| Summary: | 碩士 === 國立臺北科技大學 === 環境規劃與管理研究所 === 90 === First flush has been recognized as having the most critical impact on water quality. Storm runoff not only carries pollutants into the receiving waterbody, but also raises stream flow, resulting in a dilution effect on pollutant concentration. In theory, a stream low flow combined with a storm event might result in a strong impact on water quality. Therefore, which design hyetograph makes the critical condition for the water quality needs to be studied and confirmed further.
This study collected relevant literature and applied the HSPF model to simulate water quality：SS、TP、NH3-N by applying various design hyetographs to the Diyu Creek in the Feitsui Reservoir watershed. The purpose of this study was to investigate the first flush process which causing water quality variation and to define the critical storm of water quality impact.
The results showed that the impact of a small storm was far worse than a big storm. For a small watershed, the dilution effect was shown to be quite important for rainfall during low flow periods. The rainfall condition of 2 hours duration and 1.1 years recurrence interval would bring the worst impact, and the rainfall condition of 4 hours duration and 1.1 years recurrence interval would bring a significant impact. Due to it’s high occurrence frequency, condition of 1.1 years recurrence interval should be of concerned for controlling nonpoint source pollution.
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