Study on Urban Drainage Modeling in Incheon Gyo ... - HydroAsia

Final presentation
<strong>Study</strong> on Urban Drainage Modeling in
Incheon Gyo Watershed
Advisors: Gyewoon CHOI
Members:
2008. 8. 22
Girish Badgujar,
Nguyen Ha,
Myeong soo Ham ,
Kakuta Fujiwara,
Lei SHI,
Xuan Wang,
Qiang Zhang,
Dongeon Kim
1

Content –Team Blue
1. Introduction
2. Work Flow for Team Blue
3. Modeling of Incheon Gyo Watershed
4. Analysis of the Modeling Result
5. Conclusion
2

1. Introduction
Youngjong
Airport
Yellow sea
Songdo
Seoul
• Located in the midwest
Korea peninsula
near Yellow Sea
• With both
international port
and international
airport
• The third biggest
city in Korea
• Population : 2,730
thousand
3

1. Introduction - Recent Floods at Incheon
Damages
– Flooding in
1997 to 2001
(except 2000)
–Total 3,318
Houses and
buildings were
flooded in 2001
4

1. Introduction - Flooding
Direct damages: Material loss
Indirect damages: Time=$, Traffic, Production, Diseases
Social consequences: Decrease of Property value of
flooded areas…
5

1. Introduction - Objectives
Statement of Problem
• Incheon City has experienced flood in recent years.
• Most of the areas were flooded even with from year 1997 to 2001.
• Hence to overcome flooding situation some technical
recommendations are needed
Objective of the study
To construct the model to simulate 1997 year flood condition
To evaluate the existing sewer system of Incheon city
To design and examine some technical solution to alleviate the
flooding situation
To provide recommendations for flood alleviation.
6

2. Work Flow for Team Blue
- Water Level
at each node
- Link water
level,
discharge, and
velocity
- Flood extent
and flood
depth, etc.
General Analysis
Data Collection
Analysis of the collected
data
Model Choosing and Setup
Calibration and Validation
of model parameters
Evaluation of the existing
drainage capacity of the
system
Design and examine
technical solutions for flood
alleviation
Results and
Recommendations
- Hydrologic & Hydraulic Data: Rainfall,
rain gauge coordinates, gate and pump
operation, retention pond condition, etc.
- Catchment Data: Coordinates, area,
impervious area, population, time of
concentration, Length, hydrological losses
for the individual catchment, Manning
number, land use type, etc.
- Links: Material (Manning number),
longitudinal profile, Cross section data
(shape, size)
- Nodes: manholes, basins, outlets,
- Road system, building system
- Available GIS Digital Map (0bserved
flood inundation map, etc.)
7

2. Work Flow for Team Blue
General Analysis of Rainfall Runoff Process for Urban
watershed
Mark et al, 2004
8

3. Modeling of Incheon Gyo
Watershed
Approach for modeling
• The phenomenon of flood could be understood by modeling, if we
could represent the reality with some assumption in the model.
• Selection of Model
Dynamic, User-friendly, Professional Engineering Package
Capabilities like dynamic memory allocation and data structure
It should have produced good applications in the past
• MOUSE (main)
MOUSE is advanced, powerful surface runoff, pipe flow
modeling package.
It has been used since 1970 for urban modeling
Capable of simulating surface flow and pipe flow
•MIKE SWMM (optional)
MIKE SWMM is a free powerful model but with some limitations
9

3. Modeling of Incheon Gyo
Watershed
MOUSE wants following data……..
MOUSE will be used here for two purposed
• To produce surface runoff from rainfall
•To produce pipe flow developed from the surface
flow
Data required for MOUSE
Catchment and catchment characteristics for surface flow
Node, Link and hydraulic characteristics for pipe flow
Time series
•Rainfall
• Water level at different outlets
10

3. Modeling of Incheon Gyo
Watershed
Drainage network of Incheon Gyo Watershed
constructed in MOUSE
11

3. Modeling of Incheon Gyo
Surface Runoff Modeling
Watershed
Runoff was estimated using Time Area Curve A
The factors affecting runoff process
•Reduction factor
•Average slope
•Time of concentration
•Initial loss
Above factors are depends on the following catchment characteristics
•Area of the catchment
•Surface cover of the catchment
12

3. Modeling of Incheon Gyo
Watershed
Assigned different value
Using the catchment
characteristics
13

3. Modeling of Incheon Gyo
Watershed
- Land Utilization
Location
Incheon Gyo
Covered
Open
Channel
Sulnam
Hwasu
Left
Right
Subtotal
Total
1,183.6
997.2
2,180.8
910.9
302.8
Residence
734.3
364.8
1,099.1
204.4
161.6
Market
145.9
47.8
193.7
38.4
67.4
Industrial
226.3
353.3
579.6
357.9
61.7
Green
77.1
231.3
308.4
310.2
12.1
Total
3,394.5
(100%)
1,465.1
(43.2%)
299.5
(8.8%)
999.2
(29.4%)
630.7
(18.6%)
• Distribution of Elevation
Elevation Range
Less than 5m
5~7m
More than 9m
Total
Area(ha)
20.7
1,102.7
2,271.1
3,394.5
Rate of Composition (%)
0.6
32.5
66.9
100.0
14

3. Modeling of Incheon Gyo
Watershed
- Pipe flow computation
•Pipe flow starts with inflow from
the surface runoff.
•The underground flow is computed
as pipe flow or open channel flow.
•Full form of St Venant equation and
Modified St Venant equation
15

3. Modeling of Incheon Gyo
Watershed
- MOUSE Results
16

3. Modeling of Incheon Gyo
Watershed
- Calibration!!!
Why??? :
For the evaluation of the performance of the model
compared preferably against measurements
Select
starting
estimate
Run the
model
Compare
computed
&
observed
Ok
?
Ye
s
Finish
No
Improve
estimate
Flow Chart for Calibration
17

3. Modeling of Incheon Gyo
Watershed
- Calibration Result for the Flood in 1997
Figure: Maximum Flood result at
nodes shown in MIKE VIEW for
a storm of 4, Aug. 1997.
Figure: Observed Inundation
Map for Year 1997.
18

3. Modeling of Incheon Gyo Watershed
- Results from MIKE VIEW for storm in year 1997
Figure: Time series flood for a
storm of 4, Aug. 1997 at node
20066
Figure: Water level profile from node
24699 to node 25098 at 03:00 4/8/97.
19

4. Analysis of the Modeling Result
- Construction of flood inundation map
Generation of DEM from contour level
‣ DEM should be fine for urban area
‣ Size of 1x1 to 5x5 is recommended for urban analysis
DEM can be created by: contour map or spot elevation
Present case DEM of 5x5 m created using contour map as a input
MOUSE output was transferred to GIS using MIKE 11 GIS
Generation of water surface grids
waterlevel =
h1
h
2
h
+ +
d1
d2
d
1
d + d + d
1
2
3
3
3
Flood
= GeneratedW.
S.
−
DEM
20

4. Analysis of the Modeling Result
- 3-D DEM for Incheon Gyo Watershed
Fig.DEM for Incheon Gyo
Watershed with Buildings
Fig.DEM for Incheon Gyo
Watershed without Buildings
21

4. Analysis of the Modeling Result
Comparison of 1997
flood
22

4. Analysis of the Modeling Result
- SWMM Input Data
RUNOFF
- Rainfall
- Catchment
EXTRAN
- Conduits
-Junctions
- Outfalls
- Boundary conditions
23

4. Analysis of the Modeling Result
- SWMM Control Data
RUNOFF
- Infiltration Equation: Horton
- Simulation length: 24 hours
- Time step: 30sec
EXTRAN
- Ehanced Explicit Solution
- Start time:19970804
- Length:24h
24

4. Analysis of the Modeling Result
MIKE SWMM Output
The model A
The model B
The runoff output
25

4. Analysis of the Modeling Result
- Objective 2: Evaluation of Existing System!!!
Why Evaluation?????
•The Conditions which system can sustain without
Being producing harm
• Evaluation by subjecting precipitation.
•The rainfall intensity for different return period was available, but
how to generate the storms??????
Generation of Precipitation events using IDF formulae and
“Alternating block method”
26

4. Analysis of the Modeling Result
- Objective 2: Evaluation of Existing System!!!
Generated Rainfall Hyetograph for 5 Year Return Period using
Rainfall Return Period Formula (IDF) and Alternating Block Method
Rainfall (mm)
Time (min)
27

4. Analysis of the Modeling Result
- Objective 2: Evaluation of Existing System!!!
Evaluation of System with 5 year and 20 year return period 24 hr
storm
5 Year Return Period
20 Year Return Period
Rainfall
Rainfall
28

4. Analysis of the Modeling Result
- Objective 3 To design and examine different technical
Scenarios
1. Effect of retention pond water level on the flood
1a. With 25% higher water level
1b. With 25% lower water level
2. Effect of Manhole diameter on the flood
3. Effect of Manning number on the flood
29

4. Analysis of the Modeling Result
- Objective 3 To design and examine different technical Scenarios
Scenario 1a. Effect of higher water level at retention pond
30

4. Analysis of the Modeling Result
- Objective 3 To design and examine different technical Scenarios
Scenario 1b. Effect of lower water level at retention pond
31

4. Analysis of the Modeling Result
- Objective 3 To design and examine different technical Scenarios
Scenario 2.Effect of Manhole Diameter on Flood
32

4. Analysis of the Modeling Result
- Objective 3 To design and examine different technical Scenarios
Scenario 3: Effect of Manning’s Number
33

4. Analysis of the Modeling Result
- Objective 4: Recommendations
• From Scenario 1a and 1b: The water level at retention pond affects
flooding. If retention pond is maintained at higher water level, more
flooding will occur and vice versa. Hence it is important to limit rise of
water level at the retention pond.
By increasing the pond volume (pond expansion is not possible
because of existing infrastructure, hence dredging is necessary
Introduce high capacity Pump to discharge water quickly into
the sea
Develop retention pond operation rules
•From Scenario 2: Effect of the Manhole diameter: Not much
significant.
•From Scenario 3: Effect of Manning number. Higher manning number
means more resistance and hence more flooding.
Manning number depends on Material of the Pipe
Scale formation on surface of the pipe.
Its impossible to change pipe material throughout the system.
Periodic maintenance is necessary
34

5. Conclusion
‣ Flood event for year 1997 was simulated and compared with
observed map.
‣ The existing network was evaluated with different return period
rainfall events.
‣ Different scenarios were simulated to check the effect on
flooding and then some recommendations were subsequently
introduced to alleviate inundation problem in Incheon city
‣ From above analysis it could be concluded that retention pond
water level is the major factor affecting the flooding also the scale
formation at the inner surface enhances flooding process. And
hence higher capacity retention pond or quicker water removal
mechanism would be effective.
35

5. Conclusion
Limitations and related recommendations
‣ Above calibration result for flood of Aug. 1997 just compared
simulated and observed inundation locations, but not depth and
extent of flood
So, calibration should carry out with recent flood events and base
on field survey at some specific locations for example:
By Interviewing the local people for past events
By installing depth measurement mechanism
‣ No validation
‣ There are some uncertainties in making some assumptions for
the model, hence calibration result was not really good
To improve calibration result we should establish reliable
measurements of water level at retention pond during flood
occurring.
36

The method against urban flood
Huge tank underground (Tochigi)
The other methods
(1)River
・divide river into underground
stream
・construct a super bank
・pomp up
(2)Open channel
・construct pipes underground
・build a house above flood level
Multiplypurpose pond(Tokyo)
Main-1
trunk
New
Line 2
New
Line 1
For
Main-2
catch
ment
Main-2
trunk
For
Main-1
catch
ment
Flood in 1991
38