Abstract: The middle stream and upstream of main rivers in western Taiwan exists serious subsidence situation. The changes in the real-time water level and scour depth during flood and typhoon seasons influence the safety of bridges significantly. Bridge management unit often use water level elevation as a bridge closure decision basis. Although simple, but this is lack of a strong technical support. Therefore, scour depth monitoring system capable of functioning in the floods impact is very important. Among existing automatic observation methods for scour, the instruments and equipments are limited to the river course silting form, high sand content, high salinity, difficult device installation and conflict between onsite laying and construction. They may not reflect local scour behavior of submerged bridge foundation in a timely manner. Therefore, this study cited the Sutong Bridge scour monitoring technology, through the sunk piezometer under riverbed and water level real-time measurement to comparison of the head difference to find the scour depth. However, the Sutong Bridge is a sandy riverbed. In this study, the bridge is a gravel riverbed. Due to the long and narrow terrain of Taiwan, the river is steep and fast. For the construction and preservation of monitoring equipment is more difficult to measure than the Sutong Bridge. This study has considered the safety monitoring of civil engineering suitable for the harsh environment. The use of a sturdy and sealed steel hoop helped the piezometer not only maintain a high degree of reliability and stability in the long-term monitoring process, but also can be operation in the harsh environment.

Key words: scour depth, piezometer, real-time scour monitoring, river-crossing bridge