Flowing wells: history and role as a root of groundwater hydrology

The spewing of groundwater in flowing wells is a phenomenon of interest to the public, but little attention has been paid to the role of flowing wells on the science of groundwater. This study reviews that answering to problems related to flowing wells since the early 19th century led to the birth of many fundamental concepts and principles of groundwater hydrology. The concepts stemmed from flowing wells in confined aquifers include permeability and compressibility, while the principles include Darcy's law, role of aquitards on flowing well conditions and the piston flow pattern, steady-state well hydraulics in confined aquifers, and transient well hydraulics towards constant-head wells in confined or leaky aquifers, all of which are applicable even if flowing well conditions have disappeared. Due to the widespread occurrence of aquitards, there is a long-lasting misconception that flowing wells must be geologically-controlled. The occurrence of flowing wells in topographic lows of unconfined aquifers was anticipated in 1940 and later verified in the 1960s, accompanying with the birth of the theory of topographically-driven groundwater flow, which has been considered as a paradigm shift in groundwater hydrology. Based on studies following this new paradigm, several preconditions of flowing wells given in the 19th century have been found to be not necessary at all. This historical perspective of the causes of flowing well conditions and the role of flowing wells on the science of groundwater could lead to a deeper understanding of the evolution of groundwater hydrology.

A generalized model for pumping well hydraulics in confined aquifers

A generalized model for well hydraulics in confined aquifers is presented. The lattice Boltzmann method (LBM)-based altered-velocity model is used to simulate well hydraulics in homogeneous and heterogeneous confined aquifers for different pumping conditions. LBM is applied to simulate well hydraulics in two different configurations of heterogeneous aquifer, where (1) a circular disk of material or (2) an infinite linear strip of material is embedded in a matrix of differing hydraulic properties. The effect of hydrogeologic boundaries on drawdown curve in confined aquifers is simulated using LBM. The LBM is further applied to simulate drawdown during harmonic pumping well test. The LBM data in lattice units are scaled to physical units using non-dimensional discharge rate and diffusion length. The results from LBM were found to be sensitive to the relaxation parameter and the RMS error for drawdown was found to be less than 1% for later time. This work will verify the potential of LBM to simulate well hydraulics in homogeneous and heterogeneous confined aquifers for constant, step, and harmonic pumping.