Journal of The School of Marine Science and Technology,Vol.1 No.2
Tidal Flow in Mangrove Forests and the Eddy Viscosity
Yoshihiro MAZDA, Satoshi OKADA and Daijiro KOBASHI
Abstract
The hydraulic resistance characteristics in tidal scale in mangrove forests, on which soil-accumulation processes
depend,were studied in the Aira-Gawa mangrove area,Iriomote Island,Japan,which is a riverine type mangrove area.The
results are as follows.
１)In the mangrove swamp near the bank of the tidal creek the tidal current velocity prevails in the direction along the
creek, while in the inside of the swamp the velocity decreases.
２)In the mangrove swamp near the bank the momentum equation along the creek is reduced to a balance between the
drag force due to mangroves and the eddy viscosity including the shear stress due to mangroves.
３)The coefficient of eddy viscosity in the swamp is estimated to be1x10 3-100x10 3cm 2/s,which is a high value unexpected
in usual coastal areas.The coefficient tends to increase with increasing value of the Reynolds number which is defined
using the effective vegetation length scale.
４) The above findings suggest that the shear stress due to mangroves plays an important role in water movement in
mangrove swamps.
The use of the quantified coefficient of eddy viscosity and the drag coefficient which has been quantified is effective
to estimate not only the flow field but also the soil accumulation in mangrove swamps.