著：（美）羅伯特·瑞恩 譯：于冰沁

城市流域面臨著土地利用方式快速變化的挑戰(zhàn)，這些變化威脅著快速增長(zhǎng)的人口所需的水資源供應(yīng)環(huán)節(jié)，迫切地需要?dú)夂蜻m應(yīng)型城市，以應(yīng)對(duì)洪水增加、干旱期延長(zhǎng)等氣候變化。綠色基礎(chǔ)設(shè)施是一種積極應(yīng)對(duì)土地利用變化的方法，即在大尺度上保護(hù)自然資源，同時(shí)也在小尺度中發(fā)展創(chuàng)新方法，保護(hù)生態(tài)系統(tǒng)服務(wù)與功能。美國(guó)的城市流域中，許多土地利用變化的誘因是郊區(qū)住宅區(qū)的開發(fā)，導(dǎo)致了自然植被和農(nóng)田大量被草坪所代替。這些變化往往是城鎮(zhèn)規(guī)劃的決策或業(yè)主個(gè)人共同導(dǎo)致的。然而，個(gè)人決定如何能影響更大尺度的城市流域呢？影響業(yè)主改造庭園等住宅景觀的綠色基礎(chǔ)設(shè)施的因素有哪些？對(duì)于這些問題我們知之甚少。

因此，本文作者通過美國(guó)馬薩諸塞州波士頓以北的伊普斯維奇河（Ipswich River）流域的案例研究，探究如何在多尺度上利用綠色基礎(chǔ)設(shè)施進(jìn)行流域規(guī)劃。由于雨水徑流受污染、社區(qū)用水過度，伊普斯維奇河被認(rèn)為是美國(guó)最受威脅的河流之一[1]。當(dāng)?shù)卣畽C(jī)構(gòu)面臨著頻繁缺水、水質(zhì)污染等問題，因此水資源保護(hù)和雨水管理是流域規(guī)劃的當(dāng)務(wù)之急。本研究包括為跨越市政邊界的整個(gè)流域制定綠色基礎(chǔ)設(shè)施規(guī)劃方案，以及調(diào)查公眾對(duì)住宅區(qū)綠色基礎(chǔ)設(shè)施改造的接受程度。其中，住宅區(qū)的綠色基礎(chǔ)設(shè)施包括雨水花園和耐旱景觀等。本研究將為其他同樣面臨水資源問題的城市流域規(guī)劃提供寶貴經(jīng)驗(yàn)。

1 研究背景

伊普斯維奇河流域面積約為400 km2，人口16萬(wàn)人[2]，橫跨15個(gè)城鎮(zhèn)的部分區(qū)域[3]i；然而，伊普斯維奇河為35萬(wàn)左右人口提供飲用水，其中大多數(shù)人生活在流域外。過度用水導(dǎo)致過去幾十年里出現(xiàn)了嚴(yán)重的枯水事件。此外，郊區(qū)住宅不透水表面覆蓋與草坪面積的增加也對(duì)水質(zhì)和水量產(chǎn)生了負(fù)面影響。流域內(nèi)的地表覆蓋方式主要是林地（70%）。此外，除伊普斯維奇河及其支流外，還有77個(gè)池塘和湖泊[3]2-4。該流域位于波士頓都市區(qū)的東北邊緣，都市區(qū)人口為470萬(wàn)人（2014年美國(guó)人口普查估算），預(yù)計(jì)會(huì)繼續(xù)增加。流域上游為發(fā)展成熟的郊區(qū)，住宅密度中等，下游為有大量土地保護(hù)區(qū)的小城鎮(zhèn)（圖1）。

1 伊普斯維奇河流域的區(qū)位圖與現(xiàn)有土地利用情況Location map and existing land use—Ipswich River Watershed

2 伊普斯維奇河流域的多尺度規(guī)劃方案Multi-scalar approach to watershed planning—Ipswich River Watershed

為解決河水流量過低的問題，當(dāng)?shù)爻擎?zhèn)對(duì)住宅戶外用水采取了自愿和強(qiáng)制性措施，例如限制居民澆灌花園及草坪的天數(shù)。由州和聯(lián)邦環(huán)境屬資助的綠色基礎(chǔ)設(shè)施示范項(xiàng)目已在伊普斯維奇河流域開展，以便展示創(chuàng)新的風(fēng)景園林解決途徑，如使用本地植物和利用雨水花園蓄留雨水徑流，促進(jìn)地下水滲透。研究表明，這些舉措可以有效改善水質(zhì)和補(bǔ)充地下水，但需要大規(guī)模應(yīng)用才能對(duì)整個(gè)流域產(chǎn)生改變的作用[4]。

當(dāng)?shù)厮Y源保護(hù)的另一個(gè)重要參與者是伊普斯維奇河流域協(xié)會(huì)，一個(gè)促進(jìn)流域保護(hù)意識(shí)、教育和宣傳的非政府組織[2]1。該協(xié)會(huì)致力于將當(dāng)?shù)鼐用衽c河流連接起來(lái)，并游說(shuō)政府為了人民和生態(tài)環(huán)境保護(hù)制定維持水平衡的政策。該協(xié)會(huì)實(shí)施了一系列的項(xiàng)目，致力于增進(jìn)居民對(duì)河流的了解，并收集有關(guān)當(dāng)?shù)厮h(huán)境和生物多樣性的重要信息。

2 風(fēng)景園林設(shè)計(jì)工作室

本研究項(xiàng)目由羅伯特·瑞恩教授領(lǐng)導(dǎo)的馬薩諸塞大學(xué)安姆斯特分校的研究生風(fēng)景園林設(shè)計(jì)工作室參與完成。該工作室與當(dāng)?shù)卣鸵疗账咕S奇河流域協(xié)會(huì)合作，致力于發(fā)展綠色基礎(chǔ)設(shè)施計(jì)劃，目的是保護(hù)該地區(qū)的水資源造福子孫后代[5]。工作室運(yùn)用多尺度途徑，使學(xué)生理解小尺度場(chǎng)地設(shè)計(jì)的力量是如何影響大尺度城鎮(zhèn)和社區(qū)尺度的規(guī)劃決策的。本項(xiàng)目運(yùn)用地理信息系統(tǒng)（GIS）來(lái)識(shí)別重要的環(huán)境特征，包括含水層補(bǔ)給區(qū)、休閑游憩特征（如現(xiàn)狀或規(guī)劃中的路徑和保護(hù)用地）、歷史文化特征。本項(xiàng)目的景觀評(píng)價(jià)階段則利用了Fabos[6]、Benedict和McMahon[7]提出的綠道與綠色基礎(chǔ)設(shè)施方法。

采用嵌套式的方法從多個(gè)尺度處理水資源問題。首先，在區(qū)域尺度，分析包含伊普斯維奇河在內(nèi)的波士頓北岸都市區(qū)流域重要的水文聯(lián)系，如流向附近城鎮(zhèn)、現(xiàn)狀或規(guī)劃中的區(qū)域路徑和開放空間系統(tǒng)的流域間水系流動(dòng)。然后，進(jìn)行流域尺度的分析，即跨越多個(gè)行政管轄區(qū)，從整體上尋找生態(tài)（自然）和文化模式之間的聯(lián)系。結(jié)果顯示，根據(jù)河流的位置或河段的不同，該流域有3種不同的土地利用模式和特征。流域的上游地區(qū)多為發(fā)展成熟、密度中等的郊區(qū)；中部地區(qū)正在城市化，擁有較多低密度的大面積住宅；而河口則有大片的保護(hù)用地圍繞著歷史悠久的伊普斯維奇（Ipswich）和埃塞克斯（Essex）鎮(zhèn)中心。

3 伊普斯維奇河流域的綠色基礎(chǔ)設(shè)施規(guī)劃Ipswich River Watershed green infrastructure plan

4 托普斯菲爾德的重點(diǎn)區(qū)域Topsfield focus area

在經(jīng)過初步的區(qū)域和流域尺度整體分析后，將9名研究生組成的工作室分為3個(gè)小組，分別研究3個(gè)子流域。子流域?qū)用娴脑敿?xì)分析有助于確定社區(qū)尺度的整體規(guī)劃和場(chǎng)地設(shè)計(jì)應(yīng)關(guān)注的重點(diǎn)區(qū)域，這有助于更大尺度規(guī)劃的實(shí)施。雖然這種分析、規(guī)劃和設(shè)計(jì)是由大到小尺度分級(jí)進(jìn)行的，但這個(gè)過程并不是嚴(yán)格的線性過程，而是循環(huán)的、相互作用的、不斷進(jìn)行反饋的。例如，當(dāng)發(fā)現(xiàn)了新的細(xì)節(jié)和新的關(guān)聯(lián)時(shí)，會(huì)整合子流域規(guī)劃，以修改最初的流域尺度的規(guī)劃。這種迭代性質(zhì)是多尺度流域規(guī)劃的一個(gè)重要特點(diǎn)（圖2）。

對(duì)水資源的景觀評(píng)價(jià)表明，流域上游的開發(fā)導(dǎo)致含水層補(bǔ)給區(qū)和水源保護(hù)區(qū)出現(xiàn)了大量的不透水覆蓋面，但這種現(xiàn)象在下游地區(qū)較少。此外，筆者研究伙伴[8]的一項(xiàng)獨(dú)立研究發(fā)現(xiàn)，流域內(nèi)不同城鎮(zhèn)的不透水地表的面積也大小不等。例如，靠近河口的伊普斯維奇和埃塞克斯鎮(zhèn)的不透水地表面積約為5%，而位于上游的威爾明頓（Wilmington）和雷?。≧eading）則高達(dá)20%。此外，伊普斯維奇和埃塞克斯鎮(zhèn)中居住區(qū)的草坪覆蓋面積約為6%～8%，而威爾明頓和雷丁的草坪覆蓋面積則分別是13%和16%。這些不透水表面的油、重金屬、鹽和草坪中肥料等非點(diǎn)源污染惡化了流域的水質(zhì)。

根據(jù)項(xiàng)目第一階段的景觀評(píng)價(jià)的結(jié)果，研究者制定了綠色基礎(chǔ)設(shè)施規(guī)劃（圖3）。規(guī)劃提出要保護(hù)水源地等流域開放空間，以便在伊普斯維奇河及其支流沿岸建立一個(gè)相互聯(lián)系的綠地網(wǎng)絡(luò)。其目的是保護(hù)含水層補(bǔ)給區(qū)和水源保護(hù)區(qū)。此外，規(guī)劃還提出加強(qiáng)休閑道路的連接性，以便把當(dāng)?shù)鼐用衽c開放空間網(wǎng)絡(luò)、歷史文化資源聯(lián)系起來(lái)。由于評(píng)估發(fā)現(xiàn)流域上游等諸多水資源區(qū)正在經(jīng)歷快速的發(fā)展過程，該規(guī)劃建議對(duì)現(xiàn)有社區(qū)進(jìn)行景觀更新，以增加雨水的管理措施，促進(jìn)雨水滲透，并用本土植物代替大面積草坪，以豐富生物多樣性和棲息地。

3 社區(qū)重點(diǎn)關(guān)注的領(lǐng)域：改善生態(tài)環(huán)境健康

社區(qū)尺度的研究與實(shí)踐重點(diǎn)關(guān)注流域范圍內(nèi)面臨典型關(guān)鍵問題的區(qū)域，并通過創(chuàng)造性的風(fēng)景園林設(shè)計(jì)方案來(lái)解決問題。本研究介紹兩個(gè)具有上述特征的案例。其中一個(gè)研究和實(shí)踐項(xiàng)目由研究生薩曼莎·安德森（Samantha Anderson）完成，重點(diǎn)關(guān)注托普斯菲爾德（Topsfield）小鎮(zhèn)中的一個(gè)社區(qū)。該社區(qū)建在現(xiàn)有的含水層補(bǔ)給區(qū)上（圖4）。為了應(yīng)對(duì)這一挑戰(zhàn)，該項(xiàng)目建議沿現(xiàn)有街道設(shè)置雨水花園，以收集道路上的雨水徑流，并在雨水滲入地下水和含水層之前進(jìn)行過濾與凈化。這些雨水花園種植了本地的多年生草本植物。為了提高區(qū)域道路網(wǎng)絡(luò)中韌性系統(tǒng)的連通性，在人行道的區(qū)域鋪設(shè)透水鋪裝（圖5）。對(duì)于平行于伊普斯維奇河支流的道路，采用植草溝、滲透池等，在道路徑流匯入河流前進(jìn)行收集與處理（圖6）。

另一個(gè)由研究生鄧恩·玉（Ngoc Doan）開展的項(xiàng)目在鄰近河流的伊普斯維奇鎮(zhèn)進(jìn)行社區(qū)微更新。設(shè)計(jì)方案將筆直的道路變得彎曲，并在彎道上添加雨水花園和植物種植池，以取代6%的不透水表面（如人行道等，圖7、8）。早期研究發(fā)現(xiàn)[9]63，當(dāng)?shù)鼐用駥?duì)于在庭園中安裝綠色基礎(chǔ)設(shè)施的成本問題存在顧慮。因此，該項(xiàng)目使用成本計(jì)算器①預(yù)估移除草坪并替換為雨水花園的成本。該設(shè)計(jì)方案還提議移除該社區(qū)64%的草坪，取而代之的是本土植物和菜園等生產(chǎn)性景觀。草坪移除的比例是基于一項(xiàng)研究成果確定的。該研究表明，如果雨水花園的設(shè)計(jì)符合文化取向并具有較好的視覺效果[9]66，那么當(dāng)?shù)鼐用窈推渌胤降臉I(yè)主可能會(huì)愿意用本土植物和雨水花園取代多達(dá)一半的草坪[10-11]。此外，為了提高人們對(duì)流域水環(huán)境問題的認(rèn)識(shí)，該設(shè)計(jì)方案提議在重要區(qū)域安裝教育標(biāo)識(shí)來(lái)宣傳雨水花園，解釋其對(duì)生物多樣性和水質(zhì)的影響（圖9）。

4 住宅景觀偏好與綠色基礎(chǔ)設(shè)施

5 為托普斯菲爾德城鎮(zhèn)規(guī)劃的雨水花園Topsfield — proposed rain garden

6 托普斯菲爾德小鎮(zhèn)新型草地與街道效果圖Topsfield — new native meadow and street section

除風(fēng)景園林設(shè)計(jì)工作室外，本文作者與同事（包括副教授安妮塔·米爾曼和艾莉森·羅伊等）參與了一項(xiàng)由聯(lián)邦政府資助的伊普斯維奇河流域研究項(xiàng)目。該研究的目的是調(diào)查影響居住區(qū)水資源保護(hù)和管理的因素。其中一個(gè)子項(xiàng)目是調(diào)查流域內(nèi)居民對(duì)水資源管理的態(tài)度，尤其是參與綠色基礎(chǔ)設(shè)施景觀改造（例如用雨水花園代替現(xiàn)有草坪）的意愿[9]46。其中幾項(xiàng)措施是在工作室的規(guī)劃設(shè)計(jì)項(xiàng)目中提出的，并且已經(jīng)在流域內(nèi)開展實(shí)施，成為環(huán)境機(jī)構(gòu)資助的示范項(xiàng)目的一部分。通過對(duì)225位業(yè)主的調(diào)查，發(fā)現(xiàn)業(yè)主了解并支持水資源保護(hù)與管理的規(guī)定。業(yè)主關(guān)心綠色基礎(chǔ)設(shè)施方案（如雨水花園）的視覺效果，他們更喜歡整齊、簡(jiǎn)單、裝飾性強(qiáng)的方案，而非復(fù)雜方案。由此表明，他們認(rèn)同的是風(fēng)景園林設(shè)計(jì)研究員瓊·納賽爾（Joan Nassauer）所說(shuō)的“情景認(rèn)知與細(xì)節(jié)關(guān)懷”的理論[10]167。業(yè)主們也關(guān)注雨水花園的安裝和維護(hù)成本與傳統(tǒng)草坪相比是否有優(yōu)勢(shì)。當(dāng)?shù)亓饔騾f(xié)會(huì)在保護(hù)河流方面發(fā)揮了重要作用——協(xié)會(huì)成員比普通公眾更支持這些創(chuàng)新的風(fēng)景園林方案。此外，政府資助的雨水花園示范項(xiàng)目是一種值得推廣的模式，因?yàn)槿绻a(bǔ)貼能抵消一部分安裝成本，居民更愿意安裝雨水花園。因此，從多個(gè)尺度制定公共政策是十分重要和必要的。流域尺度的規(guī)劃項(xiàng)目對(duì)局部區(qū)域和場(chǎng)地也能產(chǎn)生影響，鼓勵(lì)居民在社區(qū)的建設(shè)與微觀更新過程中模仿這種創(chuàng)新性的景觀。

5 對(duì)風(fēng)景園林師和水資源規(guī)劃的啟發(fā)

本項(xiàng)目為那些致力于流域水資源規(guī)劃的風(fēng)景園林師提供了一些可以參考的經(jīng)驗(yàn)。

1）本項(xiàng)目說(shuō)明了多尺度制定規(guī)劃的重要性。因?yàn)榱饔蛲ǔ?huì)被劃分為多個(gè)政治管轄區(qū)，例如伊普斯維奇河流域被劃分為15個(gè)城鎮(zhèn)轄區(qū)，每個(gè)城鎮(zhèn)都擁有對(duì)土地使用的規(guī)劃決策權(quán)，因此需要采用嵌套式的方法。而在較小尺度上進(jìn)行分析時(shí)，則能發(fā)現(xiàn)大尺度中難以察覺和處理的新問題。例如考慮到行政管轄范圍和私人土地所有權(quán)的重疊問題，地面覆蓋面硬化問題只有在更小尺度的細(xì)節(jié)方案中才易于被識(shí)別與改善。

2）研究與實(shí)踐發(fā)現(xiàn)水資源會(huì)受到前期開發(fā)的影響，這在城市流域發(fā)展中是常見現(xiàn)象。因此，需要風(fēng)景園林師為社區(qū)的更新與改造提出適合的解決方案，以改善城市雨水的管理，增加蓄水層的滲透性，有效補(bǔ)充地下水，以及為附近的河流和溪流的供水。本項(xiàng)目的實(shí)施成為伊普斯維奇河流域郊區(qū)社區(qū)開發(fā)的示范性改造工程。風(fēng)景園林師需要根據(jù)一個(gè)地區(qū)的城市化程度來(lái)有針對(duì)性地制定綠色基礎(chǔ)設(shè)施的解決方案[12]。在城市化程度較高的地區(qū)，設(shè)計(jì)師需要考慮雨水花園等綠色基礎(chǔ)設(shè)施的安裝空間有限的問題。因此，在城市環(huán)境中，在人行道上沿著行道樹鋪設(shè)多孔的可滲透鋪裝及生態(tài)植草溝等方法比采用大型雨水濕地更合適。在流域中欠發(fā)達(dá)的地區(qū)，在開發(fā)前應(yīng)考慮預(yù)先的保護(hù)措施，如設(shè)置防護(hù)性的河岸緩沖區(qū)、雨水濕地等，這種方法與工程建設(shè)相比，能低成本地提升流域的水質(zhì)和水量[7]67。

3）本項(xiàng)目展示了如何將研究融入風(fēng)景園林的教育和實(shí)踐中。這種交叉學(xué)科的理論與設(shè)計(jì)實(shí)踐參見納賽爾和奧普丹（Opdam）關(guān)于結(jié)合科學(xué)研究與設(shè)計(jì)的開創(chuàng)性理論成果[13]642。無(wú)論是實(shí)證的研究項(xiàng)目，還是風(fēng)景園林設(shè)計(jì)工作室，每一種途徑都為解決城市流域所面臨的挑戰(zhàn)提供了不同的經(jīng)驗(yàn)和啟發(fā)。工作室的實(shí)踐項(xiàng)目展現(xiàn)了場(chǎng)地設(shè)計(jì)的重要性，場(chǎng)地設(shè)計(jì)方案使抽象的區(qū)域流域規(guī)劃更切實(shí)和具體，也可以使當(dāng)?shù)鼐用?、政府決策者和非政府組織有機(jī)會(huì)看到、評(píng)價(jià)并反饋創(chuàng)新性的風(fēng)景園林方案。本研究亦表明，了解當(dāng)?shù)鼐用駥?duì)設(shè)計(jì)師提出不同類型的綠色基礎(chǔ)設(shè)施技術(shù)的偏好至關(guān)重要，特別是對(duì)于那些主要由私人土地所有者做決策的景觀基質(zhì)，這一點(diǎn)尤為重要。此外，本研究和既往的研究發(fā)現(xiàn)，風(fēng)景園林師和工程師等專家的態(tài)度偏好可能與居民的偏好截然不同。如果設(shè)計(jì)師事先沒有考慮到這種偏好的差異性，那么很可能會(huì)阻礙綠色基礎(chǔ)設(shè)施的有效實(shí)施，因此需要通過充分的調(diào)查研究來(lái)發(fā)現(xiàn)這些差異[9,14]。這類研究能幫助我們發(fā)現(xiàn)那些受居民歡迎的、生態(tài)友好的綠色基礎(chǔ)設(shè)施解決方案。但這并不是忽視設(shè)計(jì)師的決策能力。設(shè)計(jì)師基于因地制宜的調(diào)查研究提出的設(shè)計(jì)方案仍發(fā)揮著關(guān)鍵作用[13]636。

4）本研究展現(xiàn)了流域協(xié)會(huì)等非政府組織在城市河流治理中發(fā)揮的重要作用。從很多方面來(lái)看，這些協(xié)會(huì)都充當(dāng)了當(dāng)?shù)鼐用窈驼疀Q策者之間的橋梁。此外，本研究發(fā)現(xiàn)這些組織在流域教育、河流清理和環(huán)境監(jiān)測(cè)的管理保護(hù)方面都發(fā)揮著至關(guān)重要的作用。

在城市人口增長(zhǎng)的過程中，風(fēng)景園林師有能力也有遠(yuǎn)見成為保護(hù)水資源的重要參與者。設(shè)計(jì)師通過多資源、多尺度的規(guī)劃方法，利用綠色基礎(chǔ)設(shè)施來(lái)改善流域的生態(tài)環(huán)境，同時(shí)為居民提供有價(jià)值的休閑資源和便利設(shè)施。更重要的是，無(wú)論流域是發(fā)展成熟還是未開發(fā)狀態(tài)，風(fēng)景園林師都要從流域全局出發(fā)，制定整體解決方案以應(yīng)對(duì)城市流域所面臨的挑戰(zhàn)。

（本文以作者在2018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。）

致謝：

本文所述的流域規(guī)劃由美國(guó)馬薩諸塞大學(xué)安姆斯特分校風(fēng)景園林與區(qū)域規(guī)劃系的LA607景觀設(shè)計(jì)工作室于2013年秋季開展（全部組員名單參見參考文獻(xiàn)[2])。感謝所有的研究生為此研究項(xiàng)目付出的辛勤努力和創(chuàng)造性工作，感謝伊普斯維奇河流域協(xié)會(huì)工作人員和流域的城鎮(zhèn)工作人員對(duì)此項(xiàng)目的幫助。

本文所述的研究由馬薩諸塞大學(xué)農(nóng)業(yè)、食品與環(huán)境中心（MASS000445）和景觀設(shè)計(jì)與區(qū)域規(guī)劃系資助。同時(shí)也要感謝馬薩諸塞大學(xué)安姆斯特分校的其他研究人員，包括環(huán)境保護(hù)系的安妮塔·米爾曼副教授、環(huán)境保護(hù)系與美國(guó)地質(zhì)勘探局的艾莉森·羅伊助理教授、環(huán)境保護(hù)系的佩奇·沃倫教授、美國(guó)地質(zhì)勘探局推廣教育工作人員瑪麗·歐文、斯托克布里奇學(xué)院景觀系系主任麥克·達(dá)維德松、研究生喬安娜·史黛西、瑞秋·丹佛和艾米麗·阿爾戈。此外，還要感謝佛羅里達(dá)大西洋大學(xué)的科林·波爾斯基教授（曾工作于克拉克大學(xué)）在伊普斯維奇河流域所做的草坪測(cè)繪工作。感謝莫拉·羅比塔耶幫助修改本文圖表。

注釋(Notes)：

①www.raingardenalliance.org/right/calculator。

圖片來(lái)源：

圖1～3?參考文獻(xiàn)[5]；圖4～6?薩曼莎·安德森；圖7～9?鄧恩·玉。

Urbanizing watersheds face the challenge of rapid land use change that threaten the water resources that are needed for growing populations.Variability in climate is expected to exacerbate this situation with increased flooding as well as prolonged droughts. Green infrastructure is one approach to proactively deal with land use change by protecting natural resources at the large-scale, while developing innovative approaches to protect ecosystem services and function at the site-scale. In urbanizing watersheds in the United States, much of the landuse change comes in the form of suburban residential development where lawns are the dominant new land cover that replaces natural vegetation and farmland.These changes are often the result of both town-scale planning decisions, as well as individual homeowners.However, little is known about how individual decisions affect the larger watershed, and what are the factors that may influence homeowners to engage in innovative residential landscapes, such as green infrastructure in their own yards?

This paper will focus on a multi-scalar approach to using green infrastructure for watershed planning using a case study in the Ipswich River watershed north of Boston, Massachusetts (USA). The Ipswich River is considered one of the most threatened rivers in the US, due to polluted stormwater runoff and overdraft of water by local communities[1]. Water conservation and stormwater management are critical priorities for local government agencies faced with frequent water shortages and impaired water quality.The project included developing a green infrastructure plan for the entire watershed that crossed municipal boundaries, as well as a research study into public acceptance for innovative green infrastructure improvements at the residential scale, such as rain gardens and drought-tolerant landscapes. This paper will focus on lessons learned for other urbanizing watersheds that are dealing with water resource issues.

1 Background

The Ipswich River Watershed covers an area of approximately 400 km2and has a population of 160,000[2]and spans portions of 15 towns[3]i;However, the river is used to supply the drinking water for about 350,000 people, the majority who live outside of the river basin. This heavy use of the river for water withdrawals has led to significant low flow events during the past decades.In addition, the increases in impervious surfaces from new development and lawns in suburban residential yards has negatively impacted water quality and quantity. The dominant land cover in the watershed is forest land (70%) and there are 77 ponds and lakes in addition to the Ipswich River and its tributaries[3]2-4. The watershed is on the northeastern edge of the Boston Metropolitan region which has a population of 4.7 million people (2014 US Census estimate), and is expected to continue growing in population. The upper reaches of the watershed include mature suburbs with medium density residential development while the lower reaches include small towns with large areas of conserved land (Fig. 1).

In order to address the low- flow in the river,local towns have relied on voluntary and mandatory water restrictions on outdoor residential water use that include limiting the days that residents can water their gardens and lawns. Green infrastructure demonstration projects funded by the state and federal environmental agencies have been built in the Ipswich River Watershed to show innovative landscape approaches including using native plants and rain gardens to capture and treat stormwater runoff in a manner that increases groundwater infiltration. Research has shown that these efforts can improve water quality and quantity, but would need to be replicated at a large scale to make a difference across the watershed[4].

Another important player in water conservation is the Ipswich River Watershed Association,which is a non-governmental organization that promotes watershed awareness, education, and advocacy[2]1. The Watershed Association has been instrumental in connecting local resident to the river, as well as lobbying for policies that protect the water balance in the river for people and ecology. The organization has a series of programs that engage local residents in learning about the river and at the same time gathering important information about local water conditions and biodiversity.

2 Landscape Architecture Studio

The project involved a graduate landscape architecture studio from the University of Massachusetts Amherst led by Professor Robert L. Ryan that worked with local town governments and the Ipswich River Watershed Association to develop a green infrastructure plan that would protect the water resources of the region for future generations[5]. The studio took a multiscalar approach to teach students how regional forces affect town and neighborhood scale planning decisions. The project used Geographic Information System (GIS) layers from the Mass GIS to identify critical environmental features,including aquifer recharge areas; recreation features, such as existing and proposed trails and conservation land; and historic and cultural features. The greenway and green infrastructure methods proposed by Fabos[6]and Benedict and McMahon[7]were used in the landscape assessment phase of the project.

A nested approach was used to address water resource issues at multiple-scales. First,the regional scale that encompassed the Ipswich River Watershed in Boston’s North Shore metropolitan region was analyzed to reveal important connections, such as the inter-basin transfer of water to nearby towns and cities, as well as existing and proposed regional trails and open space systems. Next, the watershed scale analysis was conducted to look holistically across multiple political jurisdictions for both ecological (natural)and cultural patterns and connections. This revealed that the watershed had three different characteristic land use patterns depending upon the location or reach of the river. The upstream sections of the watershed are more heavily developed with mature,medium-density suburbs. The middle section is urbanizing with low-density large lot homes, while the mouth of the river has large areas of conserved land surrounding historic town centers of Ipswich and Essex.

After the initial regional and watershed scale analysis, the studio of nine graduate students was divided into three teams that looked at one of the three sub-watersheds of the river. This detailed analysis at the sub-watershed scale helped identify critical areas for focused neighborhood scale master planning and site scale designs that illustrate how the larger-scale plan could be implemented. While this analysis, planning and design was conducted from the large to the small-scale, the process was not strictly linear, but circular and iterative. For example, the sub-watershed plans were consolidated in order to revise the original watershed-scale plan as new details and connections emerged. This iterative nature is an important aspect of multiscalar watershed planning and design (Fig. 2).

The landscape assessment of water resources revealed that in the upper reaches of the watershed significant areas of impervious surfaces from development had already occurred in aquifer recharge areas and well-head protection zones, but less so in the lower, downstream areas. In addition,a separate analysis by research partners[8]found that impervious surface areas of the towns in the watershed varied from low coverage of around 5% in Ipswich and Essex near the mouth of the river to 20% in the upper reach towns of Wilmington and Reading. Lawn areas covered an additional 6%-8% in the towns of Essex and Ipswich, and 13% and 16% respectively in Wilmington and Reading. These impervious surfaces and lawn areas contribute to negative water quality in the watershed through non-point source pollution in the form of oil, heavy metals, road salt, and lawn fertilizers.

A green infrastructure plan was developed using the landscape assessment results from the first phase of the project (Fig. 3). This plan proposed conserving unprotected open space,especially in water resource areas to create a linked network of greenspace along the Ipswich River and its tributaries. The goal was to conserve land in the aquifer recharge areas and well-head protection zones. In addition, recreation trail connections were proposed to link local residents to the open space network, as well as historic and cultural resources.Since the assessment found that many water resource areas had already experienced significant development, especially in the upper reaches of the watershed, the plan proposed landscape retrofits to existing neighborhoods to increase stormwater management and infiltration, as well as replace large areas of lawn with native plantings to improve biodiversity and habitat connections.

3 Neighborhood Focus Areas: Improving Ecological Health

7 伊普斯維奇小鎮(zhèn)的街區(qū)改造平面圖Neighborhood retrofit: town of Ipswich

8 伊普斯維奇街區(qū)的街道新規(guī)劃Street Redesign — Ipswich neighborhood

The neighborhood-scale projects focused on sites that exemplified the critical issues facing the watershed and demonstrated creative, landscape design solutions. This paper describes two of these projects. One of the projects by graduate student Samantha Anderson focused an existing neighborhood in the town of Tops field that was built on the existing aquifer recharge zone (Fig. 4). To address this challenge, the project proposed installing rain garden infiltration beds along existing streets to capture stormwater runoff from the roads and filter it before it infiltrated to the groundwater and aquifer below. These rain gardens would be planted with perennial, herbaceous native plants. In order to improve pedestrian connectivity as part of the regional trail networks, sidewalks of permeable pavement were proposed (Fig. 5). In other locations,where the roads ran parallel to existing tributaries of the Ipswich River, these infiltration basins capture and treat road runoff before it reaches the stream (Fig. 6).

Another project by graduate student Ngoc Doan proposed a neighborhood retrofit in the town of Ipswich adjacent to the river. This plan proposed replacing 6% of impervious surfaces(i.e., pavement) by adding slight curves to the straight roads and adding native plating beds with rain gardens to the meanders (Fig. 7, 8). Our earlier research project[9]63found that local residents were concerned about the costs of installing green infrastructure in their own yards. Thus, this project used a cost calculator①to determine the estimated cost of lawn removal and replacement with a rain garden. The plan also proposed removing 64% of lawn area in the neighborhood and replacing it with native plantings and productive landscapes such as vegetable gardens. This percentage of lawn removal was based on the research that suggests local homeowners here[9]66and in other locations are willing to replace up to half their lawn area with native plantings if the designs respond to cultural values and exhibit intentional design[10-11]. In order to raise awareness for watershed issues, the plan proposed educational signs be installed at key areas to interpret the rain gardens and their impacts on biodiversity and water quality (Fig. 9).

4 Residential Landscape Preference and Green Infrastructure

In parallel to this landscape architecture studio, the lead author was engaged in a federally funded research project in the Ipswich River watershed with fellow collaborators, including Associate Professors Anita Milman and Allison Roy (see Acknowledgement section). The goal of this research study was to understand the factors that influence residential water conservation. One sub-study in this larger project was a survey of homeowners in the watershed about their attitudes toward water conservation and particularly their willingness to engage in landscape practices involving green infrastructure, such as replacing their existing lawns with rain gardens[9]46. Several of these techniques were proposed in the studio projects and had already been built in the watershed as part of the demonstration projects funded by environmental agencies. This survey of 225 homeowners found that they were aware of and support water conservation regulations.Homeowners were concerned about the aesthetic appearance of green infrastructure solutions,such as rain gardens and preferred those that were more neat and ornamental in appearance rather than messy. In this manner, they subscribed to what landscape architect researcher, Joan Nassauer, describes as “cues to care”[10]167.The homeowners were also concerned about the cost of installing and maintaining rain gardens compared to traditional lawns. The local watershed association played a key role in advocating for the river — its members were more supportive of these innovative landscape practices than the general public. In addition, the demonstration projects where the government funded rain gardens are a good model to expand as residents were more willing to have rain gardens installed if there were grants or subsidies to offset the installation costs. Thus, the multi-scalar nature of public policy is also important here where watershedwide programs can make an impact at the site scale by encouraging neighbors to emulate innovative landscapes that they see built in their neighborhood.

5 Lessons for Landscape Architects and Water Resource Planning

This project provides several lessons for landscape architects who are interested in planning water resources in developing watersheds. First,it shows the importance of taking a multi-scalar approach since watersheds are often divided among multiple political jurisdictions. For example,the Ipswich River Watershed is divided into 15 towns that each have land use planning power over development decisions. A nested approach is needed as analysis at smaller scales reveals new issues that are difficult to detect and address at the larger scale. For example, impervious surfaces need to be removed in smaller scale design solutions that are recognizable and implementable in the context of local jurisdictions and multiple private landowners.

Second, the project found that the existing water resources had already been impacted by previous development, which is a common occurrence in developing urban watersheds. Thus,there is a need for landscape architects to develop solutions to retrofit existing neighborhoods to improve treatment of urban stormwater and increase infiltration to recharge aquifers that provide groundwater drinking supplies as well as supply water for nearby rivers and streams. In this project, pilot retrofit projects were developed for the suburban neighborhoods that are typical of the Ipswich River Watershed. Landscape architects need to tailor green infrastructure solutions to a site’s location along the urban to rural transect[12].In more urban conditions, green stormwater infrastructure need to respond to the limited space for rain gardens and other green solutions.Techniques such as porous paving and infiltration trenches along street tree plantings can fit better than larger stormwater wetlands in urban settings.In less developed areas of a watershed, proactive approaches such as protection of riparian buffers,wetlands and other is a more cost effective approach to protect water quality and quantity before development occurs than engineered infrastructure solutions[7]67.

Third, the study showed how research can be incorporated into landscape architectural education and practice. (See Nassauer and Opdam’s[13]642seminal work on integrating scientific research and design for the theoretical underpinnings of this interactive approach). Each approach, the empirical research study and the landscape architectural studio,adds complementary insights into the challenges facing urbanizing watershed. The studio shows the importance of developing site-scale designs that allow local residents, government policy makers, and non-governmental organizations the opportunity to visualize and respond to innovative landscape solutions, and which make the more abstract regional watershed planning scale plans more concrete and tangible. The research study shows how critical it is to determine local residents’ landscape preferences for the different type of green infrastructure techniques that are being proposed by designers, especially in a landscape matrix where private landowners make the majority of decisions on their own residential landscape. Moreover, our study and previous research show that experts such as landscape architects and engineers can have different attitudes and preferences than local residents, and research is needed to ascertain these differences, which can be a barrier to implementing green infrastructure if not considered beforehand[9,14]. Integrating research about landscape preferences does not eliminate the vital role that designers play in tailoring solutions to existing conditions at the site-scale, but research informs the range of ecologically beneficial solutions that may be embraced by local residents[13]636.

Finally, the study shows the important role that non-governmental organizations, such as watershed associations, play in advocating for urban rivers. In many ways, these organizations act as the conduit between local resident and government policy makers. In addition, in this study, we found these organizations play a critical role in watershed education, as well as stewardship through local river clean-ups and environmental monitoring projects.

Landscape architects have the skills and vision to be important players in protecting and enhancing water resources for growing urban populations. By taking a multiple-resource and multi-scalar approach to planning, they can use green infrastructure to enhance ecological health of a watershed while providing valuable recreational resources and other amenities for local residents.It is vital that landscape architects engage with the entire landscape, whether already developed or in a more natural state, to develop holistic solutions to the challenges facing urban watersheds.

(This paper is revised on the basis of the speech delivered by the author at the International Landscape Architecture Symposium in 2018.)

Acknowledgements:

The watershed plan described in this paper was developed by LA 607 graduate studio, Fall 2013 at the University of Massachusetts, Amberst, Department of Landscape Architecture and Regional Planning (See Reference[2]for full list of team members). Thanks to all the graduate students for their hard work and creativity on this project.Also, thanks to the Ipswich River Watershed Association staff for their help on the project, as well as the municipal staff in the watershed towns.

The research study described in this paper was funded by the UMass Center for Agriculture Food and the Environment(MASS000445) and the Department of Landscape Architecture and Regional Planning. Thanks also to other University of Massachusetts-Amherst researchers on this project including: Associate Professor Anita Milman (Dept. of Environmental Conservation), Assistant Research Professor Allison Roy (Dept. of Environmental Conservation and USGS), Professor Paige S. Warren (Dept. of Environmental Conservation), Mary Owen (UMass Extension Educator),Mike Davidsohn, (Director of Landscape Contracting,Stockbridge School), and graduate students Johanna Stacy,Rachel Danford and Emily Argo. Also thanks to Professor Colin Polsky (formerly at Clark University, currently at Florida Atlantic University) for his work on lawn mapping in the Ipswich River Watershed. Thanks to Maura Robitaille for help revising figures for this manuscript.

Sources of Figures:

Fig. 1-3 ? reference [5]；Fig. 4-6 ? Samantha Anderson;Fig. 7-9 ? Ngoc Doan