水庫集水區主要功能係可以滙集雨水，使其成為乾旱時備用之水源，臺灣地區降雨量隨季節變化極大，尤其南部地區降雨量偏低，需要利用大型水庫調節蓄水資源。然而曾文水庫集水區內的土地包含國有土地及私有土地，國有土地部分所佔面積廣大，因此管理困難，造成曾文水庫集水區內有大量的國有土地被居民占用。本文即以曾文水庫為例，主要研究目的在於探討曾文水庫集水區內土地使用現況及國有土地被占用之情形，分析曾文水庫集水區內目前土地管理制度與相關法令，進而評估如何落實集水區之土地管理並加強集水區內土地的保育及防災。經本研究分析結果發現，國有土地被占用之原因可歸納為以下五點：一、台灣光復前祖先即於此地耕作；二、因管理機關轉換未辦理續約而變成占用；三、國有耕地違規建築使用無法辦理續約；四、國有耕地未自任耕作無法辦理續約；五、因生活需求，占用國有土地耕作。而曾文水庫集水區應依「分區」「分級」的方式訂定「水庫集水區土地開發與管理辦法」，不同的分區、等級應區分不同之法令限制。距離水庫集水區越近及對環境影響較大範圍內應禁止開發，距離水庫集水區較遠及對環境影響較小地區或無影響地區應適度的開放，再配合「國有土地管理辦法」，將可解決曾文水庫集水區內國有土地占用之問題。

Reservoir watersheds can store rainfall as the backup water in case of the drought. The quantity of rainfall varies significantly in different seasons. The southern area needs large reservoirs to condition the water storage resources because it rains less here. However, Tseng-Wen reservoir watershed includes state-owned lands and private ones. The state owns so many lands that it’s difficult to manage these lands. The problem is that a great number of the state-owned lands are occupied by the local people. The purpose of this study is to investigate the situation of how the state-owned lands in Tseng-Wen reservoir watershed are used and occupied. This study also analyzes the related laws and management system, value how to put into practice the land management and improve the environmental protection, and prevent the disasters from happening. The study finds that there are five reasons to explain why the state-owned lands are occupied: 1.People have started farming there before Kuomintang government came to Taiwan; 2.The authorities of the lands have changed, but the contract was not renewed;3.The contract cannot be renewed because the state-owned farming lands are used for construction illegally; 4.The contract cannot be renewed because the state-owned farming lands are not cultivated by the owners themselves; 5.People occupied the state-owned lands because of their living demands. The study concludes that to solve the problem of occupying the state-owned lands in Tseng-Wen reservoir watershed, the authorities should regulate different uses of these lands according to their zonings and levels. The authorities should prohibit the lands close to and have more effect on Tseng-Wen reservoir watershed from being occupied and used. The authorities should appropriately allow people to use the lands far away from and have less or no effect on Tseng-Wen reservoir watershed. In accord with state-owned administrative measures, the authorities can solve the problem of occupying the state-owned lands in Tseng-Wen reservoir watershed.