EXAMINATION OF BOUNDARY MIXING COEFFICIENTS BEFORE AND AFTER DEFORESTATION IN THE OTOTSU RIVER BASED ON NUMERICAL SIMULATIONS

The boundary mixing coefficients, which is used for estimation of boundary shear stress due to vegetation in quasi 2D simulations, in the Ototsu river is investigated numerically. Firstly, the relation between the boundary mixing coefficients f and vegetation density is examined through comparison of numerical resuts between quasi 2D and 2D simulations. From the relation, a value of f is found to be 0.08 in the Ototsu river. And it is shown that the quasi 2D model can reproduce the observation data of the water level in the three different flooding when the f =0.08 is used. The effects of deforestation to the boundary mixing coefficient f is also examined. It shows that deforestation is not effected significantly on the value of f in the Ototsu river.