire saturated thickness. As
one would expect, it is observed that, even without pumping, the water level in the wells lies below the water table. Type
curves relating the steady-state drawdown to the vertical gradient and to the hydraulic conductivity anisotropy are presented.
These curves were obtained using a groundwater flow numerical model (FREESURF: Neuman and Witherspoon, 1970). The theoretical
results are checked with field data from deep wells in the detrital Madrid aquifer. In this particular aquifer, it is observed
that the effect of vertical gradients is important both in terms of drawdowns and flow rates.
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