A Method for Evaluating Coastal Underground Barrier Wall Using Groundwater Tidal Response.

Tidal response methods are usually used to estimate the hydraulic parameters of coastal aquifers. In this study an analytical model for aquifer tidal response was used. An existing analytical solution for tidal response of groundwater levels was extended to evaluate a subsurface barrier wall to prevent saltwater penetration in a coastal aquifer. A field feasibility study was conducted at the Komesu Dam, Japan. Groundwater levels were observed at pairs of sites on the seaward and reservoir sides of the wall. Groundwater-level time series data collected from a reservoir-side site near a horizontal hollow pipe penetrating the wall contained a visible sinusoidal tidal component, whereas data from another reservoir-side site did not. Analysis of these observations on the groundwater tidal response derived hydraulic parameters of the barrier wall between the paired observation sites. Although the parameters derived by the used simple formulas seem only approximate or apparent, the difference of the results for the two pairs indicated that the extended tidal response method can be useful for evaluation of the barrier function of the wall.