降雨特性對田區排水斷面設計之影響

本文主要是分析臺灣彰雲嘉地區與日本兩地之間的降雨強度及降雨重心，來評估臺灣彰雲嘉地區農田排水標準斷面。降雨強度方面，本文利用臺灣地區常用之極端值第一類分佈法分析最大頻率降雨量，並與岩井法比較，再利用各頻率年降雨量計算降雨強度。由研究結果可知，十年頻率之臺灣彰雲嘉地區六小時平均降雨強度約與日本地區四小時平均降雨強度相同，且臺灣彰雲嘉地區四小時平均降雨強度約為日本地區者之4/3倍。而在降雨重心方面，經由兩地之實際降雨型態分析可知，臺灣彰雲嘉地區之降雨重心與日本地區者大致相同。因此臺灣彰雲嘉地區之旱田排水能力若欲採用與日本相同之十年頻率四小時降雨四小時排除之標準時，將需要較大之設計排水斷面，而使建設成本增加。因此在設計排水斷面時，其排水標準除了可參考日本之設計基準外，亦需基於作物値、作物耐淹程度、工程費等之本益比分析來加以調整，以訂出合於當地之合理排水斷面。

關鍵字

降雨重心；極端值第一類分佈法；岩井法；排水斷面

並列摘要

The main purpose of this study is to evaluate the standard cross section of the drainage system in the middle area of Taiwan by comparing rainfall-intensity and rainfall fulcrum between Taiwan and Japan. The extreme value type I distribution, which is usually applied in Taiwan, is used to analyze the maximum frequency of rainfall-intensity and compared with Iwai method. The result of frequency analysis shows that 6-hour rainfall intensity in the middle area of Taiwan is similar to 4-hour rainfall intensity in Japan and that 4-hour rainfall intensity in the middle area of Taiwan is four-thirds as that of Japan. On the aspect of the rainfall fulcrums, the result of this study shows that the rainfall fulcrums in the middle area of Taiwan and Japan are quite the same. Consequently, the standard cross section of drainage channel of upland field in the middle area of Taiwan will be bigger and the cost of it will be higher if it follows the Japan's criterion. Therefore, no only the Japan's criterion, but also the cost and benefit analysis according to crop output value, the inundation tolerance, construction cost and so on must be considered to adjust and decide what is the reasonable cross section of the drainage channel of upland field in that area.

並列關鍵字

Rainfall fulcrum ； Extreme-value type I distribution ； Iwai method ； Cross section of drainage channel

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