著：（加）丹尼爾·勒爾 譯：鮑沁星 校：王思思

自2015年海綿城市在中國(guó)16個(gè)城市開展以來，低影響開發(fā)（LID）已取得了廣泛的成就[1]（圖1）。LID的目標(biāo)是模擬場(chǎng)地在未受人類干涉的自然狀況下雨水徑流的運(yùn)作模式。LID措施包括：綠色屋頂、生物滯留設(shè)施、透水鋪裝、生物洼地、儲(chǔ)存/調(diào)節(jié)塘、雨水收集和儲(chǔ)存裝置（圖2）。戴莉萍在最近的一篇文章中詳細(xì)探討了這一中國(guó)新型城市雨洪治理項(xiàng)目在管理結(jié)構(gòu)方面的利弊及面臨的融資挑戰(zhàn)[2]。幾個(gè)世紀(jì)以來，中國(guó)各級(jí)政府都試圖通過大壩等結(jié)構(gòu)性措施和政策等非結(jié)構(gòu)措施來降低城市洪澇災(zāi)害[3]。邵薇薇在其海綿城市研究的文章中列舉了過去8年間的重大洪災(zāi)以及因此造成的人員傷亡和經(jīng)濟(jì)損失，由此強(qiáng)調(diào)構(gòu)建海綿城市數(shù)據(jù)計(jì)劃對(duì)于改善城市設(shè)計(jì)和建設(shè)的重要性[4]。文中還指出“海綿城市的建設(shè)是一項(xiàng)非常復(fù)雜的系統(tǒng)工程任務(wù)”[4]，而海綿城市數(shù)據(jù)的收集對(duì)于提高防汛效率有重要作用，有利于海綿城市的成功建設(shè)。

對(duì)中國(guó)來說，治理洪水并非話題。事實(shí)上，中國(guó)人民5 000多年來不得不創(chuàng)造性地想出各種防洪措施來應(yīng)對(duì)頻發(fā)的洪災(zāi)[3,5]。吳慶洲在1989年的文章中不僅詳細(xì)解釋了中國(guó)的防洪歷史、治理結(jié)構(gòu)和政策，還介紹了古代中國(guó)城市規(guī)劃政策中關(guān)于開展防洪實(shí)驗(yàn)的天才技術(shù)智慧和決心[5]。中國(guó)悠久的防洪歷史與許多城市的地理位置有一定關(guān)系，它們往往建設(shè)于沿海地區(qū)或是廣闊的河流三角洲地帶，這些地區(qū)由于季風(fēng)性氣候定期受到洪水的侵?jǐn)_。這些區(qū)域有著大量居民，常因季風(fēng)而飽受洪災(zāi)之苦（圖3）。而我們知道，中國(guó)的降水量，從東南向西北地區(qū)是逐步減少的[3]。

當(dāng)下城市面臨的眾多挑戰(zhàn)使得雨洪問題進(jìn)一步復(fù)雜化，這直接促使了2015年海綿城市快速地啟動(dòng)。隨著中國(guó)人口增長(zhǎng)，越來越多的農(nóng)業(yè)用地用于城市化，改變了原有的土地利用模式[3]。經(jīng)濟(jì)繁榮帶動(dòng)了如火如荼的新城建設(shè)，成千上萬的人們涌入城市的“曠地”。城市中大量不透水下墊面，阻礙了土壤對(duì)雨水的滲透吸收。另外氣候變化使得降雨情況更加難以預(yù)測(cè)[3]。短時(shí)間內(nèi)的高強(qiáng)降水將會(huì)提高雨洪的峰值流速，導(dǎo)致雨洪徑流不可控，加重土壤、河道、海洋的水污染[3]。

1 海綿城市示例Sponge City example

2 綠色屋頂： LID措施及LID系統(tǒng)組成部分Living roofs: a tool and systems component of LID

但是，對(duì)于擁有如此漫長(zhǎng)防洪治洪歷史的中國(guó)來說，怎樣才能積極有效地解決這些問題呢？中國(guó)人適水而生。生活在烏鎮(zhèn)、南潯、同里等江南水鄉(xiāng)的人們幾個(gè)世紀(jì)以來都與當(dāng)?shù)氐暮雍椭C相處（圖4）[6]。如果公眾和決策者能夠?qū)W習(xí)水鄉(xiāng)人看待水的態(tài)度，不將城市中的雨水徑流看成是一種威脅，而視為一種需要保護(hù)的珍貴資源，并通過設(shè)計(jì)使之成為L(zhǎng)ID這一雨水管理體系中的一部分，不失為解決上述雨洪問題的一個(gè)可能性方案。這些LID系統(tǒng)能夠減少徑流量、削減洪峰、實(shí)現(xiàn)源頭控制和雨水就地收集利用。“簡(jiǎn)單式”綠色屋頂就是這樣一種有效的LID措施，能在城市雨水管理方面發(fā)揮重要作用，尤其是市中心區(qū)域，這些地方由于缺少透水面層，往往無法管理地表的雨水徑流。

景觀設(shè)計(jì)師在利用LID進(jìn)行雨洪管理這項(xiàng)任務(wù)上處于有利地位。他們不僅在實(shí)施階段，還能在LID倡導(dǎo)和可視化階段發(fā)揮主導(dǎo)優(yōu)勢(shì)。LID系統(tǒng)的成功創(chuàng)建需要景觀設(shè)計(jì)師和工程師從項(xiàng)目伊始就進(jìn)行合作，前者負(fù)責(zé)LID系統(tǒng)的設(shè)計(jì)并對(duì)規(guī)模進(jìn)行預(yù)估，后者則負(fù)責(zé)計(jì)算確定最終規(guī)模。景觀設(shè)計(jì)師不僅能夠從場(chǎng)地、城市和區(qū)域3個(gè)層面上對(duì)場(chǎng)地及其周圍復(fù)雜互聯(lián)的環(huán)境進(jìn)行全面解讀，而且掌握需要實(shí)施LID的其他因素的完整知識(shí)，包括當(dāng)?shù)貧夂?、土壤排水能力、?chǎng)地總體情況、分級(jí)和排水情況、場(chǎng)地現(xiàn)狀。他們還懂得適時(shí)適地選擇相應(yīng)的LID措施以及實(shí)現(xiàn)最優(yōu)效益的LID組合方式。可以說，如果能在城市整體規(guī)劃階段伊始就進(jìn)行LID雨水管理體系規(guī)劃，而不是作為一種事后補(bǔ)救措施，那么就能在一開始確定更為合理的建筑規(guī)劃，有利于實(shí)現(xiàn)雨洪的就地管理。隨著中國(guó)先進(jìn)的海綿城市規(guī)劃的就位，應(yīng)用“簡(jiǎn)單式”綠色屋頂管理城市雨洪政策的相應(yīng)實(shí)施，中國(guó)城市有望很快引領(lǐng)世界LID設(shè)計(jì)研究的前沿。

1 國(guó)際性“簡(jiǎn)單式”綠色屋頂

在過去幾年中，有關(guān)“簡(jiǎn)單式”綠色屋頂?shù)挠旰檎{(diào)控能力方面的研究可謂是相當(dāng)科學(xué)和成功?！昂?jiǎn)單式”綠色屋頂是指：“單獨(dú)或組合式的單層或多層人工綠色屋頂系統(tǒng)（通常包括：排水層，栽培介質(zhì)層和植物層）?！?jiǎn)單式’綠色屋頂?shù)脑耘嘟橘|(zhì)在25～150mm之間，表面可以是水平或具有一定低緩地形的，植物層通常栽植矮生植物”[7]。本文作者提及的綠色屋頂指“簡(jiǎn)單式”綠色屋頂，因?yàn)椤盎▓@式”屋頂綠化建造和維護(hù)都十分復(fù)雜，不符合城市雨洪管理經(jīng)濟(jì)、易行的要求。

3中國(guó)2018年洪水災(zāi)害案例Flood example China 2018

4同里水鄉(xiāng)Water City Tongli

綠色屋頂削減屋面徑流的能力主要與當(dāng)?shù)貧夂颉⒄羯⒙剩‥T）、工程土壤介質(zhì)、屋頂組件和植物有關(guān)。因此屋頂植物的選擇和種植環(huán)境的構(gòu)建應(yīng)該適應(yīng)當(dāng)?shù)貧夂驐l件，保證綠色屋頂成功運(yùn)作。伊麗莎白·法斯曼·貝克說：“就綠色屋頂?shù)挠旰楣芾砉δ芏?，栽培介質(zhì)層可能是最重要的組件—因?yàn)樵耘嘟橘|(zhì)本身就像海綿一樣。[7]”單靠綠色屋頂并不能完全成功解決雨洪管理問題。在極端氣候下，比如在夏季漫長(zhǎng)的干旱期，屋頂?shù)闹参镄枰~外的澆灌，而普通綠色屋頂無法提供貯水和水資源再分配所需的能量。又比如，在屋頂沒有LID雨水管理系統(tǒng)的情況下，就必須在建筑內(nèi)部設(shè)置額外的蓄水池來滯留極端降水事件時(shí)屋面的雨水徑流。也就是說，普通的綠色屋頂只能應(yīng)對(duì)常規(guī)的降水事件。謝菲爾德大學(xué)副教授弗吉尼亞·斯圖文，在她2015年的論文中稱，在她的實(shí)驗(yàn)場(chǎng)地“在常規(guī)暴雨情況下，降雨截流效益良好……但是沒有一處能夠達(dá)到暴雨強(qiáng)度為2L/s/hm2時(shí)峰值截流能力的要求（等同于綠地雨水徑流截留能力），來應(yīng)對(duì)更極端的降水事件（例如，實(shí)測(cè)的日降水量P＞10mm的情況或者模擬30年一遇的情況）”[8]。由此看出，綠色屋頂只是一種階段性措施，為了有效管理甚至凈化雨水，需要結(jié)合其他LID措施協(xié)同應(yīng)用，如生物滯留設(shè)施、洼地、儲(chǔ)存/調(diào)節(jié)塘等，形成完整的雨水治理鏈。當(dāng)“簡(jiǎn)單式”綠色屋頂?shù)挠晁畯搅髁窟_(dá)到田間持水量時(shí)，便失去了雨水調(diào)控能力，變得與普通屋頂無異，這時(shí)候協(xié)同的LID措施能夠幫助有效處理屋面的峰值雨水徑流。出于對(duì)綠色屋頂雨水管理能力和成本的考量，中國(guó)的政府和設(shè)計(jì)實(shí)踐界尚未完全接受綠色屋頂理念。但是有很多學(xué)者堅(jiān)信綠色屋頂?shù)挠旰橹卫硇б?，比如同?jì)大學(xué)董楠楠副教授和駱天慶副教授，他們是中國(guó)綠色屋頂研究的開拓者，現(xiàn)有的相關(guān)研究大部分都來自他們。

在過去幾年中，一些重要的國(guó)際性研究已經(jīng)證明了綠色屋頂?shù)挠旰楣芾硇б?。例如，斯圖文和她的團(tuán)隊(duì)多年來一直在謝菲爾德大學(xué)實(shí)驗(yàn)室測(cè)試不同基質(zhì)媒介（介質(zhì)）和植被組合的水文性能，并在2015年的一篇最新論文中得出結(jié)論，“研究表明，市面上最典型的‘簡(jiǎn)單式’綠色屋頂?shù)慕Y(jié)構(gòu)，即磚底基質(zhì)層和景天類植物層的組合方式在雨水截流和滯留方面具有最全面優(yōu)異的水文性能。然而，應(yīng)該指出的是，淺層的‘簡(jiǎn)單式’綠色屋頂系統(tǒng)需要與位于LID治理鏈下游的截流和滯留措施相結(jié)合，形成更為整體的可持續(xù)城市排水系統(tǒng)（SUDS），這樣即便最大的暴雨事件下的洪水風(fēng)險(xiǎn)也能降低”[8]。她同時(shí)指出：“長(zhǎng)期植被覆蓋、分級(jí)良好、基質(zhì)滲透性較弱的綠色屋頂?shù)挠晁亓髂芰?yōu)于配備大孔徑滲透性強(qiáng)基質(zhì)的屋頂。[8]”

在德國(guó)，景天類植物作為屋頂綠化材料中的“主力軍”已經(jīng)成功使用40余年（圖5）[9]。斯圖文的新研究再次證實(shí)，景天類植物與滲透性較弱基質(zhì)的組合方式在雨水截流方面卓有成效。澳大利亞的另一支團(tuán)隊(duì)在評(píng)述了不同植物組合方式和用水模式對(duì)雨水截流能力的影響后得出結(jié)論：“與我們的假設(shè)相反，植物層種植用水可塑性植物的綠色屋頂?shù)挠晁亓餍Ч⒉槐仍灾踩缫遗模⊿edum pachyphyllum）之類的保守型用水的多肉植物的屋頂好。另外，多種植物混植的屋頂綠化也沒能比單一植物截流更多的雨水。這是因?yàn)槎喾N植物混植的屋頂綠化雖然提高了屋面植物層的生物總量和生產(chǎn)力，但屋面的整體雨水調(diào)蓄性能會(huì)受到其關(guān)鍵物種—彎藥百合（Stypandra glauca）的不利影響。其根系很容易穿過基質(zhì)形成優(yōu)先徑流通道，造成雨水流失，從而降低基質(zhì)的儲(chǔ)水量、蒸散量和雨水截流量。因此為了優(yōu)化屋面的雨水截流能力，提高植物存活率，屋頂綠化的植物選擇不能僅考慮植物用水模式或物種多樣性，還應(yīng)考慮植物的根系性狀，因?yàn)橹参锔敌纬蓛?yōu)先徑流通道造成的影響遠(yuǎn)遠(yuǎn)超過了用水可塑性植物的用水特點(diǎn)帶來的好處。[10]”

上述兩個(gè)例子展現(xiàn)了現(xiàn)有綠色屋頂雨水截流效益和局限性研究中的研究深度、細(xì)節(jié)和嚴(yán)謹(jǐn)性。而中國(guó)海綿城市建設(shè)為這些研究提供了契機(jī)。如上述實(shí)驗(yàn)，現(xiàn)有的大多數(shù)實(shí)驗(yàn)都是在屋頂或同等規(guī)模下可控的小型實(shí)驗(yàn)地完成的。中國(guó)現(xiàn)在有機(jī)會(huì)借海綿城市建設(shè)之東風(fēng)將實(shí)驗(yàn)擴(kuò)展到城市規(guī)模，包括對(duì)綠色屋頂從建成之初就開始進(jìn)行全面監(jiān)測(cè)。這不僅能幫助中國(guó)人延續(xù)自古以來前沿的防洪研究傳統(tǒng)，而且有助于保護(hù)城市免遭重大洪水的侵害，引導(dǎo)公眾將雨水視為城市設(shè)計(jì)中的積極因素。綠色屋頂在LID雨水處理鏈中屬于前期措施，如上文所述，單獨(dú)使用綠色屋頂并不能可靠有效地應(yīng)對(duì)大型暴雨事件。因此，在城市尺度下設(shè)計(jì)和構(gòu)建基于LID的綠色屋頂至關(guān)重要。

綠色屋頂對(duì)LID雨洪管理系統(tǒng)的好處：1）通過植物和土壤蒸發(fā)減少進(jìn)入市政雨水管道的雨水徑流。2）減少因應(yīng)對(duì)氣候變化所需的市政雨水管道的升級(jí)。3）在城市密集區(qū)實(shí)現(xiàn)雨水源頭凈化和地下水補(bǔ)充。4）形成構(gòu)筑物與周圍環(huán)境間連續(xù)的生態(tài)棲息地。5）豐富“視覺體驗(yàn)”，有利于人類健康。6）改善相鄰建筑物周圍的小氣候。

2 設(shè)計(jì)師的責(zé)任

景觀設(shè)計(jì)師在進(jìn)行綠色屋頂和LID設(shè)計(jì)時(shí)需要承擔(dān)一定的責(zé)任。一旦出了問題，設(shè)計(jì)單位乃至整個(gè)行業(yè)的經(jīng)濟(jì)和名譽(yù)都會(huì)遭受重大損失，后果十分嚴(yán)重。因此，在設(shè)計(jì)和施工監(jiān)理的過程中需要始終保持嚴(yán)謹(jǐn)和專業(yè)。景觀設(shè)計(jì)師們應(yīng)該在設(shè)計(jì)過程中早早行動(dòng)，在所有項(xiàng)目的城市規(guī)劃階段就提倡綠色屋頂建設(shè)。事實(shí)上，他們應(yīng)是同城市規(guī)劃師和建筑師一起在項(xiàng)目現(xiàn)場(chǎng)的第一批設(shè)計(jì)師。海綿城市理念為景觀設(shè)計(jì)師成為項(xiàng)目主導(dǎo)提供了一個(gè)絕佳機(jī)會(huì)。LID是項(xiàng)目啟動(dòng)時(shí)考慮的第一個(gè)問題。戴莉萍在其文章中介紹了從中央政府到地方當(dāng)局自上而下式的海綿城市管理機(jī)制[2]。她強(qiáng)調(diào)做好城市防洪工作不僅僅是技術(shù)問題，而且還是一個(gè)管理問題—尤其是在海綿城市規(guī)劃之初[2]。設(shè)計(jì)師們應(yīng)該試著充分認(rèn)識(shí)理解項(xiàng)目所在地的管理結(jié)構(gòu)，在此基礎(chǔ)上提出與之適應(yīng)的LID策略。戴莉萍將中國(guó)海綿城市的管理結(jié)構(gòu)分成四類模式：自發(fā)型；規(guī)制型；供給型；賦能型[2]。這樣的管理結(jié)構(gòu)為設(shè)計(jì)師提供了一個(gè)框架，指導(dǎo)他們?nèi)绾螀⑴c到上述4類管理模式中。

自發(fā)型管理是海綿城市的自我管理，比如像戴莉萍在論文中解讀武漢案例那樣分析建成項(xiàng)目[2]。景觀設(shè)計(jì)師可以通過LID可視化方式強(qiáng)調(diào)綠色屋頂?shù)挠旰楣芾硇б?，通過在線動(dòng)畫向公眾生動(dòng)形象地解釋LID整體系統(tǒng)，在TED上公開演講來宣揚(yáng)LID的重要性，還可以協(xié)同當(dāng)?shù)鼐用窈驼餐_演示LID這一新措施。目前中國(guó)海綿城市建設(shè)的政策中并沒有強(qiáng)制要求公眾參與[2]，這與中國(guó)的傳統(tǒng)文化的價(jià)值觀念有關(guān)—國(guó)家利益高于集體，個(gè)人利益在最后。這些觀念深植在中國(guó)人的規(guī)劃理念里，當(dāng)下依然盛行，在今后的LID設(shè)計(jì)中仍需要引起重視[2]。景觀設(shè)計(jì)師需要不斷學(xué)習(xí)LID技術(shù)和專業(yè)知識(shí)，還要通過出版著作、研討、會(huì)議、公開課、展覽以及社交媒體等形式向公眾宣傳相關(guān)知識(shí)，想方設(shè)法提高公眾參與，與公眾分享他們的專業(yè)技能和想法。規(guī)制型管理是運(yùn)用傳統(tǒng)的法律法規(guī)進(jìn)行管理的模式[2]。景觀設(shè)計(jì)師們可以提倡將LID措施作為一種強(qiáng)制性的法規(guī)納入城市治水法律體系之中，強(qiáng)調(diào)綠色屋頂在城市尤其是高密度城市區(qū)域雨洪管理的效益。通過回顧現(xiàn)有最新的國(guó)內(nèi)外業(yè)內(nèi)研究，可以肯定的是，技術(shù)性條例需要根據(jù)城市當(dāng)?shù)氐牡乩砬闆r特點(diǎn)制定[2]。在供給型模式下，設(shè)計(jì)師可以向當(dāng)局主動(dòng)提供LID的資源、工具包（比如LID計(jì)算器等）、國(guó)際性的技術(shù)知識(shí)。甲方、政府人員、施工人員和研究人員是LID的共同決策者，景觀設(shè)計(jì)師在項(xiàng)目規(guī)劃之初“教育”他們深入理解項(xiàng)目位置、雨洪現(xiàn)狀及項(xiàng)目背景是十分重要的?？梢哉f，景觀設(shè)計(jì)師充當(dāng)了研究學(xué)者和甲方、當(dāng)局和施工安裝人員之間的橋梁。由于私人投資者對(duì)政府不信任，在中國(guó)實(shí)現(xiàn)賦能型管理是十分困難的[2]。景觀設(shè)計(jì)師可以提供更全面的總體規(guī)劃來解決這個(gè)問題。總體規(guī)劃不僅應(yīng)包含設(shè)計(jì)方案、技術(shù)細(xì)節(jié)和成本，還需包括規(guī)劃、施工和檢修各階段的時(shí)間進(jìn)度表。如果擁有一份與政府商定的明確的施工進(jìn)度表，這應(yīng)該能增加私人投資方對(duì)投資的信任。需要特別注意的是，進(jìn)度表里應(yīng)該預(yù)留充足的前期現(xiàn)場(chǎng)分析和方案設(shè)計(jì)時(shí)間。當(dāng)前武漢的海綿城市項(xiàng)目因當(dāng)初僅給了3個(gè)月的設(shè)計(jì)和規(guī)劃期限而深受其苦[2]。

3 未來的對(duì)策

中國(guó)現(xiàn)有的洪水防御相關(guān)研究建議：可以通過公眾教育，促進(jìn)中央政府和地方當(dāng)局之間的合作，加強(qiáng)防汛通信預(yù)警系統(tǒng)以減少洪水災(zāi)害[2-3]。這些建議同樣適用于引進(jìn)LID和綠色屋頂削減城市雨水徑流的情況。但目前綠色屋頂仍被認(rèn)為是高投入，并且有可能導(dǎo)致水資源破壞的措施。另外，大部分國(guó)際綠色屋頂制造商常常會(huì)極力倡導(dǎo)綠色屋頂?shù)挠晁芾硇б妫袊?guó)缺乏這樣成熟的綠色屋頂制造行業(yè)。進(jìn)口的綠色屋頂材料運(yùn)輸和建造成本都很高，因此需要盡快運(yùn)用本土產(chǎn)品構(gòu)建中國(guó)綠色屋頂市場(chǎng)，這樣不僅能夠降低進(jìn)口成本，還能根據(jù)城市基地特性，因地制宜地調(diào)整屋頂工程方案和用材。地方的LID持續(xù)運(yùn)營(yíng)需求同樣需要重視，具體來說是需要海綿城市項(xiàng)目總體設(shè)計(jì)和建設(shè)指南。戴莉萍在武漢指出：“現(xiàn)有的設(shè)計(jì)建設(shè)指南只注重施工，忽略了大量后期的運(yùn)營(yíng)和維護(hù)。[2]”景觀設(shè)計(jì)師們應(yīng)該在設(shè)計(jì)階段就做出項(xiàng)目運(yùn)營(yíng)和維護(hù)的日程表以平衡施工和運(yùn)營(yíng)維護(hù)之間的關(guān)系，而且強(qiáng)調(diào)這一長(zhǎng)期的花費(fèi)應(yīng)當(dāng)納入地方當(dāng)局每年的年度預(yù)算之中。LID的施工和維護(hù)應(yīng)由訓(xùn)練有素的專業(yè)人員進(jìn)行，因?yàn)榫G色屋頂系統(tǒng)屬于工程系統(tǒng)，需要定期檢查以確保其運(yùn)作達(dá)到設(shè)計(jì)目標(biāo)?，F(xiàn)有研究表明，中國(guó)當(dāng)下洪水防御和LID方面的專家十分緊缺，國(guó)內(nèi)外的設(shè)計(jì)教育者，制造商和LID施工安裝人員可以抓住這個(gè)機(jī)會(huì)，從中央到地方開展各級(jí)培訓(xùn)。最后，邀請(qǐng)?jiān)鴧⑴c歐洲或北美地區(qū)創(chuàng)新且成功運(yùn)營(yíng)的LID項(xiàng)目的設(shè)計(jì)師、工程師和安裝人員到中國(guó)交流想法和知識(shí)應(yīng)該也會(huì)大有裨益（圖6～11）。

5景天屋頂Sedum Roof5-1 細(xì)節(jié)Detail5-2 屋頂Roof

4 結(jié)論

中國(guó)近期海綿城市建設(shè)將雨水作為設(shè)計(jì)氣候適應(yīng)型城市時(shí)的創(chuàng)新設(shè)計(jì)約束條件，開創(chuàng)了世界先例。不論是在防洪歷史、復(fù)雜的城市防洪政策發(fā)展還是在管理結(jié)構(gòu)方面，中國(guó)都是世界上最古老的國(guó)家之一[5]。當(dāng)下中國(guó)的海綿城市戰(zhàn)略有利于將綠色屋頂納入雨洪管理綜合系統(tǒng)，作為雨洪治理的主要手段之一發(fā)揮效益，尤其是在高密度不透水的市中心區(qū)域，因?yàn)樗赡苁菫閿?shù)不多能夠與公共空間靈活結(jié)合使用的雨水截流裝置。綠色屋頂緊急溢流的情況始終存在，因此我們需要設(shè)計(jì)傳統(tǒng)的雨水溝或基于LID技術(shù)的截流、滯留池來配合使用。在新城市設(shè)計(jì)階段，地上和地下的水處理都始終需要關(guān)注[2]。

The achievements of Low Impact Development(LID) in China since the sponge city initiative was launched in 2015 in 16 cities have been extensive[1](Fig.1). The goal of LID is to emulate the stormwater/rainwater runoff function that a site had in its natural state, before alteration by humans. LID techniques include: living roofs, bio-retention areas, permeable paving, bio swales, water retention/detention ponds,rainwater harvesting and storage(Fig.2). A recent article by Dai Liping explores in detail the pros and cons of the governance structure behind the new city program in China and its financing challenges[2].The Chinese government at all levels tried to reduce flooding of its cities for centuries with structural measures such as dams and non-structural measures such as policies. Deadly floods have occurred regularly for thousands of years[3]. Weiwei Shao listed in his article on sponge cities examples of major flooding events over the past 8 years, detailing lives lost and the cost of economic damage to demonstrate how important it is to have a detailed sponge city data plan to improve city design and construction[4]. He clarified through his article that “the construction of sponge cities is a very complex task of systems engineering”[4]and acknowledged the importance of sponge city data collection to improve flood protection performance so that the sponge city initiative would be successful .

Managing floods is not new in China. In fact,for over 5000 years the Chinese have had to be extremely creative in dealing with flood protection[3,5].Wu Qingzhou’s article from 1989 explains in detail not only the history, governance structure and policies,but also China’s technical genius and willingness for experimentation in initiating flood protection in urban planning policies of its ancient cities[5]. This long history of flood protection stems partially from the geographical location of many urban settlements in the vast river deltas in Eastern China and along the coast, both regions inundated regularly with dramatic floods due in part to seasonal monsoons (Fig. 3). The precipitation pattern in China decreases from the Southeast to low in the Northwest[3].

Today additional challenges complicate matters which have primarily led to the rapid initiation of the sponge city initiative in 2015. Land use practices have changed as more and more agricultural land is used for urbanization due to China’s population growth[3].Intense construction of entire new cities populated with millions of people in the “open field”, spurred by the economic boom, has created vast areas of impervious surfaces in cities, impeding soil absorption of rain and stormwater. Additionally, climate change has made rainfall events more uncertain[3]. Shorter rainfall duration and higher intensity events increase stormwater peak flow rates resulting in uncontrollable surface- flooding and extensive water pollution of the soil, rivers and the ocean[3].

But how can these problems be actively addressed in China with such a long flood protection history? The Chinese are used to water and have lived harmoniously with rivers and lakes in their water towns such as the Jiangnan’s heritage water towns Wuzhen, Nanxun or Tongli for centuries (Fig. 4)[6]. One of the answers might lie in the hands of the public and decision makers’willingness to accept, as they did with water towns in the past, that water, in this case rain and stormwater runoff in cities, is not only a threat but a valuable resource to be protected and designed for as part of a holistic stormwater management system called LID. These LID systems slow down the stormwater to reduce increased peak flows, mitigated at source on site and recycled for reuse. It is here where “extensive” living roofs,as one of the LID tools in cities, can play a key role in partially managing rain and stormwater.Impervious downtowns especially will benefit from the stormwater mitigation effects from living roofs,as often there is not the space to manage water at grade alone due to lack of pervious surfaces.

This issue is a task where landscape architects are well positioned to address and take on a leading role in LID advocacy and visualization, and not only in its implementation. Landscape architects can design and pre-dimension LID, engineers are responsible to calculate the final dimensions of LID, and both need to work hand in hand from the outset to create a successful LID system. Landscape architects are equipped with a holistic understanding and reading of region, urban and site scales, and the complex interconnected environmental systems. They also have the knowledge and knowhow to interpret the other parameters needed to implement LID: local climate, soil drainage capacity, overall site conditions,grading and drainage, and site context. Finally, they have the know-how about which LID tools should be applied and in what combination to provide the most benefits. It could be argued if applied in the initial overall urban planning process, not as an afterthought,that LID could determine the allowable building footprint to manage stormwater on site. With China’s leading-edge sponge city plan in place and a rigorous policy applying extensive living roofs in cities as a stormwater management tool, their cities could be at the forefront in LID design and research very soon.

1 Extensive international living roof research

Research on “extensive” living roofs stormwater capabilities have been very rigorous and successful over the last years. “Extensive” living roofs are: “a single or multilayered living roof system (drainage,growing media and plants) designed individually or as composite, manufactured system. The growing media depth may be 25-150mm, while the surface may be either level or graded with low topographic features.Extensive living roofs are vegetated with typically low-growing plants”[7]. This article addresses only“extensive” living roofs as “intensive” living roofs do not qualify as economically and technically acceptable stormwater management tools for cities and are too complex to construct and maintain.

Living roofs water mitigation capacity depends mainly on local climate, evapotranspiration rate(ET), engineered soil medium, roof assembly and vegetation. Plants and growing conditions should match climate conditions to have a successfully functioning roof. Elizabeth Fassman-Beck states:“Growing medium is perhaps the most important functional component of a living roof system in terms of stormwater management - growing medium is like a sponge”[7]. Living roofs are not successful stormwater management tools alone. If the climate is extreme, for example long dry summer periods where the vegetation needs extra irrigation to survive, water has to be stored and distributed using energy. Or, extreme rainfall conditions may require additional storage in the building to detain the roof run off, if there is no space for LID at grade. Living roofs are only able to capture routine storm events. Virginia Stovin a Reader at the University of Sheffield concludes in her 2015 paper that her test plots could: “offer good retention performance for routine storm events …. none is reliably able to achieve a 2 l/s/hm2peak runoff requirement (a green field run off equivalent) for large events (i.e. measured events where P＞ 10mm or a simulated 1 in 30 year return period event)”[8].Living roofs are only one tool and should be applied with other LID tools at grade, such as bio-retention areas, swales and retention/detention ponds creating a treatment train, managing and possibly cleaning stormwater. At grade LID tools could deal with roof water peak runoff, when the extensive living roof reaches field capacity and its runoff acts like a conventional roof. In China living roofs are still not fully accepted by the design profession nor the government, as there is still hesitation about their stormwater capabilities and cost. Most research in China is initiated by individual pioneering efforts such as that of Prof. Dr.-Ing. Dong Nannan and Prof. Dr. Luo Tianqing both Tongji University who believe in their stormwater capabilities.

6 停車場(chǎng)改造—雨水削減實(shí)驗(yàn)結(jié)果Carpark retrofit—water mitigation results

In the last years significant international research has proven living roofs stormwater management capabilities. Stovin and her team,for example, have been testing the hydrological performance of soil media (substrate) and vegetation configuration in test beds at the University of Sheffield for years and conclude in one of their latest papers 2015: “Overall the study has demonstrated that the configurations most typical of commercial extensive green roof systems,i.e. Sedum vegetation on a brick-based substrate,will offer the best all-round performance in terms of both retention and detention. However, it should be noted that shallow, extensive, green roof systems need to be combined with downstream retention and detention measures to provide more holistic Sustainable Drainage Systems (SuDS)solutions that can mitigate flood risk for even the largest storm events”[8]. She also observed: “that long term vegetated living roofs with well graded,less permeable substrate have a higher retention capacity than large-pored permeable substrate”[8].

In Germany Sedum has been seen as the “work horse” for living roofs successfully for 40 years (Fig.5)[9]. This new research confirms again that this species in combination with less permeable substrate is useful for stormwater retention. Another team in Australia reviewed how plant composition and water use strategies could in fluence stormwater retention and concluded: “Contrary to our hypotheses, green roof modules planted with species with water use plasticity did not always retain more water than the conservative water using succulent,Sedum pachyphyllum. Also, the mixtures of plant species did not retain more water than monocultures. Although the mixed species treatment had higher biomass and productivity, the performance of the mixture was adversely affected by the key species,Stypandra glauca. The root systems ofS. glaucalikely created preferential flow pathways through the substrate,limiting substrate water contents, evapotranspiration,and rainfall retention. To optimize rainfall retention and plant survival, species selection for green roofs should therefore not only consider water use strategies or species diversity. Root traits should also be considered when selecting green roof plants, due to the importance of preferential flows overriding the benefits of plastic plant water use strategies”[10].

7 停車場(chǎng)改造屋頂平面圖—設(shè)計(jì)階段Carpark retrofit roof plan—programming

8 停車場(chǎng)改造場(chǎng)地平面圖—LID系統(tǒng)布局Carpark retrofit site plan—LID systems layout

9 軸測(cè)圖Axon

These two current examples demonstrate the depth, detail and rigor of existing research on living roof water retention capacities and its limitations. It is here where the opportunity for China lies with the sponge city initiative. Most of the experiments like the two above have been done in controlled smallscale test bed environments on roofs and at grade.China has now the opportunity with the sponge city initiative to expand these experiments to an urban scale including monitoring the constructed living roofs from the outset. This would not only continue their historic leading-edge tradition of flood control research but it might help to safeguard the cities from major floods and entice the public to see rain and stormwater as a positive element in urban design. Living roofs are at the front end of the LID treatment train. As mentioned above, alone they are not a reliable tool for large storm events. Therefore,it is important to design and construct living roofs at urban scale in combination with at grade LID.

Living roof benefits for LID include:1) Reducing rainwater runoff entering public stormwater sewers through plants and soils evapotranspiration. 2) Reducing upgrades of existing public stormwater sewers needed otherwise due to climate change. 3) Cleaning runoff and recharging the water table at source in dense urban areas.4) Providing a continuous ecological habitat from built structures to grade and vice versa. 5) Providing a “viewing experience”, that can also have a positive impact on health. 6) Improving the microclimate around adjacent buildings.

2 Designer responsibility

Landscape architects are potentially liable when designing living roofs and LID at grade. It’s a serious matter, if it goes wrong, and the economic and reputation damage to an of fice and the profession could be significant. Therefore, a rigorous understanding is needed to design and supervise their construction. This is indeed common knowledge but landscape architects could do more earlier on in the design process. They should be involved in living roof advocacy, and at the initial urban planning stage of any design project. In fact, they should be the first designers on site together with urban designers and architects. The sponge cities concept provides an excellent opportunity for landscape architects to take a leading role. LID should not be an afterthought; in fact, it should be the first question when a project is initiated. Liping Dai describes the governance structure of the sponge city program in his article from the top-down, from central government to local government[2]. He emphasizes that preparing cities for flooding is not only a technical but also- especially at the beginning of planning a sponge city—a governance issue[2]. Designers should try to recognize where they are working and understand these structures to provide LID solutions acceptable to these governance structures. Ling Dai divides China’s governance into four categories: governing by example,authority, provision, and through (co)funding[2]. This structure could provide a framework for where and how the designers could be involved in all four.

10 停車場(chǎng)改造屋頂LID系統(tǒng)—細(xì)節(jié)和裝置Carpark retrofit roof LID system—details &assembly

11-1 露天劇場(chǎng)南北剖面North-south section at amphitheatre11-2 啤酒花園南北剖面Noth-south section at Beer Garden

Governing by example could be the sponge city initiative in itself, and analyzing already built projects such as Liping Dai’s paper does with the Wuhan case study[2]. Landscape architects could provide LID visualizations emphasizing living roofs stormwater benefits, explanatory animated online movies explaining the holistic LID systems,public talks in TED talk manner to elevate the importance of LID and starting a new culture of public presentations in local municipalities including the residents. Currently public participation is not compulsory in sponge city policies in China[2]. This has to do with traditional Chinese culture were the national interest is above the collective and ‘lastly’individual interest. These principals are rooted in the Chinese planning ideology and will need to be reviewed closely in the future when designing LID[2],as at the moment national interests still prevail.Landscape architects should not be deterred from promoting their LID skills and knowledge and seek opportunities to integrate public participation through informing them through publications,discussions, conferences, public talks, exhibitions and Chinese social media. Designers should be public advocates of their skills and ideas. In governing by authority where traditional regulations and sanctions are used[2], landscape architects could advocate to help shape those regulations including LID tools as a necessity, and emphasize living roofs stormwater management benefits, especially in dense city areas.Existing international and recent national peerreviewed research could help make a convincing argument. Technical guidelines should be tailored to local geographic conditions[2]. In governing by provision, designers could provide LID resources,toolkits such as LID calculators and international technical knowledge to authorities. “Education” in reading project sites, existing stormwater conditions and their context at the beginning of the planning phase is important for LID decisions made by clients, governmental employees, public and future installers of LID. Landscape architects are the link between researchers on one side and clients,authorities and installers on the other. Governance through (co)funding is difficult in China as private investors distrust the government[2]. In this instance landscape architects could provide a masterplan which not only includes design, technical details and cost, but an overview plan for the planning,construction and maintenance schedules. This might reduce the current distrust by private investors to invest money, if a clear construction timeline is agreed upon with the government. Important to note is to include ample preliminary site analysis and design time, as current sponge city projects in Wuhan suffered from very short 3-month design and planning deadlines[2].

3 Future steps

Current research on flood control and prevention in China recommends: citizen education, promoting cooperation between federal governments and local authorities, and functioning flood communication systems to reduce flood damage[2-3]. These recommendations could also be applied to introduce LID and living roofs in cities to reduce stormwater runoff. But at the moment living roofs are still seen as expensive and a risk for water damage. Additionally,there is no established living roof industry in China to advocate their benefits as mostly international manufacturers are used. Material transportation and construction costs for those roofs are high and it would make sense to initiate a Chinese living roof market using local products to reduce import costs and adapt the engineered roof assembly to local conditions and availability of materials. Also of importance are LID’s local ongoing operational needs. Specifically, for sponge projects’ general design and construction guidelines,Liping Dia noted in Wuhan: “that they ignored largely operation and maintenance, while the focus was mainly on their construction”[2]. Landscape architects could provide project operation and maintenance schedules as part of their design package to balance out the current focus on construction and emphasize that this longterm cost should be included in the local authorities’annual budget. LID construction and maintenance should be carried out by trained staff, as living roofs and at grade systems, being engineered systems, need regular checks to make sure they function to their design objectives. Current research notes there is a lack of trained flood control professionals including LID specialists in China, which is an opportunity for international and local design educators, manufactures and installers to provide training from federal to local levels. Finally, it would be useful to invite the designers,engineers and installers involved with innovative wellfunctioning LID projects in Europe or North America,to China, to exchange ideas and knowledge (Fig. 6-11).

4 Conclusion

China’s recent sponge city initiative sets a precedent for the rest of the world to use storm and rainwater as a creative design constraint when designing cities for climate change adaption. China’s flood prevention history, sophisticated urban flood policy development and governance structure is one of the oldest[5]. The current sponge projects are a great opportunity now to integrate living roofs stormwater management benefits as one of the main tools of LID,especially in dense impervious downtowns, where they may be one of the only tools in conjunction with public spaces used as flexible water retention facilities.Living roof runoff should always have an emergency overflow, we therefore are going to need to continue designing conventional storm drains or retention/detention ponds in conjunction with LID. We should always focus on both above ground and underground services when we design new cities[2].

Notes:

① This paper is revised on the basis of the speech delivered by the author at the International Landscape Architecture Symposium in 2017.

② Fig. 1 is quoted from https://cleantechnica.com; Fig. 2 ?reference [7]; Fig. 2 is quoted from https://www.express.co.uk;Fig. 4 is quoted from https://zx.sztravel.gov.cn; Fig. 5 ? Daniel Roehr; Fig. 6-11: Living roofs and LID should be integrated in all urban design, architectural, landscape architectural and planning syllabi. Drawings from the University of British Columbia, Vancouver, Canada “Advanced Living Roof Seminar LARC 582E” final UBC SEEDS Report 2018. Drawn by Jericho Bankston, Josh Harvey, Instructor: Assoc. Prof.Daniel Roehr.

(Editor / WANG Yilan)

注釋：

① 本文以作者在2017世界風(fēng)景園林師高峰講壇上的發(fā)言稿為基礎(chǔ)進(jìn)行補(bǔ)充。

② 圖1來自https://cleantechnica.com；圖2引自參考文獻(xiàn)[7]；圖3來自https://www.express.co.uk；圖4來自https://zx.sztravel.gov.cn；圖5由作者拍攝；圖6～11：綠色屋頂和低影響設(shè)計(jì)，來自2018英屬哥倫比亞大學(xué)（UBC）社會(huì)生態(tài)經(jīng)濟(jì)發(fā)展研究（SEEDS）LARC 582E報(bào)告，由杰里科·班斯頓、喬什·哈維繪制，指導(dǎo)老師為丹尼爾·勒爾副教授。

（編輯/王一蘭）