Numerical model is used to simulate the flow characteristics of Taoyuan Irrigation Channel for finding out the bottleneck of flow discharges capacity. The EXTRAN of SWMM (Storm Water Management Model) is used for simulated flow of 18,363 channel from Taoyuan Irrigation Channel inlet to outlet of bridge No. 4. The results appeared that the bridge No. 1、No. 2 and No. 3 are bottlenecks of flow discharges capacity. The improvement effect is equivalent between channel roughness reducing plans and sections dredging near water bridge plans. Limit the water surface below channel bank elevation, the increasing flow discharges capacity are 1.1, 1.5 and 2.4m3/s due to reducing channel roughness to 0.014、0.013 and 0.012. The increasing flow discharges capacity are 0.6, 1.9 and2.0m3/s due to sections three dredging near water bridge plans.
