open channel model

1. Unsteady Flow Model for Past Flood
Events Estimation. Case Study :
Surabaya City, East Java, Indonesia
M1 - Putika Ashfar Khoiri
Water Engineering Laboratory
Department of Civil Engineering
May, 25th 2017
20th Cross-Boundary Seminar
International Program of Maritime and Urban Engineering
Osaka University

2. Introduction
1
Previous flooding events in
Surabaya
Surabaya city area
Date District name
Inundation height
(cm)
Duration
(days)
15 – 01 - 2012 Medokan Semampir 5 up to 10 1 up to 2
Sukolilo 10 up to 20 1 up to 2
18 -12- 2013 Wonorejo 10 up to 20 2
11 – 02- 2015 Rungkut Lor 50 up to 70 2
Mejoyo 50 up to 70 2
Kali Baru 50 up to 70 2
20 – 02- 2015 Krikilan 10 up to 30 1
Rungkut 11 up to 30 1
24 – 02- 2016 Sukolilo 20 up to 30 1
Table : previous flooding events
• Surabaya as the capital city of East
Java which 70 % of the area are
residential and industrial area
(Ministry of Surabaya City
Development and Planning, 2012)
• Many past flooding events in
Surabaya was recorded between
December to March by Surabaya
Agency of Disaster Management
(2016)

3. Introduction
2
Previous flooding events in
Surabaya
1. Although flood defence projects
have been established and
improved since 2004 by local
governments , the flooding risk still
found due to the global warming
effect and rapid urban
development.
2. Therefore, to improve flood
management in Surabaya City
flood simulation for several past
flood events in Surabaya is
important
January 17, 2017
April 14, 2016

4. Previous study
3
(Susetyo, 2008) Analysis about current river flow regulations
Structural defense adjustment during flood events
Flood Management

5. Previous study
4
Develop model based on raising percentage of water discharge entering Surabaya River
Flood Modeling

6. Previous study
5
Flood risk variation based on raising precentage of water discharge entering Surabaya River
Flood Risk Analysis

7. Objectives
6
What I want to improve ?
1. Calculate the water head
difference at each cross-section
by unsteady flow simulation
Update :
Hydrological data
(Inflow discharge and rainfall)
• Land-use data
• Change manning’s n value variation
2. Analyse river channel capacity
from each cross-sections
3. Improve model simulation by generating
2d model to know better inundation area
and flood depth
ShorttermgoalLongtermgoal

8. Methods
7
Generate 1D Unsteady Flow Model
GIS data development
-Set map projection and boundary
condition
-Create stream centre line, cross-
sectional lines, flow path layer
Export to HEC-RAS, modify bank
lines, determine manning’s n,
coefficient of expansion, etc
Flow path
Flow path
River Bank line River Bank line
River line
Cross-
section
cut lines
Complete unsteady flow data
Input : Hydrograph calculation, Water
elevation data
Results

9. Equation
8
Computation procedure
∆𝑥
𝜃𝐹𝑓
Saint Venant equation
Continuity equation
𝜕𝐴
𝜕𝑡
+
𝜕𝑄
𝜕𝑥
= 0
Momentum equation
1
𝐴
𝜕𝑄
𝜕𝑡
+
1
𝐴
𝜕
𝜕𝑥
𝑄2
𝐴
+ 𝑔
𝜕𝑦
𝜕𝑥
+ 𝑔(𝑆𝑓 − 𝑆0) = 0
A = flow area (m2)
x = distance along the flow path
Q = lateral inflow per unit channel (m3/s)
g = Acceleration due to gravity (m2/s)
y = hydraulic depth (m)
S0 = bed slope
Sf = friction slope
• All the flow variables are function both time and
distance along the channel
• Time, distance , depth and other variable vary with
time
• The flow is sub-critical, so it only need one boundary
condition at each upstream/downstream,
1D unsteady flow routing

10. Equation
9
Computation procedure
j j+1
Flow direction
Xc
∆𝑥
𝜕𝑡
n
n+1
x
t 0.5∆𝑥
𝜭𝑡
• The values at time stage (n+1) as well as stage
n are used to approximate the spatial space
and time derivative
• Space derivative and function values are
evaluated at (n+𝜭)∆t. Thus, the value of
(n+1)∆t enter into all terms in the equation
Implicit Finite Difference Scheme
Time derrivative
Space derrivative
𝜕𝐴
𝜕𝑡
≈
𝐴𝑖+1
𝑛+1
+ 𝐴𝑖
𝑛+1
− (𝐴𝑖+1
𝑛
+ 𝐴𝑖
𝑛
)
2∆𝑡
𝜕𝐴
𝜕𝑡
≈
𝑄𝑖+1
𝑛+1
+ 𝑄𝑖
𝑛+1
− (𝑄𝑖+1
𝑛
+ 𝑄𝑖
𝑛
)
2∆𝑡
𝜕𝑄
𝜕𝑥
≈
𝜃 𝑄𝑖+1
𝑛
− 𝑄𝑖
𝑛+1
+ (1 − 𝜃)(𝑄𝑖+1
𝑛
− 𝑄𝑖
𝑛
)
2∆𝑥

11. Boundary condition
10
Surabaya River
Wonokromo River
Mas River
Mlirip gate
River Name Boundary Condition
Surabaya Flow Hydrograph
Mas Stage Hydrograph
Wonokromo Stage Hydrograph
Normal depth
If recorded gage data and stage hydrograph are not
available, the normal depth boundary condition is
used with user entered friction slope as a stage of
uniform flow conditions
𝑆𝑓 =
𝑄
𝐾𝑖
2
K = conveyance
Sf = friction slope
Q= input discharge

12. Boundary condition
11
Downstream
station
Location Upstream boundary Downstream boundary
Available
data
Hourly water level data, rainfall and
hourly discharge data at Mlirip Gate in
2014-2015
Hourly surface water elevation at 2 stations
in Surabaya City
Source
PERUM JASA TIRTA (Bureau of Water
Resource of East Java Province)
BPOL (Indonesia Agency of Ocean Research
and Observation )
∆𝑄 𝑘
𝑛+1
= 𝑄 𝑘
𝑛
- 𝑄 𝑘
Equation for flow hydrograph
Upstream boundary
k = upstream node of reach
n = time stage
Downstream boundary
Equation for stage hydrograph
At the time step (n+1)∆t
∆𝑍 𝑁 = 𝑍 𝑁
𝑛+1
- 𝑍 𝑁
𝑛
Z = water depth
N = ordinate
n = time stage

13. Boundary condition
12
Hydrograph Calculation
Nakayasu Synthetic Unit Hydrograph (SUH) method has applied in Brantas river catchment
Time : during flood event (February 11, 2015 - February 13, 2015)
0
200
400
600
800
1000
1200
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51
0
20
40
60
80
100
120
140
Period (hours)
Rainfall(mm/hour)
rainfall
discharge
Discharge(m3/s)
Time peak (Tp) Time from rain begin to peak of hydrograph = 3.6 hours
Peak discharge (Qp) = 923.24 m3/s

14. Boundary condition
13
Downstream-end water elevation
Kali Mas
5.3
5.35
5.4
5.45
5.5
5.55
5.6
5.65
5.7
0 10 20 30 40 50 60 70
stage(m)
period (hours)
6.5
6.55
6.6
6.65
6.7
6.75
6.8
6.85
6.9
6.95
0 10 20 30 40 50 60 70
stage(m)
period (hours)
Kali Wonokromo

15. Boundary condition
14
Initial Condition
0 1000 2000 3000 4000 5000
30
35
40
45
50
55
60
project3surabaya Plan: Plan 23 2017/05/15
Main Channel Distance (m)
Elevation(m)
Legend
EG 11FEB2014 0100
WS 11FEB2014 0100
Crit 11FEB2014 0100
Ground
Critical depth
Water surface elevation
Energy gradeline
Surabaya River

16. Simulation Result
15
Discharge (Q) – Water surface
elevation (H) curve
0
10
20
30
40
50
60
0 50 100 150 200 250 300 350
Watersurfaceelevation(m)
discharge (m3/s)
upstream
downstream
middle reach
0
10
20
30
40
50
60
0 50 100 150 200 250 300 350 400 450 500
watersurfaceelevation(m)
discharge (m3/s)
upstream
middle reach
downstream
Surabaya River
After 8 hour
simulation
Mas River

17. Simulation Result
16
Profile plot
05:00
0
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
0 1000 2000 3000 4000
Elevation(m)
Main Channel Distance (m)
initial condition
4 hours
8 hours
ground
04:00
Wonokromo River

18. Simulation Result
17
Profile plot
05:00
0
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
0 1000 2000 3000 4000 5000 6000
Elevation(m)
Main Channel Distance (m)
initial condition 5 hours 8 hours ground
Mas River

19. Summary
18
• One dimensional models require many assumptions including the accurate
representation of a river using available cross-sections data, input
hydrograph, and manning coefficient.
• Inundation area can't represent well in 1D model because of limitation of
cross-sectional plane, although water stage elevation can be examine easily.
• Critical depth and head loss from each cross section need to be examined as
well as another parameter change (hydraulic roughness, topography
difference)
• Simulation can’t continue after the end of hydrograph, some parameters
need to examine :
1. Calculation tolerance in the iteration process
2. Maximum error in water surface solution

20. Future task
19
• Modify some parameter and boundary condition to complete 1D simulation
• Examine drainage channel capacity after model become stable
• Validate result by compare result with Brantas river discharge capacity from
local government data
• Generating 2D unsteady flow model to know better inundation area and
flood depth

24. 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
0
5
10
15
20
25
30
35
40
45
50
55
60
project3w onokromo2 Plan: Plan 27 2017/05/17
Main Channel Distance (m)
Elevation(m)
Legend
EG Max WS
WS Max WS
Crit Max WS
Ground

25. 0 1000 2000 3000 4000 5000
0
5
10
15
20
25
30
35
40
45
50
55
60
project3mas Plan: Plan 28 2017/05/15
Main Channel Distance (m)
Elevation(m)
Legend
EG Max WS
WS Max WS
Crit Max WS
Ground