分散を考慮した海岸地下水の挙動に関する研究 ＩＩＩ 那賀川河口および喜木川河口における分散長

Abstract

A three-dimensional steady state hydrodynamic dispersion model with the velocity-dependent dispersion coefficient was used to simulate seawater encroachment in the confined aquifers in the estuaries of the Naka River, Tokushima Prefecture, and the Kiki River, Ehime Prefecture. The main results are as follows: 1) The longitudinal and lateral dispersivities are 1, 000 to 1, 250 m and 100 to 125 m in the estuary of the Naka River, respectively. In the estuary of the Kiki River, the corresponding values are 200 m and 200 to 20 m, respectively. 2) Examining the local distribution of the dispersion coefficient values computed from the dispersivity and velocity fields of groundwater, the same value as estimated in the analysis with the constant dispersion coefficient (KAKINUMA et al., 1985) is located in the middle layer of the aquifer. 3) In the estuary of the Naka River, the piezometric surface predicted using the dispersion model with the velocity-dependent dispersion coefficient in almost the same as the one predicted with the dispersion model with the constant dispersion coefficient. They are 5 to 10% lower than the one predicted with the interface model (KAKINUMA et al., 1984), but about 1.3 times the observed one.