Technical Report No. 39
MODEL STUDIES OF TIDAL EFFECTS ON GROUND WATER HYDRAULICS
John A. Williams, Ronald N. Wada, Ru-yih Wang
May 1970
ABSTRACT
This report presents the results of a model study on the propagation of periodic fluctuations in the piezometric head through a saturated porous media. Three different models were employed: a hydraulic model, a mathematical model, and an electrical analog model. The hydraulic model consisted of one or more layers of polyurethene foam placed in a lucite tank. The foam was tested in a confined and unconfined condition using both a no-flow and a constant-head boundary condition at the internal boundary. The mathematical and electric analog models duplicated the conditions in the hydraulic model. The results of the study indicate that diffusion theory can describe the propagation of such disturbances provided that the boundary conditions are satisfied and that the correct diffusion coefficient is employed. The calculation of the correct diffusion coefficient requires that an appropriate storage coefficient and an apparent porosity be used for the confined and unconfined models, respectively. For the unconfined case, the ratio of the apparent porosity to the true porosity is of the same order of magnitude for both the polyurethene foam and a Sacramento River sand.