iRIC Software
Changing River Science

Nays2D Flood
ExamplesDirected by Yasuyuki Shimizu
Edited by Takuya Inoue
Eiichi Suzuki
Satomi Kawamura
Toshiki Iwasaki
Michihiro Hamaki
Tomohiko Yoshida
Jagriti Mishra
Kensuke Omura
Eriko Kakegawa

iRIC version 4.0

Last Update: 2024.5.27
Release Date: 2023.6.28

Copyright 2013 iRIC Project All Rights Reserved.
1

Contents
CHAPTER 1 USING NAYS2D FLOOD ...................................... 4
1.
2.
3.
4.

Nays2D Flood basic operating procedures ............................................. 5
Launching Nays2D Flood ........................................................................ 6
The sample data ...................................................................................... 8
Simulation conditions of Nays2D Flood ................................................. 9

CHAPTER 2 EXAMPLES OF FLOOD CALCULATION FOR AN
ACTUAL RIVER SECTION....................................................... 10
1. Creating the calculation grid .................................................................. 11
1

Importing cross-sectional river survey data ...................................................... 112

Selecting an algorithm for creating a grid ......................................................... 17

3

Creating a grid .................................................................................................... 18

2. Setting the calculation conditions ........................................................... 20
8Open "Calculation Conditions" ........................................................................... 20

9

Setting the inflow boundary conditions ............................................................. 21

10 Setting the initial water surface profile ............................................................. 22
11 Setting the time .................................................................................................. 23
12 Other settings ..................................................................................................... 24
13 Setting inflow rivers ........................................................................................... 25
14 Setting roughness condition ............................................................................... 30
15 Setting obstacle cells ........................................................................................... 34
16 Setting Areal fraction that buildings occupy ..................................................... 37
17 Setting for the box culvert .................................................................................. 40

3. Making a simulation ................................................................................ 45
4. Visualizing the calculation results.......................................................... 46
8Open the "2D Post-Processing" window ............................................................. 46

9Visualizable quantities ....................................................................................... 47

10 Visualizing the max. water depth ...................................................................... 48
11 Visualizing the max. flow velocity ...................................................................... 50
12 Visualizing the inflow discharge hydrograph .................................................... 51

CHAPTER 3 EXAMPLES OF TSUNAMI RUNUP ANALYSISUSING SRTM DATA ................................................................. 54
1. Creating the calculation grid .................................................................. 55
1

Importing geographic data ................................................................................. 55

2

Selecting an algorithm for creating the grid...................................................... 59

3Creating a grid .................................................................................................... 60
2

2. Setting the calculation conditions ........................................................... 62
1Open [Calculation Condition] ............................................................................. 622

Setting the inflow boundary conditions ............................................................. 63

3

Setting the initial water surface profile ............................................................. 66

4

Setting the time .................................................................................................. 67

5

Other settings ..................................................................................................... 68

6

Inflow settings ..................................................................................................... 69

7

Setting the roughness ......................................................................................... 75

8

Correcting elevation of sea area ......................................................................... 78

3. Making a simulation ................................................................................ 80
4. Visualization of computational results ................................................... 81
1

Open the 2D Post-processing window ................................................................ 81

2

Quantities that can be visualized....................................................................... 82

3

Visualizing the water depth ............................................................................... 83

4

Visualizing flow vector ........................................................................................ 85

5Visualizing animated changes............................................................................ 86

6

Visualizing time series data ............................................................................... 87

5. Important information............................................................................. 91

CHAPTER 4 EXAMPLES OF RAINFALL INDUCED FLOODING
IN ACTUAL RIVER ................................................................... 92
1. Creating the calculation grid .................................................................. 93
1

Importing geographic data ................................................................................. 93

2

Selecting an algorithm for creating the grid.................................................... 101

3

Creating a grid .................................................................................................. 102

2. Setting the calculation conditions ......................................................... 104
1Open [Calculation Condition] ........................................................................... 104

2

Setting the inflow boundary conditions ........................................................... 105

3

Setting the initial water surface profile ........................................................... 107

4

Setting the time ................................................................................................ 107

5

Other settings ................................................................................................... 108

6

Inflow settings ................................................................................................... 109

7

Setting the roughness ....................................................................................... 113

3. Making a simulation .............................................................................. 115
4. Visualization of computational results ................................................. 116
1Open the 2D Post-processing window .............................................................. 116

2

Visualizing the water depth ............................................................................. 117

3

Visualizing flow vector ...................................................................................... 119

4Visualizing animated changes.......................................................................... 120

3

Chapter 1
Using Nays2D Flood
This manual explains the basic operation and startup procedures of Nays2D Flood, whichis compiled with iRIC. TheNays2D Flood solver simulates two-dimensional plane river
flow and riverbed deformation. It was developed by Professor Yasuyuki Shimizu of
Hokkaido University. The following explanation is based on the assumption that you haveinstalled the iRIC software on your computer. If you have not installed the iRIC software,
download it from the following URL and install it on your computer.
URL:

http://i-ric.org/download

Software:

iRIC version4.0 or later41. Nays2D Flood basic operating procedures
The following are the basic procedures for operating Nays2D Flood with iRIC:

5

2. Launching Nays2D Flood
The following is the procedure to launch Nays2D Flood on iRIC.

When launching iRIC, the [iRIC Start Page] window will open.
Click on [Create New Project] in the [iRIC Start Page] window.

The [Select Solver] window will open.
Select [Nays2D Flood v5.0] in the [Select Solver] window, and click on [OK].

6

A window with the title bar "Untitled-iRIC v4 [Nays2D Flood v5.0]" will appear.

Nays2D Flood v5.0 is ready for use.

7

3. The sample data
The sample data used for the sample simulations explained in this manual are available
at:
URL:

http://i-ric.org/en/download

Examples of simulation: Nays2D FloodTo run Nays2D Flood according to this manual, data should be downloaded from the abovesite or provided by the staff in an iRIC training course.
The project files (*.ipro) in the description and sample data of each chapter in this manualis created by following solver. Although the project file cannot be used without change if
the solver version is different, resetting calculation conditions and so on, following thismanual enables calculation with other versions.
Solver: Nays2D Flood v5.0
Sample data and corresponding solver version
Data nameContents

versionN2F

Examples of flood calculation for an

Nays2D Flood 5.0

actual river section
N2F_2

Examples of tsunami runup analysis

Nays2D Flood 5.0

using SRTM data
N2F_3

Examples of rainfall induced flooding in
actual river

8

Nays2D Flood 5.0

4. Simulation conditions of Nays2D Flood
This manual teaches how Nays2D Flood is used to simulate river flow during flood events
for two relatively simple examples. There are some omissions in the explanations of thephysical and numerical aspects of the simulation conditions that are to be set. Nays2D
Flood has other functions (setting conditions) in addition to those explained by thismanual and these two specific examples. For more complete details, please refer to the
Nays2D Flood Solver Manual.

9Chapter 2
Examples of flood calculation for an
actual river section
Objectives
Simulate the flow regime (water depth and flow velocity) using Nays2D Flood for an
actual river section with a flood discharge, and check to see whether the simulation is
successfully run.

Outline1. Creating the calculation gridUsing elevation data of an actual river section, create a calculation grid.

2.Setting the calculation conditions
Set flood discharge for unsteady flow. Set various other conditions necessary for
simulation.

3. Making a simulation
4. Visualizing the calculation results
Here, we introduce how to display a water-depth contour map and a flow velocity vector
map.

10

1. Creating the calculation grid
1

Importing cross-sectional river survey data
Importing geographic data

On the menu bar, select [Import] - [Geographic Data] - [Elevation].

11

Open [\\SampleData\\N2F], select [N2F.tpo] and click on [Open].

On the dialog [Import Setting], check [Space] for "Delimiters" and input [1] for "Headerlines to ignore" and select [OK].
Set a larger number for the filter value and filter the dataset if the operation is slow
because of the high number of data points. In this example, Skip rate is set at [1]. The
filter simply skips over the data; i.e., if the filter is one, each data point is read into
iRIC, but if the value is two, only every other data point is read in, and so forth.

Delimiters: Space
Header lines to ignore: 1

12

If the [Pre-Processing] window shows the shape of the river section that you are
simulating, the data have been successfully imported.

How to change the contour
map of elevation to points
data; select Point Cloud
Data 1 in the Object
Browser, then right click,and open Property thenselect Points in TIN.

13

Importing a background image
On the menu bar, select [Import] - [Background Image].

Background image
When creating grids forcalculation, importing
background images suchas maps and aerial
photos makes it possible
to create grids thatincorporate riverbanks
and land use. Obstacle
cells and roughness cells
mentioned below can be
set in reference to thebackground image.

Open [\\SampleData\\N2F] and select [N2F.jpg].

14

Using the [Move], [Rotate] and [Zoom] functions, match the background image with theelevation data.
[Move] [Rotate] [Zoom] refer to mouse hint

Hint
It is convenient to findthe geographic featuresand mark on the
background image when
you match thebackground image withelevation data.
In this case, the frameline is drawn and you
can use this frame line
to match.

Referring to the hint above, match the background image with the elevation data.

15

Click on [Background Image]-[N2F.jpg] on the object browser.
Fix the background image with [fix position].

You can also set the position of the background image by right-clicking the object
browser [Background Image]-[N2F.jpg] and specifying coordinates from [Properties].

16

2

Selecting an algorithm for creating a gridOn the menu bar, select [Grid] - [Select algorithm to create grid].
The [Select Grid Creating Algorithm] window will open.

Select [Create grid from polygonal line and width] from the list below the [Select Grid
Creating Algorithm] window, and click on [OK].
Nays2D Flood primarily creates a grid from polygonal lines and grid widths.

17

3Creating a grid

Right-click on several points through which the grid centerline passes, and press the“Enter” key.

Set the grid centerline
from the upstream end,
where flood flow enters,
to the downstream end,
where the flood flow
exits. To finish, doubleclick on the end of thecenterline, or hit the“Enter” key.

In the [Grid Creation] window, make the following settings and click on [OK].

Number of divisions in thelongitudinal direction : 63
Number of divisions in thetransverse direction : 30
Grid width in the transverse
direction : 6000 m

18

Click on [Yes] in the [Confirmation] window.

Mapping geographic data
Elevation data areapplied to the grid.

A grid will be created.

It is possible to move, add
or remove centerline
points under [GridCreating Conditions]even after the grid iscreated.

19

2. Setting the calculation conditions
8

Open "Calculation Conditions"

On the menu bar, select [Calculation Conditions] - [Setting].
The [Calculation Conditions] window will open.

20

9

Setting the inflow boundary conditions

Click on [Inflow/ Outflow Boundary Conditions] from the [Groups] list to make thefollowing settings:

Time unit ofdischarge/water surface
elevation files: Second
Boundary Conditions for
j=1: Inflow
Boundary Condition for
j=nj: Outflow
Water surface atdownstream: Free Outflow
Rainfall: without
Note : Inflow conditions are
decided at [6.Setting the
inflow river conditions]Use constant value or readfrom file when the stage at
downstream is effected bysea level or overflow levelat the outflow.

21

10

Setting the initial water surface profile

Click on [Initial Water Surface Elevation] from the [Group] list to make the following
settings:

Initial water surface:
Depth = 0
Note: When the water
surface elevation of thedownstream end may beaffected by the sea levelor the downstream floodlevel, use a constantvalue (a line).

22

11

Setting the time

Click on [Time] from the [Group] list to make the following settings:

Output time interval (sec):
600
Calculation time step (sec):
0.2
Start time of output (sec): 0
Start time of bomber (sec): 0

23

12

Other settings

Click on [Other] from the [Group] list to make the following settings:

Finite difference methodof advection terms:
upwind scheme
Maximum number of
iterations of water
surface calculation: 10
Relaxation coefficient forwater surface calculation:
0.8
Minimum water depth:
0.01
A for eddy viscosity….: 1
B for eddy viscosity….: 0
Number of threads ….: 1

Many other conditions can be set; however, they do not need to be set for this simulation
as the default values are acceptable. After making the settings above, click on [Save andClose] to close the window.

24

13

Setting inflow rivers

Set the inflow rivers (or the bank opening point) at the upstream (red line) and rightside (blue line) since you set the [boundary condition for j = 1] as [inflow] in the inflow/
outflow boundary conditions.

In this river section, tworivers (including
agricultural canals) flow
across the red line andone river flows across theblue line, as indicated by
the red arrows.
No river comes in thearea from the outlet i=ni
or the other bank j=nj
and these boundary
conditions are outflow
only.

In the Object Browser, select [Boundary condition setting]-[Add inflow]

25

While selecting the [Inflow], enclose the sides of “Inflow” locations with polygons.
When the location is confirmed, the [Boundary condition] setting dialog opens.

Name: arbitrary name, we use New
Inflow 1
Slope value at inflow: 0.001

26

In the [Boundary Condition], click on [Discharge time series]

In the [Calculation Condition], click on [Import]27

In [Choose a text file] click on [qt1.csv] and then [open].
Open the discharge data.

Click on [OK].
Repeat above operations for New Inflow 2 to New Inflow 3.

Correspondence of the
inflow river and thedischarge data are as
follows;
Inflow1: qt1.csv
Inflow2: qt2.csv
Inflow3: qt3.csv
Note: The time step of
the discharge files need
to be set the same.

28

Click on [Grid] on the menu bar [Attribute Mapping]-[Execute].

Position setting of inflow
boundary condition

Inflow rivers are set on the sides.

29

14

Setting roughness condition

In the Object Browser, check [Grid] – [Cell attributes]-[Roughness condition].

Right-click on the object browser [Geographic Data]-[Roughness condition] and click [Add][polygon].

30

Click on Object Browser[Geographic Data]-[Roughness condition]－[Polygon1].
Double-click the cell with the same roughness surrounded by polygons.
In [Edit Roughness condition value], directly input the desired Manning roughness.

Roughness condition:0.03
Note: Set Manning's
roughness coefficient by
taking comprehensive
consideration of
calculation model, land
use and past floodingdata.
In setting the roughness
coefficient, refer to page
33 of Flood Simulation
Manual (draft) and page89 of Hydraulic Formula
1999 Edition (both inJapanese).

Click on [Grid] on the menu bar – [Attribute Mapping]-[Execute].

31Roughness is reflected in the cell.

32References:
Extract from pp. 33 of

Flood Simulation Manual (Draft) – Guide for simulation and verification of new model,
Urban River Research Lab, River Section, Public Works Research Institute (Japan),February 1996
1) Find the area of each land use within each mesh. Land use: building; farmland A1,road A2 and other land use A3. Here, "farmland" means rice paddy, upland field ororchard. "Road" includes sidewalks along the road. Wilderness, grass fields andwetlands are included in "other land use."
2) The roughness coefficients by land use are set as follows: The bottom roughness
coefficient other than that of buildings is calculated from the following weighted
average:
𝑛 𝐴

𝑛

𝑛 𝐴
𝑛 𝐴
𝐴
𝐴
𝐴

where, n1=0.060, n2=0.047 and n3=0.050.
3) The composite equivalent roughness coefficient of the land and buildings is givenby the following equation:𝑛𝑛0.020 ∗

𝜃
∗ℎ /
100 𝜃

where, θ is the proportion of land occupied by buildings and h is water depth.

33

15

Setting obstacle cells

In the Object Browser, check [Grid]-[Cell attributes]-[Obstacle].

Right-click the object browser [Geographic Data]-[Obstacle] and click [Add]-[Polygon].

34

Click the object browser [Geographic Data]-[Obstacle]-[Polygon1].
Double-click a cell that will become an obstacle cell with polygons.
In [Edit Obstacle value], select Obstacle.

Set obstacles such as
roads, banks andembankments.
Note: Unless thecalculation grid cells are
small enough to depict
roads, banks andembankments as a partof the topography, setroads, banks andembankments as
obstacles.

Click on [Grid]on the menu bar –[Attribute Mapping]-[Execute].

35

Obstacle is reflected in the cell.

Repeat above operations from Polygon1 to Polygon2.

36

16

Setting Areal fraction that buildings occupy

Check the Object Browser [Grid] - [Cell attributes]-[Areal fraction that buildings occupy].

Right-click the Object Browser [Geographic Data] - [Areal fraction that buildings occupy] andclick [Add] - [Polygon].

37

Click the Object Browser [Geographic Data]-[Areal fraction that buildings occupy]-[Polygon1].
Double-click the cell with the same building occupancy surrounded by polygons.
In [Edit Areal fraction that buildings occupy value], enter directly the building occupancy fraction.

Building occupancy ratio:
0.3
Note: Resistance bybuildings is based on thephenomenon that flow isaffected by buildings andflooding occurs inbuildings. For thisreason, the premisediffers from the abovementioned obstacle
setting, so be careful.
If the areal fraction thatbuildings occupy is larger
than 0.95, the model set
the value to 0.95.
Because this model is amodel for permeable
obstacles and can notconsider completely
impermeable obstacles.
When you want to put
impermeable obstacles,
please use [Obstacle cell].

38

Click the menu bar [Grid]-[Attribute Mapping]-[Execute].

The building occupancy rate is reflected in the cell.

39

17

Setting for the box culvert

Set “inside” geometry of box culvert.
Click the Object Browser [Boundary Condition Setting]-[Add Box culvert].

Pass the water throughthe box culvert to theroad set for the obstacle
cell.
Note: The setting methodof gate, pump is the sameas the setting method ofbox culvert.

Click the Object Browser [Grid] – [Boundary Condition Setting] – [New Box Culvert].
Surround the cell at the "inlet" position of the box culvert with polygons.

In the figure on the left,
the object browser [grid] [cell attribute] - [obstaclecell] is checked so thatthe location of the
obstacle cell can be seenon the figure.

40

Double-click to confirm the position of “inside”.
The boundary Condition screen is displayed.

Change the name on [Boundary Condition] screen to [new Box Culvert_in] and set it as aninside.

Name：arbitrary, we use New
Box Culvert_in
A couple of code number： 1
Inlet/Outlet： Inlet
Width(m)： 1
Height(m)： 1
Elevation(m)： 140
Multiply： 1
Extended formula: No
Coefficient of submerged flow：
0.75
Coefficient of free flow： 0.79
Note: Combine the code number
at inlet/outlet.

41

Set “Outside” of the Box culvert.
In the Object Browser, select [Boundary condition setting]-[Add Box Culvert]

Click the Object Browser [Boundary Condition Setting]-[New Box Culvert].
Enclose the cell at “outside” position of the box culvert with polygons.

42

Double-click to set the position of “outside”.
The Boundary Condition screen is displayed.

Set the conditions of the box culvert from the dialog.

Name: New Box
Culvert_out
Coupling code number: 1
Inlet/Outlet : Outlet

43

On the menu bar, select [Grid] - [Attributes Mapping] – [Execute…]

The box culvert is set in the cell.

44

3. Making a simulation

On the menu bar, select [Simulation] - [Run].
Save the project.

The [Solver Console [Nays2D Flood] (running)] window will open to start thesimulation.

45

4. Visualizing the calculation results
8

Open the "2D Post-Processing" window

On the menu bar, select [Calculation Result] - [Open new 2D Post-Processing Window].

The "Post-Processing (2D)" window will open.

46

9Visualizable quantities

DESCRIPTIONS

IN

THE

OBJECT DESCRIPTION OF EACH QUANTITYBROWSER● CONTOUR
DEPTH(MAX)The max. water depth by the time ofvisualization (m).

DEPTH

The water depth at the time of visualization(m)

ELEVATION

The ground height of calculation grid (m)WATERSURFACEELEVATION

The water surface elevation at the time ofvisualization (m)VELOCITY (MAGNITUDE MAX)

The max. flow velocity by the time ofvisualization (m/s)

VELOCITY (MAGNITUDE)

Flow velocity at the time of visualization(m/s)● VECTORVELOCITY

Vector of flow velocity (m/s) at the time ofvisualization● STREAMLINEVELOCITY

Displays a streamline.

● PARTICLESVELOCITY

Displays particles.

● CELL ATTRIBUTESOBSTACLE

CELL(A

NORMAL Displays a normal cell.

CELL)
OBSTACLE CELL (A CELL WITH Displays an obstacle cell.
AN OBSTACLE)
BOMBER CELL (A NORMAL CELL) Displays a normal cell.
BOMBER CELL (A CELL WITH Displays a bomber cell.
ANBOMBER)

47

10

Visualizing the max. water depth

In the Object Browser, select [Nays2D Flood Grids] - [iRICZone] – [Scalar] - [Depth(Max)].
A contour map of water depth will open.

In the Object Browser, select [Nays2D Flood Grids] - [iRIC Zone] - [Scalar]. Right-click on[Depth(max)] to select [Property].
The [Contour Setting] window will open.

48

In the [Scalar Setting] window, make the following settings and click on [OK].

Value range :Remove ☑ from Automatic
Max : 1
Min : 0.01
Colors : No change
Remove ☑ from Fill lower area
Transparent: No change
Color Bar Setting: No change

The contour map is clear.

49

11

Visualizing the max. flow velocity

In the Object Browser, check [Nays2D Flood Grids] - [iRIC Zone] - [Scalar] - [Velocity(magnitude Max)].

Value range :Remove ☑ from Automatic
Max : 2
Min : 0.01
Colors : No change
Remove ☑ from Fill lower area
Transparent: No change
Color Bar Setting: No change

50

12

Visualizing the inflow discharge hydrographOpen [New Graph Window].

51

[Data Source Setting] screen is displayed.

Unit: m3/s

52

Select [Calculation Result] - [Point data] - [New Inflow1], [New Inflow2] and [New Inflow3] [Add].
The hydrograph of the incoming river is displayed.

Select [Calculation Result] - [Point data] –[New Box Culvert_in], [New Box Culvert_out] [Add].
The hydrograph of box culvert is displayed.

53

Chapter 3
Examples of Tsunami Runup Analysis
Using SRTM data
◆ Objectives
The objectives are to use Shuttle Radar Topography Mission (SRTM) data, to simulate
and visualize the simulated flow regime, such as water surface elevation and flow velocity,
at a river mouth when tsunami-runup-induced flooding occurs with Nays2D Flood.

◆ Outline
1. Creating the calculation gridUsing elevation data of an actual river basin, create calculation grids: 101 division points
in the transverse direction, and 131 division points in the longitudinal direction.

2. Setting the calculation conditions
Set a value for tsunami wave height assuming that a large-scale earthquake has occurred.
Set various other conditions necessary for simulation.

3. Making a simulation
4. Visualizing the calculation results
Here, we introduce how to display a waterdepth contour map and a flow velocity vector
map.

54

1. Creating the calculation grid
1

Importing geographic data

In the Object Browser, right-click [Geographic Data]-[Elevation].Click [Import Elevationfrom web].

[Select Coordinate System] screen is displayed.
Search with JGD and select [EPSG:2452:JGD2000/Japan Plane Rectangular CS X].

The coordinate system of
the target area can beunderstood from the hinton the coordinate systemat the bottom of thescreen.

55

[Select Region] screen is displayed. Drag the target part and click [Next].

To enlarge or reduce the map,
click [Zoom In] / [Zoom Out]at the bottom of the screen.

Zoom Level Setting] screen will be displayed.
Specify the zoom level and select the source.

Zoom level：11
Source：USGS（SRTM）
Note: Since theresolution of the SRTM
data is 90 m mesh, even
if the zoom level is set to
11 or more here, thedata does not change
because the maximum
resolution has beenreached. Therefore, thezoom level is set to 11.

56

Reading is successful if the shape of the watershed to be calculated is displayed on [Preprocessing Window] screen.

When one of the items in the background image of the object browser is checked, thebackground image is displayed.

Background image
When creating grids forcalculation, importing
background images suchas maps and aerial
photos makes it possible
to create grids thatincorporate riverbanks
and land use. Obstacle
cells and roughness cells
mentioned below can be
set in reference to thebackground image.

57

Since the coordinate system is selected, it is set automatically.

If your PC specifications are insufficient, you may not be able to process very large
arrays of elevation data. To speed up processing, remove geographic data in the areasthat are not needed.
Click on [Fit] to display the entire data. Select [Object Browser] - [Geographic data 1] andkeep the data ([Geographic data 1]) selected. Select the area you wish to delete by
dragging and right clicking. (The gray area in the figure below. An area slightly larger thanthe background image must remain). Delete the unnecessary areas by clicking [Delete
selected points].
Repeat the above procedure. The area slightly larger than the background image willbe left.
Tips:
In the event that the PC
specifications are
insufficient, you may not
be able to process large
numbers of elevation data.
To speed up processing,remove geographic data in
the areas that are notneeded.
Such removal is notnecessary when your PC
has specifications highenough to maintain stable
operation even when large
numbers of data areprocessed.

58

2

Selecting an algorithm for creating the gridOn the menu bar, select [Grid] - [Select algorithm to create grid].
The [Select Grid Creating Algorithm] window will be displayed.

Select [Create grid from polygonal line and width] from the list under the [Select Grid
Creating Algorithm] window, and click on [OK].
Nays2D Flood generates a grid from polygonal lines and widths.

59

3Creating a grid

Click on several points through which the grid centerline passes and press the Enter key
on your keyboard to draw a centerline.

Setting the gridcenterline
Set the grid centerline
from the upper reaches of
the river (upstream) to
the sea (downstream). To
finish, press the Enter
key or double click.

In the [Grid Creation] window, make the following settings and click on [OK].

[nj] (Number of divisions in
the longitudinal direction): 100[ni] (Number of divisions in
the transverse direction): 130[W] (Grid width): 3000 m
Note: In this example, grid cellintervals di, dj are set ataround 30 m.

60

Click on [Yes] in the [Confirmation] window.

Mapping geographic data
Elevation data areapplied to the grid.

A grid will be created.

Adjusting the calculation
grid
It is possible to move, add
or remove any vertexes
by selecting the [GridCreating Condition] evenafter the grid is created.

61

2. Setting the calculation conditions
1

Open [Calculation Condition]

On the menu bar, select [Calculation Condition] - [Setting].
The [Calculation Condition] window will open.

62

2

Setting the inflow boundary conditions

Click on [Inflow Boundary Condition] from the [Group] list to make the following settings:
Click on [Stage at downstream time series] to edit.
The [Calculation Condition] window will open.

[Time unit ofdischarge/water surfacefile]: Second[Boundary Conditions forj=1]: Inflow[Boundary Conditions forj=nj]: Outflow[Water surface atdownstream]: Read fromthe file
Rainfall: without
Note 1: Inflow boundary
conditions are set at "6.
Inflow Settings".
Note 2: When "Water
surface elevation at
downstream end" isaffected by the sea
surface level or flood
water level ofdownstream, select[Constant value] or [Readfrom file].

63

Click on [Import] on the [Calculation condition] window.
The [Select text file] window will be displayed.

Select [\\SampleData\\N2F_2] - [H01.txt] and click on [Open].
Time series of tsunami wave height data is displayed.

64

Click on [OK].
Here, we assume a tsunami whose wave height is 7 m and half-wavelength is 600 sec.

The time steps of thetsunami wave heightmust be kept at the samevalue, including at the
inflow location.

65

3

Setting the initial water surface profile

Click on [Initial Water Surface] from the [Group] list to make the following settings:

Initial water surface:constant slope
Initial water surface
slope of main channel:
0.0001
Note: In order to give anearly horizontal sea
level in the downstream
area, a very small value
is given to [initial water
surface slope of main
channel].
The first water level data
set for [Stage at
downstream time series](0 m in this sample) isregarded as the waterlevel at the downstream
end, and the initial waterlevel is set to achievenearly horizontal sea
water level.
At locations where theground elevation is set
higher than the water
surface elevation, thewater-surface elevation
will not be set.

66

4

Setting the time

Click on [Time] from the [Group] list to make the following settings:

Output time interval(sec): 20
Calculation(sec): 0.1

time

step

Start time of output (sec):
0

67

5

Other settings

Click on [Others] from the [Group] list to make the following settings:

Finite differential
method of advection
terms: CIP method
Maximum number of
iterations of water
surface calculation: 10
Relaxation coefficient forwater surface calculation:
0.8
Minimum water depth:
0.01
A of eddy viscosity
coefficient: 1
B of eddy viscosity
coefficient: 0

After making the settings above, click on [Save and Close] to close the window.

68

6

Inflow settings

Inflow river settings (or bank failure location settings) are made at the upstream end(red line). Note: This sample does not incorporate river discharge. However, Nays2D
Flood requires at least one inflow location to be set on the upstream end.

Note: In this basin, an inflow
to the mainstream occurs on
the red line, as is shown by
the blue arrow. Because thissample focuses on tsunami
runup, a dummy inflow
discharge datum (Discharge
0 m3/s) is applied.

In the Object Browser, right-click [Boundary Condition Setting] and click [Add Inflow].

69

In the Object Browser, click [Boundary Condition Setting]-[New Inflow].Surround the side of theposition of the incoming river with polygons.

Double-click to confirm and the [Boundary condition] screen will be displayed.

70

On the [Boundary Condition] window, input "New Inflow 1" to the [Name] box, and select[Edit] for the [Discharge time series] box under [Setting].
The [Calculation Condition] window will be displayed.

Name: Arbitrary name of
inflow
Slope value at inflow:
0.001

Click on [Import] on the [Calculation Condition] window.
The [Select text file] window will be displayed.

71

Open [\\SampleData\\N2F], select [Q01.txt] and click on [Open].
Time series dummy discharge data (all discharges are zero) will be displayed.

Click on [OK].

The time steps of thetsunami wave heightmust be kept at the samevalue, including at the
inflow location.

72

In the menu bar, click [Grid]-[Attributes Mapping]-[Execute].

Inflow rivers are set on the sides.

73

The grid node indexes of the inflow location of the sample data is given below:

Inflow
Inflow 1

Grid node indexes

Discharge(i, j)

data(1, 17)～(1, 20)

Q01.txt

Note

Inflow locations cannot
be set at a grid nodeother than i=1, j=1 or
j=nj.
When you set grid nodes
other than those above as
inflow locations, an error
occurs and the simulation
stops.
In such a case, select thegrid node and right click
to select [Delete].

74

7

Setting the roughness

In the Object Browser, select [Geographic Data] - [Roughness] and right click to select[Add] - [Polygon].

75

Click on several points to set several vertices such that the vertices enclose the grid area,and press the Enter key on your keyboard to complete the operation.
Then, input a value of Manning's roughness coefficient for [Roughness condition] in the[Edit roughness condition value] window.

Setting Polygon
A polygon is set byenclosing the area by theline linking vertices madeby clicking the location
you want to set as avertex. To finish, press
the Enter key or double
click.
Note: When setting
Manning's roughness
coefficient, first you makea polygon that encloses
all grid nodes. Then, youmake polygons that coversmaller regions withadditional detail, if
desired. In this way, you
can set roughness
coefficients, where
necessary.

76Referring to the background image, repeat the procedure to add polygons as shown the
figure below.
Name each polygon: In the Object Browser, select [Geographic Data] - [Roughness] andright click to open the [Edit Name] box. Input a simple name that expresses the roughnessof the area specified by the polygon.
In the sample data, roughness coefficients are set as below:
Name of polygon

Description

Roughnesscoefficient

Forested
mountains
Low building
density area
High building
density area

0.040

HighDensityArea2

Ditto

0.080

HighDensityArea3

Ditto

0.080

Sea

Sea area

0.025

River

River

0.025

Forest
LowDensityArea
HighDensityArea1

Note

0.030

0.080

77

Residentialarea, etc.
Industrial
area, etc.

Note: Manning's roughness
coefficient iscomprehensively set byconsidering simulation
models, land use in the basin
and past records. Refer topage 33 of Flood Simulation
Manual (Draft) and page 89
of The Collection of
Hydraulic Formulae (Japan
Society of Civil Engineers(FY 1999).

8

Correcting elevation of sea area

In the Object Browser, select [Geographic Data] - [Roughness] - [sea]. Then, select [Copy]
from right click.
Select [Elevation] on the [Select Geographic Data] window, and click on [OK].
Input [-3] on the [Edit Elevation value] window, and click on [OK].

78Remove the check mark from the [Geographic Data] box in the Object Browser.
In the Object Browser, select [Grid] - [Cell attributes] - [Roughness] and make a check
mark in the [Roughness] box.
In the Object Browser, select [Grid] - [Grid shape] and make a check mark in the [Gridshape] box.

Note: Check whether theroughness coefficients areproperly displayed on the
grid.

79

3. Making a simulation

On the menu bar, select [Simulation] - [Run].

The [Solver Console [Nays2D Flood] (running)] window will open to start thesimulation.

80

4. Visualization of computational results
1

Open the 2D Post-processing window

On the menu bar, select [calculation results] - [Open New 2D Post-Processing Window].

The [Post-processing Window (2D)] will open.

81

2

Quantities that can be visualized

Names on the Object Browser

Description● Contour
Depth(Max)The max. depth achieved by the end time ofvisualization (m)DepthWater depth at the time of visualization (m)Elevation

Altitude of the grid for calculation (m)WaterSurfaceElevation

Water level at the time of visualization (m)Velocity (magnitude Max)

The max. flow velocity achieved by the end timeof visualization (m/s)

Velocity (magnitude)

Flow velocity at the time of visualization (m/s)● Vector
Velocity

Vector of flow velocity (m/s) at the time ofvisualization● Streamline
Velocity

Displays the streamline● Particles
Velocity

Displays particles● Cell attributes
Obstacle cell (normal cell)

Displays normal cells

Obstacle cell (obstacle cell)

Displays obstacle cells

Bomber cell (normal cell)

Displays normal cells

Bomber cell (obstacle cell)

Displays bomber cells82

3Visualizing the water depth

In the Object Browser, select [Nays2D Flood Grids] - [iRICZone] - [Scalar] - [Depth] bymaking a check mark in each box.
A contour map of water depth will open.

In the Object Browser, select [Nays2D Flood Grids] - [iRICZone] - [Scalar]. Right click on[Depth] to select [Property].
The [Scalar Setting] window will open.

83

On the [Scalar Setting] window, make the following settings and click on [OK]:Value range:
Remove ☑ from
[Automatic]
Max: 7
Min: 0.01
Remove ☑ from [Filllower area]
Colors : No change
Remove ☑ from Filllower area
Transparent: No change
Color Barchange

The contour map is easier to see now.

84

Settiing:No4Visualizing flow vector

In the Object Browser, select [Nays2D Flood Grids] - [iRICZone] - [Arrow] - [Velocity].
In the Object Browser, select [Nays2D Food Grids] - [iRICZone] - [Arrow]. Right click on[Arrow] to select [Property].
The [Contour Setting] window will open.

On the [Arrows Setting] window, make the following settings and click on [OK]:LengthRemove ☑ from [Auto]
Standard value: 8.00
Length on screen: 40
Minimum value to draw:
0.008
Sampling:
Sampling rate (Idirection): 2
Sampling rate (Jdirection): 2
Resion:
Do not change any
settings.

85

5Visualizing animated changes

On the menu bar, select [Animation] - [Reset].
On the menu bar, select [Animation] - [Start/Stop Animation].
Animated changes in inundation depth and flow vector will be displayed.

86

6

Visualizing time series data

On the menu bar, select [View] - [Pre-processor].
Zoom in on an arbitrary location. (Refer to [Mouse Hints])
In the Object Browser, select [Grid] - [Grid shape] and make a check mark in the [Gridshape] box.
Select one grid cell of arbitrary location by dragging it, and right click.
Click on [Edit Coordinates].
The [Edit Grid Coordinates] will open. Find the grid node indices.

87

On the menu bar, select [Calculation Results] - [Open New Graph Window].
In the [Calculation Result] tab, select [WaterSurfaceElevation] and [Velocity (magnitude)]from [Two dimensional Data] to add [Selected Data].
Click on [OK].

Note: Unit: m3/s

88

The grid node indices from an arbitrary location that were identified before are input to the[I] and [J] box

boxes of [Controller].

Click on [Draw Setting] to set the [Draw Setting] window as below and click on [OK].
Click on [OK].
Time series graph of the arbitrary location will be displayed.

Draw Setting:Y-axis: RightLine Style:
Do not change any
settings.
Color:
Blue

89

Click on [CSV Export].
Set the [CSV Export] window as below, and click on [OK].
Click on [OK].
The time series data of an arbitrary location will be exported.

Folder: Any(The folder can be thesame as that for storing
the sample data)
Prefix: Do not change any
settings.
Region: Do not change
any settings.
Time: All Time steps90

5. Important information◆ Tsunami runup
In this tutorial, tsunami waves are generated by inputting only the water level at thedownstream end. For an accurate simulation, a wide-area analysis of tsunami wave
propagation from the wave origin should be made to input boundary conditions of watersurface elevation AND flow velocity. The objective of the example introduced by thistutorial is to assess the inundation area by a simple method. In future, we will improve
this simulation software so that the results of tsunami wave propagation analysis (water
surface elevation and flow velocity) can be input as data to the boundary condition at thedownstream end of the simulation.
For details of updates, refer to http://i-ric.org/ja/downloads.

91Chapter 4
Examples of Rainfall Induced Flooding inActual River◆ Objectives
The objectives are to use Shuttle Radar Topography Mission (SRTM) data, to simulate
and visualize the simulated flow regime, such as water surface elevation and flow velocity,
at a river when rainfall induced flooding occurs with Nays2D Flood.

◆ Outline
1. Creating the calculation gridUsing elevation data of an actual river basin, create calculation grids: 101 division points
in the transverse direction, and 131 division points in the longitudinal direction.

2. Setting the calculation conditions
Set a value for Elevation, Rainfall and Inflow Discharge. Set various other conditions
necessary for simulation.

3. Making a simulation
4. Visualizing the calculation results
Here, we introduce how to display a water depth contour map and a flow velocity vector
map.

92

1. Creating the calculation grid
1

Importing geographic data

In the Object Browser, click [Option]-[Preferences]

In [Preferences] scroll to [Background Images (Internet)]

93

Google Map can also
be used instead of
Ortho-images but it
requires registration
with Google.

Select [GSI (English) (Japan only)] and [GSI (Ortho images) (Japan Only)]94

In the Object Browser, right-click [Geographic Data]-[Elevation].Click [Import elevationfrom web].

[Select Region] screen is displayed. Drag the target part and click [Next].

[Select Coordinate System] screen is displayed.
Search with JGD and select [EPSG:2454:JGD2000/Japan Plane Rectangular CS XII].

95

Select [GSI (English)(Japan Only)] in Background Images[Zoom In] towards ‘Japan’Japan[Zoom In] towards ‘Japan’ so that you can spot ‘Sapporo’96

[Zoom In] towards ‘Sapporo’
Try to Spot ‘Chitose’ and [Zoom In] towards ‘Chitose’97

[Zoom In] towards ‘Chitose’ so that you can spot ‘Lake Utonai’

Lake Utonai

Drag the target part and click [Next].

To enlarge or
reduce the map,
click [Zoom In] /[Zoom Out] atthe bottom of
the screen.

Mouse Hint:
Ctrl+ Right Click = Pan98

[Zoom Level Setting] screen will be displayed.
Specify the zoom level and select the source

Zoom level：11
Source：USGS（SRTM）

Note: Since the resolutionof the SRTM data is 90 mmesh, even if the zoom
level is set to 11 or morehere, the data does notchangebecausethemaximum resolution has
been reached. Therefore,
the zoom level is set to 11.

Reading is successful if the shape of the watershed to be calculated is displayed on [Preprocessing Window] screen.

99When one of the items in the background image of the object browser is checked, thebackground image is displayed.
Whencreating

grids

calculation,forimportingbackground images such as
maps

and

aerialphotosmakes it possible to create
grids

that

incorporate

riverbanks and land use.
Obstacle cells and roughness
cells mentioned below can besetinreference

background image.
Since the coordinate system is selected, it is set automatically

100

to

the

2

Selecting an algorithm for creating the gridOn the menu bar, select [Grid] - [Select algorithm to create grid].
The [Select Grid Creating Algorithm] window will be displayed.

Select [Create grid from polygonal line and width] from the list under the [Select Grid
Creating Algorithm] window, and click on [OK].
Nays2D Flood generates a grid from polygonal lines and widths.

101

3

Creating a grid

Click on several points through which the grid centerline passes and press the Enter key
on your keyboard to draw a centerline.

Setting the gridcenterline
Set the gridcenterline fromthe upper
reaches of theriver (upstream)
to the sea(downstream). To
finish, press theEnter key or
double click.

In the [Grid Creation] window, make the following settings and click on [OK].

[nj] (Number of divisions in
the longitudinal direction): 120[ni] (Number of divisions in
the transverse direction): 100[W] (Grid width): 10000 m
Note: In this example, grid cellintervals di, dj are set ataround 70 and 100 m
respectively.

102

Click on [Yes] in the [Confirmation] window.

Mapping geographic data
Elevation data areapplied to the grid.

A grid will be created.

Adjusting the
calculation
grid
It is possible
to move, add
or remove any
vertexes byselecting the[Grid
Creating
Condition]even after thegrid iscreated.

103

2. Setting the calculation conditions
1

Open [Calculation Condition]

On the menu bar, select [Calculation Condition] - [Setting].
The [Calculation Condition] window will open.

104

2

Setting the inflow boundary conditions

Click on [Inflow Boundary Condition] from the [Group] list to make the following settings:
Click on [Stage at downstream time series] to edit.
The [Calculation Condition] window will open.

[Time unit of discharge/water
surface file]: Hour
[Boundary Conditions forj=1]: Inflow[Boundary Conditions forj=nj]: Outflow[Water surface atdownstream]: Free Outflow
Rainfall: withRainfall time Series: Import
Chitose_Rainfall.csv fromtest file

Click on [Import] on the [Calculation condition] window.
The [Select text file] window will be displayed.

105Select [\\SampleData\\N2F_3] - [Chitose_Rainfall.csv] and click on [Open].
Time series of rainfall data is displayed.

Click on [OK].
Here, we assume a tsunami whose wave height is 7 m and half-wavelength is 600 sec.

The time stepsof the tsunami
wave heightmust be kept at
the same value,
including at the
inflow location.

106

3

Setting the initial water surface profile

Click on [Initial Water Surface] from the [Group] list to make the following settings:

Initial water surface:constant slope
Initial water surface
slope of main channel:
0.0001

4

Setting the time

Click on [Time] from the [Group] list to make the following settings:

Output timeinterval (sec): 360
Calculation
step (sec): 1

time

Start time of output(sec): 0
Start
time
bomber (sec): 0

107

of

5

Other settings

Click on [Others] from the [Group] list to make the following settings:

Finite differential
method of advection
terms: CIP method
Maximum number of
iterations of water
surface calculation: 10
Relaxation coefficient forwater surface calculation:
0.8
Minimum water depth:
0.01
A of eddy viscosity
coefficient: 1
B of eddy viscosity
coefficient: 0

After making the settings above, click on [Save and Close] to close the window.

108

6

Inflow settings

Nays2D Flood requires at least one inflow location to be set on the upstream end.
In the Object Browser, right-click [Boundary Condition Setting] and click [Add Inflow].

In the Object Browser, click [Boundary Condition Setting]-[Add Inflow].Surround the side of theposition of the incoming discharge with polygons.

Zoom the Grid tomake it easier to
add Inflow points.

Mouse Hint: Ctrl+Mouse wheel = Zoom IN/Zoom OUT

109

Double-click to confirm and the [Boundary condition] screen will be displayed.

On the [Boundary Condition] window, input "Inflow 1" to the [Name] box, and select [Edit]
for the [Discharge time series] box under [Setting].
The [Calculation Condition] window will be displayed.

Name:
Arbitrary nameof inflow
Slope value at
inflow: 0.001
Click on[Import]on the[Calculation
Condition]
window

110

Open [\\SampleData\\N2F_3], select [BibiRIver_Inflow_dummy.csv] and click on[Open].
Time series dummy discharge data (all discharges are zero) will be displayed.

Click on [OK].

111In the menu bar, click [Grid]-[Attributes Mapping]-[Execute].

In Attribute Mapping bar -click [Check All]- [OK]

112

7

Setting the roughness

In the Object Browser, select [Geographic Data] - [Roughness] and right click to select[Add] - [Polygon].

113

Click on several points to set several vertices such that the vertices enclose the grid area,and press the Enter key on your keyboard to complete the operation.
Then, input a value of Manning's roughness coefficient for [Roughness condition] in the[Edit roughness condition value] window.

Setting Polygon
A polygon is set byenclosing the areaby the line linking
vertices made byclicking thelocation you want
to set as a vertex.
To finish, press theEnter key or double
click.
Note: When setting
Manning's
roughnesscoefficient, first you
make a polygonthat encloses all
grid nodes. In thisexample, you want
to set the sameroughnesscondition for theentire grid.

114

3. Making a simulation

On the menu bar, click

symbol to run the simulation

The [Solver Console [Nays2D Flood] (running)] window will open to start thesimulation.

115

4. Visualization of computational results
1

Open the 2D Post-processing window

On the menu bar, click [Open New 2D Post-Processing Window] icon

The [Post-processing Window (2D)] will open.

SelectBackground
Image

116

2

Visualizing the water depth

In the Object Browser, select [Nays2D Flood Grids] - [iRICZone] - [Scalar] - [Depth] bymaking a check mark in each box.
A contour map of water depth will open.

In the Object Browser, select [Nays2D Flood Grids] - [iRICZone] - [Scalar]. Right click on[Depth] to select [Property].
The [Scalar Setting] window will open.

117

On the [Scalar Setting] window, make the following settings and click on [OK]:Value range:
Remove ☑ from
[Automatic]
Max: 5
Min: 0.05
Remove ☑ from [Filllower area]
Colors: Do not change
any settings
Transparent: Do notchange any settings.
Color Bar Setting: Do notchange any settings.

The contour map is easier to see now.

118

3

Visualizing flow vector

In the Object Browser, select [Nays2D Flood Grids] - [iRICZone] - [Arrow] - [Velocity].
In the Object Browser, select [Nays2D Food Grids] - [iRICZone] - [Arrow]. Right click on[Arrow] to select [Property].
The [Contour Setting] window will open.

On the [Contour Setting] window, make the following settings and click on [OK]:LengthRemove ☑ from [Auto]
Standard value: 8.00
Length on screen: 40
Minimum value to draw:
0.008
Sampling:
Sampling rate (Idirection): 2
Sampling rate (Jdirection): 2
Color:Do not change any
settings.

119

4Visualizing animated changes

On the menu bar, Click [restart]
On the menu bar, Click []Animated changes in inundation depth and flow vector will be displayed.

120

To Reader● Please reference the iRIC software, if you publish a paper withresults from the iRIC software.
● The datasets provided at the Web site are sample data. Therefore you
can use it for a test computation.
● Let us know your suggestions, comments and concerns at
http://i-ric.org.

iRIC Software
Nays2D Flood Examples
Editors

and Yasuyuki SHIMIZU (Hokkaido Univ., Japan)

Editing

writers

Eiichi SUZUKI (Hokkaido Univ., Japan)

Editing

Satomi KAWAMURA (Hokkaido Univ., Japan)

Editing

Takuya INOUE (CERI., Japan)

Editing/Writing

Toshiki IWASAKI (Hokkaido Univ., Japan)

WritingMichihiro HAMAKI(Kaihatsu Koei Co., Ltd., Japan) Writing
Tomohiko Yoshida (Docon Co.,Ltd., Japan)

WritingJagriti Mishra (CERI., Japan)

Writing

Kensuke OMURA (Hokkaido Univ., Japan)
Eriko KAKEGAWA (Hokkaido Univ., Japan)
Supported byRiver center of Hokkaido, Japan.

121