屏東老埤地區雨滴粒徑與沖蝕動能之研究

Drop Size Characteristics and Erosive Kinetic Energy of Natural Rainstorms in Pingtung Laopi Area

10.29417/JCSWC.199606_27(2).0007

吳嘉俊(Chia-Chun Wu)；王阿碧(A-Bih Wang)

雨滴粒徑分佈 ； 降雨特性 ； 降雨沖蝕指數 ； 通用土壤流失公式 ； Drop Size Distribution ； Rainfall Characteristics ； Rainfall Erosivity Index ； USLE

中華水土保持學報

27卷2期（1996 / 06 / 01）

151 - 165

繁體中文

臺灣地區年等降雨沖蝕指數分佈圖於1981年由黃俊德君繪成，該圖乃是沿用美國Wischmeier與Smith（1959）的動能方程式E = 916 + 331 log_(10) I推導而成。但由於降雨沖蝕指數受到地區性自然降雨型態及雨滴粒徑的影響，因此本硏究旨在瞭解屏東老埤地區自然降雨之特性及其雨滴粒徑的分佈，以染色濾紙法進行自然降雨的承接，並配合自行研發成功的自動粒徑分析與動能計算軟體，作長時間的收集與分析，以求得該地區之降雨動能公式。屏東老埤地區自然降雨雨滴粒徑的收集工作及降雨動能的研究始於1992年7月下旬。若以連續三年之瞬間降雨強度對雨滴中值粒徑廻歸分析，可得一迴歸方程式如下：方程式略其中D_(50)爲雨滴中値粒徑（mm），I爲降雨強度（mm / h）。同時，根據連續三年實測資料分析的結果，屏東老埤地區的降雨動能公式爲：方程式略其中E爲每公頃單位降雨深度之降雨動能（MJ / ha-man），I爲降雨強度（mm / h）。本研究亦將研究所得之降雨動能公式（Wu and Wang）與Wischmeier and Smith、McGregor and Mutchler及Hudson等人的降雨動能公式相比較。比較中發現無論降雨型態爲何，沿用Hudson的降雨動能公式來估算屏東老埤地區的降雨總動能則有一致的低估現象。一般而言，Wischmeier與Smith及McGregor與Mutchler的降雨動能公式均能滿意地估算本地區之降雨總動能；其年平均差異百分比分別爲-2.23及-0.56％。當然，單場降雨之降雨總動能或全年降雨總動能估算的良窳，得視降雨歷程或全年所有降雨場次中發生大、小強度降雨所佔的比例而決定。至於Wischmeier與Smith或McGregor與Mutchler的降雨動能公式是否可以用於估算降雨強度較偏中、高強度的降雨之降雨動能或臺灣其他地區的降雨動能，仍有待吾人繼續研究探討。

Taiwan's isoerodent map was developed by C. T. Huang in 1981 based upon Wischmeier and Smith's rainfall kinetic energy equation. However, the rainfall kinetic energy equation as well as the rainfall erosivity index is highly dependent on local rainfall characteristics, rainfall patterns, and drop size distribution. Therefore, the objectives of the study are to understand raindrop size distributions in Pingtung Laopi area and to understand how they are related to different rainfall characteristics. The stain method was used for the drop size collection, and self-developed computer softwares were used for dropsize analysis and kinetic energy calculation. The drop size collection was initiated in July, 1992. A regression equation relating rainfall median volume drop diameter and rainfall intensity was obtained by using the data collected since then. The regression equation can be written as: The equation is abbreviated in which, D_(50) is the median volume drop diameter (mm) and I is the rainfall intensity (mm/h). A rainfall kinetic energy equation representing the area of Laopi was also obtained based on field collections since 1992. The kinetic energy equation is: The equation is abbreviated Rainfall kinetic energy equation (Wu and Wang) developed in this study and that by Wischmeier and Smith, Hudson, and McGregor and Mutchler were compared to evaluate the applicability in kinetic energy estimation. Regardless the rainfall patterns occurred in Laopi in 1994, Hudson's kinetic energy equation consistantly underestimates total rainfall kinetic energy. Generally speaking, Wischmeier and Smith, and McGregor and Mutchler's equations provided satisfactory estimation in rainfall kinetic energy for Laopi area. Of course, the performance of any kinetic energy equation in rainfall energy estimation is highly dependent upon the percentage of occurrence of intensities with various magnitudes. The applicability of these four equations at high intensity ranges or that for rainfall events having high percentage of high intensities is still needed to be validated.

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