iRIC Software
Changing River Science

Nays2D Flood
Solver Manual
Directed by Yasuyuki Shimizu
Edited by Takuya Inoue
Eiichi Suzuki
Satomi Kawamura
Toshiki Iwasaki
Michihiro Hamaki
Kensuke Omura
Eriko Kakegawa
Tomohiko Yoshida

Last Update:2024.09.10
Release Date: 2015. 06.23

Copyright 2011 iRIC Project All Rights Reserved

Contents
I. OUTLINE .................................................................................................................... 1
I.1 Nays2D Flood is .... ................................................................................................. 1
I.2 Features of the flow field simulation model............................................................ 2
II. BASIC EQUATIONS ................................................................................................ 3
II.1 Basic flow equations .............................................................................................. 3
II.1.1 Basic equations in a rectangular coordinate system ...................................... 3
II.1.2 Mapping to a general curvilinear coordinate system ..................................... 4
II.1.3 Basic equations in a general curvilinear coordinate system .......................... 6
II.2 Simulation method applied to turbulent flow fields .............................................. 8II.2.1 Zero-equation model ....................................................................................... 8
II.3 Simulation method applied to bottom friction ....................................................... 9II.4 Simulation method applied to a box culvert ........................................................ 10
II.4.1 Roles of a box culvert.................................................................................... 10
II.4.2 Simulation method ........................................................................................ 10
II.4.3 Equations for calculating the discharge through the culvert ....................... 14
II.5 Simulation method for a sluice pipe .................................................................... 15
II.5.1 Roles of a sluice pipe .................................................................................... 15
II.5.2 Simulation method ........................................................................................ 15
II.5.3 Equations for calculating the discharge through a sluice pipe .................... 21
II.6 Simulation methods for pumps ........................................................................... 22II.6.1 Roles of pumps .............................................................................................. 22II.6.2 The simulation method .................................................................................. 22
III. CALCULATION CONDITION ........................................................................... 24
III.1 Explanation of names of items in [Boundary Conditions] ................................. 24
III.2 Setting inflow/outflow boundary conditions ...................................................... 25
III.3 Setting initial water surface profile .................................................................... 27
III.4 Setting time condition......................................................................................... 28
III.5 Other settings ...................................................................................................... 29
III.6 Setting the inflow river ....................................................................................... 31
III.7 Setting riverbed roughness coefficient ............................................................... 33
III.8 Setting obstacles ................................................................................................. 34
III.9 Setting building occupancy ratio by area ........................................................... 35
III.10 Setting for a box culvert ................................................................................... 37
III.11 Setting for a sluice pipe .................................................................................... 40
III.12 Setting for a pump ............................................................................................ 43
IV. INPUT/OUTPUT FILES ....................................................................................... 46
IV.1 Input file for grid cell numbers of inflow ........................................................... 46
IV.2 Discharge file (Inflow boundary conditions) ..................................................... 47
IV.3 Discharge file (boundary conditions for banks) ................................................. 48

I. Outline
I.1 Nays2D Flood is ....
Nays 2D Flood is a flood flow analysis solver that relies on unsteady 2-dimensional
plane flow simulation using boundary-fitted coordinates 1 as the general curvilinear
coordinates. This solver adopts the 2-dimensional plane flow simulation of the Nays2D
Solver developed by Professor Yasuyuki Shimizu of Hokkaido University for flood
flow analysis.
The solver easily enables the user to set the inflow conditions of an arbitrary number of
inflow rivers that enter from the upstream end or sides of a river. It has been applied to
the flood flow analysis of small/mid-scale rivers. Because the solver does not require
river channel data, it is also used for the flood process analysis of primitive rivers andrivers in developing countries.

1

Boundary-fitted coordinates are set along the boundaries because a rectangular
Cartesian coordinate system has difficulty reproducing complicated, winding
boundaries. The governing equations in the rectangular Cartesian coordinate system are
mapped to the general curvilinear coordinate system and are calculated. Because of its
features, the system is also called a boundary-fitted coordinate system.
1

I.2 Features of the flow field simulation model
The data needed for an overflow calculation by Nays 2D Flood are a topographic data,
and data of inflow discharge and roughness of each river or each inflow point. The basic
process to begin the overflow calculation is the following;
Create calculation
grids

Set calculation
condition-load topographic data

-set inflow discharge-set roughness

Run calculation

And in this model, as necessary, it is able to consider or set as followings;① The use of a general curvilinear coordinate system enables complicated boundaries
and riverbed topography to be incorporated directly.
② As the difference method of the advection terms of equations of motion, the user
can choose between upwind scheme (first-order accuracy) and constrainedinterpolation profile (CIP) 2.
③ It enables various parameters to be set for the boundary conditions of the
upstream/downstream ends, such as the water surface elevation of the downstream
end and the flow velocity of the upstream end.
④ As the boundary condition for a bank, the user can choose between [Inflow] and[Outflow]. By selecting [Inflow], it is possible to reproduce complicated flooding
situations, such as bank overtopping on several rivers.
⑤ As [Initial Water Surface Profile], the user can choose between [Water depth = 0]
and [Constant slope].
⑥ The bottom friction is set using Manning's roughness coefficient. The Manning's
roughness coefficient can be set for each grid cell.
⑦ Obstacles in the area subject to simulation can be incorporated into the simulation
by grid cell. A flag is set for each grid cell to define the obstacle. This enables theeasy incorporation of bridge piers and other river structures into the simulation.
⑧ You can incorporate discharge by a box culvert, a sluice pipe or a pump into thesimulation.

2

A high-order accurate finite difference method. It interpolates a third-order polynomial,
reduces numerical diffusion and enables local, high-accuracy interpolation.
2

II. Basic Equations
II.1 Basic flow equations
II.1.1 Basic equations in a rectangular coordinate system
The following are the basic equations in a rectangular coordinate system (x、y) before
those equations are mapped to a general curvilinear coordinate system.
[Equation of continuity]∂h ∂ (hu ) ∂ (hv )
+
+
=q+r
∂t
∂x
∂y

(1)

[Equations of motion]( )∂H τ x∂ (uh ) ∂ hu 2 ∂ (huv )+= −hg− + Dx
+
∂t
∂x
∂y
∂x ρ

( )

∂ (vh ) ∂ (huv ) ∂ hv 2
∂H τ y++= −hg− + Dy
∂t
∂x
∂y
∂y ρ

(2)

(3)

where,

τx= C f u u 2 + v2
ρτy
= C f v u 2 + v2
ρ

(4)

Dx =

∂  ∂ (uh )  ∂  ∂ (uh ) 
νt
νt
+
∂x 
∂x  ∂y 
∂y 

(5)

Dy =

∂  ∂ (vh )  ∂  ∂ (vh ) 
νt
+
νt
∂x 
∂x  ∂y 
∂y 

(6)

where, h is water depth, t is time, u is flow velocity in the x direction, ν is flow velocity
in the y direction, g is gravitational acceleration, H is water surface elevation, τx isriverbed shear stress in the x direction, τy is riverbed shear stress in the y direction, Cf isriverbed friction coefficient νt is eddy viscosity coefficient, ρ is the density of water, q is
inflow through a box culvert, a sluice pipe or a pump per unit area and r is rainfall.

3

II.1.2 Mapping to a general curvilinear coordinate system
Next is the mapping of basic equations of 2-dimensional plane flow in a rectangularcoordinate system to a general coordinate system (ξ, η). By mapping the equations to a
general coordinate system, the simulation mesh can be set to any shape according to theboundary conditions. The following is the method of mapping from a rectangularcoordinate system to a general curvilinear coordinate system.
∂ ∂ξ ∂ ∂η ∂=+∂x ∂x ∂ξ ∂x ∂η

(7)∂ ∂ξ ∂ ∂η ∂=+∂y ∂y ∂ξ ∂y ∂η

(8)

 ∂ 
∂ 


 
ξ
η
x  ∂ξ  ∂x  =  x ∂   ξ y η y  ∂   ∂y  ∂η 

(9)orwhere,

ξx =

∂η
∂η
∂ξ
∂ξ
, ξy =, ηx =, ηy =
∂y
∂x
∂y
∂x

(10)

As well as,∂x ∂ ∂y ∂∂+=∂ξ ∂ξ ∂x ∂ξ ∂y(11)∂∂x ∂ ∂y ∂=+∂η ∂η ∂x ∂η ∂y

(12)

 ∂ 


 ∂ξ  =  xξ ∂   xη

 
η
∂



(13)

or

∂ 
 
yξ  ∂x yη  ∂   ∂y 

where,
xξ =

∂x
∂x
∂y
∂y
, xη =, yξ =, yη =
∂η
∂ξ
∂η
∂ξ

4

(14)

Hence,

 ∂ 


 ηy
1
 ∂ξ  = ∂  ξ η −ξ η −ξy
y x 
x y


 ∂η ∂  − η x  ∂x   xξ=
ξ x  ∂   xη  ∂y ∂  yξ  ∂x yη  ∂   ∂y 

(15)

Assuming J = ξ xη y − ξ yη x , then,1  ηyJ  − ξ y− η x   xξ
=
ξ x   xη

yξ 

yη 

(16)

Consequently,
1111xξ = η y , yξ = − η x , xη = − ξ y , yη = ξ x
J
J
J
J
or

(17)

η y = Jxξ , η x = − Jyξ , ξ y = − Jxη , ξ x = Jyη

(18)

J = ξ xη y − ξ yη x = J 2 (xξ yη − xη yξ )

(19)

Thus,
J=

1
xξ yη − xη yξ(20)Assuming ( u ξ , uη ) are (ξ, η) components of flow velocity, thenu ξ = ξ xu + ξ y v(21)uη = η x u + η y v(22)

 u ξ   ξ x ξ y  u 
 =
 
 u η  η x η y  v 
 
  

(23)

u  1  η y  = 
 v  J  −η x

(24)

or

− ξ y  u ξ  ξ x  u η 5

II.1.3 Basic equations in a general curvilinear coordinate system
The following are the basic equations after the equations in a rectangular coordinate
system (x, y) are mapped to a general curvilinear coordinate system.
[Equation of continuity]∂  h  ∂  hu ξ  ∂  hu η  q + r
=

+

 +
J
∂t  J  ∂ξ  J  ∂η  J 

(25)

[Equations of motion]
∂u ξ
∂u ξ
∂u ξ
+ uη
+ uξ
+ α 1u ξ u ξ + α 2 u ξ u η + α 3u η u η =
∂ξ
∂t
∂η

∂H
∂H 
− g  ξ x2 + ξ y2
+ (ξ xη x + ξ yη y )
∂ξ
∂η 


(

uξ
−Cf
hJ

)

(η u − ξ u ) + (− η u + ξ u ) + D
y

ξ

y

η 2

x

ξ

x

η 2

ξ

(26)

∂u η
∂u η
∂u η
+ uξ
+ uη
+ α 4u ξ u ξ + α 5u ξ uη + α 6uη uη =
∂t
∂ξ
∂η

∂H 
∂H
+ η x2 + η y2
− g (η xξ x + η y ξ y )
∂η 
∂ξ


(

uη
−Cf
hJ

)

(η u − ξ u ) + (− η u + ξ u ) + D
y

ξ

y

η 2

x

ξ

x

η 2

η

(27)

where,

α1 = ξ x


∂2x
∂2 y
∂2x
∂2 y 
∂2x
∂2 y


2
ξ
α
ξ
ξ
ξ
ξ
α
=
+
+
+
=
,
,
2
3
x
y
y
y
 x ∂ξ∂η∂ξ∂η 
∂η 2
∂η 2
∂ξ 2
∂ξ 2


(28)

α4 =ηx


∂2x
∂2 y
∂2x
∂2 y 
∂2x
∂2 y


+
η
,
α
=
2
η
+
η
,
α
=
η
+
η
y
5
y
6
x
y
 x ∂ξ∂η∂ξ∂η 
∂ξ 2
∂ξ 2
∂η 2
∂η 2


(29)

Dξ =


∂u ξ ∂    ∂u ξ∂
∂u ξ  ∂    ∂u ξ∂
 (30) +  ξ y ν t  ξ y
+η y
+η y
 ν t  ξ x ξ x+η x+ηx∂η ∂η    ∂ξ∂η   ∂ξ∂η    ∂ξ
 ∂ξ
Dη =


∂u η ∂    ∂u η∂
∂u η  ∂    ∂u η∂
 (31)
 +  ξ y ν t  ξ y
+η y
+η y
 ν t  ξ x ξ x+η x+ηx∂η ∂η    ∂ξ∂η   ∂ξ∂η    ∂ξ
 ∂ξ

6

ξx =

∂ξ
∂ξ
∂η
∂η
, ξy =, ηx =, ηy =
∂x
∂y
∂x
∂y

(32)

u ξ = ξ xu + ξ y v , uη = η x u + η y v

J=

(33)

1
xξ yη − xη yξ

(34)

Because when developed, the numbers of terms are huge, the following conditions are
assumed for the advection terms of D ξ and Dη in the equations of motion in a generalcurvilinear coordinate system to simplify the calculation.
1) The second derivative of a metric parameter is locally set as zero.
2) A quasi-general curvilinear coordinate system is adopted locally as for theadvection terms.
Consequently, the advection terms can be expressed by approximation as follows:−Dξ ~∂u ξ ∂ ∂u ξ  ∂ ν tη r2
ν t ξ r2
 +
∂η 
∂ξ 
∂ξ  ∂η 

(35)

Dη ~
−

∂u η ∂ ∂u η  ∂ ν tη r2
ν t ξ r2
 +
∂ξ 
∂ξ  ∂η 
∂η 

(36)

where, ξ r and η r are parameters expressing the local ratio of grid size in a generalcurvilinear coordinate system over the corresponding distance on actual topography,
and are defined by the following equation:

∆ξ
∆η
=ηr
~ = ξr ,
∆η~
∆ξ

(37)

To derive the approximate equations of D ξ and Dη above are based on the following
relationships by assuming a local orthogonal relationship between axes.
~~(38)
ξ x2 + ξ y2 = ξ r2 ξ x 2 + ξ y 2 = ξ r2 sin 2 θ + cos 2 θ = ξ r2

(

)

(~

(

~

)

)

ξ xη x + ξ yη y = ξ rη r ξ xη~x + ξ yη~y = ξ rη r (− cos θ sin θ + cos θ sin θ ) = 0()

η x2 + η y2 = η r2 η~x 2 + η~y 2 = η r2 (sin 2 θ + cos 2 θ ) = η r2

(

)

(40)

~
~
J = ξ xη y − ξ yη x = ξ rη r ξ xη~y − ξ yη~x = ξ rη r sin 2 θ + cos 2 sin θ = ξ rη r()

Where, θ is the angle between x-axis and ξ -axis (or y-axis and η -axis).

7

(39)

(41)

II.2 Simulation method applied to turbulent flow fields
Turbulent flow is irregular flow involving many small and large eddies. Nays2D Floodemploys a zero-equation model for turbulent flow field simulation.

II.2.1 Zero-equation model
The eddy viscosity coefficient νt is generally expressed by the multiplying therepresentative velocity of turbulent flow ν and the representative length l of the
turbulent flow. Therefore,(42)

vt = vl

In a flow field where water depth and riverbed roughness gently change in the crosssectional direction, if we assume that eddy viscosity coefficients in the vertical and thehorizontal directions have the same order and that bottom friction velocity and water
depth are the dominant factors in momentum transfer, then the eddy viscosity
coefficient νt is given by the following equation.

ν t = au* h(43)where, a is a proportional constant.
Fisher1) and Webel and Schatzmann2) found in their experiments that the value of a inrelation to momentum transfer in the vertical direction is about 0.07. Here, eddy
viscosity coefficient νt is given by the following equation using the Karman constantκ=0.4):

κν t = A u* h + B(44)
6
Since this modeling does not require any transportation equation for turbulence statistics,
it is called the "zero-equation model." A and B are a user defined parameters for an eddy
viscosity coefficient. Default value of A and B is 1 and 0, respectively. In horizontal two
dimensional flow calculations, since three dimensional flow structures are completely
neglected, unrealistic horizontal large vortices tend to be generated. The user can adjust
A and B for modelling such vortices.

8

II.3 Simulation method applied to bottom friction
Nays-2D Flood sets the bottom friction by using the Manning's roughness coefficient. In
Equation (4), riverbed shear stress τx and τy are expressed by riverbed friction coefficient
Cf. The relationship between riverbed friction coefficient Cf and the Manning's
roughness coefficient nm is as follows:gn
C f = 1m
h3

2

(45)

nm can be given to each grid cell by setting [Cell attributes].

<References>

1) Fisher, H.B.: Longitudinal Dispersion and Turbulent Mixing in Open-Channel Flow,
Annual Review of Fluid Mechanics, Vol. 5, pp.59-78, 1973.
2) Webel, G., Schatzmann, M.: Transverse Mixing in Open Channel Flow, Journal of
Hydraulic Engineering, Vol. 110, No. 4, pp. 423-435, 1984.

9

II.4 Simulation method applied to a box culvert
II.4.1 Roles of a box culvert
A box culvert is a closed conduit buried in a road or bridge embankment. When morethan two box culverts with the same dimensions are applied, to obtain the total drainage
flow rate, first calculate the drainage discharge of one unit of box culvert, and thenmultiply that calculation result by the number of box culverts.

II.4.2 Simulation method
For simulation, the entrance and exit of the box culvert are regarded as a unit, anddifferent cells are set for entrance and for the exit. The drainage flow rate of the box
culvert is determined by the difference in water level between the entrance cell and theexit cell. Refer to the following schematic.
Entrance

Embankment

Exit

Entrance

Entrance

water level

water depth

Box culvert

Entrance

Elevation ofExitelevation

structureelevation

E.L.

above thebottom above

above the(datum)datum

the datum

datum

Exit water

Exit water

depth

level

Embankment
Width (inside)

Height (inside)

Elevation of structure
bottom above the datum

E.L. (datum)

Figure II－1 Schematic of a box culvert (side view and section view)

10

The water levels at the entrance and the exit of a box culvert are used in simulations asfollows.
Entrance water level
Entrance water level= Entrance elevation above the datum＋ Entrance water depth
Exit water level
Exit water level = Exit elevation above the datum ＋ Exit water depth
The simulation method for discharge of a culvert is as follows.
① When there is no water
Entrance

Embankment

Entrance

Exit

Embankment

Exit⇒ No water flow
② When “Entrance water level > Exit water level” and “Entrance water level ≦Elevation of structure bottom above the datum”

Entrance

Embankment

Entrance

Exit⇒ No water flow

11

Embankment

Exit

③ When “Entrance water level < Exit water level” and “Exit water level ≦ Elevationof structure bottom above the datum”
Entrance

Embankment

Exit

Entrance

Embankment

Exit⇒ No water flow
④ When “Entrance water level > Exit water level” and “Entrance water level >Elevation of structure bottom above the datum”
Entrance

Embankment

h1

Exit

Discharge

Entrance

Embankment

h1

h2

Exit

Dischargeh2

The higher water depth between entrance and exit (h1)
= Entrance water level － Elevation of structure bottom above the datum
The lower water depth between entrance and exit (h2)
= Exit water level － Elevation of structure bottom above the datum⇒Water flows from entrance to exit. Discharge through a sluice pipe is calculated byequations (50) and (51) in II.4.3.
⑤ When “Entrance water level < Exit water level” and “Exit water level > Elevationof structure bottom above the datum”
Entranceh2

Discharge

Embankment

Exit

Entrance

h1

h2

12

Discharge

Embankment

Exit

h1

The higher water depth between entrance and exit (h1)
= Exit water level － Elevation of structure bottom above the datum
The lower water depth between entrance and exit (h2)
= Entrance water level － Elevation of structure bottom above the datum⇒Water flows from exit to entrance. Discharge through a sluice pipe is calculated byequations (50) and (51) II.4.3.
Note: Even when the elevation of structure bottom is lower than the entrance or the exit
elevation, the higher water depth between entrance and exit (h1) or the lower water
depth between entrance and exit (h2) is obtained as the elevation difference from theelevation of the structure bottom.
Entrance

Embankment

Entrance

Exit

h1

Embankmen

Exith1
Discharge

h2

h2

13

Discharge

II.4.3 Equations for calculating the discharge through the culvert
Discharge through the culvert is calculated by the equations below. The initial setting is
submerged flow and free outflow. Any values can be set for the discharge coefficients
C1 and C3. Their initial values are set as C1=0.75 and C3=0.79.
When h2 ≥ H , Q = nC1 BH 2 g (h1 − h2 ) is submerged flow

(46)

When h2 < H , Q = nC3 Bh2 2 g (h1 − h2 ) is free outflow(47)

However, when h1 h2 ≥ 3 2 , h2 = 2/3h1.
Here, Q is discharge (m3/s), n is the number of box culverts, B is width (m), H is height(m), h1 is the water depth at the entrance/exit whose elevation is higher than theelevation of the structure bottom above the datum (m), h2 is the water depth at theentrance/exit whose elevation is lower than the elevation of structure bottom above thedatum (m) and g is the gravitational acceleration.
Note: As an option, you can add a case of subsurface flow. Any values can be set for thedischarge coefficients C1, C2 and C3. Their initial values are set as C1=0.75, C2=0.51
and C3=0.79.
When h2 ≥ H ,Q = nC1 BH 2 g (h1 − h2 )submerged flow

When h2 < H

h1 H ≥ 3 2 ,Q = nC 2 Bh2 2gh1

interflow

When h2 < H

h1 H < 3 2 ,Q = nC3 Bh2 2 g (h1 − h2 )free outflow

However, when h1 h2 ≥ 3 2 , h2 = 2/3h1.

14II.5 Simulation method for a sluice pipe
II.5.1 Roles of a sluice pipe
A sluice pipe is a closed conduit that is buried transverse to the embankment. It has agate on the river channel side. At normal times, the gate is open to drain water from thearea protected by the embankment. At times of flooding, the gate is closed to prevent
river water from flowing back into the area protected by the embankment. When morethan two sluice pipes of the same size are applied, to obtain the total drainage discharge,
first calculate the drainage discharge of one unit of sluice pipe, and then multiply that
calculation result by the number of sluice pipes.

II.5.2 Simulation method
For simulation, the sluice pipe entrance is set on the protected side of the embankment(hereinafter: “the inside”) and the sluice pipe exit is set on the river channel side of theembankment (hereinafter: “the outside”). Different cells are set for entrance and exit.
The discharge through a sluice pipe is determined by the differences in water levels
between the entrance cell and the exit cell, or the open or closed status of the gate. Referto the following sluice pipe schematic.

Entrance

Embankment

Exit(inside)Entrance

Entrance

water level

water depth(outside)

Sluice pipe

Exit water

Exit water

depth

level

Entrance

Elevation of

Exit elevation

elevation above

structure bottom

above theE.L.

the datum

above the datum

datum(datum)15

Embankment
Width (inside)

Height (inside)

Elevation of structure bottom above the datum

E.L.
(datum)Figure II－2 Schematic of a sluice pipe (side view and section view)

16

The water levels at the entrance and the exit of the sluice pipe are used for calculation as
follows.
・Entrance water level (inside)
Entrance water level= Entrance elevation above the datum ＋ Entrance water depth・Water level at the exit (outside)【When the water level at exit is not set】
Exit water level = Exit elevation above the datum＋ Exit water depth【When the water level at the exit is set】
Exit water level = The water level input by the time series
Simulation methods for discharge through a sluice pipe when the sluice pipe
“automatically opens/closes” and when the “open/close of the sluice pipe is set by thedata” are as follows.
【When the sluice pipe automatically opens/closes】① When there is no water
Entrance

Embankment(inside)Exit

Entrance(outside)(inside)Embankment

Exit(outside)

Sluice pipe (open)

Sluice pipe (open)⇒ No water flow
② When “Entrance water level > Exit water level” and “Entrance water level ≦Elevation of the structure bottom above the datum of the sluice pipe”
Entrance

Embankment(inside)Exit

Entrance(outside)(inside)Sluice pipe (open)

Embankment

Exit(outside)

Sluice pipe (open)⇒ No water flow17

③ When “Entrance water level > Exit water level” and “Entrance water level >Elevation of the structure bottom above the datum of the sluice pipe”
Entrance(inside)h1

Embankment

Sluice pipe

Exit

Entrance(outside)(inside)Discharge(open)

h1

h2

Embankment

Exit(outside)

Sluice pipe
Discharge(open)

h2

The higher water depth between entrance and exit (h1)
= Entrance water level － Elevation of the structure bottom above the datum
The lower water depth between entrance and exit (h2)
= Exit water level － Elevation of the structure bottom above the datum⇒Water that flows from the entrance to the exit discharge through a sluice pipe iscalculated by equations (50) and (51) II.4.3.
④ When “Entrance water level < Exit water level”
Entrance(inside)Embankment

Exit

Entrance(outside)(inside)Embankment

Exit(outside)

Sluice pipe

Sluice pipe

(closed)(closed)⇒No water flows, because the sluice pipe gate is closed to prevent backflow from theriver.
⑤ When “Entrance water level < Exit water level” and “Entrance water level >Elevation of the structure bottom above the datum of the sluice pipe”
Entrance(inside)Embankment

Exit(outside)

Sluice pipe (closed)18⇒ No water flows when there is certain entrance water depth and the entrance waterlevel is lower than the exit elevation above the datum.
【When open/close of a sluice pipe is set by data】① When there is no water
Entrance

Embankment(inside)Exit

Entrance(outside)(inside)Sluice pipe (open)

Embankment

Exit(outside)
Sluice pipe
(open)⇒ No water flow
② When “Sluice pipe is closed”

Entrance(inside)Embankment

Exit (outside)

Entrance(inside)Embankment

Exit (outside)

Sluice pipe

Sluice pipe

(closed)(closed)⇒ No water flow
③ When “Sluice pipe open”, “Entrance water level > Exit water level” and “Entrance
water level ≦ Elevation of the sluice pipe bottom above the datum”
Entrance

Embankment

Exit (outside)

Entrance(inside)Embankment

Exit (outside)(inside)Sluice pipe (open)

Sluice pipe (open)⇒ No water flow

19

④ When “Sluice pipe open”, “Entrance water level < Exit water level” and “Exitwater level ≦ Elevation of the sluice pipe bottom above the datum”
Entrance

Embankment

Exit (outside)

Entrance(inside)Embankment(inside)Exit (outside)

Sluice pipe

Sluice pipe (open)(open)⇒ No water flow
⑤ When “Sluice pipe open”, “Entrance water level > Exit water level” and “Entrance
water level ≦ Elevation of the sluice pipe bottom above the datum”
Entrance(inside)h1

Embankment

Exit

Entrance(outside)(inside)Sluice pipe
(open)

Dischargeh1

h2

Embankment

Exit(outside)

Sluice pipe
(open)

Discharge

The higher water depth between entrance and exit (h1)
= Entrance water level － Elevation of structure bottom above the datum
The lower water depth between entrance and exit (h2)
= Exit water level － Elevation of the structure bottom above the datum⇒Water that flows from the entrance to the exit discharge through a sluice pipe iscalculated by equations (50) and (51) II.4.3

20h2

⑥ When “Sluice pipe open”, “Entrance water level < Exit water level” and “Exitwater level > Elevation of the sluice pipe bottom above the datum”
Entrance

Embankment

Entrance

Exit (outside)(inside)(inside)h2Discharge

Sluice pipe

Embankment

Exit(outside)

Sluice pipeh1h2

(open)

h1(open)

Discharge

The higher water depth between entrance and exit (h1)
= Exit water level － Elevation of the structure bottom above the datum
The lower water depth between entrance and exit (h2)
= Entrance water level － Elevation of the structure bottom above the datum⇒ Water that flows from the exit to the entrance discharge through a sluice pipe iscalculated by equations (50) and (51) II.4.3.
Note: When the elevation of the structure bottom above the datum is lower than theentrance elevation or the exit elevation, the higher water depth between entrance andexit (h1) and the lower water depth between entrance and exit (h2) are calculated as thedifferences from the elevation of the sluice pipe bottom above the datum.
Entrance(inside)h1

Embankment

Exit(outside)

Entrance(inside)Embankment

Sluice pipe
(open)

Sluice pipe (open)
Discharge h2

h2

Exit
(outside)h1

Discharge

II.5.3 Equations for calculating the discharge through a sluice pipe
The same equations used for calculating the discharge of a box culvert are used. (Refer
to II.4.3.)

21

II.6 Simulation methods for pumps
II.6.1 Roles of pumps
Pumps drain water in the area protected by the embankment to the river channel. Pumps
are installed at drainage pumping stations and on pumping vehicles. A pump starts
operating when the water level inside the area protected by the embankment reaches thepreset operation start water level, and it stops operating when the water level reaches thepreset operation stop water level that is determined in consideration of submergence andother factors that prevent the pump from operating.

II.6.2 The simulation method
For the simulation, the side of the pump in the area protected by the embankment is set
as the “entrance” and the side of the pump on the river channel as set as the “exit”;
different cells are set for entrance versus exit. A pump starts operating when the“entrance water level” on the side of the pump in the area protected by the embankment
reaches the operation start level, and it stops operating when the water level reaches thepreset operation stop level. The latter is set in consideration of situations when the pumpis inoperable, such as due to submergence. Pump displacement is based on the
maximum displacement; however, no more water than exists at the entrance cell isdischarged. A pump schematic is shown below.
Pump’s drainage discharge
Entrance(inside)Entrance
water level

Exit(outside)

Embankment

Entrance
water depth

Exit water
depth
Exit elevation
above the datum

Entrance elevation
above the datum

Exit water
level

E.L.
(datum)Figure II－3 Schematic of a pump (side view)

22

The calculation methods of pump drainage discharge for “when there is an entrance”
and “when there is only exit” are shown below.
【When there is an entrance】
Instances of “when there is an entrance” can be with or without an exit. When there isan entrance and an exit, the pump’s drainage discharge at the entrance is given to theexit. “When there is only an entrance” means that water is discharged other than in thecalculation domain. The pump’s drainage discharge at the entrance cell decreases, butwater is not discharged into any other cells. The entrance pump discharge can be set byeither of two methods: “automatic setting of the pump’s drainage discharge” or “datasetting of the pump’s drainage discharge”.
・When the pump’s drainage discharge is set automatically①Entrance water level < Pump operation start water level⇒ No pump flow
②Pump operation start water level ≦ Entrance water level < Pump operation stop
water level⇒ Pump drainage discharge is the maximum displacement of the pump.
(However, no more water than exists at the entrance cell is discharged.)③Pump operation stop water level ≦ Entrance water level⇒ No pump flow
Entrance(inside)Pump operation
stop water level
Pump operation
start water level③

Pump's drainage discharge

Exit(outside)②①

・When the pump drainage discharge is set by data
The pump drainage discharge is given by the time-series data of pump displacement.
(However, no more water than exists at the entrance cell is discharged.)【When there is only exit】
The time-series data of pump displacement are given to the exit.

23III. Calculation condition
In this chapter, the calculation conditions of Nays2D Flood are explained with setting
dialogs of iRIC calculation conditions.

III.1 Explanation of names of items in [Boundary

Conditions]

Boundary conditions for j=nj

(1, nj)Inflow boundary

Outflow boundary(ni,nj)j(1, 1)i

Boundary conditions for j=1(ni, 1)Figure III-1 Grid cell modeling
Boundary conditions need to be set for each four lines of a grid.
- "[Inflow Boundary Conditions]" mean the boundary conditions of the line
between (1, 1) and (1, nj) of the grid. The line between (1, 1) and (1, nj) must
be set as [Inflow]. Here, "discharge," which is necessary for calculation, isgiven.
- "Boundary conditions for j=1" means the boundary conditions of the line
between (1, 1) and (ni, 1) of the grid. Either [Inflow] or [Outflow] can be set
for the line between (1, 1) and (ni, 1).
- "Boundary conditions for j=nj" means the boundary conditions of the line
between (1, nj) and (ni, nj) of the grid. Either [Inflow] or [Outflow] can be set
for the line between (1, nj) and (ni, nj).
- "Outflow boundary conditions" means the boundary conditions of the line
between (ni, 1) and (ni, nj) of the grid. The line between (ni, 1) and (ni, nj)
must be set as [Outflow]. Here, "water surface elevation," which is necessary
for calculation, is given.

24

III.2 Setting inflow/outflow boundary conditions

Figure III-2 Dialog for setting [Inflow/ Outflow Boundary Conditions]#

Table III-1 Items of [Inflow/ Outflow Boundary Conditions]
Item
How to set the item
Notice1Time unit ofdischarge/water
surface file

Input time unit for the time seriesof discharge and of water surface
elevation of downstream end.
[Second] or [Hour] can be selected.

2

Boundary
Conditions for
j=1

Select from [Wall], [Free outflow]and [Inflow].

3

Boundary
Conditions for
j=nj

Select from [Wall], [Free outflow]and [Inflow].)

Water surface atthe downstream

Set water surface at thedownstream. Select between[Constant value], [Read from a file]and [Free outflow].

4

25

The same time unit isapplied to time series of
inflow discharges fromthe bank sides and thewater surface elevation
at the downstream end.

The data format is given
in Chapter III-6 Setting
the inflow river files.

5Constant value(m)

Input it when [Constant value] isselected for the water surface
elevation at the downstream end..

6

Stage atdownstream
time series

Input it when [Read from a file] isselected for the water surface
elevation at the downstream end.

7

Rainfall8

Rainfall timeseries (mm/h)(i.e., time series
file of rainfall)

Set with/without rainfall. Selectbetween [with] and [without.]

Input water surface
elevation (m) for thecolumn of [Water
Surface Elevation].
The [Time] column
should be set the same as
the time column of thedischarge file.

When [with] is selected for[Rainfall], click on [Edit] to set[Rainfall hyetograph].

Notes:
1) Grid cells not specified as "Inflow" cells are regarded as "Wall."2) "Wall" means a boundary condition where no inflow/outflow occurs.
3) Free outflow means the simulation results for the grid cell adjacent to the boundary
grid cell are given to the boundary grid cell as its boundary condition.

26

III.3 Setting initial water surface profile

Figure III-3 Dialog for setting [Initial water surface]#
1

2

Table III-2 Items for setting [Initial water surface]
Item
How to set the item
NoticeInitial water
surface profile

Initial water
surface slope ofmain channel

Select between [Constant slope (line)]and [Depth =0].

Input it when [Constant slope (line)] isselected for [Initial water surface
profile].
The water surface slope is set as aconstant slope whose origin is thewater surface elevation of thedownstream end.

27

A flat surface
elevation can be set
by setting the slope
gradient as zero.
The location where
the ground elevation
is higher than theinitial water surface
profile has a water
depth of zero.

III.4 Setting time condition

Figure III-4 Dialog for setting [Time Settings]
#

Item

1

Output timeinterval (sec)Table III-3 Items for setting [Time settings]
How to set the item

NoticeInput the output time interval.

2

Calculation time
step (sec)

Set the time interval of calculation
step.

3

Start time of output(sec)Input the start time of the output.

28

Importantparameter todetermine theefficiency andstability ofcalculation.

III.5 Other settings

Figure III-5 Dialog for setting [Other information]
Table III-4 Items for setting [Other information]
How to set the item
Notice#Item

1Finite differential
method ofadvection terms

Select between [Upwind
scheme] and [CIP method]3).

2

Maximum numberof iterations ofwater surface
calculation

Number of iterations of water
surface calculation.

3

Relaxation
coefficient forwater surface
calculation

Relaxation coefficient forwater surface calculation.

4

Minimum water
depth

Minimum water depth forwater surface calculation.

5

A for eddy
viscosity
coefficient (k/6u*hx A+B)

Set parameter “A” of eddy
viscosity coefficient (k/6u*h x
A+B).

6

B for eddy
viscosity
coefficient (k/6u*hx A+B)

Set parameter “B” of eddy
viscosity coefficient (k/6u*h x
A+B).

29

Adjust when the water
surface calculation is notstabilized.

7

Number of threads
for parallel
computation (onlyfor multi-core PC)

Set the number of threads forparallel computation.

<References>

3) Yabe, T., Ishikawa, T.: A Numerical Cubic-Interpolated Pseudoparticle (CIP)
Method without Time Splitting Technique for Hyperbokic Equations, Journal of the
Physical Society of Japan, Col.59, No.7, pp.2301-2304, 1990.

30

III.6 Setting the inflow river
Set inflow rivers (or flood levee breaches) directly to the calculation cell: upper end,side (j=1) and side (j=nj). After making a grid for calculation, right click on [Boundary
Condition Setting] under [Object Browser] to select [Add Inflow]. Select [Object
Browser] - [Boundary Condition Setting] - [New Inflow] to add a river [Inflow]. While
selecting the [Inflow], enclose the sides of “Inflow” locations with polygons. When thelocation is confirmed, the [Boundary condition] setting dialog opens. Set changes indischarge by time and profile of inflow. Run [Attribute mapping] under [Grid] on themenu bar to set the inflow as a side of a grid.

Figure III-6 Dialog for setting [River Inflow]

31

Figure III-7 Dialog for setting [Boundary Condition]
Table III-5 Items setting for [Boundary Condition]
Item
How to set the item
Notice#1

Name

Input names of inflow river (orflood levee breach) arbitrary.

2

Discharge timeseriesClick Edit and set the dischargehydro-graph.

3

Slope value at
inflow

Input the slope value at inflow.

4

Color

The color of inflow point.

5

Transparent

The transparent of inflow point.

32[Second] or [Hour]can be selected astime unit and [m3/s]
as discharge.

III.7 Setting riverbed roughness coefficient
Set the riverbed roughness coefficient for each grid cell. After making a grid for
calculation, select [Object Browser] - [Grid] - [Cell Attributes] and check [Roughness].
In the Object Browser, select [Geographic Data] - [Roughness] and right click to select[Add] - [Polygon]. While selecting a polygon that has been added to [Roughness
condition] under [Geographic Data], enclose cells of the same roughness in the polygon.
Upon confirming the polygon, the [Edit Roughness condition value] dialog opens. Then,input the coefficient of roughness. Run the [Attributes mapping] under [Grid] on themenu bar to set the coefficient of roughness for the cells.
The default setting is 0.0 (Manning’s roughness coefficient). Set it by adjusting to theland-use conditions of the floodplain.

Figure III-8 Dialog for setting [Roughness Coefficient]33

III.8 Setting obstacles
Obstacles such as roads, banks and embankments can be set as necessary. After making
a grid for calculation, select [Object Browser] - [Cell attributes] and check [Obstaclecell]. Select [Object Browser] - [Geographic Data] - [Obstacle cells]. Right click on[Obstacle cells] to select [Add] - [Polygon]. While selecting a polygon that has been
added to [Obstacle cells] under [Geographic Data], enclose the obstacle cells in thepolygon. Upon confirming the polygon, the [Edit Obstacle value] dialog opens. Select[Obstacle cells]. Run the [Attributes mapping] under [Grid] on the menu bar to set
obstacle cells.

Figure III-9 Dialog for setting [Obstacles]34

III.9 Setting building occupancy ratio by area
Set the building occupancy ratio by area for each cell. After making a grid for
calculation, select [Object Browser] - [Grid] - [Cell Attributes] and check [Areal
fraction that buildings occupy]. Select [Object Browser] - [Geographic Data] [Areal fraction that building occupy] and right click on [Areal fraction that the building
occupy] to select [Add] - [Polygon]. While selecting a polygon that has been added to[Areal fraction that building occupy] under [Object Browser] - [Geographic Data],
enclose cells that have the same building occupancy ratio by area in the polygon. Upon
confirming the polygon, the [Edit Areal fraction that building occupy] dialog opens.
Input the new value. Run [Attributes mapping] under [Grid] on the menu bar to set the“areal fraction that building occupy” or the building occupancy ratio by area for thecells.

Figure III－7 Windows to set “Areal fraction that building occupy” or building
occupancy ratio by area

35

The building resistance is simulated assuming to have the conditions in which buildings
affect the flow and are inundated. Note that the preconditions differ from those for thesetting of obstacle cells. Because the calculation tends to diverge when the void ratio is
close to 0%, the solver limits values of the void ratio (the structural occupancy ratio is0.95 or less and the void ratio is 0.05 or more) to converge the simulation.
Note: Flow velocities between
cells are calculated based on“building occupancy ratio by area"for each cell. Because buildings areinundated, there is little water level
rise outside the cell.

Note: Flow velocities between
cells that face obstacles are notcalculated. Because buildings are
not inundated, the water leveloutside the cell tends to rise.

Building occupancy
ratio setting cellObstacle cells
Flow velocity calculation
locations: Take into consideration ofbuildings: Flow velocity 0

Figure III－8 Schematic of building resistance (left) and obstacle resistance(right) (side view)36III.10 Setting for a box culvert
For a box culvert, [Inside] (i.e., the entrance) and [Outside] (i.e., the exit) are
regarded as a unit, and different cells are set for [Inside] and for [Outside].
After making a grid for calculation, select [Object Browser] - [Boundary Condition
Setting], and right click on [Boundary Condition Setting] to select [Add BoxCulvert].
While selecting the added box culvert (the initial setting is [New BoxCulvert]) which
has been added to [Boundary Condition Setting] under [Object Browser], enclose thesides of the cells at the location of the box culvert in a polygon. When the polygon is
confirmed, the [Boundary Condition] setting dialogue opens. Select or input for fieldsof “Inside/Outside”, “Width”, “Height”, “Elevation” (i.e., elevation of the structure
bottom above the datum) and the number of units and coefficient of discharge of thebox culvert. Run [Attributes mapping] under [Grid] on the menu bar to set box culvert
on cells.

Figure III－9 Box culvert setting window

37

Figure III－10 Boundary conditions setting window
Table III－6 Explanation of boundary condition setting#

Item

Setting method

1

Name

Input arbitrary name of box culvert

2

Code number

Specify the code number of the box
culvert3

Inside (i.e.,
entrance)/Outside (i.e.,
exit)

4

Width (m)5Height (m)6Elevation (i.e., elevationof the structure bottom
above the datum)

Selection can be made between"Inside” (i.e., entrance) and "Outside”(i.e., exit) of the box culvert
Set the inside width (m) of the box
culvert.
Set the inside height (m) of the box
culvert.
Set the elevation of the structure
bottom above the datum (m) for thebox culvert.

7

Multiply

Set the number of box culverts.

38

Important information

The same code number
should be used for Inside(i.e., entrance) and Outside(i.e., exit)

Refer to Figure II－1
Refer to Figure II－1
Refer to Figure II－1

8
9
10
11

Extend formula (i.e.,taking into account thesubsurface flow)
Coefficient of submerged
flow
Coefficient of subsurface
flow
Coefficient of free flow
(i.e., free outflow)

Set whether the subsurface flow istaken into account. Select between"Yes" and "No."Set the coefficient of submerged flow.
Set the coefficient of subsurface flow.
Set the coefficient of free flow (i.e.,free outflow).
Set the color to identify the box
culvert.

12

Color

13

Transparent

Set the transparency of the box culvert.

14

Show name

Check it if you want the drawings todisplay the name of the box culvert.

39III.11 Setting for a sluice pipe
For simulation, [Inside] (i.e., entrance) and [Outside] (i.e., exit) of the sluice pipe
are set, respectively. Different cells are set for [Inside] and for [Outside].
After making a grid for calculation, select [Object Browser] - [Boundary Condition
Setting], and right click on [Boundary Condition Setting] to select [Add Gate]. While
selecting the sluice pipe (the initial setting is [New Gate]) that has been added to the[Boundary Condition Setting] under [Object Browser], enclose the cells at the locationof the sluice pipe in a polygon. When the polygon is confirmed, the [Boundary
Condition] setting dialogue opens. Select or input fields of “Inside/Outside”, “Width”,“Height”, “Elevation” (i.e., elevation of the structure bottom above the datum) and thenumber of units and coefficients of flow of the sluice pipe. Run [Attributes mapping]under [Grid] on the menu bar to set the sluice pipe for the cells.

Figure III－11 Sluice pipe setting window
40

Figure III－12 Boundary condition setting window
Table III－7 Explanation of boundary condition setting#

Item

Setting method

1

Name

Input the arbitrary name of the sluice pipe.

2

Code number

Specify the code number of the sluice pipe.

3

Inside (i.e.,
entrance)/Outside (i.e.,
exit)

Selection can be made between “Inside (i.e.,
entrance)" and "Outside (i.e., exit)” of thesluice pipe.

4

Width (m)Set the inside width (m) of the sluice pipe.

41

Important information

The same code
number should be used
for Inside (i.e.,
entrance) and Outside(i.e., exit)

Refer to Figure II－2

5

Height (m)Set the inside width (m) of the sluice pipe.

Refer to Figure II－2

6

Elevation (i.e.,elevation of thestructure bottom above
the datum)

Set the elevation of the structure bottom above
the datum (m) for the sluice pipe.

Refer to Figure II－2

7

Multiply

Set the number of sluice pipes.

Extend formula (i.e.,taking into account thesubsurface flow)
Coefficient ofsubmerged flow
Coefficient ofsubsurface flow
Coefficient of free flow
(i.e., free outflow)

Set whether the subsurface flow is taken into
account. Select between "Yes" and "No."

8
9
10
11

Set the coefficient of submerged flow.
Set the coefficient of subsurface flow.
Set the coefficient of free flow (i.e., free
outflow).
Sets the open/close status of the slice pile.
You can select “Automatic” or “Set data”.
When “Automatic” is selected, the open/close
status of the sluice gate is determined basedon the calculated water levels in the inlet andoutlet cells.
When “Set data” is selected in ”Open/Close
operation”, time series can be input. Enter thetime in the first row and the open/close status(open: 0, close: 1) in the second row.
Select “Set data” when you want to use
observed values or calculated values fromanother model for the water level on the outlet
side.
Enter the time in the first row and the waterlevel on the outlet side in the second row.

12

Open/Close operation

13

Open/Close operation
time series

14

Outside water level

15

Water level time series

16

Color

Set the color to identify the sluice pipe.

17

Transparent

Set the transparency of the sluice pipe.

18

Show name

Check it if you want the drawings to display
the name of the box culvert.

42III.12 Setting for a pump
For simulation, [Inside] (i.e., entrance) and [Outside] (i.e., exit) of the pump are set,
respectively. Different cells are set for [Inside] and for [Outside].
After making a grid for calculation, select [Object Browser] - [Boundary Condition
Setting], and right click on [Boundary Condition Setting] to select [Add Pump]. While
selecting the pump (the initial setting is [New Pump]) that has been added to[Boundary Condition Setting] under [Object Browser], enclose the cells at the locationof the pump in a polygon. When the polygon is confirmed, the [Boundary Condition]
setting dialogue opens. Select or input fields of “Inside/Outside”, “Maximum drainage
discharge”, “Begin operating water level” (i.e., water level at which the pump starts
operating), “Stop operating water level” (i.e., water level at which the pump stops
operating) for the pump. Run [Attributes mapping] under [Grid] on the menu bar to set
the pump for the cells.

Figure III－13 Pump setting window
43

Figure III－14 Boundary conditions setting window
Table III－8 Explanation of boundary condition setting#

Item

Setting method

1

Name

Input the arbitrary name of the pump.

2

Code number

Specify the code number of the pump.

3

Inside (i.e.,
entrance)/Outside (i.e.,
exit)

4

Auto/Set data

Selection can be made between “Inside (i.e.,
entrance)" and "Outside (i.e., exit)” of thepump.
Set the pump operation method.
Select between “Auto” and “Set data” (i.e.,manual operation.)

5

Maximum drainage
discharge (m3/s)

Set the maximum drainage discharge of the
pump.

6

Begin operating waterlevel (m)Set the water level at which the pump starts
operating.

44

Important information

The same code
number should be used
for Inside (i.e.,
entrance) and Outside(i.e., exit)

Refer to Figure II－3

7

Stop operating waterlevel (m)Set the water level at which the pump stops
operating.

8

Drainage discharge
time-series

Click on [Edit] to set the time-series data of
maximum drainage discharge when [Auto] isselected for the pomp operation method.

9

Color

Set the color to identify the pump.

10

Transparent

Set the transparency of the sluice pipe.

11

Show name

Check it if you want the drawings to display
the name of the pump.

45

Refer to Figure II－3

IV. Input/Output files
IV.1 Input file for grid cell numbers of inflow
Select a grid cell number of inflow (and/or a bank opening). Numerical values can beseparated by a tab, a comma or a space. When the boundary condition of the bank is set
as [Inflow], an input file for the grid cell numbers where inflow starts and ends to bemade for each river/bank opening.
2
8
・
・
・

4
9
・
・
・

Grid cell numbers where inflow starts

Inflow riv

Grid cell numbers where inflow ends

Notes:
1) For [Inflow Boundary Conditions], input the number ? of the grid cell (1, ?).
2) For boundary conditions for j=1, input the number ? of the grid cell (?, 1).
3) For boundary conditions of j=nj, input number ? of grid cell (?, nj).
Figure IV-1 Example of input file for grid cell number of inflow

46

Boundary conditions for j=nj

Inflow grid cell numbers of
inflow river 1: 7 - 8(1, nj)(ni,nj)Inflow boundary

Outflow boundary

Inflow grid cellnumbers of inflow
river 2: 8 - 9

内容
j(1, 1)i

Inflow grid cellnumbers of inflow
river 1: 3 - 4

Inflow grid cell numberof inflow river 2: 6
(ni, 1)

Boundary conditions for j=1
Figure IV-2 Input file for grid cell numbers of inflow

IV.2 Discharge file (Inflow boundary conditions)
Input an inflow river discharge (and/or bank overtopping discharge.) Numerical values
can be separated by a tab, a comma or a space.
Time(Sec.,
hour)
0
1
・
・
・

Discharge of
inflow river 1(m3/s)
100
140
・
・
・

Discharge of
inflow river 2(m3/s)
200
300
・
・
・

Discharge of
inflow river 3(m3/s)
20
40・・・Discharge of
inflow river 4(m3/s)
200
250
・
・
・

Discharge of
inflow river 5(m3/s)
60
80
・・・

Figure IV-3 Example of discharge file (Inflow boundary conditions)47

IV.3 Discharge file (boundary conditions for banks)
When the boundary condition of a bank is [Inflow], set the discharge as that of the
inflowing river (or discharge at the bank opening). Numerical values can be separated
by a tab, a comma or a space.
Discharge of
inflow river 1(m3/s)
100
140
・
・
・

Discharge of
inflow river 2(m3/s)
200
300
・
・
・

Discharge of
inflow river 3(m3/s)
20
40・・・Discharge of
inflow river 4(m3/s)
200
250
・
・
・

Discharge of
inflow river 5(m3/s)
60
80
・・・

Note: The time data of [Inflow Boundary Conditions] (IV of Chapter 2) is used for thetime column of the discharge file of a bank opening.
Figure IV-4 Example of discharge file (Boundary conditions for banks)48

To Reader● Please indicate that using the iRIC software, if you publish a paper withthe results using 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 Solver Manual
Editorsandwriters

SupportedbyYasuyuki SHIMIZU (Hokkaido Univ., Japan)
Eiichi SUZUKI (Hokkaido Univ., Japan)
Satomi KAWAMURA (Hokkaido Univ., Japan)
Takuya INOUE (Hiroshima Univ., Japan)
Toshiki IWASAKI (Hokkaido Univ., Japan)
Michihiro HAMAKI(Kaihatsu Koei Co., Ltd., Japan)
Kensuke OMURA (Hokkaido Univ., Japan)
Eriko KAKEGAWA (Hokkaido Univ., Japan)
River center of Hokkaido, Japan.

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