中華民國內政部建築研究所中華民國內政部建築研究所

一、研究緣起
近年來，隨著都市快速發展及極端降雨事件的影響，洪災事件頻傳，都市防災以傳統工程手段做為因應策略已趨近極限，因此由流域整體治理觀點所提出的治水方式已成為重要之輔助作法。該方式係透過土地使用管制、減災策略等非工程措施進行滯洪及減洪，漸次提高都市的防災量能，強化都市減災與調適能力，並確保民眾生命財產安全。
基於土地開發會減少入滲而增加地表逕流且改變流路，因而造成洪災風險增加，受到氣候變遷的影響，亦可能加劇水文環境的變化。故本研究將運用成長管理的觀點（包括成長總量、區位及優先順序等），在考量水文環境與容受力的都市發展的規劃過程中，尋找適宜的開發區位和時機，並結合空間規劃之減洪調適韌性策略及透過逕流分擔措施的操作，以達到提升未來城鄉發展地區之災害調適韌性能力。
二、研究方法及過程
本研究選定橫跨數個都市計畫區之鹽水溪流域，佈置其符合都市分區之演算格網。考量流域綜合治理之逕流分擔，透過鹽水溪流域各子集水區逕流分擔量，計算各都市計畫區之逕流分擔量。運用成長管理觀念（包括成長總量、區位、優先順序等）結合減洪調適韌性策略，評估容易淹水範圍加以限制或降低開發強度，並應用水理模式模擬集水區內的逕流現象，分析可有效減洪之地區及可有效滯洪之區位，並考量現行排水系統、綠色基盤設施之串連及非都市範圍土地之活用等，以減災布局引導發展出具災害韌性的空間規劃減洪策略。
以都市計畫規劃之成長管理觀點跨域結合水理分析，在規劃都市發展計畫的同時，切實考量防洪減災，對於現況之淹水災害高風險區，限制或降低開發強度，亦可以分析有效減洪地區或有效滯洪之區位，進而研擬空間規劃減洪策略；針對新發展區之土地，規劃其成長管理邊界、成長區位、優先發展順序等，以整體性之減洪調適韌性策略，供未來地方層級國土計畫及都市計畫規劃、通盤檢討、審議及開發管理參考，期能降低因未來都市發展需求及氣候變遷影響之淹水災害。
三、重要發現
(一)由民國107年0823豪雨與民國108年0813豪雨兩場多峰降雨歷程之豪雨事件演算結果可知，兩場豪雨事件於永康排水與鹽水溪匯流處附近、安南區新吉工業區周邊及十二佃附近均有淹水，實測水位與模式模擬值比較，其NSE值為0.69~0.91，顯示模式可合理演算降雨形成之測站逕流歷程。
(二)演算於都市計畫施行前後之逕流體積增幅，在275mm/24hr與350mm/24hr降雨情境下，各都市計畫施行前後逕流體積平均增幅分別為3%與2.4%，以臺南市安平港歷史風貌園區特定區計畫施行前後逕流體積增幅0.2%為最小，善化都市計施行前後逕流體積增幅15.8%、13%為最大。
(三)佈設逕流設施於高速公路永康交流道附近特定區計畫，對鄰近且位於下游之永康六甲頂都市計畫亦有逕流減少之影響。在重現期10年（275mm/24hr）降雨情境之逕流模擬下，逕流體積可有比大豪雨（350mm/24hr）降雨情境較佳之減少百分比；臺南科學工業園區特定區計畫因有較高速公路永康交流道附近特定區計畫2倍以上之逕流分擔措施總體積，故其逕流體積亦有較大之減少百分比。整體來說，逕流分擔措施在此兩區具有降低逕流百分比19.32%至39.75%之成效。
(四)為探討設置單一措施於臺南科學工業園區特定區計畫及高速公路永康交流道附近特定區計畫之減洪成效，演算此兩個都市計畫單獨佈設逕流抑制措施1（公共設施用地）與措施2（土地使用分區），以及單獨佈設逕流暫存措施3（公共設施用地）與措施4（土地使用分區）前後之逕流體積與面積減幅。在重現期10年（275mm/24hr）降雨情境之逕流模擬下，無論是單獨設置何種措施，逕流體積之減幅均比大豪雨（350mm/24hr）降雨情境大。單獨設置措施4具最佳減洪效果，兩個都市計畫平均減幅，於重現期10年與大豪雨情境下，分別為6.262%、4.367%，措施1平均減幅為4.066%、3.512%，減洪效果次之，其次為措施3（1.774%、1.412%）及措施2（1.025%、0.674%）。於臺南科學工業園區特定區計畫以單獨設置措施4減洪效果最佳，其次為措施1、措施2、措施3，高速公路永康交流道附近特定區計畫以單獨設置措施4減洪效果最佳，其次為措施1、措施3、措施2。前述於兩都市計畫區之單獨設置措施之減洪成效良好程度排序，與措施蓄洪體積大小排序一致，可知在此兩都市計畫區之措施減洪成效受設置措施之體積影響較措施之類型為大。
(五)臺南科學工業園區特定區計畫與高速公路永康交流道附近特定區計畫，於氣候變遷降雨情境下，新訂擴大都市計畫施行前後之逕流增加體積分別為0.68萬立方公尺、19立方公尺，增加百分比分別為0.1%、0.002%。永康新化擴大都市計畫因土地使用分區類型為工業、住宅、農業，與原土地使用分區類型相近，CN值變化不大，逕流體積增量不多。
(六)臺南科學工業園區特定區計畫與高速公路永康交流道附近特定區計畫，於氣候變遷降雨情境下，都市計畫施行後上游地區實施逕流暫存措施前後之逕流減少體積分別為8.9萬立方公尺、0.66萬立方公尺，減少百分比分別為1.28%、0.67%。整體來說，在氣候變遷及新訂擴大都市計畫施行之影響下，逕流暫存措施在此兩區仍具有降低逕流百分比0.67%至1.28%之成效。因此，新訂擴大都市計畫施行後可考慮利用非都市計畫區之農業用地，降挖0.5公尺，提供補償等相關配套措施進行減洪。
四、主要建議事項
建議一
建議以成長管理觀點進行之減洪調適規劃：中長期建議
主辦機關：縣市政府水利局、都發局
協辦機關：內政部建築研究所
本年度已完成氣候變遷下以成長管理觀點研擬城鄉發展區空間規劃減洪調適韌性策略之研究，未來建議可以將城鄉發展區空間規劃減洪調適韌性策略納入「國土計畫」、「新訂擴大都市計畫」或「都市計畫發展率較低」之地區，在實施通盤檢討時將其作為考量，以因應都市發展與氣候變遷造成之逕流影響。
建議二
建議在進行因應氣候變遷之調適策略規劃時，應同時考慮氣候變遷及新訂擴大都市計畫施行之影響：短期建議
主辦機關：縣市政府水利局、都發局
協辦機關：內政部建築研究所
本年度已完成氣候變遷下新訂擴大都市計畫施行後之逕流情境模擬，並透過農地降挖50公分之方式設置上游逕流暫存措施，逕流演算後在此兩區具有降低逕流體積百分比0.67%至1.28%之成效。建議在進行因應氣候變遷之調適策略規劃時，應同時考量氣候變遷及新訂擴大都市計畫施行之影響，新訂擴大都市計畫施行後可考慮利用非都市計畫區之農業用地，降挖0.5公尺，提供補償等相關配套措施進行減洪。

Background and objectives
In recent years, with the rapid development of the cities in Taiwan and the impact of extreme rainfall events, the frequency of flood events has increased, and traditional structural flood mitigation measures have reached their limits. The flood mitigation measures proposed from the viewpoint of comprehensive management of river basins have become important auxiliary measures. Flood detention and reduction can be achieved through nonstructural measures such as land use control and disaster mitigation strategy in order to gradually improve urban flood mitigation energy, strengthen urban disaster mitigation and adaptation ability, and protect the lives and property of the people.
As land development reduces infiltration, increases surface runoff, and changes the flow path, flood risks for developed areas increase, and aggravates the hydrological environment when coupled with climate change.  Thus, this study will be conducted from the viewpoint of growth management (including total quantity control, growth location, and priorities) and put into consideration the hydrological environment and environmental carrying capacity to find suitable development locations and timings, then combine the aforementioned with “resilient strategies for flood mitigation and adaptation for spatial planning” and “runoff allocation measures” to improve the disaster mitigation and adaptation ability of urban and rural development areas.
Method and approach
This study selected the Yanshui River basin, which spans several urban planning divisions, as the study area. This study was conducted from the viewpoint of growth management and used resilient strategies for flood mitigation and adaptation to evaluate flood-prone areas and limit or reduce the intensity of development of those areas. The hydraulic model was used to simulate the runoff in catchments and analyze effective flood mitigation areas and detention locations. Resilient strategies with spatial planning are then developed while putting into consideration current drainage systems, linking green infrastructures, and the utilization of non-urban land.
From the viewpoint of growth management, combined with hydraulic analysis, we designed resilient strategies for flood mitigation and adaptation while taking note of  urban development plans and of flood mitigation. For current flood-prone areas, we limited or reduced the intensity of development. Analysis of effective flood mitigation areas and detention locations can be used to design flood mitigation strategies.  For newly developed areas, this study designed the growth boundary, growth location, and the priorities of development. Combining flood mitigation and adaptation strategies, this study aims to provide reference for future local level spatial planning and urban plan designing, overall review, and deliberation and development management of urban planning, in hopes of reducing future urban development needs and the impact of climate change on flooding disasters.
Main results
1.Simulating the rainfall events from  August 2018 and August 2019, areas around the confluence of the Yongkang drainage and the Yanshui River, Sinji industrial park, and the Shi’erdian were subject to floods. The NSE values of the comparison of the simulation and actual water levels is 0.69 to 0.91, showing that the PHD model can reasonably calculate the runoff of the study area.
2.For heavy rain events and 10-year return period rainfall, the runoff volume increased by an average of 2.4% and 3% after the enforcement of urban planning, respectively. Anping Harbor historic special district planning had the smallest increase in terms of runoff volume percentage, and Shanhua urban planning had the largest increase.
3.Setting up runoff allocation facilities in the special district planning project near Yongkang Interchange location also reduces the runoff amounts in the Lioujiading (Yongkang) urban planning area downstream of the Yanshui River. Flood mitigation effects were better for 10-year return period rainfall than for heavy rain situations. As the size of runoff allocation facilities in The Tainan Science Park Special District planning area are about two times the size of those in the planning project near Yongkang Interchange, the reduction percentage for runoff volume was also higher. Setting up runoff allocation facilities had the effects of lowering runoff percentage by 19.32% to 39.75%.
4.Simulating the Tainan Science Park Special District planning area and the special district planning project near Yongkang Interchange area, we compare the effects of flood mitigation of only setting up runoff suppression facilities against only setting up runoff temporary facilities. In simulations, reduction of runoff volume was more pronounced for a rainfall event with a 10-year return period than for heavy rain events.  The flood mitigation effects for both urban planning areas was more dependent on facility size than on the type of facility.
5.Because of the impacts of the enforcement of new or expanded urban planning and the impacts of climate change, runoff volume for the Tainan Science Park Special District planning area and the special district planning project near Yongkang Interchange area increased by 6800 cubic meters and 19 cubic meters, respectively. The CN values of the Expanded Yongkang and Sinhua urban plannings area did not vary greatly from original values due to the types of land use remaining much the same, and runoff increases remained small as a result.
6.Runoff temporary storage can be reduced by 0.67% to 1.28% for the  Tainan Science Park Special District planning and the special district planning project near Yongkang Interchange areas when under the effects of climate change and the enforcement of new or expanded urban planning.  After the enforcement of new or expanded urban planning, non-urban planning for detention in agricultural use land or  compensation measures can be put under consideration.
Major suggestions
This study proposes one long-term and one short-term strategies as follows:
For Bureau of Urban Development and Bureau of Water Resources of municipalities and county government （long-term strategy）
We have completed the study on resilient strategies of flood mitigation and adaptation for urban-rural development areas under climate change this year, and suggest merging urban-rural development area resilient strategies for flood mitigation and adaptation into spatial planning.
For new or expanded urban planning or less developed urban planning areas, flood mitigation strategies are taken into account when enforcing overall review, to respond to the effects of urban development and climate change on runoff.
For Bureau of Urban Development and Bureau of Water Resources of municipalities and county government （short-term strategy）
We have completed the simulation of runoff situations after new or expanded urban planning, and through the measure of digging 50 centimeters from agricultural lands to pass the area off as runoff temporary storage, we have achieved the result of reducing runoff volumes by 0.67 to 1.28% for both areas. We suggest taking into consideration the effects of climate change and new or expanded urban planning when designing adaptation methods in response to climate. After the enforcement of new or expanded urban planning, we suggest using non-urban planning agricultural land as flood detention facilities by digging 50 centimeters from the ground and offering compensation as a complimentary measure.