Numerical Simulation Of Tree Planting And Slope Protection Under The Conditions Of River Water Flow

The roots of the plants grown in the flood plain have following functions like protecting bank soil from erosion, preventing the bank from collapse due to high flood, storm surge, etc. The plants have also changed the flow conditions, e.g. the resistance to the flow, the momentum exchange pattern between the main channel and the flood plain, the turbulent structure of the flow and in turn the apparent shear stress. Therefore, in order to use this ecosystem to protect the bank and improve the bio-environment of the river and maintain the capacity of flood control, the advantage and disadvantage of the measure have to be analyzed thoroughly. This is an important issue in engineering practice.Beginning from the N-S equations, the planar two dimensional shallow water equations were derived. The finite element method was employed in developing numerical model for simulating the flow over the channel with the compound cross section. The Garlerkin residual-weighted scheme was used in discretizing spatial parts of the set of shallow water equations. The time derivatives in those equations were discretized by weighted time difference scheme. The resulted set of non-linear algebraic equations was solved by Newton-Raphson iteration method.This model was applied to the typical channel in the Peal river delta area. The results from the computations were first compared with the data from physical experiments. The computational results were well agreed with the measured data. The computational results were also analyzed from various aspects of the effect of the plants grown in the flood plain on the flow. For example, the effects on the flow pattern, the cross-sectional distribution of the velocity, the distribution of the discharges between the main channel and the flood plain, the capacity of conveyance flood and the water level in the river, etc, were analyzed thoroughly. Two method in simulating the effect of the plants were used in this thesis. One was so-called equivalent roughness method, Another was simulating the each stem of the tree deliberately. The results show that the flow pattern from the later simulation method is more resemble than that from equivalent roughness method.This research proposed that the model used in this thesis is a good tool in investigating the effect of the trees planted in the flood plain on the flow.