鯉魚潭水庫為大安溪水系之離槽水庫，1992 年完工開始蓄水操作；大安溪士林堰在2003 年完工開始越域引水操作，引入豐水期水源，水庫之蓄水量及水質產生變化。本文蒐集1994~2010 年水庫水質監測資料，以多變量分析方法中主成份分析及因素分析（最大變異法、直接斜交法與Promax 法），探討水庫水質污染之影響，並評比各種轉軸法在水質研究之適合性。
研究結果顯示以Promax 轉軸法在選取負荷量0.7 條件下，可以得到變數特徵值最高的影響因子。根據因素分析結果，越域引水後鯉魚潭水庫水量增加造成稀釋作用，使碳、氮、磷等營養物質濃度降低，為水質變化的主要原因。2005 年到2008 年在總庫容沒有明顯增加的情況下，水庫總入流量逐年升高，水庫滯留時間降低使葉綠素-a 等含量逐漸降低。2007 年之後越域引水量佔總入流量百分比逐漸
升高，鯉魚潭水庫水質逐年趨向良好狀態。

This study contains water quality monitoring data of the Liyutan Reservoir from 1994 to 2010, and analyzes the differences in the water quality of reservoir after the establishment of the Shilin Weir and the operation of transbasin diversion by Multivariate Technics. The major influence factors for the water contamination of the Liyutan Reservoir are analyzed by using the principal component analysis and factor analysis (varimax, direct oblimin, and Promax methods) of multivariate statistical analysis. The study results can be used as references to manage the catchment area of the reservoir, and to compare with the factors analyzed for the feasibility of different rotation methods in studying reservoir water quality. The results indicate that the influential factor with the highest variable eigenvalue can be attained by using Promax rotation method under a loading factor of 0.7. Furthermore, according to result of factor analysis, the water volume of the Liyutan Reservoir increased after implementing transbasin diversion, which resulted in dilution of the concentration of nutrients such as carbon, nitrogen, and phosphor. This phenomenon of dilution is the main cause that changed the water quality of the reservoir. In addition, although the total reservoir storage capacity did not significantly rise from 2005 to 2008, the total inflow of the reservoir increased annually. That is, by reducing the retention time of the reservoir water, the contents of chlorophyll-a were gradually decreased. After 2007, the proportion of the volume of transbasin diversion to the total inflow increased by degrees, which steadily improved the water quality of the Liyutan Reservoir year after year.