Abstract

Hydraulic scours is one of the major reasons causing bridge failures. Rivers in Taiwan are usually steep with rapid flows. Thus the exposure of bridge foundations is dangerous due to the impact of debris, especially during the typhoon seasons. Both total scour and general scour data near Ming-Chu Bridge of Cho-Shui River, the longest river in Taiwan, during Typhoons Dujuan and Mindulle were successfully collected using the “numbered–brick columns” in 2003 and 2004. Separating the local scour and general scour before comparing the data with existing local scour formulas is helpful to increase our understanding of different physical processes.

It was found that most of these equations overestimated the local scour depths. The peak duration of the flood, the ratio of pier diameter to bed sediment size, and the flow conditions (clear-water/ live-bed scour) are important factors influencing the local scour predictions. The effect of bed armoring is also significant for the gravel-bed river with a wide bed material gradation. The “numbered scour-bricks” were found to be suitable for measuring both the general and the local scours in the steep gravel river reach. The effect of peak flow duration on the estimation of local scour depth was also discussed.

Keywords: Bridge scour, numbered–brick column, steep river