從逕流責任觀點下探討減洪土地使用規劃

Investigating Flood Mitigation Strategies Applying to Land-use Planning from a Perspective of Managing Public Runoff as a Shared Responsibility

傳統治水工程手段已無法完全因應氣候變遷及都市快速發展造成的水文環境改變，非工程手段逐漸受到重視，如：海綿城市、低衝擊開發、逕流分擔及出流管制等概念，然而各種方法有其適用尺度，防洪治水應納入大尺度的上位計畫做為指導。本研究嘗試以土地部門角色落實逕流分擔概念於土地使用計畫，以河川集水區為空間單元探討土地逕流責任─水責任，藉由建立水責任架構，作為土地規劃由下而上銜接逕流分擔與出流管制的因應對策。本研究從三個方向釐清水責任，分別為：土地開發水責任、地理環境水責任、貯留潛力水責任，以及將地理環境水責任依面積比例分配給土地單元的基本責任。藉由驗證初探得知水責任確實可以落實於空間，並且藉由不同保護標準進行情境模擬，得出土地開發若同時負擔基本責任和貯留潛力水責任，能達到較佳的減洪成效。依據水責任所繪製的地圖係以水環境作為基礎分析，可視為如環境敏感地的功能應用於土地規劃，位於逕流分擔區應加強對未來開發的管制，要求其負擔水責任才得以開發；非逕流分擔區之土地因其開發行為不須額外負擔基本責任，開發成本較低，在逕流分擔之觀點上具備較佳之開發條件，然仍應視該土地之其他環境敏感項目條件，並綜合評估土地開發與規劃適宜性。

Structural measures for managing flooding are insufficient for managing the runoff caused by climate change and rapid urban growth. Non-Structural measures like Sponge City, LID and Runoff Allocation Policy are gradually being taken seriously. However, a different scale is applied for each of these measures. Therefore, a master plan is needed to measure the total runoff in the river basin scale to guide the urban planning. This study applied the concept of Runoff Allocation Policy on land-use Planning. We define the framework of “Runoff Responsibility” by identifying the causes of flood. Based on this framework, Taichung Dali River Basin was selected for empirical analysis. In scenario analysis, by affording all the “Runoff Responsibility” we define, the flooding situation will be improved. The map of “Runoff Responsibility” can be regarded as the master plan to guide the land-use planning. Development activities should afford certain amount of detention if they are located in high “Runoff Responsibility” area. The map should indicate environmentally sensitive land so that the land-use plan can consider other environmental conditions as well.