Hydraulic Parameters of Coastal Aquifer Systems by Direct Methods and an Extended Tide-Aquifer Interaction Technique

Adequate and reliable parameters are key to the sustainable management of vital groundwater resources. Present study focuses on the evaluation of direct methods (tidal efficiency and time lag methods) and an extended tide-aquifer interaction technique for determining the hydraulic parameter of coastal unconfined and confined aquifer systems. The hydraulic diffusivities of unconfined and confined aquifer systems were estimated using the tidal efficiency and time lag methods as well as they were optimized using the tide-aquifer interaction model and the Levenberg-Marquardt optimization technique. The hydraulic diffusivities were optimized by the Levenberg-Marquardt technique following two approaches: lumped tidal component approach and multi-tidal component approach. The effect of spring and neap tidal data on parameter estimates was also analyzed. The tide-aquifer interaction data for two unconfined sites and three confined sites were used in this study. For all the five sites under study, the aquifer hydraulic diffusivities based on the time lag method were found to be much larger (2 to 14 fold for the unconfined sites and 5 to 8 fold for the confined sites) than those based on the tidal efficiency method. The analysis of the optimization results indicated that the hydraulic diffusivities following “multi-tidal component approach” are more reliable and accurate for both unconfined and confined aquifers than those obtained following “lumped tidal component approach”. Consequently, the use of “multi-tidal component approach” is strongly recommended for the determination of aquifer parameters by the tide-aquifer interaction technique. Furthermore, the tide-interaction data corresponding to spring and neap tidal events were found to significantly affect the aquifer diffusivities yielded by the tide-aquifer interaction technique. It is concluded that a judicious use of tide-aquifer interaction technique is indispensable for the reliable estimates of hydraulic parameters of coastal aquifer systems.