Technical Studies

The research areas of this project are San-Yei-Creek and Kang-Wei-Kou- Creek drainages in Tainan City. Traditionally, regional drainage’s main purposes are preventing flood and draining accumulated water. Because of climate change, short-time rainfall often exceed the design protection standard. Therefore, regional inundation events are unavoidable. After the completion of regional drainage regulation plan, there still exist possibilities of flood in protected areas if the rainfall-runoff is over design protection standard or climate becomes abnormal. Therefore, by non-engineering methods like warning stage and warning rainfall, we can provide references of flood early warning and response for Tainan City used in San-Yei- Creek and Kang-Wei-Kou- Creek drainages. Research results of this project are below: 1.In hydrological analysis, like past planning reports, we use logarithmic Pearson type III distribution to estimate each return period of rainfall in research area. Taking 10-year rainfall in 24 hours as example, the planning value is 295 mm in San-Yei- Creek drainage in 2008, and the analysis value in this study is 401.6 mm; the planning value is 329.00 mm in Kang-Wei-Kou Creek drainage in 2007, and the analysis value is 410.0 mm. The main difference is that this study considers the influence of Typhoon Morakot in 2009, and this event makes analysis values significantly larger than planning values in past planning reports. 2.According the potential flooding area and bottlenecks of drainage in these two basins, we establish the warning stage levels. We finish the establishment of warning stage levels in five places in San-Yei- Creek drainage, and three places in Kang-Wei-Kou-Creek drainage. The analysis results are listed in abstract Table 1. 3.After the establishment of warning stage levels, by historical water stage, rainfall information, hyetograph analysis, time of concentration, and the characteristics of the water level rise in Chi-Tan Bridge, Yang-Tzu-Hsia Bridge, Wu-Kung Bridge, and Kang-Wei-Kou-Chi Tai 86 Bridge, we can get statistical regression relationship of water stage and rainfall. Through the rainfall situation, we can predict the water stage level in each gauging station of regional drainage in the next 1 to 3 or 4 hours, and it is available for disaster prevention and early warning. 4.Warning rainfall of regional drainage is established for the districts and villages along the drainage. The approach is based on models of channel hydraulics, storm sewer, and inundation simulation. With the setting of rainfall, hyetograph, and the water stage of regional drainage gauging station, we proceed the simulation, analysis and statistics. We establish 18 villages’ warning rainfall along San-Yei-Creek drainage in Yong-Kang District, Rende District, and East District. We also establish 5 villages’ warning rainfall along Kang-Wei-Kou- Creek drainage in Rende District. The results are listed in abstract Table 2. 5.Develop a flood early warning system for San-Yei-Creek and Kang-Wei-Kou-Creek drainages in Tainan City. When warning rainfall situation occurs, it will send warning information to specific personnel automatically for response instantly. The system can dynamically grab the latest information, and translate into warning indicator value. Besides, when accumlated rainfall coupled with forecast is above warning indicator value, it will send e-mail to specific personnel automatically and also remind related personnel of attention. 6.After the establishment of warning rainfall, we suggest that the city government should test and review the whole system during the flood season in 2013. Upon completion of the review, the city government must rerun the system for satisfying the actual situation. There are some other regional drainages in Tainan City, and research method and system in this study can be applied to these basins for disaster prevention in each village.