木質生態工程之劣化；植物復育及環境效益之探討

Abstract

台灣地區近年來陸續受到1999年的九二一集集大地震、2001年桃芝及納莉颱風引發的土石流侵襲，中部地區災況嚴重。有關單位投入了大量的資源進行復建工作。部分的復建工程採行「因地制宜、就地取材」原則，如砌石護岸、蛇籠、格柵式擋土牆等生態工程進行。這當中，一些以木質生態材料建造之復建工程也已通過後續如2004年敏督利颱風及其他強颱豪雨等的考驗。然而，台灣地區有關利用木質材料製作之生態工程案例，仍少有針對其工法設計、後續監測與評估或植物復育狀況進行較深入的探討及研究。故本研究即以此為目標，希望透過調查，能有明確的數據，讓一般大眾對木質生態工程的使用更具信心。 研究中針對行政院農委會林務局、水土保持局以及臺大實驗林管理處於災後在宜蘭縣與南投縣興建之節制壩、擋土牆以及河道護岸等木質生態工程結構物進行分析。包括結構物的腐朽程度、後續之結構變位、碳素貯存量及建造完成後植生覆蓋之效益。調查結果顯示，木質結構物雖歷經後續之颱風豪雨侵襲，不過材料的腐朽強度仍維持良好狀態，即使有部分腐朽較嚴重，但結構監測點的變位仍屬輕微，表示工程具相當程度的穩定性；而取代傳統硬式混凝土工程之木質材料生態工程，不但有助於碳素固定，可有效降低二氧化碳排放，於完工之後更利於植物的生長被覆，顯示其對植生復育具有正面之效益，且可讓工程結構物更融入週遭環境，一舉數得。本研究並能提供未來利用木質材料進行生態工程設計時之重要參考。

Recently, debris flows resulted from Chi-Chi Earthquake in 1999, Typhoon Toraji and Nali in 2001, have caused severe damages to Taiwan, especially in the central area. Rehabilitation work was undergoing by the authorities who invested a lot of money and resources. Part of the work adopted ecological techniques to reconstruct the facilities, such as the articulated blocks bank, gabion and geogrid walls, by following the 'local material was first chosen to utilize' principle to reduce the usage of concrete. Among these facilities, some of them was made by plantation wood and had suffered from Typhoon Mindulle in 2004. However, there are less studies focusing on the design, following monitor, and assessment, and vegetation restoration of the ecological engineering cases by using wooden materials in Taiwan. In this study, by collecting explicit data though investigation, hopefully the results can increase confidence in using wooden ecological engineering to common populace. This study analyzes several kinds of wooden ecological works, including decay level, the following displacement, carbon sequestration, and the coverage of plants after construction. These cases which include check dams, retaining walls, and revetments were constructed by the Forest Bureau, Water and Soil Conservation Bureau, and the Experimental Forest of National Taiwan University in Yilan and Nantou County, respectively. The investigation results showed that after the following typhoons and heavy rain attacks, the residual strength of wooden structures remains in well condition. Despite part of them may decay more seriously, the monitored point displacement was slightly, and indicated that wooden structures were still in stability. Meanwhile, replacement of traditional RC structure by wooden ecological engineering not only is helpful to carbon sequestration which can effectively reduce the emission of carbon dioxide, but also favors to plants growth. The results also show that it benefits to vegetation restoration, and can also make the structure assimilate to the environment. This research indicates many advantages of wooden ecological engineering, and provides a key reference to set the design regulations and rules in the future.