In Cho-Shui River management projects, definition of stream width is a key topic. The appropriate river width can ensure the safety of embankments along Cho-Shui River. According to the criterion reported by Water Resources Agency (WRA), designing flood, usually equals to 100-yr flood in study area, is a primary parameter for river width and a positive correlation can be found in many studies. In Cho-Shui River, there are several empirical equations that are suggested to estimate the river width, e.g., Taiwan formula, Kyoto formula, Japan Ministry of Land, Infrastructure, Transport and Tourism (JMLIT) formula. However, these equations only estimate how river width adjusts under flow geometry condition. In nature river system, the river width changes not only associated with flow geometry condition, but also channel geometry condition. To understand the required river width for obtaining the equilibrium state under flow/channel geometry condition in Cho-Shui River, this project would analyze casues of levee failure by collecting river cross-sections and aerial maps in different years, simulate flow field and bed change by the CCHE2D model, and propose improving strategies of determining river width for Cho-Shui River.
The result of this study is that the empirical equation proposed herein is used for computing the design river width, based on design flood, bed slope, and size of bed material. Hopefully this empirical formula can be applied to other rivers, and the coefficients in the formula thus would be revised if new data are available.