Ho-Lung River, located in northern Taiwan, is one of the central authority’s rivers, and most of the flood prevention structures were built 50 years ago. Since 1983, the Review on the River Improvement Planning of Ho-Lung River had been done, which aiming at issues of hydrologic and geomorphologic characteristics and safety of river works. The latest review was finished seven years ago. Due to the continuing changes of the river morphology, the issues, including status of river migrations, erosion and deposition type of reaches, and flood stages on the safety of river works, need to be reviewed again.
For clarifying the crucial topics of the influences of the river migration on flood levels and flood prevention structures, this project collected historical flood damage sites and associated data, analyzed migration of main channel and river stability, and found three reaches prone to the flood and sediment hazard. These three reaches are the confluence of the tributary Nan-Hu River, the in-stream island upstream of Gong-Jing Bridge, and the reach between Ke-Zue Bridge and Guei-Shan Bridge. The one dimensional mobile-bed model (CCHE1D) was applied to simulate the longitudinal bed changes under floods with different return periods. Based on the results of the CCHE1D, the local flow fields and the migrations of the three study reaches can be simulated using CCHE2D.
According to historical damage records and numerical simulation results, the causes of the damages for different reaches can be identified. Several feasible countermeasures as well as the existing layouts for the three reaches were selected as the cases for simulation and comparison. Finally, the improving strategies and the countermeasures for the three damage-prone reaches are proposed.