( 77 ) Integrating Web GIS Technology and 2D Inundation Model to Develop an Inundation Simulation System 整合Web GIS技術與二維淹水模式研發 淹水模擬展示系統 XUAN-ANG LI 李 軒 昂 Shan-Shui Technical Consultant Co. Ltd, Civil Engineer SHIU-SHIN LIN* 林 旭 信 Department of Civil Engineering Chung Yuan Christian University, Associate Professor JHENG-HUA SUNG 宋 政 樺 Department of Civil Engineering Chung Yuan Christian University, Master JIHN-SUNG LAI 賴 進 松 Hydrotech Research Institute National Taiwan University, Researcher ABSTRACT This research integrates web geographic information system (GIS) technology and the two-dimensional inundation model (2DIM) to develop an inundation simulation system (ISS). ISS employs the Apache web server, MapServer, HTML (Hyper Text Markup Language), CSS (Cascading Style Sheets), JavaScript, and PHP programming languages to develop online, user interfaces allowing users to input rainfall data directly from their browsers. ISS then simulates inundation and transforms the simulated results into spatial information. The results can be shown on the web using MapServer, web GIS technology. The process of simulation is simplified by running 2DIM automatically instead of manually. Luzhou and Sanchong Districts in New Taipei City are selected in this research to test the ISS during system development and test phases. ISS chooses a single rainfall event for each case to simulate inundation, and transforms the simulated results to spatial information. The simulated results are compared with those simulated manually in a step by step approach, and then ISS displays the simulated results using ArcGIS software. Results show that that ISS is feasible and can be applied to execute 2DIM, and to display geospatial data online. This reduces the complexity of simulation to efficiently reach the objective of real-time simulation. Keywords: Online simulation, Two-dimensional inundation model, Web GIS, MapServer, Spatial inundation information. 摘 要 本研究整合網路地理資訊系統(Web Geographic Information System, Web GIS)展示技 術與二維淹水模式(Two Dimensional Inundation Model, 2DIM),研發淹水模擬展示系統 (Inundation Simulation System, ISS)。使用Apache網頁伺服器、MapServer網頁地圖伺服器、 網頁語言HTML (Hyper Text Markup Language)、CSS (Cascading Style Sheets)、JavaScript和 *Corresponding author: Associate Professor/ Department of Civil Engineering, Chung Yuan Christian University/ 200 Chung Pei Road, Chung Li District, Taoyuan City, Taiwan./ [email protected]臺灣水利 第 67 卷 第 4 期 民國 108 年 12 月出版 Taiwan Water Conservancy Vol. 67, No. 4, December 2019
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Integrating Web GIS Technology and 2D Inundation Model to Develop an Inundation Simulation System
整合Web GIS技術與二維淹水模式研發 淹水模擬展示系統
XUAN-ANG LI
李 軒 昂Shan-Shui Technical
Consultant Co. Ltd,
Civil Engineer
SHIU-SHIN LIN*
林 旭 信Department of Civil
Engineering Chung Yuan
Christian University,
Associate Professor
JHENG-HUA SUNG
宋 政 樺Department of Civil
Engineering Chung Yuan
Christian University,
Master
JIHN-SUNG LAI
賴 進 松Hydrotech Research Institute
National Taiwan University,
Researcher
ABSTRACT
This research integrates web geographic information system (GIS) technology and the two-dimensional inundation model (2DIM) to develop an inundation simulation system (ISS). ISS employs the Apache web server, MapServer, HTML (Hyper Text Markup Language), CSS (Cascading Style Sheets), JavaScript, and PHP programming languages to develop online, user interfaces allowing users to input rainfall data directly from their browsers. ISS then simulates inundation and transforms the simulated results into spatial information. The results can be shown on the web using MapServer, web GIS technology. The process of simulation is simplified by running 2DIM automatically instead of manually. Luzhou and Sanchong Districts in New Taipei City are selected in this research to test the ISS during system development and test phases. ISS chooses a single rainfall event for each case to simulate inundation, and transforms the simulated results to spatial information. The simulated results are compared with those simulated manually in a step by step approach, and then ISS displays the simulated results using ArcGIS software. Results show that that ISS is feasible and can be applied to execute 2DIM, and to display geospatial data online. This reduces the complexity of simulation to efficiently reach the objective of real-time simulation.
本研究整合網路地理資訊系統(Web Geographic Information System, Web GIS)展示技術與二維淹水模式(Two Dimensional Inundation Model, 2DIM),研發淹水模擬展示系統(Inundation Simulation System, ISS)。使用Apache網頁伺服器、MapServer網頁地圖伺服器、網頁語言HTML (Hyper Text Markup Language)、CSS (Cascading Style Sheets)、JavaScript和
* Corresponding author: Associate Professor/ Department of Civil Engineering, Chung Yuan Christian University/ 200 Chung Pei Road, Chung Li District, Taoyuan City, Taiwan./ [email protected]
臺灣水利 第 67 卷 第 4 期
民國 108 年 12 月出版
Taiwan Water ConservancyVol. 67, No. 4, December 2019
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1. INTRODUCTION
Taiwan is located, climatically, at the junction
of tropical and subtropical regions affected by
monsoons so that rainfall is unevenly distributed.
Moreover, due to Taiwan’s narrow land shape, short
rivers, and narrow areas, in summer and autumn
afternoons during thundershowers, typhoons, and
high-intensity and concentrated rainstorms; the
heavy rainfalls produced within a short time cannot
be discharged and thus the consequent inundations
cause losses to people’s lives and properties. In
order to reduce the number of disasters resulting
from inundations, many flood control facilities have been built for dams, urban drainage systems, and
dikes. But due to climate change, extreme rainfalls
exceeding historical records of precipitation
happen repeatedly, and repeatedly challenge the
flood control capacities of project facilities. In
recent years, in the fields of hydrology and disaster prevention, many have considered promoting and
integrating inundation simulation techniques by:
using information assistance systems for flood
avoidance as the orientation of flood and disaster
instance, having the advantages of a cross-operating
system with multiple programming language
compatibility, MapServer, the open source software
developed in 1990 by the University of Minnesota
in the United States, has long been applied to—
and integrated in—the fields of inundation and
disaster prevention. Tsai (2009) integrated a real-
time sewer simulation (RTSS) with MapServer
for urban internal water warning. Tsai (2009) then
developed an urban sewer warning system (USWS),
and carried out real-time simulative calculations
on rainfall data to study whether the manholes of
several pump station systems were full, and then
displayed the results on the system webpages. Lin
et al. (2014) integrated an adaptive network-based
fuzzy inference system (ANFIS) with MapServer
for sewer stage forecasting, and developed ANFIS
for a sewer stage forecasting system (ASFS),
demonstrating that the forecasting system had good
results in 5 and 10-minute advanced forecasting.
Moreover, these integration research results also
indicate that the combination of internet and Web
GIS is indispensable in the fields of inundation and disaster prevention.
The main purposes of this research are to
combine the inundation simulation model with
internet and Web GIS technology for an inundation
simulation system equipped with online real-time
simulation and display functions; to simplify the
manual operation process used in past inundation
simulations; and to discuss the structural designs
of a comprehensive warning system under
development, so as to enhance the capabilities of
inundation simulation warning technology and the
feasibility of combining with it new technologies.
2. STRUCTURE OF THE INUNDATION SIMULATION SYSTEM
2.1 Two-dimensional inundation model
The two-dimensional inundat ion zero-
inertia model (hereinafter referred to as the two-
dimensional inundation model) used in this research
was developed by the Hydrotech Research Institute
at the National Taiwan University (Lai, 1986).
Assuming that in an unsteady flow equation,
acceleration is much less than gravity (or friction)
and the flood hydrograph of the water flowing into the flooded area increases slowly; and by ignoring the effects of the Coriolis force, the wind force and
the velocity component in the vertical direction,
the phenomenon of flood wave transmission can
be described by using a zero-inertia model with
acceleration ignored. The equations are as follows:
(1)
(2)
(3)
where, x and y mark the space coordinates of
the simulation area, t is the time coordinate and
d is the depth of water, u and v are the average
flow velocities respectively in x and y direction,
nx is Manning's roughness in x direction and ny is
Manning's roughness in y direction, h is the water
level, g is the gravitational acceleration and q is
the lateral flow, rainfall intensity, extraction and
infiltration rate of unit surface area. The above
Equation (1) is a continuity equation, and Equations
(2) and (3) are the motion equations respectively
( ) ( )q
y
d
x
d
t
d=
∂∂
+∂
∂+
∂∂ vu
⋅+=
∂∂
−g
u
d
q
d
nu
x
h x
34
2
⋅+=
∂∂
−g
v
d
q
d
nu
y
h y
34
2
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in x and y direction. When the geographical
parameters, such as terrain elevation, Manning's
roughness (nx, ny), and lateral flow (q), are known,
only 3 unknown variables remain in the 3 equations
above: the inundation depth (d), and the average
flow velocities (u, v) in the directions of both axes.
Assuming that there is no water on the surface in the
research area at the initial moment, the flood wave will flow into the flood plain after overflowing or
inundation accumulation; the boundary arising from
the junction of land and water must be formed in a
downstream location, and this boundary will move
downstream over time. The alternating direction
explicit (ADE) numerical method is used to solve
the above equations to simulate the inundation
results (Lai, 1986) that included the moving
boundary condition with its quite complex physical
phenomenon.
For inundation simulation, it is required to
manually perform the following series of steps with
the original two-dimensional inundation model.
(1) Prepare input data: inflow data are optional and saved as text files (.txt). Topographic data:
Z-value of the boundary water level elevation (if no
boundary water level, then used elevation) for each
grid point are saved. In this way, coordinates and
property data of all grid points are recorded in order
and separated by commas. Rainfall data: quantity
of rainfall stations, X and Y coordinate values of
the 2-degree zone (TWD97) of all rainfall stations
and hourly precipitation are recorded. Inflow data: not necessary for conducting the two-dimensional
inundation model; data are to be recorded in the
rainfall data record format (e.g., the quantity of
rainfall stations, hourly inflow data, as well as X and Y coordinate flow data of the 2-degree zones for all hydrologic stations).
(2) Set file paths and define simulation
environment parameters: after the data are entered
and verified, the files will be saved in the same
directory as the two-dimensional inundation model.
The actions to be executed by batch files (.bat) in
the next step are set according to file names. Batch file is a text format file, with the purpose of telling the system to execute multiple files in batches or in the same time according to the file.
(3) Execute batch files and establish simulation environment: Execute the set batch files in the above step, and read and analyze the input files to acquire the simulation parameters such as rainfall duration
set as above. After this, establish a case directory.
The directory is to include the input data required
for calculation of the two-dimensional inundation
model.
(4) Execute main program of the two-
dimensional inundation model and obtain simulation
results: With access to the directory (produced
in the above step), the main program of the two-
dimensional inundation model can be executed for
calculation, upon completion of which, inundation
data files will be produced.(5) Convert simulation results into DEM
data: after getting the inundation data, execute the
conversion program in the directory. Convert the
data into the inundation information files which are two-dimensional matrix data separated by commas
in the DEM file format. The first column shows the names of the record fields in the following sequence: X-coordinate value of the 2-degree zone coordinate
system; Y-coordinate value of the 2-degree zone;
inundation depth D (m); and Z value of elevation
(m). The second and subsequent columns record the
coordinates and properties of all grid points.
2.2 Web GIS display technology
As a computer system which can calculate,
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save, inquire, analyze, and display geographic
data, the GIS has spanned half a century since its
development began in the 1960s. Established in
1994, the Open GIS Consortium (OGC) formulated
the common standards for GIS development,
namely Open Geodata Interoperability Specification (Open GIS or OGIS), and thus solved the problems
of complex data and no communication among
all platforms due to each t independent, early
stage platform development. At this point in
the development history, GIS starts to expand
and is widely applied to all fields (http://www.
opengeospatial.org).
In addition to function, data transmission rates
and user convenience should also be considered
in technology development. Unlike the previous
multifunctional and complex standalone version of
GIS system, Web GIS combined with the internet
is extensively used in all fields. This is because
it focuses on data format conversion as well as
common function inquiry and display, and is quite
a suitable tool for displaying spatial information.
Common Web GISs include ArcGIS API developed
by ESRI, TIGER (Topologically Integrated
Geographic Encoding and Referencing) developed
by the United States Census Bureau, and MapServer
owned by the Open Source Geospatial Foundation
(OSGeo).
The data used by GIS are called geospatial
data. It describes spatial characteristics and attribute
relationships, and describes the spatial information
that features constituted by three-dimensional
geometric objects of dots, lines, and planes convey.
The common digital data formats are computer
aided design (CAD) files (e.g., DXF, DWG and
DGN, KML files developed by Google for Google products, and Shapefile developed by ESRI). A
vector file format, Shapefile is the open standard
between kinds of geographic information software,
and can be used for almost all GIS software. A
complete Shapefile must contain at least geometry
entities (.shp), geometric entity indexes (.shx),
and attribute data (.dbf) to constitute complete
spatial information for GIS to read and to use.
Considering the system development combined
with the previously developed warning system, this
research adopts this file format to establish spatial
information as well.
2.3 MapServer
Developed by the University of Minnesota
in the United States in 1990, MapServer can be
operated in all mainstream operation systems
(Windows, Linux, Mac OS X) and is developed
in multiple languages. Those widely used are
Perl, Python, PHP, etc., and good API is provided
for many independent developers to easily use
MapServer to develop geographic information
display platforms. As open source software, it
has been certified by OSGeo and is now jointly
maintained and continuously updated by developers
and users around the world. (http://mapserver.org/)
MapServer communicates between webpage,
web server, GD library and other programs with
common gateway interface (CGI) to achieve
interaction with users. As a standard interface
program, CGI can enable web pages to communicate
with the web server to interact with users. Moreover,
through CGI program, web pages can be produced
dynamically to show the latest data on the server.
Users do not need to download or install any plug-
in or program but only send requests to the server
through operations on web browsers, and MapServer
will respond to demands, capture data from the
locations where spatial information is saved, and
call GD Library, and then convert the data to graphic
information and post back to the browsers to display
for users.
To achieve an online display of spatial
inundation information, MapServer has four
necessary files: start webpage, spatial information
file, map definition file, and HTML template
file. Figure 1 shows the operation procedures of
MapSever. 1) Firstly, the users use a browser to enter
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the website display platform; 2) The start webpage
sends parameters to the web server to request for
spatial information, and after receiving the requests,
the web server calls MapServer CGI to take actions;
3) At this time, definitions and parameters of the
spatial information contained in the map definition file are captured; 4) The parameters set in the map definition file are forwarded to the locations where the spatial information is saved; 5) The spatial
information needed (i.e., the shapefile) is captured; 6) Next, GD Library is called to produce the graphic
information; 7) HTML template file is reread to
verify the way to present the graphic information
and spatial information; 8) Lastly, the graphic
information is transmitted through the web server to
present on the users’ browser.
After being called by the Controller, MapServer
will look for the four necessary files mentioned
above, under the specified paths in the system, to
correctly display the spatial information. The four
necessary files are described as follows:a. Start webpage (Index.html): mainly used to start
MapServer CGI and transmit basic parameters
such as dimensions, layers, and relative paths of
all linked files.b. Spatial information file (Shapefile): the spatial
information files converted by the Controller are to be read and displayed by MapServer. In the
research, the spatial information files are produced at the interval of every 0.2 m of the inundation
depth, and after being read by MapServer, the
files are displayed as overlaid layers in browsers for users to view. In this research, the webpage
start will call 10 spatial information files in total named Layer_Catchment, Layer_xydz_0, Layer_
xydz_1, etc. These layers are the catchment area
layer; the location at inundation depth 0.0 m
layer; the location at inundation depth 0.0 m‒0.2 m layer. By analogy, the latter is the location at
inundation depth greater than 1.4 m layer.
c. Map definition file (.map): the map definition
files are MapServer-defined formats. After
being started, MapServer CGI analyzes the map
definition files of this event. The files starting
with the tag, ‘MAP’ indicate that they are map
definition files, and the last lines ending with,
‘END’ indicate that the tag ‘MAP’ is ended. Users
can define basic parameters of maps, such as
upper and lower bounds, dimensions, file formats, map tag design, etc.
d. HTML template file: MapServer is displayed on browser pages, and after MapServer captures
the above data, the results are represented in the
users’ web browsers according to the template
files. On the right side of the image, the template files show the webpage image and the control
panel for design layer opening / closing, zooming,
panning, and other operations. The template files are interpreted by MapServer CGI and the syntax
is based on the HTML structure. The description:
<!-- MapServer Template -->, must be added in
the first line of the script. This informs MapServer that these are the webpage display template files, and enables the template files and the start web
pages to transmit related spatial information
Fig. 1. MapServer operation procedures.
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parameters to each other.
2.4 Integrated design of the inundation simulation
system
Figure 2 is an integrated simulation system
(ISS) architecture diagram that includes the web
server, Controller, 2D inundation model, GIS
MapServer, and Database components. Users
can make requests to the server with the internet,
which the web server then transmits the relevant
information to the Controller components to
process accordingly. For instance, if users aim
to conduct an inundation simulation, firstly, the
web server can be used to transmit relevant input
information to the Controller components, and
then a 2D inundation model can be called by
the Controller components for an online two-
dimensional inundation simulation. After simulation
calculations are complete, the simulated inundation
results are transmitted to the Controller components
to be saved in the Database, and to make spatial
information and map files. After that, the Controller components are used to call MapServer to read the
spatial information and conduct overlay mapping.
The inundation depth layers are differentiated with
colors according to the water depth difference, so
as to present the spatial information of inundation
simulation in the users’ browsers.
Figure 3 shows the operation procedures of the
ISS Controller components on the users’ operation
interfaces, indicating that the Controller components
simulate and display the system behaviors for
the users. When entering the ISS, the users firstly
add the inundation simulation input files into 2D
inundation model and start to establish the project
directory, then conduct environment configuration
before simulation, and execute the simulation model
in the end. After the results are produced, the records
are saved to the database for filing, a Shapefile is
generated at the same time, analysis is conducted by
MapServer CGI, the maps are produced and fit to
HTML template files, then posted back to the users. Figure 4 describes the interaction between all of the
components in the ISS, with the sequence diagram
of Unified Modeling Language (UML).Message 1-18 are to describe the message
t ime series when the online real-t ime two-
dimensional inundation simulation is conducted,
which can be compared with the procedures in 2D
inundation model components shown in Figure 3,
the Controller component operation procedures.
Firstly, Message 1-10 describe the procedures for
uploading input files (or manually adding input
fields), to establishing the simulation environment.
Fig. 2. Inundation Simulation System (ISS) architecture.
definition (.map) files. After Message 13 is sent, the Controller will call the exec() function to execute
HPUMP2D_72.exe, the main program of the two-
dimensional inundation model, and will generate in
the server host, a new process. Meanwhile, Message
14 is generated to monitor the two-dimensional
inundation simulation program until the end of
execution, after the inundation simulation result files are generated. According to the cases, DEM grid
quantity calculation time differs, from a few minutes
to a few hours. After simulation calculations are
complete, and the spatial information files are
converted and generated, Message 18 will present
the results in the users’ browsers. Next, Message
19-20 describes the users’ operation systems, and
MapServer is used for spatial information display.
In the ISS sequence diagram, Message 13
conveys that, the Controller will execute the
inundation calculation and sends the exec() function
to the 2D inundation model components. However,
according to the above, the inundation simulation
calculation may be executed for hours due to grid
quantity of DEM data. Also, in Apache web server,
processes opened in webcall mode (e.g., the two-
dimensional inundation model) will be opened as a
child process, and managed by the parent process
(i.e., Apache web server). In order to ensure the
server’s efficient operation, all child processes’
operation times are restricted to normally 10 to 15
minutes. As a result, there are issues of executive
processes being timed out; and, the two-dimensional
inundation model cannot be correctly executed. In
order to successfully execute the external program
with the online execution time in a Windows
operation system, PStool suite can be used to solve
this problem.
PStool suite was developed by Winternals
Software, a company purchased by Microsoft
Corporation in 2006. Hence, PStool suite now is
owned by Microsoft Corporation and is free to the
public. Currently, the latest version of PStool suite
is v2.44 (Windows Sysinternals, https://technet.
microsoft.com/en-us/sysinternals/pstools.aspx). It
includes a kit of command line series which can
help users manage remote systems and local systems
with Windows operation systems. PStool suite is
compatible with most Windows-owned operation
systems, and can be directly used on clients or
servers without any installation files. To realize
the online real-time two-dimensional inundation
model, the PsExec tool in the PStool suite is used
to enhance the capabilities of remote computers
(namely, on the user side) to execute the server
host’s processes or software, so as to create new
execution program processes and solve overtime
issues in process operations.
In system development, executive processes’
Fig. 4. Inundation Simulation System (ISS) sequence diagram.
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timeout issues are found when executing server
processes with web pages. In order to solve the
issues, PsExec.exe, one of the programs in the
PStool library must be added to help the system
open two-dimensional inundation models as a
‘new processes’; to prevent the Apache web server
from executing the two-dimensional inundation
model as a child process, thus leading to forced
shutdown by the Apache server due to an execution
that timed out, and the unsmooth execution of
two-dimensional inundation simulations. The
code, PsExec, and the function, exec(), are used to
execute the two-dimensional inundation model’s
main program execution file (HPUMP2D_72.exe).
Now, instead of the above method, arguments are
added to the calling function exec() parameters to
call PsExec.exe to execute the two-dimensional
inundation model’s main program. The argument,
PsExec, must be placed first, so that subsequent
programs will be opened by PsExec.exe. Next, the
argument, –accepteula, executes the PStool tool;
and the argument, -d, is used since the Apache
web server process does not monitor the two-
dimensional inundation process, and as a result,
the argument can be opened as a new process.
After this step is completed, the online real-time
inundation simulation will be successfully executed
and awaiting the system’s responses, to obtain the
inundation results.
After the two-dimensional inundation model
are executed, it must be verified whether the
programs are completed. As mentioned above, in
order to prevent the two-dimensional inundation
simulation process is opened by the Apache
web server as a child process, which leads to an
abnormal execution due to the executive process
being timed out, PsExec is used to solve the
issues. However, this method prevents the Apache
web server from monitoring the return values of
the executive processes. Hence, after the system
dispatches the two-dimensional inundation process,
a script with a monitoring mechanism is introduced
to the system. Its effect is to detect whether the
two-dimensional inundation model has generated
execution result files, the basis for determining
whether the inundation simulation has completed.
Based on the online real-time two-dimensional
inundation simulation, the inundation simulation
information is obtained, and is the two-dimensional
inundation literal data. In order to use MapServer
to display the spatial information, the literal data
must firstly be converted into spatial information,
and the map definition files generated (.map). These are necessary for the execution of MapServer. In the
end, the start webpage and the HTML template file are linked, to correctly display the map on the web
pages. As a consequence, the above steps are started
after the Controller detects the inundation data files.(1) Spatial information file conversion: this
research uses BytesFall Shapefiles, licensed under
a general public license (GNU), and includes these
Shapefiles within its spatial information conversion library. The users can edit it according to their
own data formats and convert the text information
into Shapefiles for GIS to use. Developed in PHP
language in 2006, BytesFall Shapefiles can be used to convert the existing 2D graphical data and enable
the users to edit the data structure of attribute data
(DBF) files on their own. BytesFall Shapefiles is
currently in its second edition, while creat_shpfile.php and ShapeFile.lib.php are mainly used in
studies. ShapeFile.lib.php is the library to which
spatial information conversion functions are saved,
and can be called after being introduced into the
code to execute data conversion as the function,
require_once().
The source code, creat_shpfile.php, is firstly
introduced in the library, and then the maximum
coordinate value and the minimum coordinate value
of the Shapfile are respectively defined on x and y axes. After defining the boundary, all point data are imported, and title columns of the property table are
defined. Function setDBFHeader() is used to define the columns, then all data are added to the property
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table. Converting literal data to spatial information
do this, merely add the file, mapserv.exe, to the web server’s cgi-bin directory.
3. INUNDATION SIMULATION SYSTEM ACHIEVEMENT
3.1 Study area and data description
In this research, an original two-dimensional
inundation model is used to simulate single
rainfall events in Luzhou and Sanchong Districts
in New Taipei City, as test cases. Figure 5 shows
the locations of the Luzhou and Sanchong study
area, as well as all rainfall stations and hydrologic
stations. The DEM data are constituted by 40 by 40,
2-degree zone coordinate system, grids. The scope
of the X coordinate is from 295120 to 300040,
and the scope of Y coordinate is from 2771360 to
2777080, running about 5.8 km from east to west,
and a maximum elevation difference of 9.58m.
The two-dimensional inundation computational
grid coordinate system is divided into 124 inch-
sized X-direction grid squares and 144 inch-sized
Y-direction, with the total grids equal to 124*144.
Figure 6 shows the rainfall hyetographs of the
cases in this area, 4 rainfall stations independently
recording 24-hour rainfall data. It can be seen from
the rainfall map that the rainfall is focuses during
9:00 to 17:00. The inflow data and hydrograph are shown in Figure 7 for 3 rainfall stations recording
the inflow data in the area.In order to simulate the raining period for
online real-time inundation calculation, assuming
Fig. 5. Inundation Simulation System (ISS) sequence diagram.
Fig. 6. 24-hour rainfall duration hyetograph in the Luzhou and Sanchong study area. Note: (a) Rainfall station 1; (b) Rainfall station 2; (c) Rainfall station 3; (d) Rainfall station 4.
Fig. 7. 24-hour inflow duration hydrograph in Luzhou and Sanchong.
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that it takes 6 hours for one rainfall forecast: firstly, the 0-6 hours’ rainfall forecast is input into the ISS
to simulate the 6-hour inundation status; then, the
7-12 hours’ rainfall forecast is inputted; after that,
the 6-hour water state is used to reckon to the 12-
hour data and so on till the 24-hours are complete.
This simulation cannot be conducted, however,
when limited to the two-dimensional inundation
model based on events. Hence, in this research,
rainfall events are divided at 6-hour intervals, and
single rainfall events are re-divided into 6-hour, 12-
hour, 18-hour and 24-hour rainfall duration (e.g., the
12-hour rainfall duration in Luzhou and Sanchong
Districts, the 18-hour rainfall duration in Luzhou
and Sanchong Districts. In other words, among
the new event data of the rainfall records captured
before 12- and 18-hours of the original records
(for Luzhou and Sanchong Districts, there is no
rainfall record before 6-hours so it is not taken as a
simulation case for discussion), consistency between
the simulation results of all rainfall duration events,
and 24-hour rainfall duration events is verified at 6-, 12-, 18-, and 24- hours.
3.2 Test case
In order to verify the ISS, the results obtained
via the original two-dimensional inundation model
are compared with those obtained from the spatial
information exhibition by using the commercial
software ArcGIS.
Firstly, verify that the online real-time
inundation simulation can produce correct results
and compare the inundation information files
simulated online by the ISS with those simulated
by the original two-dimensional inundation model.
Table 1 shows the inundation results (partial
Table 1. Comparison of simulated results for 24-hour rainfall duration in Luzhou and Sanchong Districts
2DIM ISS system
X Y Inundation depth (m) X Y Inundation depth (m)
298320 2771360 0.1 298320 2771360 0.1
298360 2771360 0.1 298360 2771360 0.1
298400 2771360 0.1 298400 2771360 0.1
298440 2771360 0.1 298440 2771360 0.1
298280 2771400 0.1 298280 2771400 0.1
298320 2771400 0.188 298320 2771400 0.188
298360 2771400 0.193 298360 2771400 0.193
298400 2771400 0.195 298400 2771400 0.195
298440 2771400 0.195 298440 2771400 0.195
298480 2771400 0.001 298480 2771400 0.001
298240 2771440 0.001 298240 2771440 0.001
298280 2771440 0.197 298280 2771440 0.197
298320 2771440 0.194 298320 2771440 0.194
298360 2771440 0.194 298360 2771440 0.194
298400 2771440 0.194 298400 2771440 0.194
298440 2771440 0.194 298440 2771440 0.194
298480 2771440 0.002 298480 2771440 0.002
298520 2771440 0.101 298520 2771440 0.101
298240 2771480 0.001 298240 2771480 0.001
298280 2771480 0.19 298280 2771480 0.19
298320 2771480 0.19 298320 2771480 0.19
298360 2771480 0.191 298360 2771480 0.191
298400 2771480 0.192 298400 2771480 0.192
298440 2771480 0.192 298440 2771480 0.192
( 88 )
locations) simulated by the ISS and 2DIM for
24-hour rainfall duration events in Luzhou and
Sanchong Districts. Table 1 shows that the results,
from ISS online real-time inundation simulation and
the original 2DIM, are consistent.
The spatial inundation information displayed
with the ISS’S Web GIS display function is
compared with the spatial information displayed
with the commercial software ArcGIS. The
simulated results are shown in Figure 8, with the
situations at 12-, 18- and 24-hours in Luzhou and
Sanchong Districts as the examples. In Figure 8, the
left images are from the ISS webpage and the right
images are from ArcGIS. After 12-hours of rainfall,
the research area was inundated, with a heavy
inundation situation on the east side of the study
area. After an 18-hour rainfall inundation situation,
the dark block on the east side, was significantly
enlarged. As for the inundation situation within the
last 24-hours, the inundation range was vaguely
reduced. According to the spatial information map,
the continuous changes in inundation flows can
be obviously seen from the beginning; and the
maximum range of the rainfall events’ reduction at
12-hours, 18-hours, and 24-hours in the research
area, is associated with the tendency that the
precipitation gradually increases then decreases
shown in the rainfall event records in Figure 6. It
is verified that the spatial information display can
help to understand the correlation between rainfall
events and inundation flows. The spatial information displayed in Figure 8 of the maps on the left and
on the right almost coincide with each other, which
certifies that ISS can correctly display inundation
information.
3.3 Inundation simulation system displays
Figure 9 shows the ISS operation procedures.
Enter the home page of ISS to see the basic system
instructions, the two-dimensional inundation
simulation, and Web GIS display button. Click the
Web GIS display button to enter the MapServer
display page and view the system case events, and
all the users’ simulation case events. Click ‘two-
dimensional inundation simulation’ to conduct an
online two-dimensional inundation simulation,
add events, and input data (by uploading files or to inputting data), and start the inundation simulation
after the data are imported into the system. After
simulation completion, click the Web GIS display
button to enter the display page, select simulation
events in the drop-down menu, and to display the
inundation simulation spatial information with
MapServer.
The users can enter the system’s web portal
by entering its URL (http://hirg.cycu.edu.tw/
iss/) in browsers. On the home page, the system’s
purpose is briefly stated, and the simulation and
display functions are described. Firstly, click the
‘two-dimensional inundation simulation’ button to
enter the page that describes the two-dimensional
inundation simulation. The page is divided into two
parts, the main window on the right-side details the
input file content and file formats necessary for the two-dimensional inundation simulation; and the
auxiliary window on the left side has two buttons,
‘upload input data’ and ‘fill in input data’, for users to upload input files or enter rainfall information
into web forms, to build new input files.After uploading input data or inputting data
into the system, the page will display the event
contents of this simulation and generate a start
button to begin the simulation. After the simulation
is completed, a prompt message will appear in
the browser to notify users that the inundation
simulation is completed. The simulation time will be
shown and a navigation button for users to advance
to the Web GIS display system. Figure 10 is a
screenshot of the display system. System research
cases and users’ simulation cases can be selected
for display in the drop-down menu on the left side
of the screen. Figure 11 shows a 24-hour rainfall
duration simulated inundation results for the system
research case named, “Typhoon Saola_Wujie Town,
( 89 )
Fig. 8. Analysis of spatial inundation information of rainfall events at (a) 12-hours, (b) 18-hours, and (c) 24-hours in Luzhou and Sanchong Districts.
( 90 )
Yilan”. The control panel on the right side of the
screen is for users to operate the display data. Click
the ‘Update’ button to control the size of the map
after inputting the ‘Size’ value; and select to zoom
in or out with the optional button (‘Ratio’); or use
the mouse to click the locations for viewing on the
map; and re-centering selected locations on the map.
Many checkboxes on the bottom of the control panel
can be used to open or close the display images.
4. CONCLUSION AND SUGGESTIONS
4.1 Conclusion
This research integrated Web GIS and a two-
dimensional inundation simulation for web server
application to develop the ISS, with online real-
time inundation simulation functions and simulated
spatial inundation information browser-based
display. With data about many areas established
in the ISS, and combined with real-time rainfall
event data, inundation simulations were conducted
to gain inundation depth information of all points
in the areas. After the simulation was completed,
MapServer was used to display the spatial
inundation information. Luzhou and Sanchong
Districts were taken as the test cases, and through
test and analysis, the following conclusions were
drawn:
(1) From the research and case test, it is found that
the results from the two-dimensional inundation
Fig. 9. Inundation Simulation System (ISS) operation procedures.
Fig. 10. Web GIS display page.
( 91 )
model used with web server technology for real-
time online inundation simulation, are consistent
with those from the original two-dimensional
inundation simulation, so that ISS online user
interfaces can be used instead of the complex
manual operational procedures of the original
two-dimensional inundation model.
(2) Based on a practical system test, ISS indeed can
establish real-time spatial information files (i.e., Shapefiles) according to inundation depth data, and correctly display it as a map since the Web
GIS and real-time display, MapServer, and the
online two-dimensional inundation model are
integrated.
(3) Apache web server and MapServer, the
development software used in this research, are
all GNU software. No extra research expense is
needed for system development. It is a feasible
method taking into consideration the economic
factors typically involved.
(4) Apache web server executes the two-dimensional
inundation model as a child process. If the
execution takes a long time, it will be timed out
by the server and the two-dimensional inundation
model cannot successfully execute. Our research
overcomes this problem, by combining the
‘PsExec’ tool in the ‘PStool’ library, with PHP
language on the web server, to enable users to
execute the two-dimensional inundation model
online with browsers and without downloading
or installing any file.
4.2 Suggestions
(1) A complete inundation warning system must
contain four parts: real-time rainfall observation,
an inundation calculation model, spatial
inundation information display, and an alert
information report. Using network technology,
ISS firstly integrates the inundation calculation
model with spatial inundation information
display technology, to preliminarily verify
the feasibility of technology integration. It is
suggested to continuously integrate all disaster
warning technologies in the future, to achieve
the goal of disaster prevention with science and
technology; under the condition of no manual
operation for weather monitoring, disaster
warning, and alert issuing.
Fig. 11. Inundation Simulation System (ISS) system display page.
( 92 )
(2) At present, the ISS only offers 5 areas for users
to conduct online simulations, since geographic
data (such as topography and boundary) is
limited. In the future, with more geographic
data of more areas gradually imported, the
system will provide more inundation simulation
information.
(3) In the two-dimensional inundation model, the
problem of time-consuming simulation exists.
In the future, this problem must be considered
and attempted to be solved before multi-mode
integration simulations can occur. For example,
modifying the core to improve calculation
efficiency, or combining cloud technology to
enhance operation efficiency. In this way, the
system can really achieve the purpose of rapid
simulation at the earlier stages of disasters.
(4) In the future, the functions of layer overlying,
raster format layer display, and advanced
operation can be added to Web GIS display in
the ISS system, to optimize its operation and
display.
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