MEASUREMENT OF TRANSPORT-DIFFUSION PROCESS OF UNDERGROUND WATER AT THE SWASH ZONE USING NaCl METERS

Local submarine groudwater flow directing from the shore to the ocean for exfiltrating near the shoreline is known to be formed under sandy beach due to surface waves. Although the grounwater flow is one of the important factors to bring various substances (e.g. nutrients and oxygen) into the coastal water as an outlet phase of the transportation process from the land to the ocean, only a little is known because of the limitation of the measurement techniques for this kind of flow. We propose a technique to estimate transport and diffusion velocities by fitting a solution of the one-dimensional transport-diffusion equation to the experimental data obtained by measuring the evolution of the NaCl concentration under the sandy bed. The relationship between the wave conditions and transport-diffusion velocities of NaCl solution in the seepage flow is characterized through the present experiments.