著：（荷蘭）瑞克·德·菲索 譯：金石雨 校：李衛(wèi)芳

1 “綠心”（Green Heart）概況

1.1 圩田上的大都市

荷蘭的蘭斯塔德地區(qū)是由阿姆斯特丹、哈勒姆、萊頓、代爾夫特、海牙、鹿特丹和烏得勒支等歷史名城形成的環(huán)形城市群落，占地面積約3 000 km2。超過800萬人居住在這個經濟中心，幾乎是荷蘭一半的人口?！熬G心國家景觀”（the Green Heart National Landscape，簡稱“綠心”）就位于這個環(huán)形城市群的中心。對這片泥炭地的改造始于中世紀早期。泥炭地經開采泥炭燃料，并作為農業(yè)用地進行去水處理，形成如今的圩田景觀?，F在，蘭斯塔德遭受土地沉降和全球變暖導致的海平面逐漸上升的威脅（圖1、2）。

1 北京和蘭斯塔德的對比Comparison between Beijing and Randstad

2 “綠心”北部的歷史變遷Historic development in the Green Heart (northern area)

3 “綠心”和蘭斯塔德地區(qū)的高程圖：深藍色部分代表之前由開采形成的泥炭沼澤區(qū)域，這些區(qū)域曾被洪水淹沒，之后經圍墾形成圩田，目前海拔介于－6 ～－4 m。紫色部分表示臨近泥炭地有嚴重的土地沉降The height map of the Randstad Holland and the Green Heart:Dark blue parts represent the former peat bogs which were excavated.These excavated areas were flooded and later reclaimed and arranged as polders.They are currently situated 4 to 6 meters below sea level (NAP).The purple colour indicates strong soil subsidence in the adjacent peat areas

蘭斯塔德和“綠心”的海拔目前幾乎都處于荷蘭海拔標準（Normal Amsterdams Peil，簡稱NAP）水位線0 m刻度之下，即低于平均海平面（圖3）。曾經的泥炭沼澤經過人工挖掘后形成了湖泊，這些湖泊隨后被排干，以開發(fā)新的農業(yè)區(qū)，其海拔介于-6 ～-4 m。荷蘭的最低點為海拔-6.76 m，其位于鹿特丹東北Zuidplas圩田（于1841年進行圍海造田）中的一片草地上。哈勒默梅爾（Haarlemmermeer）位于阿姆斯特丹附近，史基浦國家機場也坐落在此處，1852年，這里的泥炭地被抽干，平均海拔在-5 m。由于氣候變化，這些在圩田上建造起來的大都市面臨著巨大的壓力。既要減輕海平面上升的影響，同時也要減少溫室效應。此外，還面臨著重大的空間挑戰(zhàn)：必須使農業(yè)更具可持續(xù)性，停止進一步的土地沉降，增加生物多樣性，并轉向可再生能源的形式。而另一方面，還需要在2040年之前建造100萬套住房。

1.2 氣候變化

氣候變化將對荷蘭的空間規(guī)劃產生重大影響，這一事實已毋庸置疑。《海平面的加速上升對三角洲計劃的可能影響》[1]中展示了氣候變化對沿海地基、用水安全和淡水供應的影響。在2050年之后，海平面有可能處于持續(xù)加速上升的狀態(tài)。盡管現在還沒有直接的科學證據，但越來越多的科學家指出，荷蘭將會面臨這種情況帶來的問題，原因是南極洲的陸地冰蓋融化得越來越快。海平面上升是否會加速以及加速的幅度都將取決于國際氣候政策。

荷蘭的政策旨在實現2015年巴黎舉行的聯合國氣候變化大會上達成的目標—使全球升溫控制在2℃及以下。但該目標是否可以在全球范圍內實現尚無定數。依照荷蘭現在的情形，到2100年海平面將上升0.35～1 m。鑒于海平面上升對荷蘭的影響巨大，因此有必要考慮極端情況。若21世紀內全球溫度升高4℃，到21世紀末海平面就可能上升3 m[1]。人們并不清楚哪些措施是最有效的，也不知道這些必然的變化進程是如何構建起來的。政府采取觀望態(tài)度，好的政策不應僅局限于當下，還要考慮到未來。氣候公園的出現是在呼吁政策制定者和發(fā)起者共同努力，建設可持續(xù)的、有價值的“綠心”國家景觀。不僅要把氣候變化視為威脅，更要把它視為機遇。

4 “綠心”氣候公園剖面圖①Sectional view of Climate Park①

2 “綠心”氣候公園

2.1 兩大挑戰(zhàn)

荷蘭西部面臨兩大挑戰(zhàn)。1）適應氣候變化和可持續(xù)水資源管理。“綠心”依賴于持續(xù)的排水和來自其他地方的淡水供應，這種依賴隨著氣候變化而加強，隨之而來的還有安全和洪澇問題，這不是一個可持續(xù)的局面。我們還能繼續(xù)增高堤壩多久，還能繼續(xù)從地下抽水多久呢？而且，排澇耗費大量的能源和金錢。如果遇到干旱的夏季，就沒有足夠的水來滿足巨大的需求。這就是為什么正在考慮采取嚴厲措施，例如將艾瑟爾湖（IJsselmeer）的水位提高超過1 m。不過，如果能將水蓄存在“綠心”，就不需要上述的措施了。氣候公園的出發(fā)點是為“綠心”地區(qū)建立一個封閉的水平衡系統，不再依賴外部供水。2）提高生活質量，增強蘭斯塔德的經濟競爭力。在南部以及蘭斯塔德的其他地區(qū)對高質量的鄉(xiāng)村生活環(huán)境和方便可達的休閑場所有著巨大的社會需求，但是缺乏投資方面的行政決斷力，而規(guī)劃條例也會限制市場的主動性。因此，“綠心”氣候公園的出發(fā)點是尋找經濟功能和空間質量的新的結合點，實現“紅—綠”區(qū)域的綜合發(fā)展，而不是獲得限制性的部門政策（圖4）。

2.2 4個策略

氣候公園具有四重景觀策略（圖5）。

2.2.1 水系

氣候變化對蘭斯塔德的安全構成嚴重威脅，進而也對整個荷蘭的經濟構成嚴重威脅。威脅來自2方面：海平面的上升和高地河道泄水。鹿特丹地區(qū)尤其脆弱，為了保證地區(qū)安全，需要對整個河流系統進行徹底的重新設計。由于城鎮(zhèn)化和正在進行的基礎設施建設都聚集在河流沿岸，要整合區(qū)域發(fā)展將是個艱巨的任務?！皻夂虻虊巍保╟limate dike，超寬）的建設應該同打造宜人的、具有吸引力的河岸景觀相結合。

沿著河岸，可以將城市改建、擴建與河道拓寬、堤壩加固工程結合在一起。蘭斯塔德周圍的14號環(huán)形堤壩可以被擴建為牢固的“氣候堤壩”。這項設計不能僅是純粹的文化—技術元素的組合，更應該是一個具有多種功能的景觀結構。當在自然環(huán)境中建造新的建筑和特殊居住區(qū)時，也正是建設高質量城市河道及濱水景觀的良好契機。集多功能于一體的河道濱水景觀將對氣候產生有益影響：空間的多用途、熱電聯產、高效的公共交通等優(yōu)點。河道旁的建筑、歷史悠久的沿河城鎮(zhèn)、工業(yè)遺址、獨特的河岸自然風光共同構成了“綠心”的主要景觀結構，并在設計中得以強化。

2.2.2 重要的牧場草地景觀

在農業(yè)領域，氣候問題受到重視，比如貫徹實施水、營養(yǎng)、能量的封閉循環(huán)，減少CO2排放，增加農業(yè)生物多樣性。規(guī)模化和集約化生產不符合上述要求，但是高品質生產是符合的。例如，有機乳制品產業(yè)比傳統乳品業(yè)減少1/3溫室氣體的排放。河流黏土地區(qū)和有黏土底層的泥炭地也符合。在這些區(qū)域，保持農業(yè)文化景觀和健康食品生產具有可持續(xù)的基礎。

將區(qū)域特產貼上“綠心”質量標志，通過更好的市場營銷合作，農業(yè)有可能迎來新的經濟前景。很多公司發(fā)現了這一點并已經開始相互合作。“綠心”質量標志產生的經濟效益還有可能進一步擴大，例如讓“綠心”加入國際性的“慢城”（Cittaslow）運動中。意大利托斯卡納地區(qū)是“慢城”運動的典型代表。該運動的中心思想是：采用傳統的生產方式，熱情好客，親近自然界的土地、水、氣候等?！奥恰边€包括城市中可供人們休閑的路線和生態(tài)廊道，兩者組成一個精細的網絡。如果企業(yè)家們在紀念性建筑保護和歷史景觀恢復方面進行投資，他們將有很大的自由來開發(fā)新的服務和產品。

5 “綠心”氣候公園概念The Climate Park concept

6 圩田上的伊杰堡②IJburg in the polder②

2.2.3 濕地基礎設施

我們提議在比斯博什（Biesbosch）和艾瑟爾湖（IJsselmeer）之間建設一處濕地公園，打造自然濕地和休閑空間相結合的連續(xù)性區(qū)域。這樣不僅形成了一個可靠的生態(tài)廊道，還能在結構上保護“綠心”中最脆弱的泥炭地，推動休閑旅游業(yè)的發(fā)展。濕地公園建設的核心是在最容易發(fā)生土地沉降的泥炭地區(qū)域采取截然不同的水管理措施（圖3）。通過綜合的方法，減輕對農業(yè)的影響，使寶貴的景觀結構受到保護。

自動化造成農業(yè)用水水位不斷下降，但這種現象正在被叫停，取而代之的是根據水位調整土地利用，這意味著該區(qū)域逐步向自然生態(tài)和休閑娛樂區(qū)域轉變。水位可以根據自然條件上下波動，極大地增加了這一地區(qū)的蓄水能力。因此，該區(qū)域對外部水資源的需求會大幅減少，發(fā)生洪水的可能也少得多。這樣一來，泥炭地就恢復了其“海綿”效應，地面甚至可以再次抬高，將這種地區(qū)稱為“自然氣候緩沖區(qū)”。景觀會改變地區(qū)的風貌，但肯定不會降低其吸引力。生態(tài)方面，國際上對濕地的保護不斷加強。濕地公園的建成將為大城市居民提供方便可達的自然休閑空間，也為水上運動、自然體驗和發(fā)展文化旅游提供了新機遇。濕地公園內部的村落可以形成獨特的鄉(xiāng)村生活環(huán)境。在需要跨越基礎設施的地方，會設置適合動物和人們通行的牢固的“景觀橋”。只有通過綜合的規(guī)劃建設，才能為氣候、景觀和經濟帶來更多的附加價值。

2.2.4 荷蘭湖區(qū)

被挖掘的泥炭沼澤可以說是“綠心”地區(qū)的“丑小鴨”，各種政策關注的都是泥炭草地景觀區(qū)域。這一點可以理解：這塊新圍墾的土地有著一望無際的田野和筆直的道路，與那些古老的、富含水分的泥炭圩田相比，缺少休閑和生態(tài)方面的亮點。但這并不合理，因為這里是“綠心”發(fā)生鹽堿化和干旱的源頭，是洪水發(fā)生風險最大的地方。這里才最需要進行結構性設計，使其不受氣候變化的影響。也正是在這里，人們可以從景觀、自然、娛樂、生活和工作中受益良多?！熬G心”公園接受了這些挑戰(zhàn)，將展示“丑小鴨是如何變成白天鵝”的。

這片圍墾地有多種多樣的開發(fā)方式，無論是哪種，都會使區(qū)域水位大幅上升。在許多地方，為了自然的發(fā)展，會允許洪水浸沒土地，從而給泥炭地恢復提供機會。事實上，水位逐漸升高能促進有機物質的積累，進而大量的CO2被捕獲，地面再次抬升，這稱之為“活的泥炭地”。

水產養(yǎng)殖業(yè)或沼澤種植業(yè)為圩田農業(yè)提供了新的選項。水產養(yǎng)殖是指養(yǎng)殖魚、蝦、貝類或水生植物。沼澤種植側重于種植濕地作物，如香蒲、泥炭蘚或浮萍，部分圩田可能因此被水淹沒。濕地作物提供的是健康、環(huán)保、優(yōu)質的食物，而且比從自然界直接獲取、捕獲食物的方式更加有益于環(huán)境。

“Terpen”是指“荷蘭湖區(qū)”中的綠色生態(tài)居住島，而“Terpen”的開發(fā)是最具深遠意義、最具創(chuàng)新性的。為此，圩田必須全部或大部分被水浸沒，水位最好高于海平面。形成的新水域為居民提供更多水上運動的機會，并形成濕地自然景觀。島上將設置較多的居住用地：海港村莊、綠色住宅區(qū)、濱水公寓、浮動碼頭住宅等。這些人工島嶼的建造必須使用大量的沙子，但不會超過伊杰堡（阿姆斯特丹）的用量。但是并非所有的圩田都適合。上述做法特別適合那些臨近大城市、與道路和公共交通網絡連接良好的圩田。“Terpen”可以滿足蘭斯塔德地區(qū)對鄉(xiāng)村生活環(huán)境的高要求，通過真正可持續(xù)的水資源管理，能夠創(chuàng)造出一個令人贊嘆的新景觀（圖6）。

“綠心”氣候公園不只是一紙藍圖，更是一種發(fā)展的觀點，具有四重景觀策略：1）水系：將城市功能集中到沿著河流的容納能力較大、可達性較好的河岸上，并將濱水區(qū)域擴展到鄰近的林緣開放景觀；2）重要的牧場草地景觀：通過在農業(yè)、自然管理和景觀保護之間建立新的平衡，保護“開放式牧場景觀”這一典型荷蘭文化景觀；3）濕地基礎設施（泥炭景觀和泥炭沼澤開采之間的過渡）：通過調整水位管理、根據自然（泥炭地的再生）和休閑娛樂2個方面來改變區(qū)域功能，從而保護最脆弱的泥炭地區(qū)域；4）荷蘭湖區(qū)：通過以可持續(xù)水管理、住房和旅游為重點的綜合區(qū)域開發(fā)，解決深圩區(qū)嚴重的水問題。

7 生產型景觀方案示意圖Production scenario:Schematic map

8 生產型景觀方案總體規(guī)劃Production scenario:Masterplan

3 阿姆斯特爾蘭（Amstelland）區(qū)域的實施策略

氣候的不斷變化和水資源管理成本日益增加，需要對如何應對土地沉降有一個新的認識。相關深入調查研究已經在靠近阿姆斯特丹的“綠心”中的阿姆斯特爾蘭（占地4 500 hm2）展開，所有相關的問題都集中在一個小范圍內。在與區(qū)域利益相關方和專家商討后，制定了2種空間發(fā)展方案，并分別測試了它們對土地沉降、溫室氣體排放、水資源短缺、水資源過剩、生物多樣性和景觀的影響。

3.1 生產型景觀方案

在這一方案中，解決土地沉降的方法是加速將乳牛業(yè)轉化為自然循環(huán)農業(yè)。其核心在于：在泥炭區(qū)大規(guī)模應用水下排水系統，并在毗連的圍墾地建設蓄水池。土地沉降和CO2排放量能夠減半，開放式牧場草地景觀（暫時）得到保護。蓄水池具有淡水供應和灌溉作物的雙重功能，從而加強了農業(yè)生產結構。沿河的土壤因黏土、污泥和（或）城市堆肥的堆積而抬高，變成一個帶有“城市花園”的休閑區(qū)（圖7、8）。

3.1.1 對土地沉降的影響

各種研究表明，水下排水系統能減少近50%的土地沉降。這是因為在夏季，圩田的地下水保持在高位，因此進入土壤的氧氣較少。壓力排水似乎是最有效的。中央泵將水壓進溝渠，將水通過輸送管道送入排水管道中。這種措施可以進一步減少土地沉降到60%以上。

該方案的出發(fā)點：在夏季使用水下壓力排水管道不會導致地下水位下降超過地面以下約30 cm。因為頂部30 cm仍然在氧化，土地沉降不會完全停止。到2100年Ronde Hoep地區(qū)的土地沉降不會達到1 m，而是40～50 cm。因此水位也會周期性下降，相應排水系統的位置也應有所改變。

草地鳥類保護區(qū)的土地沉降預計也是同樣的規(guī)模。雖然這里沒有使用壓力排水，但是因為地下水位在冬、春季都達到地面高度，僅在夏季結束時達到最低點，土壤氧化的總時間就相對短。挖掘后的泥炭地將成為生態(tài)蓄水池，這些地方原則上會永久淹沒，土地沉降將會完全停止。

3.1.2 對溫室氣體排放的影響

由于土地沉降減少，泥炭地的CO2排放量也將減少。假設500 hm2蓄水池的CO2排放量為零，那么剩余3 000 hm2泥炭地每年的CO2排放量約為2萬t，總共能減少3.4萬t的CO2排放。由于農業(yè)的廣泛發(fā)展和奶牛數量、牛奶產量的減少（大約35%），預計每年還將減少約1萬t的CO2排放。盡管CO2的總排放量減少了4.5萬t，每年仍有3.9萬t的CO2排放量，相當于9 000多hm2（阿姆斯特爾蘭面積2倍）荷蘭成熟林每年所吸附的CO2總量。

3.1.3 對供水需求的影響

壓力排水設施可能會直接影響圩田的地下水位，且不受溝渠水位影響，因此溝渠（最高60 cm）中水位的波動幅度可以更大。這樣，在不占用其他空間的情況下可以在圩田蓄存更多的水。岸堤的牢固性是一個需要關注的問題。如果溝渠水位低于最低水位，圩田蓄水池的水就會補充進來。蓄水池由雨水、滲水和圩田附近的剩余水補充。由于有來自滲透和排水系統的水，即使在干燥的夏季也會有水存留，同時需要防止蓄水池變干。據估計，在地表滯留區(qū)面積足夠大的情況下，即使在干燥的夏季，泥炭地對供水的需求也可以減少到零。Bovenkerker圩田的外圍區(qū)域面積約為400 hm2，蓄水400萬m3，水位波動幅度為1 m。至于填海造地的其他地區(qū)，尤其是Bovenkerker圩田西部還需要外部供給沖廁用水，需要進一步調查是否可以使用蓄水池的水，或者是否有其他方法可以減少對外部供水的需求。

3.1.4 對排水系統的影響

溝渠和蓄水池水位可以波動，因此能應對大流量洪峰和防止boezem water③發(fā)生洪水泛濫。地表水用來收集和清除圩田水。一般來說，蓄水池中的水排到河流中，河流將水帶到大海或艾瑟爾湖。通常情況下，水系統保持一定的蓄水能力是很重要的，也有利于水位管理。

3.1.5 對生物多樣性的影響

在這個方案中，草地上棲息的鳥類擁有更多的生存機會，而與大自然相容的農業(yè)也將增添溝渠和河岸的自然生態(tài)價值。因為荷蘭肩負保護草地鳥類特別是黑尾塍鷸（Limosa limosa）的國際責任，這是一個重要的加分項。濕地作物可能為水鳥和沼澤鳥類帶來額外的益處，但很大程度上與作物的精準種植相關。

3.1.6 對景觀的影響

此方案最大的優(yōu)點是，開放的荷蘭圩田景觀將得到暫時的保留。牧場上仍然有奶牛漫步，雖然這些奶牛都是其他高產的荷斯坦奶牛，但更像是諸如blark head那樣的“雙用途奶牛”。但是這里也有重要的變化：蓄水池與濕地作物交織，形成了一種全新的景觀?！俺鞘谢▓@”進一步強化了阿姆斯特爾河沿岸的綠色生態(tài)特色（圖9、10）。

3.2 自然式景觀方案

恢復泥炭地和最大限度保護生物多樣性是這個方案的核心。收集并蓄存雨水，直到水位略高于地面。天然的泥炭沼澤將通過自然變化逐漸形成。泥炭蘚是泥炭景觀的自然組成部分，但由于挖掘和排水工程，泥炭蘚幾乎完全從“綠心”消失。泥炭層會捕獲CO2，從而逆轉土地沉降。此外，活的泥炭地就像海綿一樣，可以存儲大量的水分，這意味著水源短缺和大峰值泄洪都將成為過去。這樣的整體轉型需要大量的資金投入，也會產生很多的社會阻力。但另一方面，這樣一個獨特的“氣候公園”的開發(fā)將有助于阿姆斯特丹都市圈的發(fā)展（圖11、12）。

3.2.1 對土地沉降的影響

在這個方案中，土地沉降將完全停止并轉化為地面抬升。在該地區(qū)的實地試驗表明：在裸露的泥炭土壤上播撒泥炭蘚，不到4年已經形成了8～12 cm的海綿狀泥炭層。

3.2.2 對溫室氣體排放的影響

根據最近的研究來看，阿姆斯特爾蘭泥炭地的恢復每年可以固定1.9萬t CO2當量，減少7.3萬t的CO2排放。此外，乳牛業(yè)的CO2排放將減少3萬t，這樣每年的總減排量相當于10.3萬t CO2當量。每年釋放1.9萬t CO2當量相當于4 600 hm2森林（大約相當于阿姆斯特爾蘭的面積）的吸附量。

3.2.3 對供水需求的影響

在這一方案中，對外部的供水需求將減到零。泥炭地最終達到完全依靠雨水（和圩田滲水）補給。泥炭地的海綿效應保證了土壤保持水分飽和，不會退化。

3.2.4 對排水系統的影響

有人擔心有大量開放水域的地區(qū)會導致洪水泛濫，因為雨水不能存儲到土壤中。這種想法假定了水位固定不變，水位一旦上升就會被排掉。但這個方案設定的情形不是這樣的，在一定范圍內，水位可以自然波動，這是我們希望的情況。這樣就擁有了巨大的蓄水能力，有助于防止洪水發(fā)生。因為周邊堤壩比較矮小和對水位管理的需要，泄洪峰值很容易突破，多余的水就要依靠泥炭地的海綿效應來吸收。如果在“綠心”大范圍應用這種方法，那么建造單獨的“緊急溢流區(qū)”的需求就會減少。不過這還有待進一步的調查。

3.2.5 對生物多樣性的影響

在此方案中，草地鳥類將被迫和濕地其他物種分享空間，它們可能會出現在較低密度的濕地。無論如何，物種多樣性都會大大增長。例如，稀有種類的蜻蜓和蝴蝶可以出現在貧瘠的泥炭沼澤。圩田富含養(yǎng)分的邊緣區(qū)域和泥炭地為各種水鳥和沼澤鳥提供了棲息地。從國際角度來看，泥炭地十分有價值，特別具有荷蘭三角洲的特色。

3.2.6 對景觀的影響

有人擔心在自然式景觀方案中阿姆斯特爾蘭會自動成長為森林，這種擔心是不合理的。只要有正確的水資源戰(zhàn)略和良好的過渡管理，開放式景觀可以得到保留。從長期看，泥炭地幾乎或根本不需要人工管理，因為這里的土地潮濕、貧瘠，不會生長樹木。但景觀特色一定會有所改變，溝渠將部分關閉，蘆葦地和沼澤森林會出現，牧場上的牛會消失。關于這種情況是好是壞，人們有不同的觀點。無論如何，這片充滿生機的自然區(qū)域都為人們接近自然、休閑娛樂提供了新機會。而對于脆弱的草地鳥類棲息區(qū)，該方案精心設計了自行車道、步行道以及劃船路線等游憩線路（圖13、14）。

3.3 對比兩個方案

兩個方案對減少土地沉降和水資源管理方面的作用大不相同。在生產型景觀方案中，土地沉降程度和溫室氣體排放可以減半；在自然式景觀方案中，地面將抬高，大量的溫室氣體被捕獲。這兩種方案都需要巨大投資，都會重塑城市空間，對社會帶來影響，需要進行更廣泛的社會成本效益分析來作出更佳選擇。目前，生產型景觀得到的支持更多，也最有利于實現保護草地鳥類的目標。但也不能忽視，從長遠來看，該區(qū)域將階段性或部分地向自然式景觀轉換。自然式景觀能為氣候問題帶來最大的效益（圖15、16）。

4 結語

對“綠心”氣候公園的研究和阿姆斯特爾蘭地區(qū)的發(fā)展都表明，氣候問題在未來景觀設計中非常重要。在荷蘭對于適應氣候變化的緊迫性很突出。但“塞翁失馬，焉知非?！?，氣候變化產生的挑戰(zhàn)也為景觀設計提供了許多新機遇：為了適應氣候采取的必要措施可能帶來更加可持續(xù)的農業(yè)區(qū)、新的自然區(qū)域、額外的游憩休閑空間、高品質的住宅區(qū)，達成人與自然雙贏的局面。這些都需要綜合的景觀設計來實現[2-6]。

注釋：

① 圖4現狀分析：剖面圖顯示處于低處的圍墾地涌入很多地下水，有時甚至連更深層地表的咸水都涌進來。通過大型泵站，這些水被抽走，通過boezem排入海中。這種情況導致地表水的鹽堿化和鄰近泥炭地的干涸，從而限制了依賴淡水的農業(yè)區(qū)和自然區(qū)的發(fā)展。因此，需要從河流引入大量的水，以沖刷管道并保證泥炭地的濕潤。然而這種水水質不佳，也不能無限度供給，因為河水流量會逐漸減少。在荷蘭，理論上有足夠的雨水，但是很快會被排放掉，因此在夏季有可能出現缺水的狀況。此外的一個問題是，由于農業(yè)排水，泥炭地區(qū)域地面持續(xù)下沉。隨著地面不斷沉降，水位線也越來越低，水系統必須不斷地調整，直到最后所有的泥炭都消失，而備受贊譽的泥炭景觀也一同消失掉了！

圖4未來圖景：氣候公園的本質是對“綠心”水系統做出一系列結構性的調整。最引人注目的是圩田的轉變。水系統中的低洼位置必須得到解決。一種解決方法是將圩田完全置于水下，但這將意味著巨大的土地損失。另一種方法就是用沙子將一部分地塊抬高，帶來多種新用途。剩下的部分浸沒在水中，提高“綠心”的蓄水能力。這樣發(fā)生洪水和缺水的風險都大大降低，每年抽出和引入的水要少得多，因而節(jié)省了水資源管理成本。需要采取額外措施防止泥炭地的土地沉降，但通過進一步的升高或降低水位的措施是不行的。這樣集約化精耕式農業(yè)就不可行了，新的機會留給了粗放式農業(yè)、自然（泥炭生長）和游憩休閑區(qū)域。沿河黏土土壤上的區(qū)域不易發(fā)生土地沉降，此處有充足的空間給集約化農業(yè)。

② 為了在阿姆斯特丹的伊杰堡建造大約18 000座房屋，總共用了2 500萬m3的沙子在IJmeer建造島嶼。這是以IJmeer現有的開放水域和自然環(huán)境為代價的。萊茵河畔阿爾芬北部的Vierambacht圩田地勢低洼，使用同樣數量的沙子就可以將其打造成一個位于海平面以上的不破壞生態(tài)平衡的、可持續(xù)性的建設用地。通過將周圍的土地淹沒，可以同時實現蓄水、休閑、親近自然等多種功能。伊杰堡位于“綠心”充滿活力的西側，前往蘭斯塔德北部、南翼都十分便利，它的經濟潛力顯而易見。這3張關于Vierambacht圩田的伊杰堡地圖可得出意外的結論是，“綠心”可以促進經濟，同時還能一舉解決水資源管理的可持續(xù)的調控問題。

③ 荷蘭語單詞boezem沒有準確的翻譯。boezem是一個水道和湖泊系統，作為圩田區(qū)水的中間儲存庫。圩田低洼處的水沉積在boezem上，可通過船閘或不通過泵送而排入外部水體。如果低洼區(qū)域的水位過低，可以從外部將水引入進來。在干旱時期，它用來讓外部的水進入圩田，于是boezem具有一個明確的功能—淡水供應。boezem在圩田缺水的情況下發(fā)揮作用，為圩田提供河水，并確保在圩區(qū)水過多的情況下向大?；蚝恿髋欧拧?/p>

圖片來源：

圖2來自Pieter Veen，其余圖片來自荷蘭Vista景觀與城市規(guī)劃事務所。

（編輯/劉玉霞）

1 Introduction Green Heart

1.1 Polder Metropolis

The Randstad Holland covers an area of approximately 3,000 km2and consists of a ring of historic cities:Amsterdam,Haarlem,Leiden,Delft,The Hague,Rotterdam and Utrecht.More than 8,000,000 people live in this economic center,slightly less than half the population of the Netherlands.In the middle of this ring lies the Green Heart National Landscape.The reclamation of this peat landscape started in the early Middle Ages.The current polder landscape is the result of peat extraction (fuel)and dewatering by agriculture.Randstad Holland suffers from soil subsidence,whereas the sea level is gradually rising due to global warming (Fig.1,2).

Almost the entire Randstad and the Green Heart are now below the level of 0 meters NAP,the average sea level (Fig.3).Peat bogs were excavated,resulting in lakes,that were subsequently drained to develop new agricultural areas.These polders are on average 4 to 6 meters below NAP.The lowest point in the Netherlands is located at 6.76 meters below sea level in a meadow in the Zuidplaspolder (reclaimed in 1841),northeast of Rotterdam.Schiphol National Airport is located in Haarlemmermeerpolder near Amsterdam,which was drained in 1852 and is on average 5 meters below NAP.The polder metropolis in the Netherlands is under great pressure because of Climate Change.At the same time,we must both mitigate the effects of sea level rise and greatly reduce the greenhouse effect.In addition,there are major spatial challenges:we have to make agriculture more sustainable,stop further soil subsidence,increase biodiversity,and switch to forms of renewable energy.Moreover we need to build 1,000,000 homes by 2040.

1.2 Climate Change

The fact that climate change will have major consequences for the spatial planning of the Netherlands is hardly open for discussion anymore.The report ‘Possible consequences of accelerated sea level rise for the Delta Program[1],shows the impact on coastal foundations,water safety and freshwater supply.We may already be experiencing accelerated sea level rise after 2050.No scientific evidence has been provided for this,but more and more scientists indicate that this is a scenario that the Netherlands can be confronted with.The reason is that the land ice in Antarctica is melting faster and faster.Whether and how great the acceleration will be depends on international climate policy.

9 生產型景觀效果圖—Ronde Hoep圩田：目前農業(yè)的做法，如過度排水已經導致原有泥炭層嚴重的流失，從而給CO2排放和可持續(xù)水管理問題帶來困難Ronde Hoep Polder:Current agricultural practices such as excessive drainage has led to a severe depletion of the preexisting peat layer,resulting in increasing issues regarding CO2 -emissions and sustainable water management

10 生產型景觀效果圖—Bovenkerker圩田：在生產型景觀方案中，蓄水池將自然濕地和沼澤農業(yè)融合在一起B(yǎng)ovenkerkerpolder:In the production scenario,retention basins are created to accommodate natural wetlands and areas of wet agriculture (Paludiculture)

The policy in the Netherlands is aimed at achieving the climate goals of the United Nations Climate Change Conference of a maximum of 2°C worldwide temperature rise.But whether that will succeed worldwide is very uncertain.The current scenarios for the Netherlands assume a sea level rise between 0.35 meters and 1 meter up to 2100.Given the vulnerability of the Netherlands to sea level rise,it is therefore necessary to also take extreme scenarios into account.With a warming up to 4°C this century,a 3 meter scenario is possible before the end of this century[1].Which measures are most effective is yet unclear.Nobody knows how the necessary change processes are organized.Governments take a wait and see approach.Good policies are not limited to the present,but also extend to the future.The Climate Park is a call to policymakers and initiators to work together on a sustainable and valuable Green Heart.We should not only see climate change as a threat,but also as an opportunity!

2 Climate Park Green Heart

2.1 Two Major Challenges

Two major challenges facing West Netherlands are:

Climate adaptation and sustainable water management.The Green Heart is dependent on continuous drainage and supply of fresh water from elsewhere.This dependency increases with climate change.There is also the issue of safety and flooding.This is not a sustainable situation.How long can we continue raising the dikes? How long can we keep on pumping? The drainage of polders costs vast amounts of energy and money.In a dry summer there is not enough water available to meet the huge demand.That is why we are considering drastic measures such as water level increases of more than 1 meter in lake IJsselmeer.If we retain the water in the Green Heart,such measures may not be required.The point of departure for the Climate Park is that the aim is for a closed water balance for the Green Heart,thus independence from external water supply!

Improving the quality of life and strengthening the economic competitiveness of the Randstad.In the South Wing,but also in other parts of the Randstad,there is a great social need for high-quality rural living environments and easily accessible recreational areas.But there is a lack of administrative decisiveness to really invest in this.Planning regulations limit initiatives from the market.The starting point for the Green Heart Climate Park is to look for new combinations of economic functions and investments in spatial quality:so integrated red-green area development instead of restrictive sectoral policies (Fig.4)!

2.2 Four Strategies

The Climate Park had four landscape strategies(Fig.5).

2.2.1 River Systems

Climate change poses a serious threat to the security of the Randstad,and therefore to the economy of the entire Netherlands.The danger comes from two sides:sea level rise and higher river discharges.The Rotterdam Region is particularly vulnerable.A radical redesign of the entire river system is necessary to guarantee safety.Because urbanization and the ongoing infrastructure are concentrated along the rivers,this is an outstanding task for integrated area development.The construction of “climate dikes ”(extra wide) can be combined well with the formation of attractive river fronts.

Along the rivers we can combine urban restructuring and expansion with river widening and dyke reinforcement.The dike of dike ring 14 around the Randstad can be expanded into a robust “climate dike”.This should not be designed as a purely cultural-technical element,but as a multifunctional landscape structure.There are opportunities for high-quality urban river fronts,alongside new estates and special residential clusters in a green environment.Concentration of functions along the rivers yields a lot of climate benefits:multiple use of space,combined heat and power,efficient public transport.The rivers with the many estates,the historic river towns,the industrial heritage and the unique nature of the banks are reinforced as major landscape structures of the Green Heart.

2.2.2 Vital Meadow Landscape

In the agricultural area,climate issues play a role,such as the pursuit of closed cycles (water,nutrients,energy),a reduction in CO2emissions and an increase in agro-biodiversity.Scaling-up and intensification do not fit well with this,but a switch to quality production does.For example,organic dairy farming emits a third less greenhouse gas than conventional dairy farming.The river clay areas and the peat areas with a clay deck lend themselves well to this.In these areas there is a sustainable basis for maintaining the agricultural cultural landscape and healthy food production.

11 自然式景觀方案示意圖Nature landscape scenario:Schematic map

12 自然式景觀方案總體規(guī)劃Nature landscape scenario:Masterplan

With a Green Heart quality mark for regionspecific products and better cooperation in marketing and sales,a new economic perspective for agriculture is possible.Many companies have already discovered this and are already working together.This can be further expanded,for example by joining the international Cittaslow movement.The region Tuscany (Italy) is the model for this movement.Key ideas are:traditional production methods,hospitality and a conscious approach to the natural facts of soil,water and climate.Cittaslow includes also a fine-meshed network of recreational routes and ecological networks.Entrepreneurs are given a great deal of freedom to develop new services or products,provided that they simultaneously invest in the preservation of monumental buildings,the restoration of historic landscapes.

2.2.3 Wetland Infrastructure

The Wetland park is a proposal for the development of a continuous zone of water-rich nature and recreational areas between the Biesbosch and the IJsselmeer area.Not only does this form a robust ecological connecting zone,but it also offers a structural solution for the most vulnerable peat areas in the Green Heart and an economic boost for tourism-recreational development.The core of the development is a fundamentally different water management in those parts of the peat area that are most susceptible to soil subsidence (Fig.3).With an integrated approach,the consequences for agriculture can be mitigated and the valuable landscape structure preserved.

The automatism of ever-increasing water level reductions for agriculture is being stopped.Instead,the land use is adjusted to the water level.That means a gradual transformation into nature and recreational areas.Allowing natural fluctuations in water level greatly increases the water storage capacity.Much less water has to be supplied from elsewhere and there is less flooding.This way the peat regains its ‘sponge’ effect and the ground level can even rise again.We call this “natural climate buffers.” The landscape will change its image,but it will certainly not become less attractive.Ecologically there is a strengthening of the internationally protected wetlands.Accessible peat parks will be created for the residents of the major cities,with new opportunities for water sports,nature experience and cultural tourism.The villages in the Wetland park can develop into unique rural living environments.Where infrastructure is crossed,robust “l(fā)andscape bridges” are created that are suitable for both animals and people.It is precisely through a combined development that much added value can be achieved for the climate,the landscape and the economy.

13 自然式景觀效果圖—Ronde Hoep圩田：自然景觀促進“活的泥炭地”的再生，形成豐富的濕地沼澤景觀Ronde Hoep Polder:In the nature landscape scenario,living peat is regenerated and forms a rich wetland bog landscape

14 自然式景觀效果圖—Bovenkerker圩田：自然式景觀方案中開放水域繁茂的蘆葦生機勃勃，沼澤森林也呈現到景觀中Bovenkerkerpolder:In the nature landscape scenario,open water with reedlands are allowed to flourish,with areas of swamp forest also present in the landscape

2.2.4 Dutch Lake District

The excavated peat bogs are the ugly duckling of the Green Heart.All attention in policy goes to the peat meadow areas.Understandable:the relatively young reclaimed lands with their endless fields and straight roads are much less recreational and ecologically interesting than the age-old,water-rich peat polders.But that is unjustified,because this is where the cause of salinisation and desiccation lies in the Green Heart,and here the risks of flooding are greatest.It is precisely in the polders that structural measures are needed to achieve a climate-proof design.And it is precisely in the polders that a lot can be gained for landscape,nature,recreation,living and working.The Green Heart Climate Park takes up that challenge.It shows how the ugly duck can grow into a beautiful swan.

Various developments are conceivable for the reclamation sites,with the common denominator being a substantial increase in the water level.Inundation for nature development is already being put into practice here and there.This offers a special opportunity to regain peat formation.The fact is that a gradual increase in the water level can stimulate the accumulation of organic material.This way a lot of CO2is captured and ground level can rise again.We call this “l(fā)iving peat”.

Aquaculture or Paludiculture offers another interesting perspective for agriculture in the polder.Aquaculture is the breeding of fish,shrimp,shellfish or aquatic plants.Paludiculture focuses on wet crops such as cattail,peat moss or duckweed.Parts of land reclamation could be flooded for this.Wet crops ensure healthy,environmentally-friendly,high-quality food.Compared to harvest or catch from nature,there are many environmental benefits.

The most far-reaching and most innovative is the development of “terpen”:green residential islands in a “Dutch Lake District”.For this purpose,land reclamation sites must be submerged in whole or large parts,preferably above sea level.The new ponds offer an enormous expansion of water sports opportunities and water-bound nature.On the islands there is room for numerous residential environments:harbor villages,green residential areas,waterfront apartments or floating jetty houses.For the construction of the islands a lot of sand has to be applied,but no more than for example for IJburg (Amsterdam).Not all polders are suitable for this.Especially suitable are the polders that are close to the big cities and that are well connected to the road and public transport network.Terpen can substantially meet the high demand for rural living environments from the Randstad.At the same time,a fantastic new landscape can be created with truly sustainable water management (Fig.6).

The Climate Park was certainly not designed by us as a blueprint,but as a development perspective,with four landscape strategies:1) River Systems:concentration of urban functions on the highcapacity and well-accessible river banks along the rivers,in combination with the expansion of the river zones into forested edges of the adjacent open landscape; 2) Vital Meadow Landscape:preservation of the typical Dutch cultural landscape of the open pasture landscapes,by creating a new balance between agriculture,nature management and landscape conservation; 3) Wetland Infrastructure(transition between peat landscape and peat bog excavations):preservation of the most vulnerable peat areas,through adapted water level management and function changes in the direction of nature(regeneration of peat) and recreation; 4) Dutch Lake District:tackling the serious water problems of the deep polders,through integrated area development focused on sustainable water management,housing and tourism.

3 Regional Implementation Amstelland

Climate change and the increasing costs for water management require a new vision on how to deal with soil subsidence.This has been further investigated for Amstelland (4,500 hm2) in the Green Heart near Amsterdam.All relevant issues come together here on a small scale.Two spatial scenarios have been developed in consultation with regional stakeholders and experts and tested for their effects on soil subsidence,greenhouse gas emissions,water shortage,water surplus,biodiversity and landscape.

3.1 Scenario Production Landscape

In this scenario,the approach to soil subsidence is used for an accelerated transition from dairy farming to nature-inclusive circular agriculture.The core of this scenario is the largescale application of underwater drainage in the peat areas and the construction of retention basins in the adjoining land reclamation sites.Soil subsidence and CO2emissions are halved and the open pasture landscape is (for the time being) safeguarded.The retention basins are given a dual function for freshwater supply and for wet crops,thus strengthening the agricultural production structure.The soils along the river are raised with clay,sludge and/or urban compost and transformed into a recreational zone with “urban gardens” (Fig.7,8).

3.1.1 Effect on Soil Subsidence

Various studies have shown that underwater drains can reduce soil subsidence by approximately 50%.This is because the groundwater level in the plots is kept high in the summer and therefore less oxygen enters the soil.Pressure drains seem the most efficient.The ditch water is supplied by a central pump and the drains are pushed in via a distribution pipe.The reduction in soil subsidence can then rise to more than 60%.

In this scenario,the starting point is that the use of pressure drains in the summer does not cause the groundwater level to drop further than approx.30 cm below ground level.Because the top 30 cm is still oxidizing,the subsidence will not be completely stopped.In the Ronde Hoep,the fall to 2100 will not be 1 m,but 40 to 50 cm.The water level will therefore have to be lowered periodically,and that also applies to the location of the drains.

The land subsidence in the meadow bird sanctuary is expected to be in the same order of magnitude.Although no pressure drains are applied here,but because the water level reaches ground level in winter and spring,the groundwater will only reach its lowest level at the end of the summer and the total oxidation period will be shorter.The excavated peat bog areas are set up as retention basins and are in principle permanently submerged,the soil subsidence will be completely stopped.

3.1.2 Effect on Greenhouse Gas Emissions

As a result of the reduced subsidence,CO2emissions from peat areas will also decrease.Assuming zero emissions for the retention basins(500 hm2),we arrive at an annual emission of around 20,000 tonnes (tonne=metric ton=1,000 kg) of CO2equivalents for the remaining 3,000 hm2peat area,a reduction of 34,000 tonnes..As a result of the extensification of agriculture and the reduction in the number of cows and the quantity of milk produced (by around 35%),an additional reduction in CO2emissions is to be expected with around 10,000 tonnes of CO2annually.With a reduction of 45,000 tons of CO2,emissions of 39,000 tons of CO2per year remain.This corresponds to what a mature Dutch forest of more than 9,000 hectares in a year captures,still double the surface of the entire Amstelland.

3.1.3 Effect on Water Requirement

The installation of pressure drainage makes it possible to directly influence the groundwater level in the plots,more or less independent of the ditch level.Larger level fluctuations are therefore possible in the ditches (up to 60 cm).In this way,much additional water storage can be realised in the polder without taking up space.The stability of the banks is a point of attention.If the ditch level falls below the minimum level,water is replenished from the retention basin in the polder.The retention basin is fed by rainwater,seepage water and surplus water from the adjacent part of the polder.Due to the seepage and the drainage water,water remains present even in dry summers and the retention basin is prevented from becoming empty.It is estimated that with sufficient surface retention area,the intake requirement of the peat areas can also be reduced to 0 in dry summers.The indicated peripheral zone of the Bovenkerkerpolder is approximately 400 hm2; this results in 4 million m3of water storage with 1 m level fluctuation.For the other parts of the polder,in particular the western part of the Bovenkerker polder,inlet water will still be necessary for flushing.It must be investigated further whether this water can also come from the retention basin or whether other solutions are possible to reduce the flushing inlet.

3.1.4 Effect on Water Drainage

The level fluctuations in the ditches and in the retention basins also make it possible to cope with large discharge peaks and to prevent flooding on the ‘boezem water’.This is surface water that serves to collect and remove polder water.In general,the water from the basin is discharged into a river that brings the water to the sea or to the IJsselmeer.It is important that a certain reserve capacity remains in the water system in normal situations.This is easy to arrange with water level management.

3.1.5 Impact on Biodiversity

The meadow birds get extra opportunities in this scenario,and nature-inclusive agriculture will also increase the nature value of ditches and banks.Because the Netherlands has an international responsibility for the conservation of meadow birds,in particular the black-tailed godwit,this is an important plus.The wet crops may have an additional significance for water and marsh types,but that depends strongly on the precise cultivation.

3.1.6 Effect on Landscape Image

The biggest asset of this scenario is that the image of the open Dutch polder landscape will be maintained for the time being.Even with cows in the pasture,although these are other cows that are high-yielding Holstein dairy cows,but rather“double-purpose cows” such as the blark head.Nevertheless,there are also major changes:the retention basins with wet crops form a completely new type of landscape.The green character along the river Amstel is reinforced by the new “city gardens” (Fig.9,10).

15 現狀、生產型景觀方案和自然式景觀方案對比示意圖Contrast schematics of current situation,production scenario and nature landscape scenario

16 CO2排放的整體比較Overall comparison of CO2-emissions

3.2 Natural Landscape Scenario

Peat recovery and maximum biodiversity are central to this scenario.We save rainwater until the water level reaches a little above the land.Natural moor peat will gradually be created through natural changes.Peat moss development is naturally part of the peat landscape,but has almost completely disappeared from the Green Heart due to excavation and drainage.Peat formation captures CO2and will reverse soil subsidence.Moreover,living peat works like a sponge,it retains a lot of water,which means that both water shortages and large peak discharges will be a thing of the past.Such an integral transformation requires huge investments and will generate a lot of social resistance.On the other hand,a unique “climate park” can be developed that contributes to Amsterdam Metropolitan Area(Fig.11,12).

3.2.1 Effect on Soil Subsidence

In this scenario,the soil subsidence is completely stopped and converted into soil rise.Practical tests in the area showed that a sponge-like peat layer of 8 to 12 cm had already formed within 4 years after seeding of peat moss on bare peat soil.

3.2.2 Effect on Greenhouse Gas Emissions

On the basis of recent studies,recovery of peat soils in Amstelland will fix 19,000 tonnes of CO2equivalents annually,a decrease of 73,000 tonnes.In addition,CO2emissions from dairy farming will decrease by 30,000 tonnes.The total reduction in emissions therefore amounts to 103,000 tonnes of CO2equivalents annually.The annual emissions of 19,000 tonnes of CO2equivalents corresponds to that of 4,600 hm2of forest,approximately the same area as Amstelland.

3.2.3 Effect on Water Requirement

In this scenario,the external water requirement is reduced to 0.The peat areas are after all fully fed by rainwater (and seepage in the polder).The sponge effect of the peat ensures that the soil remains water-saturated and does not degrade.

3.2.4 Effect on Water Drainage

There is a fear that areas with a lot of open water will quickly cause flooding,because rainwater cannot be stored in the soil.However,this assumes that the water is kept at a fixed level and that every cm level rise is immediately drained.This is not the case in this scenario.Natural level fluctuations are possible and desirable,within certain limits.This provides a large storage capacity and helps to prevent flooding.Due to small dikes at the edges and water level management,drain peaks can easily be capped.The sponge effect of the peat does the rest.If this is applied on a larger scale in the Green Heart,the need to construct separate “emergency overflow areas”diminishes.This still requires further investigation.

3.2.5 Impact on Biodiversity

The meadow birds will have to share their place in this scenario with other species of wetlands,and probably occur in lower densities.In any case,the diversity of species will increase enormously.For example,rare dragonfly and butterfly species can occur in the most nutrient-poor peat bogs.The nutrient-rich edges and the peat bogs in the polder form a habitat for all kinds of water and marsh birds.From an international perspective,peat bogs are particularly valuable and originally very characteristic of the Dutch delta.

3.2.6 Effect on Landscape Image

The fear that Amstelland will automatically grow into forest in the nature scenario is unjustified.Openness can be preserved with the right water strategy and good transition management.In the longer term,hardly any or no management is required in the peat bogs:due to the wet and nutrient-poor conditions,they naturally remain tree-free.The character of the landscape will certainly change.The ditches will partially close,reedlands and swamp forests can arise locally.There will be no more cows in the pasture.Opinions differ as to whether that is bad.In any case,the contiguous “robust” nature areas in this scenario offer new opportunities for nature experience and recreation.In contrast to vulnerable meadow bird areas,finer-meshed recreational access with cycling and walking paths and canoe routes is possible (Fig.13,14).

3.3 Comparison scenarios

Both scenarios differ substantially in their contribution to reducing soil subsidence and water management.In the production landscape the soil subsidence and associated emissions can be halved,in the natural landscape the soil will rise and greenhouse gasses will be actively captured.Both scenarios require substantial investments and have major spatial and social consequences.To arrive at a well-considered choice,a broader social cost-benefit analysis is needed.At the moment,the production scenario appears to have the most support and to best fit in with the meadow bird objective.But it cannot be excluded that in the long term the (phased or partial) transition to a natural landscape will nevertheless be addressed.The natural landscape provides the most climate benefits (Fig.15,16).

4 Finally

The Green Heart Climate Park studies and the Amstelland Regional Development show that the climate challenge is important for the design of the future landscape.The urgency for climate adaptation is high in the Netherlands.But sometimes that seems like a blessing in disguise.The studies show that climate adaptation also offers a lot of new opportunities for the design of the landscape.Necessary measures lead to more sustainably furnished agricultural areas,new nature areas,extra space for recreation and tourism and to exciting and high-quality residential areas.Actually all win-win situations.This requires an integrated approach from landscape architecture[2-6].

Notes:

① Current situation of Fig.4 :The cross-section shows that the low-lying reclamation sites attract a lot of groundwater.Sometimes even salt water comes up from the deeper surface.With large pumping stations,this water is pumped away and drained to the sea via the ‘Boezem’1.This situation leads to the salinization of the surface water and to the drying out of the adjacent peat areas.This limits the possibilities for agriculture and nature,because they depend on fresh water.That is why a lot of water is let in from the rivers,for flushing the drains and maintaining the peat areas.However,this water is of lesser quality and does not have an unlimited supply because the rivers will discharge less water.In principle there is enough rain in the Netherlands,but all the water is discharged quickly,therefore shortages still occur in the summer.An additional problem is the continuing subsidence in the peat areas,as a result of agricultural drainage.In order to follow this subsidence,the level is lowered again and again and the water system must be continuously adjusted until finally all the peat has disappeared.And with it the muchappreciated peat landscape!

Future situation of Fig.4:The essence of the Climate Park is a number of structural interventions in the water system of the Green Heart.The most striking thing is the transformation of the polder.These lower situated parts in the water system must be solved.Putting the polder under water is a solution,but that would mean a huge loss of land.An alternative is to raise parts with sand,creating all kinds of new uses.Other parts can be submerged which will provide an increase in the water storage capacity in the Green Heart.The risk of flooding and water shortage is thus much reduced.Much less water has to be pumped out and let in every year.This results in savings in the costs of water management! Extra measures are needed to prevent subsidence of the peat areas.This is possible by not further lowering the water level,or actively raising it.Intensive agriculture is then no longer possible,but new opportunities arise for extensive agriculture,nature (peat development) and recreation.Sufficient space remains for the intensive agriculture on the clay soils along the rivers,which are less sensitive to subsidence.

② For the construction of approximately 18,000 homes in IJburg Amsterdam,a total of 25 million m3of sand was used to build islands in the IJmeer.This is at the expense of existing open water and existing nature in the IJmeer.A sustainable building site above NAP could also be realized with the same amount of sand in a low-lying polder Vierambacht,north of Alphen a/d Rijn.By inundating the surrounding land,a substantial contribution can be made at the same time to water storage and the development of new recreational and nature areas.Located in the dynamic western flank of the Groene Hart and easily accessible from both the north wing and the south wing of the Randstad,the economic potential of the location is evident.The surprising conclusion of this map montage of the IJburg map in Polder Vierambacht is that a powerful boost can be given to the interpretation of the Groene Hart and that water management can be sustainably regulated in one fell swoop.

③ Unfortunately there is no translation of the Dutch word‘boezem’.A ‘boezem’ is a system of watercourses and lakes that serve as intermediate storage of the polder water.The water from lower-lying polders is deposited on the boezem and can be discharged into the external water through locks with or without pumping.If the water in the basin is too low,water can be brought into the basin from the external water.During dry periods,this is used to let extra water into the polder; in this way the ‘boezem’ has a clear function with regards to the freshwater supply.

The boezem functions in polders in the event of water shortage,for the supply of water from the rivers to polders,and also ensures the discharge of water to the sea or rivers in the event of water surplus.

Sources of Figures:

Fig.2 ?Pieter Veen,other figures?Vista Landscape Architecture and Urban Planning.