The ebb flow dominance in tidal creeks in riverine forest type mangrove area is hydrodynamically analysed by using a horizontal two-dimensional numerical model. The tidal flow in the creek is composed of two terms. i.e., U_H which is the same as a flow in a tidal river without flood plain and U_A which is caused by the flooding over a wide swamp with densely vegetated mangrove roots and bioturbation. U_H is tidally symmetric, while U_A dominates at flood tide because of nonlinear effect due to the drag force in the swamp. However, the total flow (U_H+U_A) dominates at ebb tide, since the phase relationship of U_A to U_H at ebb tide is extremely different from that at flood tide. Further, when the drag force in the swamp is too large, the ebb flow dominance tends to be restricted. These findings suggest that in natural mangrove systems which have been preserved regularly, the feed-back processes among the tidal flow, the siltation and the mangrove vegetation density are functioning to maintain the ecosystem.

抄録全体を表示

The settling velocity of suspended particles in the bottom layers of Osaka Bay and Etauchi Bay was studied as a function of the particle diameter by using the developed in situ settling apparatus with a camera. In Osaka Bay, the settling velocity in winter varied in the range of 0.02 to 1.5 cm sec^-1, depending upon the particle diameter, but not upon the area in the bay. In Etauchi Bay, the settling velocity in autumn and winter lay in the range of 0.005 to 0.3 cm sec^-1, which was larger than that in early summer by a factor of about 4. The settling velocity in winter was smaller than that in Osaka Bay by a factor of about 10, though temperature and salinity at both bays were almost the same. The difference in the settling velocity may be explained mainly in terms of the change in an apparent density of the particles, depending upon the organic matter contents of the particles and the turbulence of the sea water.

抄録全体を表示