项目场地位于泰国曼谷市中心孔堤区，为泰国财政部所属烟草局工厂的一部分。早在1991年12月，当地政府即批准了烟草工厂搬迁的决议，在腾退出的土地上建设了面积20.8hm2的水公园（2004年）和9.8hm2的班加科特森林公园一期（2016年）。2019年，政府发起森林公园二期设计竞赛，并计划于2021年6月前完工，以庆祝泰国诗丽吉王太后九十岁寿辰；除明确要求保留的四栋建筑外（将改造为博物馆、体育中心等场馆），其余厂房均予以拆除。场地周围为高密度居住区，森林公园建成后将成为曼谷市中心最大的公共绿地，服务周边5km范围内约25万常住人口及曼谷庞大的旅游人群。竞赛共有六支国际（联合）设计团队参加，土人设计与泰国阿颂·信建筑事务所联合设计团队的设计方案最终胜出。
2场地现状与挑战
场地西侧的城市快速路将场地与周边社区割裂，东侧为一座人工湖，南部为医院、酒店和诗丽吉王后国家会议中心，北部曾经的城市运河现已成为排水渠，水质受城市污水直排和城市径流的影响富营养化严重，水体受到严重污染（图1）。
场地中共有乔木有91个品种、865株，以垂叶榕（Ficusbenjamina）、菩提树（Ficusreligiosa）、盾柱木（Peltophorumpterocarpum）、腊肠树（Cassiafistula）、酸豆（Tamarindusindica）、杧果（Mangiferaindica）为主；胸径1m以上的乔木有49株。除场地东部及单层厂房间散布的一些林荫大树外，这些乔木主要分布于道路两侧，其中榕树发达的根系已经和部分道路融为一体。因此，如何保护这些树木并使其与场地未来功能
规划相契合，就成了摆在设计团队面前的一道难题。
此外，本项目的预算极为有限（上限为20美元/m2），同时在项目工期上要求10个月内建成——后因新型冠状病毒感染疫情，最终要求于18个月内建成。出于建设速度考虑，项目的实施主体确定为本地部队工程兵，因其缺乏景观类项目建设管理经验，需要采取易于施工的设计策略。另外，在本项目之前落成的森林公园一期维护成本较高，在消耗了大量水资源用于灌溉的情况下，树木长势依然堪忧，因此如何降低后续维护成本也成为了本项目的挑战之一。
3设计目标和策略
湿地是重要的生命支持系统[3]，并在防洪抗旱、保持水土、维护生物多样性及休闲旅游等方面发挥重要作用[4][5]。设计从景观生态学的角度出发，在充分尊重场地现状的前提下，营造一个基于“多孔”理念的、弹性的、水－岛交织的海绵湿地系统[6]。
首先通过简单的挖填方技术，建造了4个散布着数百个小岛的湖区（即四大人工湿地），且每个湖都设计为两种不同的深度——较浅的梯级浅水带和较深的核心区域。为了实现对现有植被的最小干预，设计团队通过对场地所有乔木生长信息进行调查统计，选择占比最高的三个冠幅数值作为小岛直径设计参数——6m、12m、25m；然后以原有的树木作为每个岛屿的中心，构筑树岛（图6）。标准化便于施工，同时可将原本坚硬粘滞的表层土壤转变为海绵化生物栖息地（图7），以水作为媒介，疏通物质和能量交换；核心区水位变化提供调蓄空间的同时，可营造条件各异的多样化生境[3]。
湖区的梯级浅水带与沿公园北部和西部边缘修建的L型线性净化湿地相连，运河河水被引入湿地中并得到净化，每日净化水量可达8152m3。净化后的水体流经梯级浅水带汇入布满小岛的湖区中，依据“边缘效应”，这里的水质净化效率更高，并可促进这一水陆生境交错带物种多样性和种群密度的提升，包括促进钳嘴鹳（Anastomusoscitans）、小（Tachybaptusruficollis）、大白鹭（Ardeaalba）等重要湿地物种的活动强度和生产力。[7][8]
为提高公园的可达性、增强公园与周边社区及绿地的联系，项目设计了一条空中步道，将多年来被城市快速路分割的地块串联在一起。空中步道降低了对野生动物的干扰，也为游客提供了可以同时欣赏湿地“野性自然”及都市天际线的独特体验（图12）。
公园内部在保留和重新利用主要道路的同时，通过可渗透的生物滞留池和花圃，分隔自行车道与人行道，使原本为重型卡车设计的宽阔道路拥有更加宜人的尺度（图13）。沿着浅水湿地的边缘增设的多条相互交织的栈道可创造慢行的休闲体验，让游客沉浸式地感受人工湿地的自然景观（图14）。公园核心区域的大草坪和户外剧场（图15）、博物馆旁的水稻田（图16）、大量的林下空间等场所旨在创造多样活动的都市乐园，为曼谷市民及游客的各类公共生活提供舞台。
尽管班加科特森林公园二期面临各种严苛挑战，但事实证明，它的建造取得了巨大的成功。从生态系统服务的角度评估，公园满足了提供调节服务、供给服务、支持服务和文化服务的设计目标。2022年夏，曼谷再次经历了城市水患，公园及其附近地区并未受灾；水质净化湿地表现良好，如预期般地调蓄了足够的雨水，维系了湿地系统度过旱季，且市民可明显感受到公园的水体变得清澈、无异味。[10]此外，公园的生物多样性显著提升：自2022年5月至今，公园内已观察到鸟类近百种，数十种其他野生动物在此栖息觅食。作为曼谷市中心最大的城市公园，其所展现出的“野性自然”正在创造一种全新的、高度动态的、多样化的美学，与周围的都市景观形成鲜明对比（图17）。每天有数以万计的游客在园中进行慢跑、骑行、家庭聚会、学校庆典、野餐、艺术交流、约会和婚纱照摄影等活动。[10][11]公园已成为泰国首都的一处新地标，在社交媒体上广受欢迎。
ModularApproachCreatingLow-MaintenanceSpongeCity:BenjakittiForestParkinBangkok,Thailand
1ProjectBackground
LocatedinKhlongToeiDistrict,acentralareaintheCityofBangkok,Thailand,theprojectsitewasformerlyatobaccofactoryownedbytheMinistryofFinanceofThailand.AsearlyasDecember1991,thelocalgovernmentapprovedtherelocationofthetobaccofactory,andstartedconstructionprojectsofa20.8hm2waterpark(builtin2004)andthe9.8hm2BenjakittiForestParkPhaseI(builtin2016)onthevacatedland.In2019,thegovernmentlaunchedadesigncompetitionforBenjakittiForestParkPhaseII,whichwasscheduledtobecompletedbyJune2021tocelebratethe90thbirthdayofThailand’sQueenSirikit.Thesiteissurroundedbyhigh-densityresidentialareas,andtheForestParkwasenvisionedasthelargestpublicgreenspaceinthecenterofBangkok,servingabout250,000localresidentsinthesurroundingneighborhoodsandthousandsoftourists.Atotalofsixinternational(joint)designteamswereinvited,andtheproposalbythejointdesignteamofTurenscapeandArsomsilpCommunityandEnvironmentalArchitectwonthecompetition.
2SiteConditionsandChallenges
SittingintheChaoPhrayaRiverDelta,Bangkokisadenselypopulatedcitywithmorethan10.5millionresidents[1].Theregionexperiencesamonsoonclimatewithanaverageprecipitationofabout1,500mmperyear.Mostoftheareaofthecitywasoriginallyswampland,whichwasgraduallydrainedwithcanalsandextensivegroundwaterpumpingforagricultureirrigation;atthesametime,theover-extractionofgroundwaterhascausedseveresubsidence,which,coupledwiththeeffectsofglobalwarmingandinadequatemunicipaldrainageinfrastructure,hasresultedinincreasedfloodrisk.Inaddition,therewereonlythreeurbanparksopentothepublicinBangkok,andurbangreenspacesarehighlyfragmentedwithalowusage.Thecity’scomplexurbanecologicalenvironmentandculturalcontextposedanumberofchallengesforthedesign.
Intermsofitslocation,anurbanexpresswaytothewestcutthesiteofffromtheadjacentcommunity.Therewasalsoanartificiallaketotheeastandahospital,hotel,andtheQueenSirikitNationalConventionCentretothesouth.Thesiteissurroundedbyadrainagecanaltothenorth,whichwascontaminatedwithurbanrunoffandsewage(Fig.1).
Thesitewasdenselyoccupiedwithsingle-storywarehousesandhardpavements;exceptforfourbuildings,allon-sitestructureswereplannedtoberemovedthatwouldleavealargeamountofconstructionwastetobedealtwithafterdemolition(Fig.2).
Sitesurveyshowedthattherewere865treesonthesite,including91species.Thesetreesweremostlyfoundalongpaths,andmanyFicusbenjaminahavegrownintothepavementwiththeirrobustrootsystem.Therefore,itwasachallengeforthedesignteamtopreservethetreesandmakethemafunctionalfeaturethatiscompatiblewiththeplanofthesite.
Inadditiontothechallengesofthesiteitself,thebudgetforthisprojectwasextremelylimited(ultimately,itwascappedatUSD20/m2),andtheprojectwasrequiredtobecompletedinjust18months.AnextrachallengewasthattheprojectwasoverseenbyRoyalThaiArmyforafast,efficientconstruction,buttheydidnothaveextensiveexperiencemanaginglandscapeprojects,sothedesignhadtobeeasy-to-build.Besides,beingcostlyandusingahugeamountofirrigationwater,themaintenanceofBenjakittiForestParkPhaseIwasunsatisfactory,sohowtoreducethesubsequentmaintenancecostbecameanotherchallengetothedesignteam.
3DesignObjectivesandStrategies
Inaddressingthemultiplechallengesofthesiteanditsdenseurbansurroundings,theprojectwasenvisionedasacentralparkcapableofprovidingholisticecosystemservicestothecity(Figs.3~5).Toimprovethesite’sregulationservicestoadapttothechangingmonsoonclimate,theparkisdesignedwithatotalrainwaterretentionandstoragecapacityof187,500m3,whichallowstheparktowithstand10-yearrainfalleventswithoutdrainingtothemunicipalsewersystem.Tostrengthenthesite’sprovisioningservices,theparkisdesignedtofilterthepollutedwaterfromthepoorestClassVtoClassIII.Toenhanceitssupportingservices,thedesigncreatesanecosystemcomposedofforest,grass,andwetlandthatprovidesavarietyofhabitatsfornativespeciesandwildlife.Also,toincreaseculturalservices,theparkisexpectedtoofferbadlyneededlargepublicrecreationalspaceforcitizens’dailyrecreationalactivities,asvisitorsaswell.Threestrategiesguidedthedesigntomeettheseobjectives.
3.1CreatingModularPorousSpongeWetlands
Wetlandsareimportantlife-supportingsystems[3]contributingtofloodanddroughtprevention,soilandwaterconservation,maintenanceofbiodiversity,recreationandtourism,etc.[4][5]Highlightinganideaof“porosity,”thedesigncreatesaresilient,water-islandinterwovenspongewetlandsystemunderlandscapeecologyprinciples[6].
Firstly,fourlakesconsistedofhundredsoftreeislets(i.e.,fourconstructedwetlands)werebuiltthroughsimplecuttingandfilling,andeachlakewasdesignedwithtwodepths—ashallow,terracedshorelineandadeepercorearea.Aftersiteinvestigation,thedesignteamselectedthethreecanopymoduli(6m,12m,and25m)thatweremostfrequentlyfoundamongtheexistingtreesastheislanddiametersinordertominimizeconstructionimpactontheexistingvegetation;andthenthetreeswerepreservedinsituatthecenterofeachisland(Fig.6).Standardizedconstructiontransformedtheotherwisehardclaysurfacesoilintoaseriesofwetandspongyhabitats(Fig.7),wherewateractsasamediumtofacilitatematerialandenergyflows.Thecoreareasnotonlyserveasstoragespaces,butalsocreatediverseaquatichabitatswithchangingwaterlevels[3].
Theshallow,terracedshorelineisconnectedtotheL-shapedlinearpurificationwetlandalongthenorthernandwesternedgesofthepark,wherethewaterfromthecanalisintroducedandpurified,withadailypurificationcapacityof8,152m3.
Afterpretreatment,pollutedwaterenterstheL-shapedsurfaceflowwetlandandsubsurfaceflowwetland,flowingfromeasttowest,fromnorthtosouth,withthehelpofelevationdifference.Afteraseriesofcleansingprocesses—includingtheaerationandthepurificationbyemergentandsubmergedvegetation,microbialdegradation,andbiologicalpredation—theconcentrationofpollutants(e.g.,BOD,COD,TSS,heavymetalelements)wouldbelargelyreduced.Theeutrophicationsubstancessuchasnitrogenandphosphorusinthewatercanalsobeabsorbedasfertilizersthathelpforthegrowthofwetlandplantsandagriculturalcropsonthesite,formingaself-sufficientcycle.
Secondly,somewarehouseswereredesignedwithsportsfieldsandeco-palletislands(Fig.8),creatinganumberofluxuriant“greenbuildings.”
3.2FosteringaLow-Budget,Low-Maintenance“MessyNature”
Consideringthelimitationsinbudgetandconstructionperiod,allkindsofrecycledmaterialsonthesitewereintegratedintothedesignofthepark’slandscape:allexistingmainroadswereremainedastheskeletonofthenewparkcirculationsystem;theexistingtreesandunderstoryspacewereretainedtothemaximumextent(Fig.9);andtheconcretematerialsfromthedemolishedstructureswereusedtoreinforcethefootandslopeoftreeisletsortheparkpavements.[2]Thismodularlandscapecanbeeasilyexecutedwithasingleexcavatorandminimizesdependenceonskilledlabor(Fig.10).
Inaddition,theplantingdesignofthetreeisletsinthisprojectappliedseedlingsofnativeshadetreespeciesatthelowestcost:Themodulatedlandformwithdiversemicro-environmentswassownwithseedsandplantedwithtreeseedlings,creatingafoundationforthesubsequentevolutionofasemi-naturalplantcommunitywithlow-maintenance(Fig.11).Afteritscompletion,theparkisexpectedtoretainupto200,000m3ofstormwaterfromthesurroundingareaduringthemonsoonseason,allowingthenativeplantcommunitiestoestablishthemselveswithminimalirrigationormaintenanceneededduringthedryseason.
3.3ImprovingAccessibilityandImmersiveRecreationalExperience
Toimprovetheaccessibilityoftheparkandenhancetheconnectionbetweentheparkandthesurroundingcommunitiesandgreenspaces,askywalkrunsthroughthetreecanopiesthattiestogethertheentirepark,whichfordecadeswasslicedthroughbymajorroads,andcreatesauniqueexperienceamidstthetropicalfoliagewhilereducingthedisturbanceonwildlife(Fig.12).
Whilethemajorroadswerepreservedandreused,acutwasmadeinthemiddleofeachroadwaytocreateapermeablebioswaleandflowerbedthatseparatesabicyclelaneandpedestrianpath,helpingbringamorecomfortablescaletowhatwereoriginallywideroadsdesignedforheavytrucktraffic(Fig.13).Multipleboardwalksweredesignedalongtheedgeoftheshallowwetlandsthatallowvisitorstohaveimmersiverecreationalexperienceofurbannatureintheman-madewetlands(Fig.14).Alargelawnandanamphitheaterinthecoreareaofthepark(Fig.15),thericefieldnexttotheconvertedmuseum(Fig.16),andalargenumberofunderstoryspaceswerecreatedtoprovidestagesforvariedrecreationalactivitiesofBangkok’scitizensandvisitors.
4After-CompletionPerformanceandReflection
Despitehavingbeenbuiltonanextremelycompressedtimeframe,BenjakittiForestParkhasprovenagreatsuccess.WhilemuchofBangkokfloodedlastsummer,theparkanditsimmediatevicinitydidnot.Thewater-qualityremediatingwetlandisperformingwellandproducesenoughwatertokeepthewetlandalivethroughthedryseason.Arichvarietyofbirdsandotherwildlifehastakenupresidenceinthepark.ThemoststrikingachievementisthatthisnaturallyregenerativesystemisnowthelargestparkindenselypopulatedcentralBangkokandattractstensofthousandsofvisitorsdaily,whouseitforawidevarietyofactivities,includingjoggingandcycling,familygatherings,schoolcommencements,picnics,datesandweddingphotographs.IthasbeencelebratedextensivelyonsocialmediaasanewsymbolofThailand’scapitalcity(Fig.15).