Inundation Analysis Simulation for Underground Spaces
Introduction
Given the clustering of the population, assets, and core functions in Japanese cities,
land use—including underground spaces—is quite advanced.
Over the past several years, damage from inundation in underground shopping
areas, along subway lines, and in other underground spaces has increased alongside
the increase of flooding in cities prone to localized torrential rain. Flooding ofunderground spaces is highly likely to lead to severe and even life-threatening damage;accordingly, measures to combat underground flooding are important and urgent.
This technology makes it possible to simultaneously analyze inundation both above
ground and in the complex web of underground spaces in major cities as well as theinflow, retention, movement (including movement through subway lines), and otherproperties of flood water from above ground in and through underground spaces.
Additionally, inundation analysis simulations envisioning various types of flooding(e.g. overflow from rivers; short, sudden, extremely localized downpours) make itpossible to obtain useful information for examining appropriate flooding
countermeasures and evacuation plans, considering business continuity plans (BCP),and more.

Flooding at a subway
entrance

An inundated subway
platform

Above-ground flooding at a subway entrance

Subway entrance

Flood water inflow

Flood water inflow

Subway ticket gate

Flood water moving
through a subway line
SubwaySubway platform

Subway ticket
gate/
underground
shopping area

Image of flooding of underground spaces

Necessary background
In July 2015, the Flood Control Act was among legislation that was partially amended. The amendments made the following obligatory:
・Listing information such as means of conveying the names, locations, flood forecasting, and the like of underground shopping areas and other
underground spaces prone to inundation in local disaster risk reduction plans in each area at risk of inundation under the maximum imaginable level offlooding, inland flooding, and storm surges.
・Creation of plans to ensure evacuation and prevent flooding by owners of underground shopping areas and other underground spaces

Tasks for ensuring safe, reliable evacuation and effective plans for preventing flooding
・ Envision inundation in underground spaces under various forms of flooding (e.g. overflow from rivers, inland flooding,*1 storm surge/tsunami damage)・ Considerations for preventing the inundation of facilities in underground spaces (including proper water stop plates in consideration of evacuation, etc.)
・ In addition to and separately from the above, it is necessary to consider business continuity plans (BCP)*2*1Inundation resulting from the inability of sewer systems and other facilities to drain rainwater from short, sudden, extremely localized downpours or the like.
*2It is necessary to strategically examine business continuity (restorative measures that detail how to drain flood water and the like) in order to minimize risks
associated with interruptions attributable to flooding

Inundation analysis simulations for underground spaces are an effective method of consideration
1．Project inundation undervarious types of flooding withgood precision

・What is the area and depth of inundation under various types of flooding?
・From which above-ground openings, underground shopping areas, and the like will flood
water enter?
・Where will water pool in underground shopping areas and other underground spaces?
・How quickly will the area become inundated? When will the flood water arrive?
・How long will the flooding continue?

2．Ascertain the effects of floodprevention measureres・Consider effective placement of water stop plates
・Delay the start of inundation/timing of total submersion of underground shopping areas andother underground spaces

３．Consider drainage fromunderground spaces

・Drainage methods, routes, times, and effects

Inundation Analysis Simulation for Underground Spaces
Inundation analysis model characteristics
Modeling subway lines and all the underground shopping areas and other underground spaces that connect to them is vital for developing an accurate
understanding of inundation in underground spaces.
Additionally, simulations based on models that enable simultaneous analysis of inundation above ground and in underground spaces make it possible
to develop an understanding of inundation in underground spaces from moment to moment, the effects of different flooding countermeasures, andmore as well as to consider various scenarios of flooding.

【Simultaneous analysis of above-ground andunderground spaces】【Underground spaces model】【Above-ground model】
・Flooding analysis model based
・外水氾濫・内水氾濫・高潮・津on flood hazard maps

＋・Model for analyzing inundationin underground spaces (e.g.
underground shopping areas,
subway lines, basements,
underground parking areas)・Makes it possible to develop an understanding of＝inundation in above-ground and underground spaces frommoment to moment
・Makes it possible to envision inundation in various
scenarios

Category
Method of analysis
Avobe ground Use a planar, two-dimensional unsteady flow analysis model

Above groundas a relationship between H (water depth) and V (volume) with stores,
Underground Expressed
corridors, and other components of underground shopping areas rendered as boxes

Underground Space A

Use a Preissman slot, one-dimensional unsteady flow analysis model with thesubway lines rendered as pipes

SubwayAbove ground①⑦

Underground Space B

Level 1 analysis②

Level 1 analysis③

Overflow fromabove ground⑥

Subway entrance (above-ground opening modeled)④

Level 2 analysis

Above ground (topography modeled)

Subway analysis
Inundation of
subway line
Inundation ofunderground
shopping areas

Item

Aobve ground
UndergroundSpace A

Subway line (subway tracks and stations modeled)

Underground Space B

Underground shopping areas (undergroundshopping areas modeled)

Underground Space A

Subway tracks
UndergroundSpace B①②③④⑤

Subway analysis

Flow of analysis
Movement of flood water above ground
Inflow/outflow of flood water from above-ground entrances into the underground space
InInflow/outflow of flood water from Level 1 to Level 2 of the underground space
Inflow/outflow of flood water from Level 1 of the underground space to the subway⑤

Movement of flood water from Underground Space A to Underground Space B along
subway tracks⑥

Inflow/outflow of flood water from Level 1 of the underground space to the subway⑦【Image of the analytical model】

Inflow/outflow of flood water from above-ground entrances into the underground space【Image of the flow of analysis】

Overview of the inundation analysis model (modeling an underground space containing underground shopping areas)
In order to properly express the flow of flood water in underground shopping areas and other underground spaces, the interiors of the areas and spaces are
divided, rendered as boxes, and then modeled. The surfaces of walls and other structural components of stores are considered to simulate the flow of flood watercorresponding to the actual shapes of the spaces. Additionally, slots are established between (upper and lower) levels to simulate the flow of flood watercorresponding to the different water levels on each level of the underground shopping areas (outflow from the lower level to the upper level and fromunderground to above-ground spaces are also expressed).
Flood water only moves incorridors and store accesspoints.
Flood water does not passthrough partition walls.

Vertical connection

A box representing an
underground facility divided
from the rest of theunderground space

Legend ：Store (Underground)

Corridor
Horizontal connection

slot

Vertical connection
Boundary

Above-ground exit
氾濫水の流入Horizontal connection
Flood water moves
between levels throughstairways.

・Relationship betweenH and V modeled・Slot expresses thesubmersion ofunderground facilities

Flood water inflow

Interior of an underground

開口部諸元（上下接続諸元）

shopping area rendered as a box

高さFlood water inflow

Stores and other service facilities
Corridors for underground facilities【Image of multilayered structure of an underground space】

Corridor width/height

Floor area

【Image of inlets from above ground and connections
between underground spaces】

Inundation Analysis Simulation for Underground Spaces
Overview of the inundation analysis model (modeling a subway line)
Subway stations are modeled based on the same approach as for underground shopping areas. The subway line is rendered as a tube and then modeled. The levelof flood water in subway lines determines how it flows; when tunnels are full, the water flows under pressure, and when tunnels are not full, the water flows as it
would in an open channel. Other phenomena can also occur—for example, flood water can become backed up in subway tunnels and flow into underground
shopping areas. Preissman slot, one-dimensional unsteady flow analysis is conducted to properly simulate these phenomena.
Subway tracks

Above-ground entrances tothe subway station

Subway station platform
Subway Station A

Subway Station B

Subway station
concourse

Subway Station B
Subway Station A
Subway tracks

Subway line modeled as a pipe at eachpoint of variation along the line

Station platform・Wherever the slope of the line changes

Elevation

Subway tracks

Typical sectional height・Wherever the sectional shape changes
・Wherever subway lines merge/split

Preissman slot

Section length
Typical sectional width【Image of a modeled subway station】【Image of a modeled subway line】

Example inundation analysis simulation for underground spaces
The following is an example of an inundation analysis simulation for underground spaces conducted for virtual models of above-ground and undergroundspaces (underground shopping areas, subway lines).
Envisioned levee breach

1B1F

12

Subway Line A

1Corridors
B2F

Subway Line B

223
Subway Line D

421533344 64 7
5

B3F

658

Subway station(Line D)

10965

B4F
SubwayStation

767
8：Subway station
Low Ground elevation HighSubway station(Line A)

89Stores

Subway Line C9【State of above-ground topography and subway lines(stations expressed as numbers)】【Planar layout of underground shopping area】
Connects to Subway
Line A tracks*Up: Toward Station 3*Down: Toward Station 5

Subway station(Line D)

【Interior of underground
shopping area】

Connects to Subway Line B
tracks*Left: Toward Station 1*Right: Toward Station 3：Connection from above ground tounderground：Connection between levels
Tracks go fromunderground toabove ground

B1F
Subway station(Line A)

Subway Station*Four-level underground structure
displayed out of planar alignment
to provide a single overview of themodels of each level.

B2F
B3F
B4F

*Assuming a four-level underground space comprisingunderground shopping areas and subway and railway lines(the railway tracks travel underground from above ground)【State of multilayered structure of an underground space】【Modeled underground spaces】

Tracks go fromunderground toabove groundInundation Analysis Simulation for Underground Spaces
Visualizing inundation in underground spaces
Inundation spreads differently in underground spaces than flood water above ground, and spreads differently depending on the complex shapes, usage patterns(e.g. underground shopping areas, underground parking areas, subway lines), and individual levels of underground spaces. Creative steps must be taken tovisualize inundation from the results of inundation analysis simulations so that the results can be displayed straightforwardly and used when considering evacuationand flood prevention plans, restoration plans, and more.

Three-dimensional displays
Rendering underground spaces
in 3D and allowing users tochange viewpoints, expand
images, and watch animations
makes it possible to develop avisual understanding of themultilayered
structuresofunderground spaces, and theirstate of inundation.

Two-dimensional animations

Displaying inundation in individual facilities

Animations make it possible to develop
a visual understanding of how flood
water moves and the process by whichinundation occurs.

The state of inundation in individual
facilities is displayed separately. (2D, 3D)
凡

例

10cm未満30cm未満50cm未満
1.0m未満
2.0m未満2.0m以上凡

例

0.5m/s未満
1.0m/s未満
2.0m/s未満
2.0m/s以上

Displaying detailed inundation
information in underground spaces
Information about inundation inunderground spaces (e.g. water level
rising speeds, flow speeds) needed forevacuation plans is displayedstraightforwardly.
Example display of water level rising speed
270 minutes to submersion of underground facilities
150 minutes to start of inundation of underground facilities

Above-ground inundation
Underground inundation

Start of aboveground inundation

Submersion

Undergroundfacilities

Levee breachStart of above-ground inundation

Time since levee breach (min)Organizing inundation information in time charts
It is crucial to develop an understanding of overall
inundation in underground spaces, including facilities towhich they are connected (e.g. other underground shopping
areas, other subway lines). Accordingly, organizing
inundation start times, inundation periods, and other data
for each underground space and level in time charts makes
it possible to provide overviews. The information can also
be used in efforts such as timeline considerations.

Time charts can be used to straightforwardly display the effectsof water stop plates and other flooding countermeasures (i.e.
the effect of delaying the start of inundation), time required forrestoration via drainage, and the like.

Time since levee breach

Item
Rainfall
Design high water level
Overflow danger level

River level

Visualizes rain andriver levels and thetiming of advisories,alerts, and notices
and orders toevacuate.

Evacuation level
Overflow caution level

Advisories

Before flooding countermeasures■Heavy rain/flood advisory

The amount of inflow into
underground spaces changes,
so the amount of above-ground
inundation also changes.

Water level■Overflow danger alert■Overflow alert■Overflow advisory■Evacuation order■Evacuation advisory■Notice to prepare to evacuate

Floodforecasting
Evacuation

State of inundation

Above ground

Undergroundfacilities

Visualizes above-ground
inundation—specifically,
how it changes overtime.

Visualizes inundationof undergroundfacilities—specifically,
how it changes overtime.

Above the knee

Delay in the start of inundationachieved by placing water stop plates

Submersion
Above the knee

After flooding countermeasures

Inundation Analysis Simulation for Underground Spaces
Application in simulations of evacuation plans during inundation of underground spaces
Swift, smooth evacuation is the key to saving lives when underground spaces are inundated. Therefore, it isextremely important to ensure proper evacuation routes and stairways as well as evacuation areas. Unfortunately,
evacuation drills and other efforts taken during normal times rarely replicate the crowding and other conditions underwhich people must evacuate during disasters, and there are no decisive means of verifying the suitability ofevacuation routes and stairways or evacuation areas.
Social experiments are one way to verify the suitability of efforts to respond to tunnel fires, tsunami, flooding, trafficaccidents, and other disasters, but they are not easy to implement due to limitations of budget, labor, location, andtime. To address this problem, we worked with the Laboratory of Hitoshi Gotoh of Kyoto University to develop avirtual social experiment based on a crowd behavior simulator, and used the results of inundation analysis
simulations for underground spaces to provide helpful information for considerations for ensuring safe, reliableevacuation and effective plans for preventing flooding.
Simulation results

Ascertained evacuation times and areasfrom which evacuation is impossible,
planned information communication
methods, evacuation guidance methods,
evacuation facilities, etc.

Compared results after completion of evacuation in three
scenarios: no inundation, inundation with no training, andinundation with training

Research results produced in conjunction with theLaboratory of Hitoshi Gotoh of the Department ofCivil and Earth Resources Engineering of the Kyoto
University Graduate School of Engineering

Observation/modeling of pedestrian
behavior from an experiment in whichpeople walked through water

Crowd behavior model that accounts for the physical andpsychological contact and physical attributes of evacuees
based on the distinct element method (DEM)

Construction of a coupled model that accounts for the interaction of
fluid dynamics and crowd behavior of evacuees based on the distinct
element method (DEM) and particle method (high-precision MPSmethod)

Fukuoka Heavy Rainfall Disaster, June 1999
Source: MLIT website