Sand-box experiments of seepage into an auger hole in a confined aquifer

Whereas the boundary conditions of seepage into an auger hole in an unconfined aquifer are well known, for confined aquifers only some suggestions exist. KASTANEK and LOISKANDL (1992) have proposed to treat this problem like seepage in an unconfined aquifer. Hence the boundary between the aquifer and the impermeable top layer had been assumed to be an equipotential line. After a comprehensive consideration the assumed simplification seemed questionable. Experiments with a sand box model to determine the boundary conditions confirmed our doubts. The results of the experiments do not match with the calculated results with the previous assumptions. According to the laboratory experiments a streamline is more plausible as boundary condition at the top of the aquifer. For verification of the sand box experiments a finite element computer simulation for seepage was performed. A comparison between measured and simulated Values of the hydraulic head at the top of the aquifer confirms that the boundary condition at the top of the aquifer is a streamline.