Numerical Investigation on the Effects of the Artificial Channel on Three-dimensional Flow Structures in he Meandering Reach of the Sixaola River

The Sixaola-Guabito International Bridge is located about 10km upstream from the Sixaola River river month between Panama and Costa Rica. However, the meandering reach upstream from the bridge is considered danger of structure failures due to bed scouring and bank erosion. The artificial channel was constructed in the right side of the meandering reach (Panama side). It is expected that the artificial channel reduces the discharge in the meandering reach and makes the meandering progress slow. On the other hand, another erosion risk or backfilling of the artificial channel can be happened at distributary or junction of the meandering and the artificial channel. Thus, it is important to grasp the flow structures at the meandering reach with the artificial channel. However, it is difficult to understand watershed characteristics such as flood magnitude or frequency because of insufficient hydrologic data in the Sixaola basin. From the above reasons, this study aims to investigate the watershed characteristics in the Sixaola basin with run-off analysis and the effects of the artificial channel on the meandering reach by means of a hydraulic model.

We apply the RRI model as a runoff analysis model to the basin to obtain hydrographs at the upstream-end of the meandering reach for the boundary condition. Because of insufficient ground rainfall data, the satellite rainfall data (GSMaP) modified with ground rainfall data measured at two points was inputted to RRI model. The target was the flood in November 2008. By using discharge hydrograph estimated by RRI model as an upstream boundary condition, we investigated flow structures at meandering reach with the General Bottom Velocity Computation method, which is a depth integrated model with the ability to calculate non-hydrostatic three dimensional velocity distributions. The numerical simulation with and without the artificial channel are compared. We found that the artificial channel makes the bottom velocity slow at the left side in the main channel just upstream of the junction. It also reduces the sediment deposition at the left side and danger of erosion at the right side at the junction section. On the other hand, the river still has the risk of the erosion in the reach downstream from the meandering reach.