Estimating Hydraulic Properties of Coastal Aquifers Using Wave Setup

Wave setup is associated with the momentum transfer of breaking waves to the water column, which results in an elevated mean water table at the coast over several days. Groundwater responses to setup were observed as far as 5 km inland in a coastal aquifer in central Maui, Hawaii. Results showed that setup pulses dominate over barometric pressure effects on low-frequency groundwater fluctuations during times of energetic swell events. Matching peak frequencies in setup and observed head were identified. As is the case with tides, the setup propagation through the aquifer shows exponentially decreasing amplitudes and linearly increasing time lags. Setup was used to estimate a mean aquifer diffusivity of 2.3 x 107 m2/d. The results agree with parameters estimated using aquifer tests and tides. A one-dimensional numerical model verified the results of the estimated parameters. The methodology is expected to be applicable to high-permeability coastal environments, such as volcanic islands and atolls.