A study on debris flow capture effect of open-type steel sabo dam in Taiwan

Hiroshi KOKURYO, Su-Chin CHEN, Shuan-Pei AN and Chiang WANG

In Taiwan, there are over 1,600 debris flow prone torrents, and various sediment]related disaster prevention facilities have been installed on these torrents in the mountain areas. However, most of them are closed]type concrete Sabo dams and open]type steel Sabo dams are rare. One of the reasons is that their effect or effectiveness has not been duly recognized by Taiwan's authorities. Therefore, we installed a full]scale test piece (Open]type steel Sabo dam) on the Landow torrent in Huisun forest, National Chung Hsing University, in order to verify its debris flow capture effect. On July 13, 2013, the seventh typhoon of the season (Typhoon Soulik) struck northern Taiwan and made substantial debris flow occur in this torrent. The installed open]type steel Sabo dam also got buried under the enormous amount of sediment and gravel following the debris flow, but significantly reduced the impact of debris flow and protected the downstream bridge. This paper describes the consideration on debris flow capture effect of open]type steel Sabo dam, by analyzing the debris flow capturing and depositing process and capture form based on the monitoring camera data and field survey. From the monitoring camera data, we recognized that this dam got buried because the sediment trap capacity exceeded due to the continuous sediment flowing down even after the capturing of debris flow and subsequent flow, leading to subsequent sediment and gravel being deposited to downstream by flowing over the dam, but not because boulders and sediments passed between the members. In addition, it was also confirmed by the field survey that the opening of open]type steel Sabo dam got closed up by arched stacking efficiency between boulders to capture debris flow.