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Ocean & Coastal Management 81 (2013) 97e102

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Ocean & Coastal Management

journal homepage: www.elsevier .com/locate/ocecoaman

Case studies for urban wetlands restoration and managementin Japan

Keita Furukawa*

National Institute for Land and Infrastructure Management, 3-1-1 Nagase, Yokosuka 239-0826, Japan

a r t i c l e i n f o

Article history:Available online 21 July 2012

* Fax: þ81 46 844 1145.E-mail address: furukawa-k92y2@ysk.nilim.go.jp.

0964-5691/$ e see front matter � 2012 Elsevier Ltd.http://dx.doi.org/10.1016/j.ocecoaman.2012.07.012

a b s t r a c t

To effectively restore coastal habitats in urban areas, the surrounding dynamic coastal ecosystems, suchas wetlands must be restored. In well-developed urban areas, most aquatic environments may bedegraded in terms of water and sediment quality, as well as the essential hydraulic circulation. Restoringcoastal habitats in urban areas is therefore a challenging task. Environmental status and its effort torestoration summarized for Tokyo Bay, Japan followed by two case studies of urban wetland restoration.At Shibaura Island, Tokyo, tide pool construction is shown as hardware type restoration case study. Oneof the means to ensure success in restoring habitats in an urban area is to use a sound ecosystem-basedapproach to guide the selection of restoration sites and the application of appropriate engineering andmanagement methodologies. At Yokohama, software type restoration by terrace type habitat creation isshown. The development and management of the site with public participation, undertaken in anadaptive manner, is a key element of successful habitat restoration. This paper presents lessons learnedfrom urban habitat restoration projects in Japan as examples.

� 2012 Elsevier Ltd. All rights reserved.

1. Introduction

Coastal wetlands in the world are decreasing at an alarming rate(Green and Short, 2003; Burke et al., 2001; Spalding et al., 1997,2001). This trend cannot be reversed unless the fundamental cau-ses are resolved, including uncontrolled economic development,excessive use of natural resources and lack of public interest.

In Japan, coastlines are managed by several different govern-ment line agencies. After the enactment of the Basic EnvironmentLaw (1993), several laws were revised, including the River Law(1997), the Coast Law (1999), the Port and Harbor Law (2000), andthe Fisheries Basic Law (2001). These revised laws particularly giveimportance to environmental protection and restoration. Forexample, the Port and Harbor Law reinforces the government’scommitment to environmental conservation in the development,use and improvement of ports, harbors and channels. The CoastLaw, on the other hand, includes provisions for improving andconserving coastal environments and appropriate use of the coastsby the public, in addition to coastline protection. The Law furtherpromotes comprehensive coastal conservation approaches takinginto consideration the needs for disaster prevention, environ-mental conservation and use by the public.

All rights reserved.

This paper documents the key points regarding the develop-ment and implementation of urban habitat restoration projects,notably the National Bay Renaissance Project in Shibaura, Tokyo.Habitat restoration was done with careful site and material selec-tion as part of the government’s restoration procedure. This paperalso documents a case study on the soft approaches in urbanwetland management, involving stakeholders from a non-profitorganization (NPO), government and researchers, who had rela-tively little knowledge of the relevant laws or previous experiencein public development planning.

As Yanagi (2007), Wolanski (2007) and Lewis (2009) pointedout, it is important to consider hydrology and smooth cycling ofmaterials as driving forces of coastal ecosystems (with highproductivity and rich biodiversity). In cooperate with suchhydraulic conditions, construction of coastal habitat are tested.Okada and Furukawa (2006) pointed out importance and advan-tages of terrace type structure to enhance habitat biodiversity. It isimportant to have a tide pool in such terrace (Metaxas andSvheibling, 1996; Dethier, 1980). Kurahara et al. (2007) examinedlong-term succession of benthos with topographical change due tosedimentation in a tide pool type structure and Takikawa et al.(2010) examined semi-open boundary for constructed tidal flat toallow natural disturbance to maintain topological equilibrium.These example shows importance of retain hydraulic condition ofpools and some maintenance work should be done for retainsustainability of these habitats. This paper presents two case

K. Furukawa / Ocean & Coastal Management 81 (2013) 97e10298

studies for putting emphasis on importance of understanding thehydraulic situation and needs of management with publicinvolvement in habitat restoration under urban context afterbackground description about Tokyo Bay ecosystem.

2. Status of Tokyo Bay ecosystems and its restoration efforts

2.1. Ecosystem in the Tokyo Bay environment

Tokyo Bay is an enclosed, mostly populated, and intensivelyused bay in Japan (Furukawa and Okada, 2006). The bay is boundedby the eastern and western points of Suzaki and Kenzaki. The bayhas an open interchange with the Pacific Ocean. The KuroshioCurrent in the Pacific Ocean flows near the mouth of the bay. Tokyo,the capital of Japan, is located in the catchment area of Tokyo Bayand has a population of 8 million people. Several other major citiesare located in the inner bay catchment area: Yokohama, 3.5 millionpeople; Kawasaki, 1.3 million people; Saitama, 1.0 million people;and Chiba, 0.9 million people. The inner bay catchment area hasa total population of some 25 million. The concentration of pop-ulation and industries in the catchment area of Tokyo Bay hasbrought remarkable changes to its coastline.

Fig. 1 illustrates the changes in the bay from the 1950s to 2000.The bay had an oval, smooth coastline with a fringing tidal flat2e6 km wide, the seafloor of the shoreward area in Tokyo Bay wascovered by sand in the 1950’s (Fig. 1a). At present, the coastline hasbecome eroded, and the seafloor of this region is covered withsludge with high moisture content (weight of water/weight ofsediment � 100) of over 200 (Fig. 1b).

The direct causes of the change in sediment conditions areattributed to the reclamation of sandy areas and heavy accumu-lation of organic matter. These changes are also driven by changesin the circulation of the bay due to reclamation, since the surfacearea was reduced by 80% from 1960 to 2000. The decrease insurface area resulted in an 11% decrease in the tidal range (Unokiand Konishi, 1999). The tidal current at the mouth of the inner bayalso decreased by 20% from 1968 to 1983 (Yanagi and Onishi,1999). In addition to the reduction of barotropic circulation, thebaroclinic circulation also recued due to urbanization. With theincrease in freshwater demand in the urban area, water resourcedevelopment resulted in more input of freshwater into the bay.

Fig. 1. Distribution of sediment in Tokyo Bay; (a) main sediment fraction in the 1950s, (b) se(after Furukawa and Okada, 2006).

The average inflow of freshwater over a 10 year period in the 1920swas about 350 m3/s. The inflow significantly increased from the1960s to the 1990s to about 450 m3/s. This enhanced the barocliniccirculation, and reduced the average residence time from 30 daysto 20 days in summer, and 90 days to 40 days in winter (Takaoet al., 2004).

These changes have a possible effect on the distribution of livingorganisms in the bay. Igarashi and Furukawa (2007) drew a distri-bution map of benthos and sessile organisms on the tidal flats andseawalls. The data showed that: 1) even in the inner part of the bay,in a highly eutrophied area, the tidal flats maintained a rich benthicdiversity, and 2) the diversity of sessile organisms was attributed tochanges in water quality, such as transparency and salinity.Anthropogenic impact is one of the possible causes of thesedistributions. The inner part of Tokyo Bay suffered from severeanoxia during summer and autumn.

The other important aspect is the distributional patterns of thespecies in the bay. Several living organisms have unique life stagepatterns e larvae, juveniles and adults are transported and live indifferent places at different stages of their life cycle forming aninter-stage larval network. The network is established with nodesand passes. Nodes are the habitats, and passes are the transportsystems in the bay, mainly facilitated by water circulation. Sinceanthropogenic impacts will affect the habitats and the trans-portation of the various organisms, urbanization could possiblydestroy the functional integrity of such an ecological network.Hinata and Furukawa (2006) illustrated this phenomenon using theshort-necked clam larvae network in Tokyo Bay (Fig. 2). The studydemonstrated the existence of the ecological network. It alsoshowed that the ecosystems in Tokyo Bay could be improved ifsuitable spawning grounds, even if they are small, are conservedand restored. The ecological network was considerably weakened,especially in the northern towestern part of the bay, due to changesin the hydrology. Thus, habitat improvement in the area should beprioritized.

2.2. Action plans for Tokyo Bay renaissance

On 26March 2003, the “Action Plans for Tokyo Bay Renaissance”was endorsed by the Tokyo Bay Renaissance Promotion Council,

diment moisture (%) in the 2000s (higher moisture correlated with richer mud fraction)

Fig. 2. Schematic diagram of the larval network in Tokyo Bay. Numbers indicate thecomparative quantity of larvae transported between local regions (after Hinata andFurukawa, 2006).

K. Furukawa / Ocean & Coastal Management 81 (2013) 97e102 99

which consisted of 11 central and seven regional governmentbodies (four prefectures and three cities).

The Action Plans for Tokyo Bay Renaissance as part of the UrbanRenaissance Project was initiated by a decision of the JapaneseCabinet in December 2001. Seven prefectures and citiessurrounding the bay and related central government ministriesformed the Council to promote the restoration of Tokyo Bay. Its goalis to sustain the Bay’s natural biodiversity and to restore thebeautiful coastal environment for people to enjoy. The Councilestablished three working groups: WG1 on land-based imple-mentation, WG2 on sea-based implementation, and WG3 onmonitoring. The project period was set for ten years from the fiscalyear of 2003.

The process for assessing the achievement of the goal is unique.Several monitoring sites with specific targets were set in areasidentified for priority implementation. Each site had a specifictarget plan for restoration, and thus assessment of the project interms of specific goals could be undertaken. The priority imple-mentation areas matched the coastline that had a relatively weakecological network, as discussed in Section 2.1. Thus, localenhancement of ecological functions at the various target sites wasseen as a contribution to the holistic restoration of the bay.

Implementation of constructed habitats was promoted by WG2in order to facilitate a balance between economic use and envi-ronmental conservation. The first case study illustrates such habitatconstruction project implemented at Shibaura Island, Tokyo inDecember 2005.

2.3. Importance of public participation and an adaptivemanagement scheme for urban wetland restoration

The soft approach in urban wetland management needs toinvolve stakeholders from non-profit organization, governmentand researchers. Such organizations are motivated by their ownobjectives and a common target needs to be agreed upon before theproject is started and the project must be process-oriented.Furthermore, in order to achieve the target, it is necessary toundertake regular monitoring and assessment, and then makeappropriate adjustments based on improved understanding of thesituation (adaptive management; PIANC, 2003). The second casestudy illustrates the importance of public participation and

adaptive management in urban wetland restoration at govern-mental facility, Yokohama in March 2008.

3. Case 1: habitat creation practices at Shibaura Island, Tokyo

3.1. Studied site

A habitat restoration practice has been done at terrace of seawallaround Shibaura Island, Tokyo. Shibaura Island faces ShibauraCanal, which is connected to the ocean through two sluices andreceives major inflows of sewage. It is a typical urban brackishwater area with a complex flow pattern. Canals are 2.2e4.1 m deep,salinity ranges 5e20 for surface and 17e32 for bottom, andtemperature ranges 7e28 �C (Satoh et al., 2006).

Tidal courses (channels, creeks or gullies) are distinctive andimportant features of coastal environment. They have uniquefeatures of circulation, draining freshwater to the sea and inun-dating tidal flats, mangroves and salt marshes with seawater(Perillo, 2009). Okubo (1973) pointed out that lateral embaymentsalong a tidal course enhance longitudinal mixing. Thus, restorationof habitats in tidal courses should consider these typical features ofcirculation. Thus, the water circulation was determined throughfloat experiments, with public participation. The experimentsshowed that circulation was driven by density (estuarine circula-tion) due to stratification in various areas. This circulation intro-duced seawater to the bottom layer of the canal. Thus, it is assumedthat the canal network acts as tidal courses, but in a limited area.For example, the secondary canal where Shibaura Island locateswas stratified, and suffered by hypoxic water (dissolved oxygen lessthan 4.3 mg/l which is Japan fisheries standard water qualityrequirement) during summer season (one third of a year) at bottomwhilewater in the primary canal was well-mixed. These differenceswere determined by freshwater input, tidal range, and topographybetween the two canals.

3.2. Restoration processes

The experimental facility for the habitat construction at Shi-baura Islands is implemented since 2004 with publiceprivatecooperation (Sakurai et al., 2007). Urban re-development planhad been implemented by private sector, and new residentialtowers were built on Shibaura Island. According to deterioration ofexisting seawall, Tokyo metropolitan city ask the private sector toreinforce it. National research institute suggests to build tidal poolson the terrace for creation of fish larvae and benthos habitat whilelocal residences are willing to have restoration of canal environ-ments. The construction completed in December 2005, andpreliminary monitoring has been started since March 2006. InSeptember 2006, both of pools were filled by sand in 30 cm depthto create benthos habitat in pools.

The facility included two 4 m � 8 m pools (pools A and B),0.5 m deep with a sandy bottom, against a rocky terrace ofseawall (Fig. 3). The experimental facility was situated at a heightlower than the high water but higher than mean water. The depthof the pool was set at 0.5 m below the surrounding surface. Eachpool had a small inlet section (�0.1 m deep, 1.5 m wide) throughthe seawall to enhance water circulation during inundation anddrainage.

In 2007 and 2011, sand was added to pools A and B to elevateandmodify microtopography of the bottom andmake the sitemoreattractive to juvenile gobies. At present, monitoring is continuingwith the collaboration of citizens, scientists and local governments.The government issues a permit for monitoring the facilities,scientists design the monitoring scheme, and citizens participate inthe monitoring program. The “partners” shared the goal of “making

Fig. 3. Shibaura Island project site and conceptual diagram of the pool (after Hayakawa et al., 2008).

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the area more attractive to fish and people”. This arrangementfacilitated a more effective and adaptive approach to managementof the restoration site (Sakurai et al., 2008).

3.3. Public participation and results

Monitoring of the site has been started April 2007 as a publicparticipating project (Hayakawa et al., 2008). Four to five timesa year, water quality, benthos and fish larvae have been monitored.These monitoring were supported by Tokyo metropolitan city,Minato Ward Office, local NPO group, Tokyo University of MarineScience and NILIM. They share role of site management, publicrelations, and scientific supervision. Participants for the projectwere local families, university students, and NPO members. Inaverage, 15e20 people joined monitoring at pool, and maximum100 people joined fishing event for gobies census in summer.

Sixmonths after the construction of the facilities, juvenile gobies(Acanthogobius flavimanus), mullets and sand worms populated thepools (Table 1). The mean size of the gobies in the pools andsurrounding water indicated an interesting role for the pools. Allgobies in the pools were sampled by draining, and their lengthswere measured by image processing of photographs. Gobies insurrounding water were sampled through a fishing event. About 50people did fishing for 2 h, and the lengths of landed gobies weremeasured. It appeared that the size of the gobies increased duringJune to August, and decreased from August to the followingFebruary. Gobies hatched from eggs during JanuaryeMarch in the

Table 1Total abundance of fish and prawns in pools A and B (after Sakurai et al., 2007, 2008).

Date Eel Goby Mullet Prawn

July 2006 3 504 580 28September 2006 2 119 201 4June 2007a 1 310 50 0August 2007 0 1168 213 37October 2007 1 222 26 235

a Only pool A was sampled.

bay, while juveniles grew in a shallow estuary duringAprileOctober, and adults came down to the river mouth in the bayduring NovembereJanuary followed by spawning eggs on thedeeper mud bed in the bay. As gobies keep growing throughout theyear, the reduction in mean size indicates that large (grown) gobiesescaped from the pool. The larger gobies were actually found in thesurroundingwater. Some size differences were found depending onthe pool and period of the year, which is possibly triggered bydifferent depths in the pools. Because of sediment movement in thepools, and slightly changed drainage each year, pool A becameshallower, and pool B became deeper. It appeared that the deeperwater served as habitat for the larger gobies. This is presumablycorrelated with the hydrology of the pool (the shallower pool haswarmer water in summer, which is rich in DO).

Dissolved oxygen (DO) in the pool fluctuated more than in thecanal because of DO production by benthic algae in the pool.Nevertheless, the combination of diurnal solar radiation anda semi-diurnal tide in summer increased the occurrences of anoxicwater in the tidal pool. Furthermore, the water temperature in thepool was higher during the spring and summer and lower duringautumn and winter compared with the canal surface water,because of the small heat capacity of the pool. To construct a tidepool in the canal area as a healthy urban wetland in terms of DO,careful engineering design for suitable hydrology, such as theheight and depth of the pool, and planning for freshwater supply,are crucial (Umeyama et al., 2010).

3.4. Discussion

These findings show that the constructed habitats (pools) arenot only acting as an ad-hoc habitat for gobies, but also whensurrounded by dynamic estuarine system, are used as a habitat tosupport part of the life stage of gobies. In other words, the habitatconstruction seemed to enhance the ecological network in thecanal e bay environment. For example, heavy eutrophication of thecanal makes ongoing deterioration of sediment in the pools. It isneeded tomonitor the status of habitat, and take action in adequate

K. Furukawa / Ocean & Coastal Management 81 (2013) 97e102 101

timing (adaptive management). In this project, we did majorrehabilitation twice out of 7 years after construction. These moni-toring and actions can be one of good opportunities to local citizensto join habitat restoration project and arise awareness forecosystem services of urban wetlands. Nevertheless, it is needed tocoop with educating program. Good guidance and careful checkingof monitoring data by scientific perspective are necessary to ensureachievement of the project.

4. Case 2: public participatory monitoring and maintenancepractices in Yokohama

4.1. Studied site

Yokohama Port and Airport Technology Investigation Office,Ministry of Land, Infrastructure, Transport and Tourism (MLIT)implement terrace type habitat in inner harbor of Yokoyama Port in2008. There is a pond faces to canal connecting to the Port and isused for a base for a floating garbage correcting vessel. One of piershad been degraded, and needed to be replaced. The office decidedto restore the pier as habitat and maintain remaining pond oper-ational. The canalepond are 2e4 m deep, salinity ranges 20e30 atsurface and 27e32 at bottom, and temperature ranges 15e25 �C(Morita et al., 2009).

The terraces were set in 0 m, 0.5 m and 1.0 m above the lowwater level. Width of habitat is about 20 m � 50 m in total. Eachterraces (sand layers) were separated by wooden plate and stoppedby rocky shore for both shoreline end of habitats. Since, the pond isused as a base for the vessel and face to the inner harbor, tow waveis a dominant force for the sand layer morphology. Anoxic orhypoxic risk is relatively low compared with Tokyo area, but fewtimes a year, area is suffered by massive anoxic water intrusion andmass mortality of benthos and fish.

4.2. Restoration process

The office had constructed a terrace type tidal flat along itsseawall (Oomura et al., 2009, Fig. 4) in 2008. In advance todesigning and construction, teams from the private and publicsectors were invited to assess and setting target for the projectplanning. The team examined suitable height of terrace, materialand layout of materials against possible inhabitation species. Basicstudies (e.g. shown in Section 2.1) for Tokyo bay were used todetermine design parameters. In the same time, the team hadpointed out uncertainty of low DO effects and unstable

Fig. 4. The terrace type of tidal flat constructed at Yokohama Port and

morphological change of substrates. Thus, the team recommendedthe office to implement an adaptive management.

After completion of the project, the office has implementedmonitoring scheme by themselves and the same time, ask public formonitoring by standpoint of user-side. After the construction,structure andmorphological stabilitywere recorded. In addition, therehabilitation of the area by benthic animals was also monitored.

4.3. Public participation and results

Public group of themonitoringwas formed and implement theirmonitoring scheme. It is based on as simple as possible to enableduplicate these scheme to other public activities but based onscientific attitudes. Monthly monitoring is included topographymeasurements, visual observation for sediments property, sedi-ment sieving for benthos abundance, and diving observation forfish assemblage. Not only monitoring but also maintenance waspracticed by excavation for sediment refreshments. In the sametime, the office did seasonal quantitative quadrat type benthosmonitoring and water quality checking, and NILIM deployed waterquality sensor to obtain continual change of status.

Sixmonths after the construction of the tidal flat, colonization ofthe area by the benthic animals was very rapid, especially for short-necked clams. Short-necked clams increased in the middle terracewith a maximum of about 20,000 individuals/m2, which is themaximum density found in the richest habitat in the region.

However, in September 2009 the tidal flat suffered a massivedeath of bivalves. One of the possible explanations was the inflow ofthe anoxic water from the bottom of the bay. This seemed unlikelyas a shallow area like the tidal flats is usually a DO rich environment.It is difficult to believe that only one short-term intrusion of anoxicwater resulted in such a massive death of bivalves.

The monitoring record in the middle terrace showed DOrecovery in September during daytime inundation, while DOreduction occurred in July during nighttime inundation. Thereduction of DO is presumably caused by local consumption ofbenthos. As discussed in Section 3.3, this can happen througha combination of diurnal solar radiation and a semi-diurnal tide. Insummer, this causes many occurrences of anoxic water, even in theshallow areas. It is possible that the benthos was already damagedby the local hypoxic environment when the anoxic water intrusiontriggered the massive death. This hypothesis, however, is notconfirmed and more monitoring and observations are required tounderstand the phenomenon.

Airport Technology Investigation Office (after Morita et al., 2009).

K. Furukawa / Ocean & Coastal Management 81 (2013) 97e102102

4.4. Discussion

The monitoring group not only conducted monitoring but alsoparticipated in the establishment and management of an attractivebenthos habitat. Despite their efforts, the massive death of benthoswas not prevented. The group is continuously searching for moreeffective ways to manage the tidal flat with the help of scientistsand the public sector.

Furthermore, the monitoring group could be act as interpreterbetween scientists and local citizens. In 2011, the group initiatepublic participate monitoring campaign at the site, and more than50 people did fishing census and benthos exploration for entireregion of terrace. It is unable to achieve these accomplishmentsonly by the group, nor local citizens. A good cooperation ofmanagement side (the office), user side (local citizens) and coor-dinator (the monitoring group) is needed.

5. Conclusion

From the two case studies, we have showed and shared thelessons learned concerning the possibility of habitat restoration inan urban area. The hardware type approach, in Shibaura, Tokyo,showed the importance of careful site selection and taking intoconsideration the hydraulic regime to maintain the environment.The software type approaches in urban wetland managementinvolving stakeholders from NPO, government and research orga-nizations at Yokohama showed the importance of corporation andcoordination among stakeholders to implement intensive moni-toring so as to maintain the benthos habitat.

The most important message from these studies is that whilethe aquatic environment in a well-developed urban area has beendegraded, the wetland and aquatic habitat can still be restored.

Local citizens can play a key role in the development, moni-toring and co-management of restored habitats irrespective ofwhether they live in urban or rural areas. Public support is indis-pensable especially for regular observations through monitoring ofhabitat changes and for their long-term participation in themaintenance and management measures. It is essential to under-stand the wishes and suggestion of the stakeholders and developappropriate and strategic planning and management measures forcontinual improvements. Academic symposia for experts inmodeling and other specialized topics are needed to facilitate datacollection, data storage, development of easily used models, andanalysis of environmental restoration technologies.

Acknowledgments

The author would like to thank all stakeholders of the projectmentioned in this article. Special thanks go to: the Tokyo Metro-politan Government, Minato City and the NPOs e Umijuku on theShibaura Island Project; Association for Shore Environment Crea-tion, and the Sea Beautification Society, the research group forwise-use experiment and the MLIT for the Yokohama projects.Their contributions were crucial. The author would also like tosincerely thank anonymous reviewers for checking and givingconstructive suggestions to improve the quality of this manuscript.

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