Technical Studies

The morphology of Touchien and Fengshan Rivers’ estuary changed rapidly in the past few years. In 2005, the Water Resources Planning Institute(WRPI) had evaluated the hydraulic characteristics and the flood-prevention capability on Touchien and Fengshan Rivers’ estuary. In 2007, WRPI proposed six engineering plans to carry out the countermeasures which was based on the short-term and long-term simulations using the CCHE2D-Coast model. In 2008, WRPI decided that Case 6 was the best plan, in which both the land utilization and flood-prevention capability of Touchien River estuary could be considered in the meantime. In 2009, the Second River Bureau carried out Case 6 and proposed the engineering detail design project.

Due to the complicated nature in its flow and sediment pattern, the engineering layout of Touchien and Fengshan Rivers’ estuary is needed to do some laboratory and numerical study to insure the optimum layout proposed by WRPI. In this study, CCHE2D model was used to simulate the estuarine morphological changes under design flow for the present layout and nine proposed diversion dikes with different angles and lengths. The upstream boundary conditions (discharge and sediment transport) and the downstream boundary conditions (astronomical tide), together with the estuarine topography are necessary for predicting the estuarine morphological changes.

According to the simulation results, the best case among nine cases can be obtained (i.e., Case 3). In the present layout with Q₁₀₀ flood occurred, the discharges of left and right channels divided by the Jiugang Island were 6,293cms and 2,101cms, respectively. In the layout of Case3, the associated discharges for the left and right channels could be 4,428cms and 3,741cms respectively. The flood-prevention capability was increased due to the engineering layout was put into practice, and the water stage around the Jiugang Island had a decreasing trend.

This project will be finalized with the integration of physical and numerical models in 2011. At the present study, more information obtained from the physical experiment is needed to improve the numerical model’s reliability.