Power of City driven by Power of Nature“To the Era of Green Infrastructure”

Green Infrastructure Research Institute1

CONTENT
Chapter 01: Green infrastructure: Why now?

1. What is green infrastructure?

2. Urban issues on disaster risks are urgent issues

3. Green infrastructure that solves urban issues

Chapter 02: Urban development enhanced by green infrastructure

1. Attract people and companies through urban development using green infrastructure
2. Vibrant and attractive remodeling of parks using green infrastructure
3. Urban development adapted to the future mobility style

Chapter 03: Promotion of living environment by green infrastructure

1. Increase property’s resale values with green infrastructure

2. Urban green infrastructure that makes use of empty roof space

3. Green infrastructure will enhance economic values in (developing) residential areas

Chapter 04: Activities of green infrastructure in major cities of the United States

1. The most environmentally friendly city in the US: City of Portland

2. The green infrastructure that New York City is actively developing

3. Green infrastructure that is used for heat island mitigation in the City of Chicago
Chapter 05: Development of green infrastructure in Japan

1. Fourteen elements of green infrastructure: Technological elements and situational elements

2. Development of rainwater retention & infiltration basin
3. From single to multiple functions

4. On-site infiltration of rainwater

5. Utilization of rainwater

6. Economical stormwater capture with lawn fields

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Landscape in the City of Portland where attractive urban development with green infrastructure is progressed(Photo: Mike Houck, Urban Greenspaces Institute)

Chapter 01．Green Infrastructure: Why now?
1.What is green infrastructure?
Green infrastructure is an infrastructure or land use plan which contributes to sustainable social andeconomic development using a variety of natural functions1). However, the methods and viewpoints
depend on nations and organizations. For instance, the European Union defines green infrastructure as“a strategically planned network of natural and semi-natural areas” and implements conservation andrestoration of ecosystems, generation of ecosystem networks, urban development using ecosystemservices, disaster countermeasures etc. On the other hand, the United States recognizes green
infrastructure as“ a simultaneous method to achieve rainwater management, stormwater

countermeasures and environmental conservation”, and focuses on human-made buildings (rainwater
management facilities) reinforced with ecosystem functions2).
Both strategies aim to solve urban issues utilizing natural (green) potentials, and they are
implemented as a new concept that can facilitate integrating various components such as environmental
conservation, urban and regional development, and disaster prevention and mitigation. This brochurefocuses on the green infrastructure from a viewpoint of rainwater management based on the concept in
the US.
32. Urban issues on disaster risks are urgent issues
In recent years, urban heat island effects and localized heavy rain which may trigger urban water
disasters have become more serious globally year by year. When we think about a “good environment”
in future cities, technology that can solve the issues persistent in urban infrastructures, such as “safety”
against natural disasters or “ cities that can cool ” even under severe heat, are thought to beunquestionably necessary. Japan has taken countermeasures against stormwater using excellent
construction technology. However, these systems are ineffective against recent which are exceed theircapacity. Photo 1-1 shows a situation of localized heavy rain, and Figure 1-1 shows an upward trend ofheavy rain frequency3), which demonstrates that the countermeasures against heavy rain are an urgent
issue.

Photo 1-1 Situation of localized heavy rain (Photo:
Japan Meteorological Agency)

Figure 1-1 Annual frequency of heavy rain (>80 mm/hour)
The annual frequency of heavy rain (>80 mm/hour)
increases year by year (Photo: Japan Meteorological
Agency)3. Green Infrastructure that solve the Urban issues
In the world’s megacities, they find an answer for their urban issues using green infrastructure,
because many benefits are produced by utilizing the green potentials as an urban infrastructure. That is,
rainwater retention and infiltration, reduction of surface runoff, removal of pollutants, improvement ofwater cycle including rainwater reuse and groundwater recharge, and improvement of microclimate incities can be achieved by taking advantage of natural functions possessed by plants and soils, which resultsin new urban developments that are safe and comfortable to live in.
A major reason for the global trend of green infrastructure is its “multi-functions.” As opposed tothe single-purpose gray infrastructure that can work only during rain events, like conventional civilengineering methods, green infrastructure can provide many benefits, which is its most important point.
United States Environmental Protection Agency (USEPA) describes the advantage of green
infrastructure as “Benefits of Green Infrastructure4)” (Table 1-1).

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Table 1-1 Various benefits of green infrastructure
Cat ego ry

Water Quality & Quantity

Air Quality

Climate Resiliency

Habitat & Wildlife

Communities

Merit

Fu n ct io n

Water quality improvement

Reduce pollutant loads; Reduce stormwater discharge into combine sewers and rivers

Surface runoff mitigation

Delay and reduce stormwater discharge

Water supply

Facilitate rainwater harvesting and infiltration; Increase groundwater recharge;
Improve water cycle

Particle pollution reduction

Absorb and filter particulate matters

Health effects

Reduce respiratory ailments

Grand-level ozone improvement

Reduce air temperatures; Reduce nitrogen oxides; Reduce smog

Water disaster reduction

Infiltrate rainwater; Reduce flood risk by open space preservation

Drought mitigation

Replenish groundwater reserve; Relieve stress on water supplies

Heat island mitigation

Reduce temperature by evapotranspiration; Reduce temperature with green roofs

Lower building energy demands

Reduce indoor temperature by shading building surfaces

Lower energy usage for water
management

Reduce rainwater flows into sewer systems; Reduce pumping and treatment demands
for municipalities

Habitat improvement

Reduce erosion and sedimentation; Provide water and food; Provide places for hiding,relaxing and mating

Habitat connectivity

Facilitate wildlife movement; Connect wildlife populations between habitats

Green jobs

Create construction and maintenance jobs

Health benefits

Encourage outdoor physical activity; Reduce chronic diseases

Recreation space

Facilitate recreational activity for urban residents

Property values

Increase property values with more vegetation and tree cover; Benefit both developers
and homeowners

Chapter 02．Urban Development enhanced by Green Infrastructure

1.

1. Attract people and companies through urban development using green infrastructure
The City of Portland is the most popular “destination city” in the US, and it is globally renowned asa winner of the world city’s competition. More people have moved from centralized cities with IT
companies in California (such as Silicon Valley), and some major sporting goods companies also have
moved to the city. The movement is reflected by the transition of work style along with IT development,
as well as the attractive city development of Portland with green infrastructure.
Young and highly productive people work with outstanding concentration to achieve their highperformance. On the other hand, it is said that once work is finished, they forget all about work and go
to play outside in nature to recharge and gain energy to accomplish their next big goal. As such, cities
like Portland, which provide a rich natural environment suitable for this charge and recharging of modern
life, as well as a living environment that is enriched by greenery, they attract more high potential people,
which then leads companies to come to hire such excellent workers, which up generating a positive spiral.
As a consequence, such cities will gain more tax revenue, become more vibrant, and transform into more
popular cities. Thus, green infrastructure plays an important role in urban development (see Photos from
2-1 to 2-3).

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Photo 2-2

Photo 2-1

Photo 2-3

Photo 2-1 Tanner Springs Park, built on a former industrial site (2012); Photo 2-2 Trekking – environmental educationin nature (2012); Photo 2-3 Pioneer Courthouse Square, at a public viewing (2014)

2. Vibrant and attractive remodeling of parks using green infrastructure
The role of parks changes with the time. The “existence” of parks used to be important, while parks
are deemed to “be utilized” by many people as well as “create vibrant spaces” in today’s society. Parks
should be a place to provide comfortable spaces whenever we go, and therefore they don’t meet the role
if the environment is uncomfortable such as “parks without any shade from trees” or “parks that arealways humid”. Thus, there is need for public spaces that people want to go, and parks where people canrelax even on hot summer days.
So what tools are available to cool down the public places? Misting systems and sunshades are themost popular artificial facilities used in many places. They provide the direct cooling effects, however
they will be constant labor and maintenance costs and they may not be used in the future as the needs ofsociety change.
On the other hand, parks originally possess various natural elements such as soils, trees and water asbasic natural components. If these elements can be utilized effectively and parks can be transformed into
attractive spaces where many people can gather and enjoy themselves, then that is an ideal parkdevelopment which is sustainable and provides values continuously into the future. In fact, the Grand
Mall Park (Minato Mirai 21) in the City of Yokohama has been transformed into an “innovative park
leadingmaturedurban

development” using green
infrastructure technology5)(Photo 2-4)

Photo 2-4 Grand Mall Park in the City of Yokohama vibrant with many people (Minato
Mirai 21) “Bijutsu no Hiroba”

6Example: Grand Mall Park in the City of Yokohama
The Grand Mall Park in the City of Yokohama was renovated as a core of new urban development,
and “Bijutsu no Hiroba” was constructed in the Japanese fiscal year 2015. In order to create a vibrantspace in the park, a large water circulation system was installed using green infrastructure technology(Figure 2-1). A “cool space even in summer” was created with not only green shades but also evaporationof rainwater occurred from underground by capillary action, as well as evapotranspiration fromprogressively growing trees. This microclimate effect has been verified and a technical report was
published in Journal of the Japanese Society of Revegetation Technology (volume 42, issue 3, February2017) (Figures 2-2 and 2-3). The Grand Mall Park has become a showcase of environmental future city,
literally along with a concept of “the second urban development” held by the city of Yokohama.
Green infrastructure
Cool down by evapotranspiration

Water retentive pavers
Side trench
Capillary action

Rainwater retention and infiltration base
Figure 2-1 Sectional diagram of the Grand Mall Park
Rainwater infiltrated from water retentive pavers or side trench moves up through the rainwater
retention and infiltration base by capillary action and reaches out to the water-retentive pavers. A
temperature reduction effect occurs by evaporation of rainwater from the water-retentive pavers aswell as evapotranspiration from trees.

Figure 2-2 Results of temperature measurement at a site
installed with rainwater retention and infiltration base(at a 1.5 m height)6)

Figure 2- 3 Precipitate and groundwater level change
A heavy rain (110 mm/day) was observed on July 15,
2016, but the groundwater level at rainwater retention
and infiltration base only increased by 30 cm. There wasno flood occurred from the catchment area during themonitoring of groundwater level6).

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3. Urban development adapted to the future mobility style(1) Reduce driveway lanes and utilize walkway for green zone
In recent years, street designs have been gradually transformed from car-centered to humancentered, cyclists and pedestrians. In the City of Portland, which is the most environmentally friendly
city in the US, people often use bikes and it has become normal to bring their bikes onto trams. In Japan,
car sharing is becoming more popular and renovation of streets is planned along with bikeway installationin major cities that reduces driveway lanes and expands walkways. Conceptual diagrams are shown in
Figures 2-4. As such, urban development changes corresponding to the change of people’s lifestyle.
To reduce driveway lanes and accommodate green spaces for human wellbeing, the planting basealso has to be maintained properly. However, conventional roadbeds which are often hard and compact
are not suitable for healthy plant growth because plant roots cannot be extended in such a nonporous soilbase, which results in the inhibition of plant growth. On the other hand, considering that urban flooding
has become more frequent in recent years, it is desirable that the spaces under walkways are utilized
effectively as a rainwater retention and infiltration facility. Thus, the needs of urban development arechanging along with the transition of our society.

Figure 2-4 Human-centered street design
The 2 driveway lanes are reduced to a single lane, while bikeways and vibrant spaces (flowerbeds) are installed, along with the anticipated lower needs of car transportation. (Conceptual
diagram)8

(2) Prevent tree roots rising for safe walkway
Tree roots rising up from walkways is a phenomenon where tree roots have no extension space intree pits and end up reaching out to the bottom layers of pavements (such as interlocking blocks) which
results in the pushing up of the pavements (Photos 2-5 and 2-6). Therefore, if an enough space of good
planting base is accommodated for tree roots, this can be avoided.
Root guide and pressure-resistant base material (Power Mix) is a technology to provide good
planting base adaptable in narrow tree pit as well as to prevent tree roots rising. The Power Mix is
installed around the tree pits, whereas rainwater retention and infiltration base is installed under theentire walkway in order to accommodate an enough infiltration area.
These planting bases are a beneficial green infrastructure technology for road authorities that canminimize the risk of pedestrian accidents followed by lawsuits due to rising tree roots.

Photo 2-5

Photo 2-6

Photos 2-5 and 2-6 Phenomenon of tree roots rising and its cause
If soils around trees are compacted, their roots extend towards the road surface and causes tree roots
rising. Countermeasures are necessary to prevent lawsuits caused by pedestrian accidents.

Chapter 03．Promotion of living environment by Green Infrastructure
1. Increase property resale values with green infrastructure
Apartment exteriors enriched by greenery have become common in recent years. People tend tochoose their properties by looking at not only properties themselves but also the quality of greenery andstate of greenery maintenance. Apartment exteriors which have been guaranteed with the quality of green
for the next couple of decades will result in increasing the property values as well as a source of pride forthe residents.
Lands for large housing developments are often within ecologically preserved sites. Therefore, it ispossible to create ecologically friendly, green-enriched, and space that are cool even in summer by using
green infrastructure technology. In addition to the hardware aspects, developers have to be aware thatthe maintenance of green spaces is also an important key factor for the satisfaction of residents. Also, soft
aspects such as the maintenance plan has to be clear from the designing phase. This is a big opportunity
for developers to differentiate product offering and therefore a firm and high-quality maintenance plan
has to be developed (Figure 3-1).
9Figure 3-1 Comfortable apartment life supported bygreen infrastructure technology (Conceptual diagram)
Possible to provide enriched green shades and cool
spaces even in summer(Please contact us for further details of the road basesystem)Photo 3-1 An example of green infrastructure whichworks for temporarily retaining rainwater as well as
providing a green space for a rooftop party

2. Urban green infrastructure that makes use of empty space
In Japan, 433.8 ha of green rooftops have been created since 2000 until 20157). In Chicago, green
rooftops are installed progressively because an ordinance that enforces to the installation of a temporal
retention system on rooftops for a half-inch of rainwater has been enacted. If the same ordinance isenacted in Japan, 56,000 m3 of rainwater can be additionally retained on rooftops, which is equivalent toabout 10% of retention volume in a large underground tunnel (Kanda River Underground Regulating
Reservoir Under the Loop Road 7, approximately 540,000 m3) constructed by the Tokyo Metropolitan
Government for as an urban flooding prevention method. When the rainwater retention at rooftop spaces
is recognized as an effective countermeasure for stormwater capture in Japan, the construction of green
rooftops will be increasingly expected as a new and effective rainwater retention system.
There are a number of rooftops left abandoned without any usage. It is also expected that newcommunication sites are created by installing the latest green infrastructure technology in there (Photo
3-1).
3. Green infrastructure will enhance economic values in (developing) residential areas
In future urban development, it is important to establish maintenance methods that make residents
feel comfortable and keep their property values stable in the long run. To achieve this, urban planning
based on residents’ point of view, the installation of green infrastructure technology, and sustainable
maintenance planning are important. In addition to “beautiful”, “rich”, “vibrant” and “proud” whichused to be recognized as “good living conditions”, sustainable urban design which can provide “cool insummer” and “safe” environment is also to be anticipated in the future (Figures 3-2 and 3-3). Also,
development of monitoring technology to verify the effects of green infrastructure will be advanced.

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Fig. 3-2

Fig. 3-3

Figures 3-2 and 3-3 Application of green infrastructure for comfortable urban development

Chapter 04．Activities of green infrastructure in major cities of the United States

1. The most environmentally friendly city in the US: City of Portland
The City of Portland is a middle-sized city in the US with a population of about 600,000 people. The
main industry of the city used to be forestry, and thereafter the city was industrialized with many steel
factories and shipyards along Willamette River, which ended up becoming the dirtiest river in the US.
The sewer system in the City of Portland is a combined sewer system which releases wastewater intorivers when its amount exceeds the capacity of wastewater treatment plants due to heavy rain. In 1993,
the federal government filed a lawsuit to restrict the amount of wastewater discharge into rivers because
the discharged wastewater polluted the river water further. As the river water became polluted, steelhead
and Coho salmon which are a vital part of the ecosystem in the City of Portland were listed as endangered
species. Therefore, the city started to take actions for stormwater management as well as watershed
restoration.
The city determined an urban growth boundary between land development areas and nature
conservation areas in order to restrict chaotic land development and the expansion of impervious area.
Green infrastructure used to be installed for the purpose of natural stormwater purification, but theapplication was expanded as a countermeasure for the overflow of wastewater from sewers due to heavy
rain, such as rain gardens and green streets with bioswales (Photos 4-1 to 4-4). Furthermore, in the city’s
infrastructure development project “Tabor to the river”, 60% of the cost for sewer pipes repair was saved
using green infrastructure, which resulted in further promoting the application of green infrastructure.
The City of Portland has become the world’s model city of green infrastructure and many people
visit the city to see the green infrastructure. The city has been ranked as “the most environmentallyfriendly city in the US,” and hence more talented people have moved in there and related companies
corresponded to them and built their offices there. Thus, the City of Portland has built a resilient city
base using green infrastructure.

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Photo4-1

Photo4-2

Photo4-3

Photo4-4

Photos 4-1, 4-2, 4-3, 4-4 Raingardens and bioswales in Portland City

2. The green infrastructure that New York City is actively developing
New York City held a competition “Rebuild by Design” for disaster prevention against hurricanes
since a serious urban flooding occurred on the east coast of the US by Hurricane Sandy in 2012. The
characteristics of the competition was that a mix of sectors got involved with projects at specific land
areas. The BIG U, which is one of the participants in the competition, proposed a comprehensive plan at
the lower Manhattan Island that not only mitigates the risk of flooding and downpour but also improves
the issues of climate change and environmental problems, ecological network and recreation, andeconomic values. The rebuild design proposed in the plan corresponds to a question of what new andmulti-purpose infrastructure is (Photo 4-5)8).
The High Line in New York City is a linear park (2.3 km) that uses former freight railroads andattracts people as greenery on artificial ground. The freight railroads have been abandoned and used to
be a poor landscape, but it has been transformed to be an attractive sky garden with full of greenery, andthe economic values around the park have increased to
300 billion JPY annually. The park is also functionalized
as a green infrastructure facility as rainwater is retained
and slowly infiltrated into underground during rainfall.
Green Infrastructure Research Institute visited New
York City on July 2016 and interviewed a representativeof the city’s green infrastructure division. There are morethan 2,300 rain gardens (rainwater retention andinfiltration facility) built in New York City, particularlyin the Brooklyn borough. The rainwater retention
capacity is 2,200 gallons (about 8.3 m3) per rain garden

Figure 4-1 Sectional diagram of rain garden (2016)
Rainwater infiltration base is installed under therain garden (Ref: New York City)(Figure 4-1), and hence the burden of rainwater discharge into sewers decreases by 19,000 m3. The
stormwater management will be implemented with a budget of $1.5 billion by 2030.
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According to NYC Green Infrastructure Plan by Michael R. Bloomberg (a part of the preface),
advanced street-pits mentioned in the preface means rain gardens which infiltrate rainwater. Also,
economic rationality was pursued in the plan as Bloomberg mentions “we can achieve all of these benefits
for billions of dollars less than the cost of the traditional tanks and tunnels that are useful only when it
rains”. Streets and residential areas are rebuilt in accordance with the plan.

Photo 4-5 Countermeasure plan for disaster prevention against hurricanes along the U-shaped region of lower
Manhattan Island (Ref: ©The Big Team/Rebuild by Design)

3. Green infrastructure that is used for heat island mitigation in the City of Chicago
The City of Chicago faces to Lake Michigan and is located in a geographically harsh region as theweather dramatically changes between summer (42℃) and winter (-17℃). Also, the city has many heatisland countermeasures because many skyscrapers worsen the phenomenon. Of the city’scountermeasures, green infrastructure application on rooftops is characteristic. Millennium Park whichis the world’s largest rooftop garden built-in 2004 plays a role in rainwater retention and as an infiltration
facility. Railways, large parking lots and concert halls have been constructed under the 10-ha park as if itwere a city park built on natural ground. The park close to skyscrapers provides a natural atmosphere
within the megacity.
Also, a large green roof is constructed on the top of the city office. Temperature in the maintenancefree greening section has found to be 30℃ lower than that in the remaining concrete section, andtherefore the cool environment is provided even on the rooftop. The cost savings of air conditioning at
the floor below the rooftop are estimated to be $3,600 annually due to the green roof. Bee farms are also
installed on the rooftop garden which almost makes you forget that it is a rooftop. The green roof also
provides unexpected advertisement effects and a number of people from all over the world visit there.
13Thus, the green roof has become a place which allows us to realize that green rooves have great potential
for green infrastructure in urban areas.
Regarding heat island countermeasure of the City of Chicago, Complete Street Project9) and Green
Alley Project10) are a part of the countermeasures currently being progressed. Photo 4-6 shows aconventional alley which is dark with puddles due to impervious road surface. Photo 4-7 shows an alley
renovated under the Green Alley Project which was installed with recycled aggregates under the groundin order to functionalize as rainwater retention and infiltration as well as heat island mitigation. The roadsurface is covered with pervious pavers, and maintenance methods have been developed by the City of
Chicago. Thus, the new alleys are rapidly developed for heat island mitigation.

Photo 4-6 Conventional alley
It is dark even during daytime and puddles
remain due to the impervious road surface

Photo 4-7 Alley after renovation
Road surface is covered with pervious
interlocking blocks and recycled aggregates are
installed under the ground which play a role asa rainwater retention and infiltration base(2014)

Chapter 05: Development of green infrastructure in Japan
In foreign countries, new urban development that makes effective use of green infrastructure is
being progressed to improve the work and living environment. Then, is it possible to develop safe andrich cities and towns in Japan using the same technology? The answer is no. Urban structure, culture,geographic situation, and/or social situation vary amongst countries or regions, and hence the best green
infrastructure technology is different accordingly. In the case of Japan, green infrastructure technology
unique Japan is necessary which is adapted to the current national issues such as narrow city spaces,
limited investments for public works, and increased management costs.

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1. Fourteen elements of green infrastructure: Technological elements and situational elements
The organization promoting green infrastructure in the US is the United States Environmental
Protection Agency (EPA). The EPA defines 11 items as green infrastructure elements11). To apply thegreen infrastructure to Japan, green parks, wall greenery and lawn square ground were added astechnological elements and the 14 elements were categorized by either technological elements orsituational elements12). Creation of various and multi-purpose infrastructure is important throughcombining the technological elements in various situations of urban development.

Technological elements(1) Downspout Disconnection
Rooftop drainage pipes are rerouted from draining rainwater
into the storm sewer to draining it into rain barrels, cisterns, orpermeable areas. Downspout disconnection could be especiallybeneficial to cities with combined sewer systems (Photo: City ofPortland)(2) Rainwater Harvesting
Rainwater harvesting systems collect and store rainfall for later
use. They slow and reduce runoff and provide a source of water for
miscellaneous use in buildings as well as for emergency use during
natural disasters. (Photo: Water level measurement in rainwater
retention base)(3) Rain Garden
Rain gardens collect and absorb runoff from rooftops, sidewalks
and streets which can be installed in almost any unpaved space. They
infiltrate the runoff into underground and treat it. They also can benatural habitats. (Photo: Kyoto Gakuen University, Uzumasa
Campus, provided by Yukihiro Morimoto)15

(4) Planter Boxes
Planter boxes are urban rain gardens with vertical walls andeither open or closed bottoms. They collect and absorb runoff fromsidewalks, parking lots and streets, and are ideal for space-limitedsites in dense urban areas. (Photo: Portland State University)(5) Bioswales
Bioswales are vegetated, mulched or xeriscape channels thatprovide treatment and retention as they move stormwater from one
place to another. As linear features, they are particularly well suited
to being placed along streets and parking lots. (Photo: City ofPortland)(6) Permeable Pavement
Permeable pavements infiltrate treat and/or store rainwater where it
falls. They can be made of pervious concrete, porous asphalt orpermeable interlocking pavers. (Photo: Morton Arboretum, City of
Chicago)Situational elements(7) Green Alleys and StreetsGreen streets and alleys are created by integrating green
infrastructure elements into their design to store, Infiltrate, andevaporate stormwater. Permeable pavement, bioswales, planter boxes,
and trees are among the elements that can be woven into street or alley
design. (Photo: City of Chicago)(8) Green Parking
Many green infrastructure elements can be seamlessly integrated
into parking lot designs. Permeable pavements can be installed in
sections of a lot and rain gardens and bioswales can be included inmedians and along the parking lot perimeter. (Photo: Morton
Arboretum, City of Chicago)16(9) Green Parks
Green parks can improve microclimate by previous pavers andevapotranspiration of trees through integrating green infrastructureelements into their design. They also enable rainwater circulation
within the parks. (Photo: Grand Mall Park, City of Yokohama)(10) Green Roofs
Green roofs are covered with artificial soil or natural soil andvegetation that enable rainfall infiltration and evapotranspiration of
stored water as well as cooling effects. (Photo: Millennium Park, Cityof Chicago)(11) Wall Greenery
Wall greenery reduces and slows downflow of rainwater hit to thewalls. In case of planter types, they can slow and reduce runoff byretaining and infiltrating rainwater temporarily. Also, they provide
temperature reduction effects by plants. (Photo: City of Portland)(12) Lawn Square Ground
Lawn Square ground infiltrates rainwater effectively and canslow runoff as well as reduce and treat rainwater. They also canprovide temperature reduction effects on road surface. (Photo:
Shoemaker Plaza, City of Philadelphia)(13) Urban Tree Canopy
Trees reduce and slow stormwater by intercepting precipitationin their leaves and branches. Also, tree canopy plays a role as asunshade and decreases temperature. (Photo: City of Philadelphia)17(14) Land Conservation
The water quality and flooding impacts of urban stormwater also
can be addressed by protecting and maintaining open spaces andsensitive natural areas within and adjacent to a city. (Photo: City of
Seattle)2. Development of rainwater retention & infiltration basin
J-Mix is a novel rainwater retention and infiltration base which enables Japanese-style green
infrastructure. J-Mix is made of recycled concrete wastes (including other recycled aggregates) with auniform particle size and coated its surface with humus. Void content ratio is 41% which can retain
rainwater in the void sufficiently (Photo 5-1).
Humus buffers and keeps the pH of rainwater from alkalization occurred by recycled aggregates (aslong as the retained rainwater is discharged from the base within 24 hours), as well as facilitates root
growth through the voids. Photo 5-2 shows a result of root growth 4 years and 4 months after installing
recycled aggregates with (left) and without (right) humus coating under a camphor tree. The root growth
was better in the recycled aggregates with humus coating (J-Mix) as the roots extended downward
uniformly in the installed base, suggesting that the structure of J-Mix is suitable for plants.

Photo 5-1 Appearance of J-Mix (Voidcontent ratio is 41%)

Photo 5-2 Root distribution of camphor tree 4
years and 4 months after planting. Root growthunder recycled aggregates with humus coating(C: left section) was pretty good

3. From single to multiple functions
Conventionally built constructions made of concretes or plastics (grey infrastructure) for stormwater
management work only during rainfall and is a single-purpose facility. In addition to the existing facilities,
natural green infrastructure with multiple functions is expected in the future. Green infrastructure
functions as rainwater retention infiltration and provides many benefits such as water treatment,
pollutants removal, drought mitigation, groundwater recharge, microclimate improvement, and tree
growth promotion (Table 1-1).
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4. On-site infiltration of rainwater
In matured cities, tall buildings are built to stand in rows and road surface is covered by asphalt.
Consequently, according to the data in Tokyo Prefecture, about 45% of rainfall has become discharged
as surface runoff directly into sewers and rivers. Rainwater beyond cities’ stormwater management
capacity overflows and seriously damages the cities. In the United States, stormwater management has
been advanced to capture on-site and infiltrate into the ground. For instance, downspouts weredisconnected and natural rainwater infiltration systems such as rain gardens, planter boxes, bioswales,and pervious pavers were installed. Figure 5-1 shows a conceptual diagram of green infrastructure incities which infiltrates rainwater into the ground through rooftop gardens and rainwater retention andinfiltration base built underground. It is important that stormwater is captured on-site in order not to bedischarged directly into sewers.

Solve with green
infrastructure!

Prevent from direct discharge into sewers
Figure 5-1 Cities need to elaborate stormwater management system to let
rainwater infiltrate into the ground (Conceptual diagram)
The basic of green infrastructure is to reduce the amount of stormwater
discharged into sewers by infiltrating rainwater into the ground

According to the City of Portland, more than 74% of rainwater was retained in rain gardens andpeak flow was reduced by 81%, suggesting that on-site stormwater management can substantially reducethe burden of surface runoff flowing into sewers. In New York City, the infiltration amount of rainwaterby rain gardens is huge (2,200 gallons (about 8.3 m3) per garden), and the city plans to manage morethan 1 inch (about 25 mm) of stormwater runoff from 10% impervious area using rain gardens.
However, large rain gardens in foreign countries with a space of one driveway lane cannot be
accommodated in the narrow land area of Japan. Therefore, one of the feasible methods is to retain andinfiltrate rainwater underground such as under the walkway (Figure 5-2). If the rainwater retention andinfiltration base is installed on permeable ground (coefficient of permeability is more than 0.14 m/hour)with a dimension of 100 m long, 4 m wide and 0.6 m deep, about 157 m3 of rainwater is captured andinfiltrated. It is economically and simply installed with effective stormwater capture in permeable land19

area, and also an additional benefit of cooling down the streets by capillary action of rainwater occurredin the base is generated by this method.

Figure 5-2 On-site method to capture rainwater fallen on road and walkway(Conceptual diagram)
Rainwater is captured and infiltrated with rainwater retention andinfiltration base, as well as streets being cooled down by capillary action of
rainwater occurred in the base. Also, the rainwater retention and infiltrationbase are good for planting. (Please contact us for further details of the roadbase system)

5. Utilization of rainwater
In the Architectural Institute of Japan Environmental Standards (AIJES) issued in 2011, the word
“Amamizu-Katsuyou (rainwater utilization)” was defined. Utilized rainwater was named “Amamizu”
which differentiates from stormwater or polluted water which is of no use and should be discharged away
immediately. The word “Amamizu” was also used in the Act on the Advancement of Utilization Rainwater
enacted in 2014. In March 2016, “Technical standards for rainwater harvesting” were issued by theArchitectural Institute of Japan and a new term “Chiku-U (rain stock)” was defined13). The term consistsof 4 categories: disaster prevention, stormwater management, environmental resilience, and rainwater
utilization. Coefficient of rain stock was also defined, and a rain stock height of 100 mm was targeted asa new approach. Also, a nonprofit organization, Rain City Support was established. Thus, a new era of“Amamizu” has kicked off in Japan.

6. Economical stormwater capture with lawn fields
Given that a countermeasure for surface runoff mitigation is applied throughout buildings or regions,a more economical and reasonable solution is found compared to a countermeasure applied to individual
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building.
In case of Tokyo’s permeability assessment14) made in each land use, permeability in green fields is
assessed to be 20 mm/hour in grass field and 50 mm/hour in lawn field as well as planted field. Therefore,
reduction amount of surface runoff in a cubic meter of green field is estimated to be only 20 L or 50 L,
respectively. This amount can be increased by installing rainwater retention and infiltration base under
the green fields (Figure 5-3).
When a 200 mm deep rainwater retention and infiltration base is installed under green fields,
quantity of infiltration Qf = influence coefficient C (0.81)×relative infiltration rate (calculated based on
infiltration occurred only into the bottom layer)×saturated hydraulic conductivity f (0.14 m/hour) =0.146 (m3/hour), and then void retention amount 0.2 m×41% = 0.81 (m3/ m2) is added to the value,
which becomes 228 L of reduction amount of surface runoff in a cubic meter of green field. Given 600
m3 of countermeasure for surface runoff mitigation required in one hectare of land development, it isfulfilled by allocating 27% of land for green field with water retention and infiltration base. Furthermore,
it has been reported that the rainwater infiltration under green fields ended up becoming a good
maintenance for them with a lower amount of irrigation.
Thus, the quality of green fields is enhanced and the cost for surface runoff reduction is decreased
by installing shallow and wide rainwater retention and infiltration base.

Figure 5-3 Stormwater management using lawn fields (Conceptual diagram)
Regional target amount of stormwater capture can be complemented by using
lawn fields as a rainwater retention and infiltration tank. The figure shows anexample of rainwater retention and infiltration base installed under a lawn
field (100 mm deep) to enhance its quality.

21Afterword
Green infrastructure is expanding all over the world. In Japan, it is becoming gradually recognized
as a new concept that merges various fields such as environment, urban development, and disasterprevention/mitigation. However, we heard many voices starting that they do not know the method forexactly realizing this. Therefore, we made this brochure as a handbook that explains simply the green
infrastructure method (draft) and its benefits. As mentioned at the first section in Chapter 01, thisbrochure was more focused on the installation of green infrastructure for rainwater countermeasures, but
we hope that people, especially living in cities, will feel the attraction of green infrastructure as somethingthat is relevant to their lives, through this brochure. We hope that green infrastructure will be adopted
and take root in Japan as early as possible.
(This brochure was supported by Professor Shiro Wakui as well as many professors and supporting staff.
We would like to take this opportunity to express our deepest appreciation to all of them.)
July 2017
Green Infrastructure Research InstitutePrincipal: Yukio Kida

Reference
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229) Complete Street Project. http://chicagocompletestreets.org/ (cited on March 27, 2017)10) Green Alley Project. http://www.greeningthegrey.org/chicagos-green-alley-program/ (cited on
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