Technical Studies


Application Study of Submerged Vanes on River Training (2/2)

1. Project background Fengshan River is one of the central government controlled rivers, that often causes damage during the period of typhoons. Although there already existed dykes and bank revetments to protect the lives and properties of the residents along two sides of Fengshan River, some of the dykes and bank revetments were collapsed due to floods in recent years, and should be repaired from time to time. Therefore, this project applies Iowa vane theory to Fengshan River (Iowa vane is submerged under design flood condition and also called submerged vane), which was developed by the University of Iowa, USA. The project considers the submerged vane system that can shift the main channel away from the eroding bank and reduce the impact at high flows, and the experiment of the submerged vane to decrease the pier scour depth. This project also modifies the 2D-EFA model to simulate the bed evolution around bridge pier with vanes being installed upstream of pier. 2. Data collection Some other countries use the submerged vane system, for example, steel plate piles were installed in West Fork Cedar River, and the wood plates were installed in East Nishnabotna bend, USA. In addition, installation of submerged vane by using the round wood piles was found in Japan’s river. At present, we have installed the submerged vane systems, including the locations near Jiou-gang dike, Mau-er-ding dike, and Bai-di dike in Fengshan River, the other site is downstream of Chu-Kang bridge left bank and Chung-Cheng bridge in Touchien River. The material of these submerged vane systems is made of steel plate piles. The choice of the vane material can be steel plate pile, pc tube pile, pc plate pile, wood pile, or reinforced concrete. The related information can be referred to Section 2.2.3. 3. Topographic survey and bed material sampling For the three locations (near Jiou- gang dike, Mau-er-ding dike, and Bai-di dike) with the installation submerged vanes, the bed topographic and cross-sectional information was surveyed in October, 2008. Another two locations (near Li-tou-shan-yi dike, and Ma-yuan dike) were surveyed in July and in August, 2008. This topographic data provides the information for the vane installation design. Through bed material analysis at five locations (including places of already installing and planning to install submerged vanes), grain size distributions can be obtained. Two holes were chosen at each location. The data provides information for simulating flow field, sediment discharge rate, and bed evolution. The analysis results of bed size gradation are listed in Table 1. 4. Application study of submerged vanes on changing flow direction . The reaches near Li-tou-shan-yi dike and Ma-yuan dike have main channels along the left bank. The submerged vane system are designed in this two reaches to divert the main channel toward the river center line. In addition, in order to make the submerged vane system design being easy to carry out, the design charts are prepared. 5. Experiment study on bridge scour protection by installing submerged vanes General bridge pier protection works, such as riprap, and gabion all need a great deal of manpower and budget, which are usually ineffective. Hence development of new bridge pier protection method is necessary. This project proposes the use of Iowa vane to protect bridge scour. Local scour around the pier is due to the down-flow and horseshoe-vortex, and reduction of the incoming flow intensity by installing vanes in the main purpose of the model test. In this experiment, two pieces of vanes are installed in front of the pier. The reduced scour depths are measured and the effectiveness of various layouts of the vanes are also discussed. 6. Preliminary numerical simulation on bridge scour protection by installing submerged vane. The EFA-2D is a depth-averaged model that ignores the flow field in the vertical direction. Hence, the impact of down-flow on the scouring depth just in front of the pier cannot be simulated. The source term for the bed evolution due to down-flow velocity, as proposed by Yen et al. (2001), and the estimation of the down-flow velocity proposed by Hanger (2007) are included in EFA-2D model to simulate the scour depth around the pier. Simulation results are compared against the experimental data . The simulated scour tendency is acceptable but further refinement of the numerical model is required. 7. Manual compilation and technique transfer training With submerged vane system manual compilation and implementation of technique transfer training, the staff of Water Resource Agency can understand the submerged-vane theory and its practical value. The manual provides the information and methodology for designing the submerged vane system.