This approach yielded a good match between observed and simulated responses for the Cape Code data set. Although Neuman argued that this term could be explained by instantaneous drainage, Moench went further and advocated superposition of several exponential kernels with different constants. This kernel is a useful concept in many practical applications. Interestingly, Horton used exponential term for description of infiltration. Later, Youngs and Gardner showed that certain assumptions about aquifer properties could lead to the exponential drainage response. Boulton made a formal effort to account for noninstantaneous drainage from above the falling water table and assumed the exponential functional form of the kernel.
#Drawdown definition water free
The decline of water table is assumed to be much smaller than d, thus a linearized free surface boundary condition will be used for the water table. An aquifer has an initial saturated thickness d and extends laterally to infinity. The semi-infinite aquitard extends downward from z = 0 to −∞. The origin of the Cartesian x, y, and z coordinates is at the aquifer/aquitard interface. Consider a point sink and a partially penetrating well in an anisotropic unconfined aquifer above an infinitely thick aquitard ( Figure 1). The purpose of this note is to investigate the aquitard effect on the unconfined aquifer-aquitard system. However, if the aquitard diffusivity is comparable to the diffusivity of the aquifer, the cross flow at the aquifer-aquitard interface may affect the head in the aquifer. Contrast between values of hydraulic conductivity implies a minor flux across the aquifer-aquitard interface. They postulated that the aquitard did not play an important role in the aquifer drawdown, but the aquitard drawdown is fully defined by flow in the aquifer. Neuman and Witherspoon studied flow in an aquitard of finite or infinite thickness adjacent to a leaky confined aquifer. One factor that was not investigated in all cited studies previously is effect of water release from an underlying aquitard. After multiple interpretations of two detailed data sets (Borden and Cape Cod sites) as benchmark cases, it is apparent that physical processes are too complex to be represented by a simple physical model. Kollet and Zlotnik focused on effects of heterogeneity and return flow. Grimestad explored the unaccounted sources of the aquifer recharge. Chen and Ayers compared existing models for field data interpretations. investigated effects of the unsaturated zone on the interpretation of unconfined aquifer pumping tests. Interpretation of pumping tests in unconfined aquifers remains a matter of ongoing studies due to the complexity of the multiparameteric problem.
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