防護性景觀規(guī)劃—氣候變暖“護盾”

2018-03-11 01:49蓋倫紐曼喬紫旭

城市設計 2018年5期

蓋倫·紐曼喬紫旭

1 背景

無論在生態(tài)、社會還是經濟方面，氣候變化都對建筑環(huán)境產生了巨大的影響。美國國家海洋和大氣管理局（NOAA）預測，墨西哥灣沿岸地區(qū)的平均海平面每年至少要上升0.2cm，到2100年將達到1.9m。一直以來，海平面上升都對沿海生態(tài)系統(tǒng)產生了重大影響，包括濕地喪失、海岸侵蝕或淹沒，颶風的持續(xù)時間和頻率也大幅增加。例如，在2008年，颶風艾克（Hurricane Ike）對德克薩斯造成了嚴重的破壞，造成113人死亡和約295億美元的經濟損失，大約200個位于德克薩斯州聯(lián)盟城（League City，Texas）的房屋受到了嚴重損害。

由于聯(lián)盟城近墨西哥灣的地理位置，其城市面臨著諸多自然災害，并且非常容易受到洪水事件和海平面上升等其他問題帶來的影響。該設計項目位于聯(lián)盟城市內靠近河岸的一塊39公頃的閑置土地。設計目標是通過“護盾工具包”的應用，使社區(qū)可以盡可能地避免受到當前和未來的洪水災害以及由大氣變暖、海平面上升所帶來的影響，從而降低社區(qū)及整個聯(lián)盟城的生態(tài)環(huán)境脆弱性和社會經濟脆弱性(圖1—圖16）。

圖1 / Figure 1氣候變暖“護盾”/ Climate Change Armor

2 區(qū)域和場地條件

洪水和颶風一直是墨西哥灣沿岸面臨的主要問題。德克薩斯州沿岸遭遇普通颶風的頻率大約是每5年一次，遭遇大型颶風的頻率大約為每15年一次。3級以上的颶風帶來的洪水就可將設計場地大面積淹沒。與此同時，海平面上升也會增加沿海社區(qū)面對洪水和颶風等災害的社會經濟脆弱性。據聯(lián)邦緊急事務管理局（FEMA）預測，到2100年，近50%的聯(lián)盟城用地將無法抵御百年一遇的洪水，同時1.9m的海平面上升意味著76%的項目土地將被洪水淹沒，并且完全無法抵御500年一遇的大型洪水。通過在GIS中疊加社會和經濟柵格數據集來繪制導致洪水脆弱性因素的地圖，得到超過41%的聯(lián)盟城用地處于相對高度的洪水脆弱性區(qū)域的結論，而項目場地正處于該區(qū)域。此外，鑒于以上因素對生態(tài)系統(tǒng)造成的災難性破壞，在過去的20年里，該項目場地已經失去了近43%的濕地面積。

圖2 / Figure 2臺風暴潮漫灘數值與歷史颶風 / Storm surge inundation&historical hurricanes

3 設計策略

通過借鑒國內和國際的彈性社區(qū)設計案例，該設計開發(fā)并整合了一個適應性洪水衰減機制（結構和非結構）—氣候變暖“護盾工具包”。結構機制是以工程方法為基礎設施，主要用于阻止和控制洪水，分為如下幾種。

干線護盾：高架公路，兼作一體化防洪墻；

堤壩護盾：植被覆蓋的斜坡，模仿天然堤壩；

閘門護盾：小型防洪閘門，可在上游洪水發(fā)生時關閉；

建筑護盾：建在樁柱上的高架建筑。

非結構性機制主要依靠自然系統(tǒng)和綠色基礎設施來減少洪水、儲存雨水并減輕頻繁洪水事件帶來的潛在影響。分為如下幾種。

濱水保留帶護盾：一系列保存完好的濕地和植被的濱水邊緣；

疏浚護盾：在河岸挖掘沉積物來儲存洪水；

生態(tài)調節(jié)溝護盾：輸送雨水至滲透和過濾雨水區(qū)域的街道與市政設施。

氣候變暖“護盾工具包”被適應性地應用于場地的不同區(qū)域，使場地自身變成了一個堅固的護盾，在避免當前和未來洪水問題的同時為居民提供了娛樂、住房和經濟機會。與現(xiàn)有河畔接壤的設計綠地既保護了社區(qū)免受洪水侵襲，又被設計成一個具有露天劇場、休閑碼頭、河畔酒店和其他文化設施的公園。它通過生態(tài)調節(jié)溝、高架林蔭小徑和生態(tài)堤壩等形成相互連接的綠色基礎設施系統(tǒng)；同時基于工程建設的住宅區(qū)、商業(yè)空間和道路交通也可作為多功能保護結構，從而減少該地區(qū)面對洪澇災害的生態(tài)脆弱性和社會經濟脆弱性（physical and social vulnerability）。

圖3 / Figure 3當前洪泛區(qū)分析與海平面上升對洪泛區(qū)的影響 / Current Flood plain change with sea level rise

該設計將分3個階段實施。

一期：遠離洪水。

重點開發(fā)位于場地兩側海拔較高的地區(qū)，同時將綠色基礎設施的開發(fā)和整合與之配套。一期開發(fā)的商業(yè)區(qū)和商住混用區(qū)域將與周邊已有的高密度住宅商務區(qū)相連，并且有策略地放置在洪水易發(fā)區(qū)域之外，從而降低該區(qū)域面對洪澇災害的生態(tài)脆弱性。具有景觀特征和可滲透鋪裝的公共城市空間不僅起到了儲存、滲透和過濾雨水的作用，還促進了鄰里間的聯(lián)系。

二期：緩解洪水。

開發(fā)低密度住宅區(qū)和公共服務設施，安置綠色基礎設施，保護居民區(qū)免受頻繁的暴風雨帶來的災難；同時，開啟工程基礎設施，以應對更大的洪水事件帶來的災害。多樣的住房類型帶來了不同年齡階段和背景的居民。公共服務設施用地將建設氣候變化博物館等公共建筑，為居民提供了參與和教育機會。

三期：控制洪水。

完成全部工程基礎設施建設，以創(chuàng)建一個完整的、多功能的“護盾”系統(tǒng)，可在極端洪水災難時阻止和控制洪水并調節(jié)水文活動。同時，形成一個相互連接的交通系統(tǒng)（包括河濱步道、人行天橋、自行車道、河上游憩設施等），以增強居民與公園的聯(lián)系、吸引游客，也制造了經濟和就業(yè)機會。

圖4 / Figure 4實物模型分析海平面上升 / Sea level rise modeling

4 設計效益評估

結構與非結構“護盾”根據其功能被應用于場地的不同位置，以保護當地居民的生命與財產，并創(chuàng)造生態(tài)和經濟效益。最后National Green Values?計算器用于評估設計中使用的綠色基礎設施的性能、成本和效益。與傳統(tǒng)方法相比，綠色基礎設施將場地的不滲透面積減少了26%，占據了所需徑流量的30.3%。同時，該設計可以捕獲6,230m3的徑流，通過減少空氣污染物和能源使用、處理污染物、增加二氧化碳吸取量、提高樹木的補償價值和改善地下水補給，每年將創(chuàng)造42萬美元的綠色效益。

氣候變暖“護盾”設施不僅可以創(chuàng)造經濟和生態(tài)效益，還可以創(chuàng)造巨大的文化和社會效益。通過“護盾”的應用，該設計在2100年之前將大幅減少100年的洪泛區(qū)，海平面上升造成的覆蓋面積將從30公頃減少到6公頃（從76%覆蓋到僅16%）。此外，近2,400名新居民受到保護，3,000多個工作崗位被創(chuàng)造，避免了約2,300萬美元的直接損失，到2,100年場地將共創(chuàng)造近13億美元的生命周期效益。

FULL TEXTS IN ENGLISH

Project Title: Climate Change Armor

Galen Newman, QIAO Zixu

1 Background / Problem Statement

Climate change effects have had observable ecological, social, and economic impacts on thebuilt environment. NOAA predicts that the mean sea level will rise at least 0.82 inches per year in the Gulf Coast region, reaching 6.29 feet by 2100. Sea level rise has had a signi ficant impact on coastal ecosystems resulting in wetland loss, increased coastal erosion/inundation, and increases in the duration and frequency offlooding from storm surge. For example, in 2008,Hurricane Ike wreaked havoc on Texas, causing 113 deaths and $29.5 billion in damage; approximately 200 of the damaged homes were located in League City, Texas.

圖5 / Figure 5洪水脆弱性分析 / Flood Vulnerability

Due to its location, League City is exposed to many hazards and is highly vulnerable to flood events and other issues effected by sea level rise. This project designs a resilient community within a 97-acre site surrounded by urban development in League City. The site is currently planned bythe city to grow as mixeduse and auto dominated residential urban low density development. The objective of this project is to design a community that is fully protected from current and future flood events and the eventual impacts of sea level rise,thereby reducing physical and social vulnerability.

圖6 / Figure 6設計場地濕地面積分析 / Wetland change in site boundary

2 Regional & Site Conditions

Flooding and hurricanes are major concerns along the Gulf Coast. The frequency of a normal hurricane along any 50 mile segment of the Texas coast is one about every 5 years,with a major hurricane occurring nearly every 15 years. The design site will be significantly inundated by storm surge from hurricanes from Category 3 and above. Relatedly, sea level rise will increase the vulnerability of coastal communities to hazards such as flooding and hurricanes. By 2100, nearly 50% of League City projects to be covered by the FEMA 100 year floodplain, should a 6 feet sea level rise occur; 76% of the land on the design site will be effected, and the entire site is covered by the 500 year floodplain. By overlaying social and economic raster data sets in GIS to map factors contributing to flood vulnerability, over 41% of League City projects to have high flood vulnerability, and the site rests as the highest flood vulnerable area in the city. In regards to the catastrophic damage these conditions have had on ecosystems, nearly 96 acres offreshwater wetlands and 154 acres of wetlands in the region have been lost since 2008. The design site has lost 43% of its wetland area in the past 20 years.

圖7 / Figure 7氣候變暖“護盾工具包” / Armor Toolkit

3 Design Strategy

Borrowing from a series of resilient community design cases nationally and internationally, this design develops and incorporates a series of adaptable flood attenuation mechanisms (both structural and non-structural),referred to as the Climate Change Armor Toolkit. Structural mechanisms are engineered infrastructure used primarily to block and control heavy floods. For example:

· Arterial Armor—an elevated highway which doubles as an integrated flood wall;

· Levee Armor—as gradual and vegetated slope mimicking a natural levee;

· Gate Armor—a sector style mechanism which can close when upstream floods occur;

·Architecture Armor—elevated buildings which are built on stilts.

Non-structural mechanisms primarily rely on natural systems and green infrastructure to reduce flooding, store stormwater, and soften the potential effects offrequent flooding events. For example:

· Riparian Armor—a collection of preserved and restored wetland areas and vegetated waterfront edges;

圖8 / Figure 8總體規(guī)劃 / Master Plan

· Dredged Armor—excavated sediment in strategic locations to store flood water which is reused to increase the elevation offuture development;

· Bio-swale Armor—streetscape and urban plaza amenities which convey floodwaters to storage areas and allow for infiltration and filtration of stormwater.

The Climate Change Armor Toolkit's mechanisms are applied throughout the site, and together compose a solid armor to defend the site from current and future flood issues while simultaneously providing recreational, housing and economic opportunities. The designed green space bordering Clear Creek both protects the community from floods and surge and is designed as a park with an amphitheater, recreational pier, riparian edge, hotel and other cultural amenities. It is connected to the designed green infrastructure system through strategically placed bio-swales, elevated trails and eco-levees; engineered based residential areas, commercial space, and transportation lines also act as multifunctional protective structures to help decrease flood vulnerability.

The design is to be implemented in three phases:

Phase (1) Retreat from flood—focuses on placing development in areas with higher elevation area and integrating green infrastructure. The designed medium density commer-cial and mixed-use spaces are connected with existing arterials integrated into the surrounding residence but are strategically placed outside offlood prone areas to limit vulnerability. Public urban spaces with landscape features and permeable paving provide connections to neighbors and promote infiltration, retention, biological treatment, and evapotranspiration processes.

Phase (2) Mitigate flood—develops lower density residences and green infrastructure to provide protection during frequent storms to and gray infrastructure to mitigate larger flood events. Diverse housing types bring in residents from different age groups and backgrounds. New institutional land uses such as a climate change museum provide engaging and educational opportunities for communities.

Phase (3) Control flood—completes major installation of structural and gray infrastructure to create a multi-funtional armor system that block and control heavy floods and regulate hydrologic activity during extreme hazard events. Simultaneously, an interconnected circulation system including pedestrian trails,boat launch points, pedestrian bridges, and bicycle paths enhance local connection to the waterfront, attract tourists, an d create economic opportunities.

4 Design Impact

The structural and non-structural armor typol-ogies are strategically applied throughout the site into the green and gray network/fabric, to protect residents and deliver valuable both ecological and economic benefits. The National Green Values? Calculator was used to assess the performance, costs, and benefits of the green infrastructure utilized within the design. Compared with conventional approaches, the Green Stormwater BMP(s)of the design decrease the site impermeable area by 26% and capture 30.3% of the runoff volume required. Simultaneously, the design can capture 221,921 ft3 of runoff, creating$419,901 annual green benefits by reducing air pollutants and energy use, providing pollution treatment, increasing carbon dioxide sequestration, escalating the compensatory value of trees, and improving groundwater replenishment (the economic benefits of these benefits by 2100 reaches $13,305,657).

圖10 / Figure 10設計周期 / Design Phas

The Climate Change Armor facilities not only create economic and ecological benefits, but also create enormous cultural and social benefits. With its application, the design decreases the 100 year flood plain by year 2100 with sea level rise from 74 acres to 15 acres (from 76% coverage to only 16%). Also, the nearly 2,400 new residents are protected, over 3,000 jobs are created, around $23 million in physical damage is avoided, and nearly $1.3 billion are generated by the life cycle benefits by 2100.