Interdisciplinary Design of Vital Infrastructure to Reduce Flood Risk in Tokyo’s Edogawa Ward

Abstract

Engineering for flood resilience of dense coastal regions often neglects the resultant impact on urban design quality. Vital subsurface infrastructure such as hydraulic systems, water networks, civil construction, transport, energy supply and soil systems are especially important in shaping the urban environment and integrating resilience. However, the complexity and resource intensive nature of these engineering domains make it a challenge to incorporate them into design measures. In the process of planning, this impedes proactive collaboration between the design and engineering communities. This study presents a collaborative design engineering exercise undertaken to find spatial solutions to flood-prone Edogawa ward in Tokyo, Japan. The team included urbanists, hydraulic engineers, water resource managers, and landscape architects. Hydraulic engineering solutions were combined with spatial planning methods to deliver two alternative strategies for the chosen site. Each alternative was then evaluated for its urban design quality and effectiveness in reducing flood risk. The exercise highlighted that successful design requires comprehensive interdisciplinary collaboration to arrive at a sustainable bargain between hard and soft measures.

Full text

geosciences
Article
Interdisciplinary Design of Vital Infrastructure to
Reduce Flood Risk in Tokyo’s Edogawa Ward
Supriya Krishnan 1,*,† , Jiabiao Lin 1,†, Johannes Simanjuntak 2,†, Fransje Hooimeijer 1,†,
Jeremy Bricker 2,†, Maayan Daniel 3,† and Yuka Yoshida 1,†
1
Department of Urbanism, Faculty of Architecture and the Built Environment, Delft University of Technology,
52628 Mekelweg, The Netherlands
2Department of Hydraulic Engineering, Faculty of Civil Engineering and Geosciences,
Delft University of Technology, 52628 Mekelweg, The Netherlands
3Department of Architecture, Faculty of Architecture and the Built Environment,
Delft University of Technology, 52628 Mekelweg, The Netherlands
*Correspondence: supriya.kr09@gmail.com
† These authors contributed equally to this work.
Received: 2 December 2018; Accepted: 16 July 2019; Published: 13 August 2019


Abstract:
Engineering for flood resilience of dense coastal regions often neglects the resultant impact
on urban design quality. Vital subsurface infrastructure such as hydraulic systems, water networks,
civil construction, transport, energy supply and soil systems are especially important in shaping
the urban environment and integrating resilience. However, the complexity and resource intensive
nature of these engineering domains make it a challenge to incorporate them into design measures.
In the process of planning, this impedes proactive collaboration between the design and engineering
communities. This study presents a collaborative design engineering exercise undertaken to find
spatial solutions to flood-prone Edogawa ward in Tokyo, Japan. The team included urbanists,
hydraulic engineers, water resource managers, and landscape architects. Hydraulic engineering
solutions were combined with spatial planning methods to deliver two alternative strategies for
the chosen site. Each alternative was then evaluated for its urban design quality and effectiveness
in reducing flood risk. The exercise highlighted that successful design requires comprehensive
interdisciplinary collaboration to arrive at a sustainable bargain between hard and soft measures.
Keywords:
hard vs. soft countermeasures; flood risk; storm surge; critical infrastructure; resilient cities
1. Introduction
Cities across the globe are threatened by increasing flooding from coastal, fluvial and pluvial
sources which must be considered in engineering and spatial design. This is compounded by urban
densification that increases the exposure of population at risk. Building flood resilience in the
built environment involves reducing the risk and damages from disasters. This ‘risk’ is defined
as the product of ‘probability’ of an event occurring with the ‘consequence’ of that event [
1
] whereas
‘resilience’ is defined as “the ability of a system to adjust in the face of changing conditions (events)” [
2
].
The scientific consensus on resilience is that it needs multidisciplinary cooperation and an integrated
approach which in flood risk consideration is about engineering and spatial design [
3
]. In the current
spatial development landscape, reduction of ‘probability’ has assumed priority by investments in
protective infrastructure such as dams, dikes, gates and levees that shield the built environment
from the impacts of the hazard. Rising intensities and frequencies of hazards due to climate change
can overwhelm such defense structures, suggesting a need to shift focus from reducing ‘probability’
towards reducing the ‘consequences’ of the hazard.
Geosciences 2019,9, 357; doi:10.3390/geosciences9080357 www.mdpi.com/journal/geosciences

Geosciences 2019,9, 357 2 of 20
This consequently implies that spatial development becomes part of the risk approach and
engineering becomes part of spatial design. The integrated approach needs more than multidisciplinary
cooperation. It requires not only respecting each other’s expertise, but also critical discussions,
questioning and understandable argumentation defined as interdisciplinarity [
4
]. Currently there is
a knowledge gap on how the new relation between spatial development and flood risk engineering
can be performed in an interdisciplinary fashion [5].
This paper reflects on interdisciplinary research performed by urbanists, hydraulic engineers,
water resource managers, and landscape architects aimed at flood resilience in dense built
environments. Due to the shift from probability to the consequences of a hazard, the research scope is
narrowed; instead of looking at the whole urban system (functions, social, economic) the focus is kept to
the consequences of flooding on vital subsurface systems (transport conduits, water systems, gas lines,
soil etc). Vital subsurface infrastructure, such as conduits for hydraulic systems, water networks
(sources, supply, drainage), civil construction, transport conduits (roads and railways), energy supply
and soil systems are long lasting and require massive initial investment. However, in general education
and practice, design and engineering are operationally independent and have evolved their own lines
of thought. This makes it hard to commit to long-term decision-making. This paper assesses the role of
vital subsurface infrastructure in shaping flood resilience strategies in current practice and explores
a test case to evaluate the integration of engineering and design.
Understanding the future renewal of urban flood defense systems through their dependence
on the subsurface infrastructure that fundamentally determines their form, is essential for long-term
thinking. Hence, the research question primary to this investigation is “how can interdisciplinary
research in planning urban flood defense systems in relation to vital (sub)surface infrastructure
improve the potential for long-term resilience?”
2. Context
Tokyo is the most populous metropolitan region in the world. It has been historically subjected
to floods, typhoons and earthquakes; the frequency and intensities of which have been rising.
As a multi-hazard urban environment, Tokyo has long formulated flood control measures, emergency
evacuation systems and a river management system [6].
Tokyo has traditionally used hydraulic structures (levees, gates, etc) for flood risk management. It is
now exploring mega projects such as ‘super levees’ to better integrate risk management measures in the
urban environment. A conventional levee is around three to four times as wide as it is high. The super
levee is a high standard river embankment which is about 30 times as wide (around 300 m) as it is high;
such that even if it is over-topped, the flowing water does not breach the levee and instead flows slowly
across its top surface [
7
,
8
]. As opposed to conventional flood barriers which essentially cut a city off from
the water, the super levee provides an opportunity for better transitions between land and water while
offering a superior level of flood protection. As one of the most ambitious attempts by any government to
integrate flood defense infrastructure with urban development, the concept sees its share of opposition
in the technical and social spheres. Criticism includes exceptionally high costs, long construction time
frames, displacement issues and the claim that it is a product of “a systemic addiction to construction
where government subsidies rather than real infrastructure need drives development” [8,9].
The objective of this research is to propose two planning alternatives to the conventional approach
to the super levee which are evaluated both for their hydraulic effectiveness and urban design quality.
The engineering and design layout of the alternatives are assessed to see how they impact the
existing subsurface infrastructure networks, what must be modified to improve the effectiveness
of the intervention and ultimately to reduce the consequences of the hazard.
3. Methods
As an ‘exploratory’ and ‘interdisciplinary’ research, a combination of quantitative and qualitative
analysis techniques were adopted by utilizing the expertise of three urbanists, one architect, three

Geosciences 2019,9, 357 3 of 20
hydraulic engineers, one water resources manager and three landscape architects. The first condition
for this type of research is performing the research in a multidisciplinary team. Multidisciplinary and
interdisciplinary are, according to [
10
], part of a sequence of typologies for enterprises within and
across disciplines. In this sequence ‘intradisciplinary’ is within one discipline; ‘cross-disciplinarity’ is
a viewing of one discipline from the perspective of another which involves several disciplines that
each provide a different perspective on a problem; and ‘multidisciplinary’ is the integration of the
contributions of several disciplines to a problem and is about assembling interdependent parts of
knowledge into harmonious relationships (see Figure 1).
The term ‘interdisciplinary’ is is best understood not as one thing but as a variety of different
ways of bridging and confronting the prevailing disciplinary approaches or, “as states the generic
all-encompassing concept and includes all activities which juxtapose, apply, combine, synthesize,
integrate or transcend parts of two or more disciplines” [
11
]. A higher level of integrated research
and practice is ‘transdisciplinary’, concerned with the unity of intellectual frameworks beyond the
disciplinary perspectives [12].
Figure 1. Stember ’s Disciplinary Typology for enterprises within and across disciplines [12].
Methods concerning interdisciplinary working attempt to reach an integrated approach via
collaboration on integrating interest and needs [
13
]. In this research there are five steps taken that can
be defined as the ‘Dutch approach’ [
14
]. This term refers to the multidisciplinary approach which Dutch
urban designers and landscape architects adopt in pursuit of solutions to complex problems. Their role
is to visualize and create connections between creativity and knowledge on the one hand with an
analysis of the relevant societal issues and stakeholder interests on the other. Designers organize this via
a process called “research by design (RbD)”. RbD is any kind of inquiry in which design is a substantial
part of the research process in which various scenarios are examined, alternatives considered and
choices made [
15
]. Designers reveal a future situation and the consequences of this creation. It forms
a pathway through which new insights, knowledge, practices or products come into being and makes
room for multiple design iterations before detailed frameworks may be laid down (see Figure 2).
However, this method has a drawback of sometimes not being detailed enough for engineering design
calculations or being too detailed for urban design [15,16].
This is an interesting method of collaboration as “design” in the fields of engineering and urbanism
do not denote the same activity. While in urban design, one finds common ground, to find the right
measures for problems and goals, especially when all are unknown or open [
17
]; for engineers, the term
design mainly refers to optimization processes to find the best solution. Here the difference between
‘tame’ problems that are clearly defined and solvable (engineering) and ‘wicked’ problems that are
unclear in a fuzzy context (urban design) is crucial [
18
]. Using the “design” outcome itself to inform
research lies at the crux of RbD.

Geosciences 2019,9, 357 4 of 20
1
Measures ↓ Problems and goals →
Familiar and with
existing agreement
Unfamiliar and there is
no agreement
Known Optimization Negotiation
Unknown Innovation Design
Figure 2.
Definition of strategies characterized by the existing interpretation on the problem and goal
definition and the agreement on measures [17].
This research aimed deliver a methodological approach to integrate knowledge on creating flood
risk resilience. It filled the knowledge gap on how the new relation between spatial development and
flood risk engineering can be performed in an integrate fashion. This paper is structured along the
following five steps (see Figure 3):
1.
Creating an inventory of existing projects for flood risk management measures (based on literature
review, refer to Supplementary Materials).
2.
Analyzing the chosen site that is under consideration for construction of the super levee
(see Figure 4).
3. Proposing planning alternatives for the test site.
4.
Evaluating the alternatives and their relationship with selected multidisciplinary perspectives
(hydraulic engineering, urban design quality and vital subsurface infrastructure).
5. Process and analysis using RbD.
Figure 3. Research method and process diagram.

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3.1. Step 1: Creating an Inventory of Existing Projects for Flood Risk Management Measures (Based on
Literature Review)
To understand flood defense interventions across different scales, an inventory of existing projects
in the city was generated for three spatial hierarchies/scales (see Table 1). The macro (city) scale was
utilized to grasp an overview of the flood defense philosophy (protective vs. adaptive). The meso
(district or ward) scale was adopted for a nuanced analysis of the components that build the built
environment. The micro (urban block) scale is an indication of how the flood defense system is
translated into the urban space that citizens experience. The selection of initiatives included projects by
public authorities, private developers, academia and allied partnerships. The objective of the inventory
was to contextualize the Edogawa ward case study within the larger scales of Tokyo’s planning through
the following steps:
•
Studying the geographical/political boundaries that control water resources management decisions
and the governing bodies involved at each scale to understand the scope of decision making.
•
Understanding geographical context, water governance systems, water usage and water-related
interventions based on ‘capacities’ and ‘impact of scale’.
•
Understanding the implications of these designs in spatial terms from city to urban block scale.
This has been done through a mapping exercise.
Based on the inventory generated, the following observations were made [6]:
1.
Tokyo allocates substantial resources to managing risk. It accepts greater residual risks and
emphasizes how to deal with them (Preparedness-response-recovery approach).
2.
Tokyo employs a composite system of protective flood defense infrastructure, river management
and social response infrastructure to combat emergencies.
3.
Tokyo uses a combination of standard levees (offering 1 in 100-year probability event protection)
combined with large-scale underground retention reservoirs to ‘divert and balance’ the water
level in the event of excess rains.
Table 1. Flood defense projects catalogued based on function and scale [4–9,19–22].
Protect Store Channel
The Capacity to Protect
Against Water
The Capacity to Store/
Buffer Water
The Capacity to
Channelize,
Discharge Water
Macro-City/Region
(Tokyo Bay)
(1) Super levee (Komatsugawa)
(1) Regulating reservoirs
(Kuromebashi/Metropolitan Area
Outer Underground Discharge
Channel, Kasukabe/Kanda
River/Ring Road No. 7
Underground Regulating Reservoir)
(1) River channel
improvement
(2) Earthquake resistant levees (2) Engineered diversion channels
(3) Shoreline protection
(floodgates, sluices, locks,
pump stations, tidal
defence walls)
(3) Floodways
Meso-Ward/district
(Edogawa) (1) The Green Tokyo Decade Project
Micro-Urban block
(urban parcels/block
in Edogawa)
(1) Disaster prevention pier-
Etchujima, Sumida River
(1) Greening of dike
slopes/riversides project
(2) Tsurumi multipurpose
detention basin
3.2. Step 2: Analyzing the Chosen Site That Is under Consideration for Construction of the Super Levee
The meso (district or ward) scale was chosen as the scale for proposing planning alternatives and
conducting analysis (see Figure 4). The Edogawa ward is situated on the north perimeter of Tokyo Bay.

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Located close to the open sea, it is protected by the recently reclaimed Kasai Rinkai Park at its southern
boundary; this is an area of relatively high elevation. Two rivers lie on the west side of Edogawa
ward. The Arakawa river is an engineered channel that diverts upstream discharge to the northern
part of Tokyo to reduce the risk of fluvial flooding in important areas. Similarly, the Nakagawa is also
an engineered water channel with the main purpose of maintaining the water balance in Edogawa’s
polder system (see Figure 5).
Figure 4.
The city of Tokyo and the site in focus for analysis (Source: www.openstreetmap.org, maps not
to scale).
Levees protect the west and east perimeters of Edogawa-ku. Within the city, several engineered
channels serve as paths to extract water from urban areas using pumping stations (see Figure 6).
The rising population density and the disappearing natural streams continue to exert pressure on the
urban system and increase vulnerability to floods [6,20].

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Figure 5.
Map of Edogawa-ku with the rivers (
left
) and the waterways within its vicinity [
19
,
23
]
(Map source: Google Maps).
Figure 6.
Risk zones (water ponding areas at the meso (ward) scale are identified using the:
(
left
) drainage map of the two rivers flanking the Edogawa ward; (
middle
) drainage system of the
Edogawa ward (data and map source: Ministry of Land, Infrastructure, Transport and Tourism (MLIT)
Japan) [
19
,
20
]. Note that the left map indicates flooding from high river water levels, which can be
caused by either high upstream (river) flows, or coastal storm surge (maps not to scale).
3.3. Step 3: Proposing Planning Alternatives for the Test Site
A two-week international workshop called ‘Rethinking the super levee’ was organized in
Tokyo [
24
] (see Figure 7). Broad urban design and hydraulic engineering frameworks were proposed

Geosciences 2019,9, 357 8 of 20
for the Edogawa-ku test site to assess how these may be adapted for the future. Given the complexity
of multiple specializations and practical knowledge involved in the assessment of subsurface
infrastructure, a common initial method called RbD was adopted.
Figure 7.
Visualization of the super levee for Edogawa-ku, Tokyo (source: base map from Google Earth
and modelled by authors).
At the workshop, hydraulic engineers developed boundary conditions for urban flood risk
management at the macro (city) scale. Threats to Edogawa-ku were qualitatively analyzed to
propose upstream and downstream mitigation measures (such as water diversions and storm surge
barriers). In addition, suggestions were made to improve existing engineered components on site
including, (1) creating a streamlined interface between the levee and the water to minimize erosion;
(2) installing sheet pile on the dike crown for additional freeboard as well as under the dike for seismic
stability (prevention of settlement during liquefaction of the foundation); (3) establishing broad levee
dimension;, and (4) optimizing the urban drainage system. Based on the advantages and disadvantages
of the proposed flood risk management framework, two teams with a mix of specialist disciplines
collaborated to propose two planning alternatives:
•
Strategy A: finding an alternative solution to the super levee that may provide the same level of
protection for the chosen boundary condition;
•
Strategy B: finding better ways of integrating the super levee into the urban area as opposed to the
conventional blanket approach where a massive large levee runs along the entire urban coastline.
3.4. Step 4: Evaluating the Alternatives and Their Relationship with Selected Multidisciplinary Perspectives
(Hydraulic Engineering, Urban Design Quality and Vital Subsurface Infrastructure)
The proposed site was evaluated primarily by using the Dutch layer approach [
25
]. The Dutch
layer approach was introduced in the national debate on spatial planning in the Netherlands. It is
a stratified model for site analysis that distinguishes planning components on the basis of the spatial
dynamics of the substratum as follows: (1) natural blue-green systems such as green buffers and
water; (2) Infrastructure (man-made structures for flood control, and conduits for transport, water,
and fuel); and (3) Occupation patterns (human settlements). The approach was applied to Edogawa
ward to understand the site thoroughly and spatially relate the existing flood control measures to the
three layers mentioned above. The second method, system exploration environment and subsurface
(SEES), was utilized to lay out the framework that looks more closely into interactions between
constructed urban elements. This method was selected to systematically relate complicated engineering
components and provide a framework with clear boundaries. for analysis. The resultant framework
helped to generate broad recommendations to guide future resilience strategies for Edogawa-ku and
to act as a template for similar cases.

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4. Process and Analysis (Using Research by Design (RbD))
The analysis and evaluation of proposed outcomes was done by using the method of
“research by design”.
This method uses design to accelerate utilization of technical data into spatial
conditions and lets the researchers understand and the unfamiliar complex context of Tokyo. The paper
concludes with insights on how to unite multidisciplinary perspectives into design strategies for
long-term resilience. The research scope was limited to data that were accessible in the public
domain. This included practical urban design layers of buildings, open spaces, infrastructure, and vital
subsurface infrastructure layers on soil, transport, power and water networks (see Table 2and Figure 8).
The following parameters were used for evaluation:
•
Urban design quality to determine changes in population density, quality of the environment and
economic impact.
•
Evaluation of hydraulic engineering measures for calculating water balances based on the
characteristics of the proposed interventions.
•
Integration with vital subsurface infrastructure networks (sewer and storm drain pipe layout and
capacity, electricity networks, waterways, transport (railways and roadways)). This was based on
available knowledge of the layout, quality and capacity of infrastructure.
Table 2.
Research scope following the Dutch layer method [
25
] and the system exploration environment
and subsurface (SEES) method [26].
Element Status in This Study
People This was left outside the scope of this research
Metabolism This was left outside the scope of this research
Buildings •Building footprint/ urban typology
•Land use
Public Space
•Parks
•Water bodies (lakes, rivers, creeks, lagoons, delta plains)
•Artificial water channels (canals, streams, open drains)
•Green cover typologies (marsh, swamp, agriculture)
Infrastructure Layers
Mapping man-made interventions for networks and utilities on the site
•
Water (flood management interventions, storm surge barriers: dikes, pumps,
pipes, artificial levees, super dikes, overflow channels, spillway structures)
•Transport lines (roads, rails, others)
Subsurface
Mapping the natural characteristics of the site and the original topography
•
Geology/geomorphology: Soil type (delta plains, reclaimed land, alluvium)
•Groundwater levels
•Topography
•Natural levees, water buffers
•Underground pipelines (water, gas, waste water)
•Underground structures (rainwater storage, tunnels, subways)

Geosciences 2019,9, 357 10 of 20
Figure 8.
The Dutch layers approach produced a three three-layer mapping of Edogawa ward, Tokyo:
(
left
) surface, (
middle
) infrastructure, and (
right
) occupant type (drawn by authors with data and
knowledge from [25–27]).
4.1. Strategy A: Anti Super-Levee
Strategy A is based on the hypothesis that it is impractical to construct a super levee along the
entire shoreline of the district. This is because of high associated costs and displacement of residents,
together with the fact that high risk exists only in specific places. The strategy utilized the principle
of re-naturalization of a dense urban area by the introduction of a large natural water buffer at the
‘meso’ (ward) scale by controlling the flow of water at the macro (city) scale. It does this by proposing
a multi-functional water basin in Edogawa-ku supported by upstream measures to reduce water flow
to the Edogawa river in the event of heavy rainfall. The strategy is based on increasing the conveyance
and storage capacities of the channel and floodplain, respectively. This option addresses the urban
problem of shrinking public green space in Tokyo while connecting the water with public lives to
improve the urban quality (see Figures 9–12). The design process can be characterized as follows:
•
Hydraulic interventions upstream (stream capacity and floodplain storage) and at the river mouth
(storm surge barrier).
•
Studying the weak spots in the urban landscape based on flood risk (inundation from pluvial and
fluvial flooding).
•Creation of water storage in the riskiest urban area to improve infiltration capacity.

Geosciences 2019,9, 357 11 of 20
•
Proposing a water retention system within this identified area by enhancing existing blue–green
networks and additional retention zones such as water storage parks, which bring surface water
into people’s lives.
•
Regeneration of built stock and relocation of people from land that will be restored to water or
floodplain is critical.
Figure 9. Design features of strategy A (anti super-levee).
4.1.1. Evaluation of Hydraulic Engineering Measures
A high-level conceptual assessment was conducted to evaluate the considered engineering
measure. A floodgate-controlled confluence of the Arakawa and Nakagawa rivers is located
approximately 3 km upstream from river mouth (see Figure 4). Thus, these rivers are expected
to share the water volume during a flood or storm surge [
6
]. The spatial intervention suggested in this
section proposes an open area on the east bank of the river which can be flooded during unfavorable
situations (See Figure 12). In other words, the area, referred to as floodplain, will only be inundated
if the flow rate exceeds a certain threshold. This floodplain is 450-m wide as shown on the simple
geometrical cross-section of Figure 10.
Figure 10.
Simplified cross-section of Nakagawa River (source: Google Earth and Arakawa Karyu
River Office [14]).
When the volume of water increases along this reach, the floodplain is responsible for providing
enough conveyance capacity to prevent the river stage from rising above the levees. Making the
zeroth-order approximation of steady flow, the water level or depth can be estimated with Manning’s
equation. A suitable Manning’s coefficient for channel would be 0.022, while the bed slope was
determined to be 3% [28].
The high-level assessment treats the flow rate as a control variable. Figure 8summarizes the
outcome of the assessment. It juxtaposes flow depth of a channel-only cross-section against a river
with an added floodplain to delineate the effect of the floodplain.

Geosciences 2019,9, 357 12 of 20
Figure 11. Flow depth and velocity as a function of flow rate (0–30,000 m3/s).
The existence of the floodplain is evident by the divergence of water depth (shown in blue
and orange) at an approximate flow rate of 5200 m
3
/s. As flow rate increases, the separation of the
two curves increases, displaying the significance of the floodplain. The floodplain helps to reduce
the flow depth by 10% at 10,000 m
3
/s flow rate and 21% at 15,000 m
3
/s. Even though this primitive
analysis assumes steady, uniform flow, it demonstrates the influence of the floodplain as additional
river capacity. However, a closer look at the significance of the floodplain is required for design by
considering unsteady, non-uniform hydraulics.
4.1.2. Analysis and Observations
A qualitative spatial analysis is done by overlaying strategy A with the subsurface infrastructure
network map (waterway, railway, roads, sewage and electricity lines) (see Figure 12). The sewage
system is aligned with the existing waterway and traffic conduits. The proposed water basin respects
the layout of the sewage system, but the other waterways are not in alignment with the traffic structure.
There is potential to create more waterways by renovating the main sewage line. The shape of the
water park is mainly based on the direction of water flow during a fluvial flooding scenario. It is not
perfectly aligned with the traffic structure or the sewage system. Most of the electricity networks are
above the ground, and some are planned to be buried underground. In principle, they do not affect
the strategy.

Geosciences 2019,9, 357 13 of 20
Figure 12.
Strategy A—anti super levee overlaid with vital infrastructure
(electricity, transport, sewage)
(source: drawn using data from MLIT Japan and the Edogawa ward data, 2016) [11,19].
4.1.3. Overall Recommendations
Based on the observed interaction between existing subsurface networks and the proposed
planning intervention, the following recommendations are made to improve the efficiency of
the strategy:
•
Engineering calculations must be involved in the initial planning and design stage to assess the
feasibility of the strategy.
•More measures to store water are needed, as the capacity of the designed system is insufficient.
•
(Soil) In the basin, the filtration and storage capacity of the soil should be maintained to contribute
to the function of storing water. Outside of the basin, the soil must be stabilized at selected sites
for development.
•
(Sewage) The other designed waterway should be aligned with the traffic infrastructure for easier
construction and better alignment with the subsurface system. More waterways can be created
along the main sewage lines and roads.
•
(Power) Laying the underground electricity line provides an opportunity to enlarge streets or
green areas along streets. These should be considered as potential areas for more water storage.

Geosciences 2019,9, 357 14 of 20
4.2. Strategy B: Pro Super-Levee
Strategy B is based on the hypothesis that the super levee is a robust flood defense concept
and must be explored to understand how it can be further integrated into the design of the urban
environment. The super levee is perceived as an additional land mass that exhibits more resistance to
inner slope failure due to erosive flow. When water exceeds the height of the embankment, the flow rate
over the inner slope of a super embankment will be less severe than over a normal levee, because the
inner slope of the super levee is much less steep than that of a normal levee. However, the problem
lies in the ‘one size fits all approach’ currently being adopted. The group worked towards a planning
strategy at the meso (ward) scale that customizes the super levee to suit the requirements of Edogawa
ward. First, geomorphology of the site is examined to determine highly vulnerable locales. Based on
the analysis, selective thickening/strengthening of the super levee will be executed in combination
with a regular levee network. The strategy suggests a better hydraulic and urban design alternative to
adapt to the super levee (see Figure 13). The design process can be characterized as follows:
1.
Studying the weak spots in the landscape based on flood risk (inundation from pluvial and fluvial
measures) along with liquefaction zones for earthquakes.
2. Integrate with current evacuation routes for emergencies (see Figure 14).
3.
Propose new urban design typologies to adapt to the interface between the super levee and
the surroundings.
4.
Making room for water storage in case of large calamities by allocating ‘sacrificial’ land parcels
for forced flooding.
5.
Reprogramming the urban plan of the super levee to transform it into a productive landscape.
Urban agriculture is proposed as an economic alternative for land acquired from original
landowners. This is to retain environmental quality for massive built infrastructure and for
owners to maintain ‘title’ to the land.
Figure 13. Design features of Strategy B (pro super levee).

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Figure 14.
Transport routes, drainage channels, and vulnerable areas in Edogawa ward (drawn by
authors using data from [19,20]).
4.2.1. Evaluation of Hydraulic Engineering Measures
Compared to the conventional embankment or dike, the super embankment (super levee) concept
differs in width but not in height. The super embankment manifests a much flatter inner slope and
reaches widths of 300 to 500 m, in contrast to the 20 to 30 m width of conventional embankments.
To compensate the substantial area it requires, the inner slope of the super embankment is envisaged
as land for new urban development area as it provides higher ground elevation and consequently less
inundation risk (see Figure 15) [8,9].
Figure 15.
Comparison of a traditional (
top
) and super embankment (
bottom
), also known as
a “super levee” (Arakawa-Karyu River Office and MLIT) [8,19].

Geosciences 2019,9, 357 16 of 20
Other than its purpose as an elevated surface, the concept also offers engineering virtues. One of
the advantages it brings is the increase of shear capacity. To be able to withstand horizontal pressure
from the water, an embankment must retain an adequate shear capacity, which largely depends
on friction and thus mass of the levee. In this case, the super embankment can be perceived as an
additional land mass standing behind a traditional dike. Therefore, the supplemental structural
weight of the embankment increases the friction force and shear capacity. Moreover, the width
of the super embankment is advantageous to minimize piping failure. Piping failure of a dike is
caused by the development of a porous flow channel beneath the structure. Chow, Thusyanthan and
Jonkman et al. [
29
–
31
] studied the flow front of them. of water in porous media with experiments and
reported porous flow velocity V [m/s] dependence on hydraulic conductivity K [m/s] and pressure
gradient i [m/m] [29–31], as shown in Darcy’s Law Equation (1).
V=Ki =K∆h/∆l. (1)
Equation (1) represents the ratio of the difference in hydraulic head h [m] to the seepage length
l [m]. Since the main function of the embankment is to separate land from water, the establishment
of a hydraulic gradient is inevitable. While water tries to penetrate through the porous medium,
flow experiences energy loss due to interaction with the soil. The broader super embankment base is
a favorable measure to prevent piping failure as it can dissipate more energy due to greater seepage
length. For the standard levee, one way to minimize piping risk is to install an impermeable layer,
usually sheet pile or cut-off wall, under the embankment. Such structures force water to cover more
distance before it finally surfaces. If water must travel a long distance from one side of the structure to
another due to subsurface interference, the probability of seepage failure is reduced.
In comparison to a regular embankment, the super levee also exhibits more resistance to inner
slope failure due to erosive flow. When water exceeds the height of the embankment, the flow rate on
the inner side of a super embankment will be less severe because of the mild inner slope. Therefore,
greater over topping is required to reach the critical flow that can erode soil or protection layers on the
inner slope. Apart from these positive traits, the construction of a super embankment demands sound
financial support not only for the construction work but also for the relocation of existing structures.
The duration of construction is also expected to be lengthy [9,19].
4.2.2. Analysis and Observations
By overlaying the proposed designs with maps of vital infrastructure, observation of how they
agree or conflict with each other can be made (see Figure 16):
1.
The adapted super levee structure and evacuation routes are designed based on the existing
urban fabric and infrastructure.
2.
The evacuation routes are aligned with the drainage system, but since they are elevated, it may
impact the layout (or depth) at which the sewage network is set.
3.
The main electricity lines (above or under the ground) are aligned with the designed infrastructure.
4.2.3. Overall Recommendations
Based on the observed interaction between existing subsurface networks and the proposed
planning intervention, the following recommendations are made to improve the efficiency of the
strategy (see Figure 16):
1.
The super levee can be adapted, but a certain minimum levee width must be maintained to make
sure the system works.
2.
(Soil) Soil should be stabilized along the levee in case of shaking scenarios. Different water
levels during flood events in different parts of the ward should be treated uniquely. For example,
the lower ground level, where development will be retained as it is. makes it vulnerable to
flooding. Thus, the infiltration and storage capacity of the soil should be increased in these areas.

Geosciences 2019,9, 357 17 of 20
3.
(Sewage) The existing sewage system within the proposed super levee area needs to be raised to
meet an effective height for the maintenance and for the strength of dike. Due to the introduction
of higher evacuation routes, lower lying areas will become more prone to flooding. The sewage
system- and water storage capacity needs to be increased within this area which can be done by
introducing a water canal and other urban block level interventions.
4.
(Power) To keep the energy distribution uninterrupted during times of flooding, the elevated
areas can accommodate elevated energy infrastructure, with energy storage units included.
This also ensures supply of electricity along the evacuation route.
Figure 16.
Strategy B—pro/integrated super levee overlaid with vital infrastructure (electricity, transport,
sewage) (Source: Drawn using data from MLIT Japan and Edogawa Ward data, 2016) [11,19].
5. Discussion
This paper proposes how interdisciplinary design can juxtapose, apply, combine, synthesize,
integrate or transcend parts of five disciplines [
11
] within the ‘Dutch approach’ [
14
] and gives
specific insights in ‘implementation’ barriers that exists between the fields of hydraulic engineering,
urban design and subsurface infrastructure planning. In relation to methodologies in literature
to improve urban resilience, this approach is focused on content integration in urban design
and not on a general holistic approach that proposes indicators or general guidelines for the
analysis phase. Serre et al. [32]
emphasizes the their front. The importance of integrated reflection on
the resilience concept to arrive at a spatial decision support system using the same set of indicators.
These are very useful—but restricted in relation to the approach proposed in this paper.
Beyond the formulation of the inventory (Step 1) and analysis of site (Step 2), the proposition
of the two Strategies A and B was done in co-creation (Step 3). The evaluation of the alternatives

Geosciences 2019,9, 357 18 of 20
(Step 4) reveals the extent of connect and disconnect between planning and engineering perspectives
in decision making for urban flood management. It became clear that, although vital subsurface
infrastructure is essential to flood management, engineering and planning disciplines do not have
a method for integrating the subsurface infrastructure in decision making (such as the levee system
with the soil or sewage networks). In literature there is the DS3 model in which resistance, absorption
and recovery capacities of all urban networks (including the subsurface) is analyzed and used to
establish indicators of the potential of resilience [
32
]. The objective is to understand and especially
integrate resilience in management and planning policies by creating a spatial decision support tool
for neighborhood-level resilience analysis. This method is, however, limited to identifying resilience
characteristics and does not integrate flood management in general urban strategy and design.
Besides integration in qualitative terms, integration in quantitative terms should be taken into
consideration. Measures used in both strategies are proven measures drawn from existing practices in
front-running cases like the Room for the River, allocating land parcels for forced flooding, reinforcing
dikes, increasing infiltration area for water, etc. While they function for this site, their suitability should
be reconsidered when they are applied to other cases. For example, in strategy A which features
a water basin, the calculations are restricted to the meso (ward) scale, as the water park and canals at
the scale are able to handle pluvial floods but not fluvial floods, while the restored floodplain addresses
only fluvial flooding. In quantitative terms, the proposal would be completed only by consideration of
the full river reach, from the upstream watershed to the sea. This proves again that generic solutions
to global problems can be utilized as long as they are contextualized and modified.
As concluded by [
33
], “research–practice partnerships underline the growing need for territories
and communities to acquire tools in order to better understand the concept of resilience, and especially
to apply it practically to their territories, habits, populations, operating modes, knowledge and
perspectives”. Crucial for the process and analysis using research by design in step 5 is the
consideration of various hierarchies (or scales) in the planning system for achieving a higher level
of resilience. In combination with the lower scales, we can not only systematically address the vital
surface infrastructure, but also allow for sufficient detail in the urban design quality, which contributes
to the feasibility of implementing changes. These changes are part of the resilience strategy and work
towards enforcing the system to be able to answer to stress or shock.
6. Conclusions
This project is an attempt by designers and engineers to jointly explore visions and methods for the
future of urban flood resilience systems. This involved gathering related literature and cases (inventory),
choosing suitable methods to approach the problem, proposing strategic design alternatives for a real
site and evaluating the designs from a multidisciplinary perspective. This included consideration
of hydraulic systems, soil type and subsurface infrastructure networks. The ‘research by design’
exploration contributed to the potential of an integrated design process in a multidisciplinary way,
which answers the research question of this paper. First, methods to approach the multidisciplinary
topics and the effectiveness of these methods are explored through the ‘Dutch layer approach’ and the
‘SEES’ methodologies. Second, the design and evaluation process highlight the gaps between urban
design and engineering perspectives; these gaps reduce the possibility of enhanced resilience in the
long-term. The design and evaluation process also helps to recommend improvement measures. These
measures not only serve as actual tools that can be used, but also serve to kick start further debate on
integrated sustainable growth. The results of the process can be applied to other projects to see how
we can improve this combination in practice, and open avenues for further research. By improving the
integration of urban quality, engineering, and vital subsurface infrastructure, a more resilient urban
system can be formed to combat the intensifying climate risks of the next century.
Supplementary Materials:
The study of urban flood risk interventions as part of this project was presented at
an exhibition at Gallery Ten Tokyo, March 2017. http://www.gallery-ten.tokyo/archives/category/22-challenge
s-in-flooding.

Geosciences 2019,9, 357 19 of 20
Author Contributions:
Conceptualization, Administration, Funding Acquisition, Resources: F.H., J.B., Y.Y.;
Methodology, Formal Analysis and Investigation: S.K., J.L., J.S., M.D.; Hydraulic Analysis: J.S., J.B.; Spatial
Planning and Design: S.K., J.L., M.D.; Writing—Original Draft Preparation: F.H., S.K., J.L., J.S., M.D.;
Final Writing—Review and Editing: S.K., J.B., F.H., J.L.; Visualizations: S.K., J.L., J.S., M.D.
Funding:
This research was funded by TU Delft Deltas, Infrastructures and Mobility Initiative: https://www.tu
delft.nl/infrastructures/, and by a bilateral grant from Netherlands Organization for Scientific Research (NWO)
and the Japan Society for the Promotion of Science (JSPS).
Acknowledgments:
The authors would like to thank Bas Jonkman, Hiroshi Takagi, and Miguel Esteban for
their support during ground research and review process. We also thank Akihiko Ono-san, Daiki Mabuchi,
Ayano Yamaguchi, Manami Hasegawa, Richard Crichton, Non Okumura, Bas Hoersten and Shaswati Chowdhury
for their support during the workshop, resource selection, fieldwork and general hospitality in Japan. Nobuyuki
Tsuchiya of the Japan Riverfront Research Center and the Edogawa ward office was also instrumental in our
information gathering.
Conflicts of Interest:
The authors declare no conflict of interest. The funders had no role in the design of the
study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to
publish the results.
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