暴雨管理策略應用於臺灣地區性都市設計審議實務之研究

Stormwater Management Strategies: Application on Local Urban Design Review in Taiwan

近年全球氣候變遷引發之極端降雨現象加劇，搭配近年臺灣都市快速擴張下產生大量的地表逕流，加劇都市地區排洪系統負擔，並造成嚴重淹水情形，成為臺灣都市近年面對災害的重要議題。近日水利法修正通過將「逕流分擔」與「出流管制」納入專章，更凸顯了以土地管理方式分擔地表逕流的概念，然而，前述概念如何落實至都市土地開發進行管制，則為都市規劃實務上急切待執行的新議題。在都市規劃層級中，都市設計具有承接土地使用分區管制，並搭配地區特性，落實建築管理聯結的職責；故國外近年以暴雨管理策略落實逕流分擔於都市設計已行之有年。因此，如何落實暴雨管理策略於臺灣的都市設計中，為現今實踐逕流分擔理念下，重要且亟待改善之議題。本研究內容分為兩部分；首先檢視我國各直轄都市現行都市設計審議制度與都市暴雨管理策略之連結現況，以了解我國各地方政府都市暴雨管理執行實務狀況遭遇之困難；另外以淡海新市鎮一期開發區中的都市已開發區為研究地區，模擬探討不同降雨強度下，依現有相關規定與暴雨管理落實於都市設計策略，在未開發與完全開發狀態下，對基地保水效果進行比較與分析，以了解實踐暴雨管理策略在逕流分擔的功效與較佳作法；並綜整現行相關機制及可執行作法，提供執行暴雨管理策略之應有作法與建議。本研究結果歸納如下：1.公共設施與私人建築基地除依一般縣市規定設置貯留設施外，皆依地理特性設置低衝擊開發（LID）設施之手法（方案三），其基地保水效果大於僅於公共設施設置各類貯留設施之作法（方案二），更大於新北市基地保水規定（方案四）及一般縣市基地保水規定（方案一）之效果；且前述保水效果以地區降雨量在5年重現期以下較為顯著。2.一般縣市基地保水規定（方案一）在不同重現期之降雨量下，對基地保水效果不顯著，洪峰流量於2年重現期下僅減少4.51％，至100年重現期下僅減少4.59％。此外，本研究建議，落實暴雨管理策略於地區都市設計中，較能有效地分擔2年至10年重現期降雨強度下的地區性逕流；在實施策略上，則以公共設施與私人建築基地皆設置各類基地保水貯留與低衝擊開發（LID）設施之開發方式（方案三）效果最佳。而在納入暴雨管理於現有都市設計審議制度時，首要應先有來自於都市計畫層級對於地區逕流量的指導，並應建構整體地區性都市設計規劃方案、整合現有都設審議在基地保水之相關審查內容與圖說、並於地方政府增加相關局處在基地保水事項之橫向溝通與審查機制，方能有效落實暴雨管理策略於都市設計審議實務中。

In recent years, the extreme rainfall due to the global climate change in recent years, and the large amount of surface runoff resulting from the rapid expansion of urban areas in Taiwan, have contributed to overload of the urban drainage system, causing severe flooding. Flooding has become a significant issue when facing disaster by urban areas in Taiwan. The water law has been amended to include a chapter ‘runoff apportion and outflow control' on reducing surface runoff by land management. However, applying this principle to urban land development management is a new issue in urban planning. Within urban planning, urban design takes the responsibility of land zoning under a detailed plan, and of applying building administration connections. Thus, urban design abroad has for a long time applied stormwater management strategies to reduce surface runoff. Hence, how to apply rainstorm management strategies to urban design in Taiwan, remains an unsolved issue. This research consists of two sections. The first section examines the link between urban design review system and urban rainstorm management strategies of the municipalities in Taiwan, in order to form an overview on the difficulties facing local governments in applying urban stormwater management in practical contexts. The second section describes simulations using the development area of Phase I Development Zone of Danhai New Town as the research target to do the simulations. Based on current regulations and applications of stormwater management, the simulation considers rainfall retention results, in order to identify the optimal solutions and the effectiveness of stormwater management strategies for runoff apportion under different rainfall intensities in undeveloped and fully developed cases. The current mechanism and executable practices are summarized to choices and recommendations for practising stormwater management strategies.The conclusions of this study are as follows: 1. In addition to keeping retention facilities, urban planners should set up Low Impact Development (LID) facilities in public facilities and private building bases according to geographic characteristics (Case 3). Case 3 provides better water retention then keeping retention facilities on in public facilities (Case 2) or obeying current regulations (Case 1 and Case 4), particularly at five-year recurrence intervals. 2. Obeying current rainfall retention regulations (Case 1 and Case 4) does not yield effective retention results, with the peak discharge declining by only 4.51% at the two-year interval to 4.59% at the 100-year interval. Additionally, this study suggests that applying stormwater management strategies on local urban design reduces local surface runoff more effectively at 2-year to 10-year intervals. The most effective strategy is to set up water retention facilities and LID facilities in public facilities and private building bases (Case 3). Some prerequisites exist for applying stormwater management on the current urban design review system and yielding effective results: guidance for regional runoffs from the urban design levels, the comprehensive local urban design that combines the contents and illustration of the current urban design review system, and establishing related departments in charge of lateral communication of the rainfall retention affairs.