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1. Study Report 3
M2 - Putika Ashfar Khoiri
Water Engineering Laboratory
Department of Civil Engineering
October 17th , 2017

2. General Purpose:
Simulate past flood event in Surabaya City to derive probabilistic flood maps in
flood prone area by assessing several uncertainties in hydraulic modelling and
flood mapping.
Problems to be discussed :
1. How river discharge and other parameters have influence on flood simulations
(How the model results change depending on the input data)
2. What is the problems while simulating floods?
Objective
Outline
1

3. Previous Task
• Development of flood scenarios and model simulations
Perform flood inundation modelling for the study area NAYS 2D Flood for 1 flood
event
Inflow discharge hourly observed discharge data from February 11st,
2015 to February 13rd, 2015
water surface at downstream free outflow
Initial water surface Depth = 0
Calculation time 42 hours
Time step 2 mins
Calculation Condition
Parameters which are included :
1. Determination of grid shape
2. Roughness coefficients of the floodplain
2

4. Current Progress
Modules Evaluation tasks
Hydrological Analysis
Flow hydrograph shape
Peak discharge estimation
water-elevation and distance relationship curve
Rating-curve rating curve estimation
Flood routing Flow hydrograph shape
Flood inundations were simulated using the flow conditions on the past
flood events between January to March in 2014, 2015 and 2016
Reported flood events obtained from National Agency for Disaster Management Data
Date Inundation Height (cm) Duration
23-01-2014 (event 1) 50-70 2 to 3 days
20-02-2015 (event 2) 10-30 2 days
24-02-2016 (event 3) 20-30 2 days
The annual maximum peak discharge during the flood events are observed in 3 weeks around
flood peak
• Initial condition : 2 weeks before the flood occurs
• Simulation period : 100 hours 3

5. Calculation setting
River length 8.64 km
Size of W 3000 meter
Grid size 30 m x 30 m
number of river
cross section data
9 points
upstream
downstream
inflow
Name of polygon Description Roughness Coefficient
Agricultural area Grass, agricultural site 0.030
Low density area Citizen house 0.040
High density area Office, school and
public facility
0.070 – 0.80
River River 0.01
(*)IRiC User Manual 4

6. Initial Condition (2 weeks before flooding inundation simulation) based on the observation data
Date Average discharge (m3.s-1) Maximum Discharge (m3.s-1)
9-01-2014 to 22-01-2014 (IC 1) 79.54010976 181.22
5-02-2015 to 19-02-2015 (IC 2) 66.41162405 182.22
9-02-2016 tp 23-02-2016 (IC 3) 60.37975238 180.1
-50.00
0.00
50.00
100.00
150.00
200.00
0 50 100 150 200 250 300 350 400
Discharge(m3.s-1)
Period (Hours)
IC 1
IC 2
IC 3
Calculation setting (initial condition)
The discharge on event 1 is relatively low before the flood events 5

7. Result (initial condition)
1. The value of river depth are varies from 0.5 m to 4 m -> the depth value need to
calibrate with the datum to produce water elevation.
2. In the middle stream area, the water depth become higher, probably due to the
effect of topographic changes or narrow changes in river cross-section width.
Water depth
6

8. Result (initial condition)-velocity
1. The velocity magnitude are varies between 0.784 m/s to 1.57m/s along the center
of the stream line.
2. Higher velocity occurs due to the meandering of the river
Velocity
7

9. Discharge routing method
The Muskingum channel routing method is employed to route the flow
through the streams
𝑄 𝑢 − 𝑄 𝑑 =
∆𝑥
𝑐3
𝜕
𝜕𝑡
𝑄 𝑑 +
1
2
−
𝐿
∆𝑥
(𝑄 𝑢 − 𝑄 𝑑)
𝑄 𝑑,𝑗+1 = 𝐶1 𝑄 𝑢,𝑗+1 + 𝐶2 𝑄 𝑢,𝑗+1 + 𝐶3 𝑄 𝑢,𝑗+1
Where the coefficients C1,C2,C3 are expressed as
𝐶1 =
−𝐾𝜃 + 0.5∆𝑡
𝐾 1 − 𝜃 + 0.5∆𝑡
𝐶2 =
−𝐾𝜃 + 0.5∆𝑡
𝐾 1 − 𝜃 + 0.5∆𝑡
𝐶3 =
𝐾 1 − 𝜃 − 0.5∆𝑡
𝐾 1 − 𝜃 + 0.5∆𝑡
K= travel time
θ = weighing parameter ( 0 to 1)
Time needed from the water at the
upstream reach the downstream end at the
simulation
∆𝑡 >
∆𝑥𝑗
𝑐𝑗
𝑛
+ 𝑢𝑗
𝑛
∆𝑥𝑗 = 𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑡ℎ𝑒 𝑟𝑖𝑣𝑒𝑟 𝑟𝑒𝑎𝑐ℎ
𝑐𝑗
𝑛
= 𝑔𝑟𝑎𝑣𝑖𝑡𝑦 𝑤𝑎𝑣𝑒 𝑐𝑒𝑙𝑒𝑟𝑖𝑡𝑦
𝑢𝑗
𝑛
= 𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑟𝑒𝑎𝑐ℎ 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 8

10. Calculation setting (2)
Inflow hydrographs used for the simulations boundary conditions
Hourly discharge data are provided at the upstream area of Surabaya River.
Date
Maximum Discharge
(m3.s-1)
Tp
(hours) T0.3 (hours)
23-01-2014 to 27-01-2014 (event 1) 367.55 28 18
20-02-2015 to 24-02-2015 (event 2) 337.53 46 32
24-02-2016 to 28-02-2016 (event 3) 335.9 35 27
Tp (lag time) = the amount of time it will take for a river to flood after a period of heavy
precipitation
T0.3 = the amount of time need from the peak of discharge to 30% peak of discharge
Event Initial Water Surface (m)
time step
(sec)
Initial manning roughness
channel floodplain slope
1 17.48514757 120 0.01 0.001
2 17.71327015 180 0.01 0.001
3 17.672942 120 0.01 0.001
A uniform routing time interval,
Δt = 30min and
Δx = 30 m was used for all the test runs.
9

11. Routing results (event 1)
1. The hydrograph peak theoretically took 72 minutes to travel between 2 gauges and relatively little
attenuation occurred. With the estimation of velocity between 0.74 m/s to 1.8 m/s
2. Peak flow occurred at the upstream end at 30 hours from the initial condition, and at downstream
end on the same day within 124 minutes
3. The downstream discharge is slightly unstable on the peak of the hydrograph
0
50
100
150
200
250
300
350
400
0 20 40 60 80 100 120
Discharge(m3/s-1)
Time (hours)
upstream boundary
downstream discharge
downstream discharge
(simulation)
10

12. Routing results (event 2 and 3)
0
50
100
150
200
250
300
350
400
0 20 40 60 80 100 120
Discharge(m3/s-1)
Time (hours)
0
50
100
150
200
250
300
350
400
0 20 40 60 80 100 120
Time (hours)
upstream boundary
downstream discharge
downstream discharge
(simulation)
1. Event 2 and 3 relatively have long peak hydrograph with duration of 4 to 6 hours
2. Using the same travel time estimation (K) for the routing calculation on event 2 and 3,
the downstream simulation result has a close relation with the calculated downstream
discharge
3. But, we still need to evaluate the relative error in the time- to peak of the routed
discharge hydrograph
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13. Rating-curve rating-curve estimation (tentative)
Flood dynamics Parameter estimation
Grid-shape accuracy
Damage
estimation
Probabilistic flood Map
water elevation-damage relations
building and land-use value
Methodology
Hydrological
Analysis
Flood routing
Damage
estimation
uncertain
12
Setting of initial condition
Analysis of hydrograph shape and water elevation
profile

14. Model Parameters
The table lists the factors which are used as calibration factors
in each model implementation.
Parameter Sampling range
Manning roughness channel 0.01-0.04
Floodplain slope 0.001-0.015
Initial water surface at downstream boundary 17.5 m – 17.8 m
Eddy viscosity coefficient 0 to 1
Calibration parameters
1. Capability of the model reproduce hydraulic behaviour of the river and
inundated floodplain
2. Time stationary of model parameter (i.e. roughness parameter)
3. Hydraulic information (i.e. flow hydrograph)
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15. Future Tasks
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