Groundwater response to tidal fluctuation and rainfall in a coastal aquifer

- An analytical approach for studying tide-wave fluctuation with rainfall in a coastal aquifer is proposed.
- The effect of the bottom slope of the aquifer on the groundwater fluctuation is substantial.
- The groundwater level undulates severely and goes farther in downward bottom cases.
- The fluctuation decays rapidly by the reflection of the bottom in upward bottom cases.
- The spatial fluctuation is unaffected by the beach slopes at certain time.

SummaryThis paper presents an analytical solution generated by linearizing the one-dimensional non-linear Boussinesq equation to characterize the variation of groundwater level induced by tidal waves and rainfall in a coastal unconfined sloping aquifer. The area of the coastal aquifer is divided into 2 zones - the coastal zone of rainfall and the inland zone of non-rainfall. The derivation of the solution is based on the Dupuit-Forchheimer assumptions of a wide range of problems in unconfined groundwater flow and the analytical solutions of coastal and inland water tables of both zones are obtained. The results indicate that the effects of the bottom slope of the aquifer and the beach slope on the groundwater fluctuation are substantial in the unconfined aquifer. Large rainfall intensity with tidal waves will enhance the fluctuation significantly, but less effect on the fluctuation is found for the cases of steeper sloping bottom under the same rainfall condition.