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Flood Management Strategies in Taiwan -- Extreme Rainfall
Dr. Chien-Hsin Lai Director-General Water Resources Agency (WRA), Ministry of Economic Affairs (MOEA)
1
Flood Management Strategies in Taiwan
Where we live
What we think
How we do
Conclusions
1
2
3
4
2
Where we live Chapter. 1
4
Geographic location of Taiwan
China
Taiwan
Japan
Russia
Mongolia
South Korea
North Korea
Philippines
Malaysia
Indonesia
Vietnam Thailand
Laos
Myanmar
Chapter 1. Where we live 5
Country Date Casualty
Taiwan 0823 7 deaths, 8492 evacuations
Philippine 0812 54,000 evacuations
Myanmar 0731 11 deaths, 120,000 evacuations
Laos 0723 Dam Break 27 deaths, 1126 missing
Japan 0705 105 deaths, 87 missing
Vietnam 0625 7 deaths, 12 missing
China 0507 6925 evacuations
Malaysia 0104 9000 evacuations
FLOOD
Asian events occurred in 2018
Penghu (1974)
1 hr 1 day 2 day 3 day
Kauai USA
(1956)
Pingdung (2009)
Réunion France (1966)
Pingdung (2009)
Cherrapunji India
(1995)
Pingdung (2009)
Réunion France (2007)
Taiwan record (mm)
World record (mm) up to 2009
Chapter 1. Where we live 6
The extreme events
are equivalent to the world records
Storm event rainfall
(mm/hr)
2016/ Nesat 181 2017/ 06.01 132 2018/ 08.23 121
Source: Taiwan WRA, 2017
Chapter 1. Where we live 7
Short concentration time
Source: River planning report.
River Concentration
time (hr)
Danshuie 15.4
Jhuoshuei 18.35
Zengwun 15.44
Yanshuei 14.55
Gaoping 14.45
Lanyang 7.13
Hualien 7.24
Mekong 458
Rhine 342
Colorado 94 Distance (km)
Rhine River (Europe)
Comparison of River Slope
Elevation (m
) Colorado River
(USA)
Taiwan’s Rivers
Japan’s River
Estuary
Mekong River (Asia)
8
No typhoon
1 typhoon
2 typhoons
3 typhoons
4 typhoons
5 typhoons
6 typhoons
7 typhoons
Picture: Lin; source: CWB
Definition of attack: 1. Typhoon center
landing 2. With no center
landing, but cause disaster on land
Number of typhoon attacks during 1911-2017
Chapter 1. Where we live
Threats by typhoons Average: 3.5 typhoons / year
Typhoon Cimaron
Typhoon Trami
Typhoon Usagi
Typhoon Fitow
Typhoon paths in 2013
Chapter 1. Where we live 9
Hazards induced by extreme events
Area Event Total rainfall
(mm)
Increased
area of
landslide (Ha)
Reduced volume
percentage (%)
Shihmen Reservoir 2004Typhoon Aere 1,022 326 12.2
Zengwun Reservoir 2009Typhoon Morakot 3,058 1,126 9.0 ? ?
Line/Scatter Plot 3Line/Scatter Plot 1曾文水庫石門水庫
賀伯颱風後
921
大地震後
桃芝颱風後
艾利颱風後
海棠颱風後
六九豪雨後
柯羅莎颱風後
卡玫基颱風後
莫拉克颱風後
凡那比颱風後
南瑪都颱風後
蘇拉颱風後
蘇力颱風後
麥德姆颱風後
蘇迪勒颱風後
尼伯特颱風後
尼莎颱風後
921
大地震前
艾利颱風前
娜克莉颱風後
Increased area of landslide 1126 ha Increased area of
landslide 326 ha
1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017
La
nd
slid
e a
rea
(h
a)
Afte
r Typ
ho
on
He
rb
Be
fore
92
1 e
arth
qu
ak
e
Afte
r 92
1 e
arth
qu
ak
e
Afte
r Typ
ho
on
Tora
ji
Afte
r Typ
ho
on
Na
kri
Afte
r Typ
ho
on
Ae
re
Be
fore
Typ
ho
on
Ae
re
Afte
r Typ
ho
on
Ha
itan
g
Afte
r Jun
e sto
rm
Afte
r Typ
ho
on
Kro
sa
Afte
r Ty
ph
oo
n K
alm
ae
gi
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r Ty
ph
oo
n M
ora
ko
t
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r Ty
ph
oo
n F
an
ap
i
Afte
r Ty
ph
oo
n N
an
ma
do
l
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r Typ
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on
Sa
ola
Afte
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ho
on
So
ulik
Afte
r Typ
ho
on
Ma
tmo
Afte
r Ty
ph
oo
n S
ou
de
lor
Afte
r Ty
ph
oo
n N
ep
arta
k
Afte
r Typ
ho
on
Ne
sat
Shihmen Reservoir
Zengwun Reservoir
Chapter 1. Where we live 10
Threaten by compound disasters
71.5%
8.4% 38.0%
1.4%
8.5%
21.5%
1.4%
Highly Flooding prone area
Highly Debris Flow
prone area
Highly Landslide prone area
What we think Chapter. 2
Chapter 2. What we think 12
Highly concentrated population in the cities
Northern and urban population has a growing trend
Population growth rate (%) in 6 major cities
(2009.10-2018.10)
City Urban Rural Total
Taipei 2.4 2.4
New Taipei 5.2 -15.3 3.3
Taoyuan 30.4 -28.4 12.2
Taichung 8.0 1.0 6.3
Tainan 2.3 -8.5 0.5
Kaohsiung 2.5 -13.3 0.1
Population growth rate (%)
Source: Statistical Yearbook of Interior- Department of statistic, Ministry of Interior (2018)
City Urban area(Ha) River area (Ha) (%)
Taipei 27,180 1,794 6.6
Chapter 2. What we think 13
Urbanization reduces river space
Source: Westerner in Taiwan (KP17)
Chapter 2. What we think 14
Near future
Near future
Near future
Near future
Mid of century
Mid of century
Mid of century
Mid of century
End of century
End of century
End of century
End of century
north central
south east
Va
ria
tio
n (
%)
Va
ria
tio
n (
%)
Va
ria
tio
n (
%)
Va
ria
tio
n (
%)
Variation of storm days
Under the RCP 8.5 scenario, the days of extremely heavy rain would increase over 70% in the end of 21 century. The highest variation is in central area (+128%).
Taiwan is threaten by climate change
Chapter 2. What we think 15
Rain
fall s
cale
Only protect for the usual events (high occurrence probability) •Protection standard for farm drainage
– 10 years recurrence interval,1-day average drainage
•Protection standard for rainfall sewer – 2~5 year recurrence interval
•Design standard for regional drainage – 10 year recurrence interval
•Protection standard for slopeland farm drainage – 10 year recurrence interval
• Build the detention facility • Building management and disaster prevention • Green infrastructure • National spatial planning and reallocation • Flood insurance
Resilient community, resilient city • Mitigate the disaster level in the system; • Reduce the recovery time of the system; • Enhance the learning capacity during the disaster
Gra
y e
ng
ineerin
g
Gre
en
en
gin
eerin
g
Extreme event Flooding
unavoidable
Normal
event
Pro
tectio
n b
y
stru
ctu
re
Pro
tectio
n b
y
no
n-s
tructu
ral
Resilient City
Source :Pao-Shan Yu, Briefing on the flooding symposium in the Mino district of Kaohsiung City(Aug 12, 2018)
How we do Chapter. 3
Strategy
17 Chapter 3. How we do
A
18 Chapter 3. How we do
Topping on the cake (Land) Parks and sidewalks were piled up in the cities; roads are the
lowest place in the city
Flooding in the roads brings inconvenience to the residents.
0702 event in 2018 (Yuanlin City)
19 Chapter 3. How we do
Road effects Problem of water blocked by roads
Guo-Gou Village
20 Chapter 3. How we do
Road effects Embankment effect
Village protection facilities
Elevated road
Wang-liao Villiage
21 Chapter 3. How we do
Utilize road design flexibly Improve collection efficiency of the inlets Improve the side-ditch size and spacing of connection pipe Apply LID facility for the sidewalk Take the embankment effect as evaluation focus in the outflow regulation
project. Check whether the discharge capacity or drainage basin is affected.
Permeable pavement Rain detention
22 Chapter 3. How we do
Integrate road and drainage system
Use traffic system to deliver flood- road discharge
Excavate divisional island- green street Detention facility in the node of road system-
interchange detention pond
Reduce the elevation of divisional island to increase water storage
Provincial Highway 61 Shalu Interchange
Set the detention pond in system interchange
Denver road discharge
Strategy
23 Chapter 3. How we do
B
Chapter 3. How we do 24
An Extreme Precipitation will exceed the capacity of rainwater sewer systems and cause flooding.
Runoff Distribution
Chapter 3. How we do 25
Runoff Distribution
River
Parking
lot
Green
land
School
Park
The runoff can be distributed over the public spaces, such as rivers, parks, parking lots, schools, and green spaces.
Chapter 3. How we do 26
Runoff distribution and outflow regulation
Share the water both in the waterway and land. The amendment of the Water Act was promulgated on June 20, 2018.
Outflow regulation
Resilience
Government
Applied in the site area
Development sector
Response to the runoff
increase by climate change
Response to the runoff
increase by development
Development case beyond
specific scale
Runoff Distribution
Specific watersheds &
basins by declaration
Prior to public land
New constructed public
facility with detention
function,ex: park, road
drainage, etc.
Apply the detention pond,
low impact practice, etc.
on site to reduce runoff
purpose
obligor
range
method
practice
27
“Maple Garden” in Taichung City has functions of flood detention, drainage and recreation.
Constructed in 2012; total storage capacity is 200,000 m3.
Maple Garden
Source:Taichung City Government
28
“Benhe Detention Park” in Kaohsiung City applied the ecological engineering to have the functions of landscape, detention and recreation.
Constructed in 2008; total storage capacity is 100,000 m3.
Benhe Detention Park
Source:Kaohsiung City Government
29 Chapter 3. How we do
Outflow Regulation
29
pre-development post-development post-development +
flood mitigation facility
outflow outflow outflow
Urbanization increases flood risk
The land developers construct the detention basins and Low Impact Development facilities.
Completed in 2014 Total storage capacity of 8,000 M3 Reduce flood risk of surrounding 10 ha,
and protect 1700 residences
Donghu Detention Basin
In Dali Software Park
Source:Taichung City Government
Completed in 2015 Total storage capacity of 32,000 M3 A multi-purpose park with ecological,
landscape, flood detention and recreation.
Flood detention Basin in
Pinglin Forest Park
Source:Taichung City Government
Strategy
32 Chapter 3. How we do
C Detention on site
33 Chapter 3. How we do
Land use fits in spatial planning
Agriculture
67.7%
Others
Traffic
Hydrological
4.5%
Building
Forest
Land use Area(Km2) (%) Agriculture 874 67.7
Forest 104 8.0 Traffic 80 6.2
Hydrological 58 4.5 Building 103 8.0 Others 73 5.6 Total 1292 100
*land use distribution in Yunlin County *Source: department of land administration, MOI
Levee
Levee
Village
34 Chapter 3. How we do
Case study in Loisach River, Germany
Flood area
Levee is constructed to protect village. Farm lands share flooding water. No destroy of the original usage. Allows flood entering the farms during the storms. Combination of levee and grass land; the landowner could get one time
compensation of 20% of current value.
Source :Bavarian State Water Authority, 2010 Bavarian Rural Development and Water Management Mission
35 Chapter 3. How we do
Detention on site
Apply the idle/ fallow farm and fishing pond to share the flood storage during storms.
Modified
Wa-Yao Village Flood simulation of 100-year return period
Flooded area 4.6 ha, flooding depth 0.4 m in village No flooding in village Farmland 80 ha
Strategy
36 Chapter 3. How we do
D
37 Chapter 3. How we do
Early warning Rainfall in Gangshan station on Sep. 19 in 2010 (Typhoon Fanapi )
0
100
200
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48
雨量(
毫米)
Flooding at 15:00 at the nursing home
Rescue team arrive at 20:00
Flood prediction get 3hr earlier for
response
24 1 2 3 4 5 6
Ra
infa
ll (
mm
)
3Hours
Before: wait for rescue Now: evacuation beforehand
Get 8 hrs for response
38 Chapter 3. How we do
Improve the rainfall radar system
Provide the higher resolution of rainfall spatial distribution
Before resolution:1.3Km x 1.3Km
After resolution:250m x 250m
The maximum rainfall observed by Linyuan radar 23mm/hr
The maximum rainfall observed by the old radar 22mm/hr
39 Chapter 3. How we do
Spatial and temporal distribution of rainfall along Xinyi Road (from east to west)
0908 storm event
Daan Forest Park MRT Dongmen station Sec. 1, Xinsheng S. Rd.
Flooding from east to west
Application of radar data for precipitation monitoring
40 Chapter 3. How we do
Real-time Flooding Forecasting System
Automatically input the next 3 hr predicted rainfall to the 2-D model to forecast the flooding in next 3 hr with the resolution of 40*40 m.
Typhoon Megi in 2016
INPUT
Future precipitation forecast by CWB
41 Chapter 3. How we do
Flood prediction online system Automatic, real-time and dynamic
Flood warning, flood
depth, flood duration Results exhibition
Big data database
AI
Big data
Machine
learning
Exhibition
Apply the simulation results of the flood models to cut down the calculation duration from 30 mins to seconds and train the AI and machine learning.
Guoxing Bridge
Xigang Bridge
Mashan Bridge Danei
Bridge Erxi Bridge
大內八號橋
大內十號橋
玉豐大橋
中正橋
曾文一橋
曾文二橋
Taitie Bridge
Not satisfied to project flood
Close to waterway or scour directly
High liquefaction potential layer
Basis depth is not sufficient
Section 1 Section 2 Section 3 Section 4 Section 5 Section 6
Liaobu levee (high risk) dam failure simulation
42 Chapter 3. How we do
Risk assessment for watershed
Risk analysis provides well information to prevent and mitigate disasters
43 Chapter 3. How we do
Smart Water Level Gauge
Smart water level gauges are set up to detect the inundation depths on the roads and to assess the accuracy of model.
The research results indicated the accuracy of the flood forecasting system has reached 88.9%.
0
0.2
0.4
0.6
9 12 15 18 21 0 3 6 9
Inu
nd
ati
on
de
pth
(m
)
Time (h)
Station D in Typhoon Megi
SimulationObservation
0
0.1
0.2
0.3
9 12 15 18 21 0 3 6 9
Inu
nd
ati
on
de
pth
(m
)
Time (h)
Station I in Typhoon Megi
SimulationObservation
0
0.1
0.2
0.3
0.4
0.5
9 12 15 18 21 0 3 6 9
Inu
nd
ati
on
de
pth
(m
)
Time (h)
Station J in Typhoon Megi
SimulationObservation
0
0.1
0.2
0.3
9 12 15 18 21 0 3 6 9
Inu
nd
ati
on
de
pth
(m
)
Time (h)
Station K in Typhoon Megi SimulationObservation
Strategy
44 Chapter 3. How we do
E
45 Chapter 3. How we do
Brick Theory
Coordinate the movable and un-movable facilities, software and hardware.
River regulation
Gate
Pumping station
Detention basin
Mobile pumps
Portable flood barrier
46 Chapter 3. How we do
Polder dyke and pumping in the Budai Township, Chiayi County
Luan Temple
8/29 20:30 Polder accomplished 8/29 21:30 Pumps distributed and start pumping 8/30 11:00 Recession
Discharge direction
Polder 300 m, about 100 bulk bags 3 mobile pumps (0.3 cms / pump, total 0.9 cms)
4 mobile pumps (0.015 cms / pump, total 0.06cms)
47 Chapter 3. How we do
Pilot projects of mobile flood barrier
County Location Length (m)
Yunlin Maming Village 4,800
Tainan Yongkang, Beimen, Madou Districts 200
Kaohsiung flexible 200
Pingtung flexible 480
Taitung Taimali, Luye, Beinan Township 320
Jinmen flexible 2,610
Total 8,610
48 Chapter 3. How we do
Induce IOT into mobile pump
Bilateral communication, pump location and operation status Save electricity, low energy consumption Low price
4 G w i r e l e s s
m o n i t o r i n g
I O T m o d u l e
R e p o r t G P S l o c a t i o n
M o n i t o r b a t t e r y v o l t a g e
M o n i t o r p e t r o l e u m l e v e l
M a n u a l o p e r a t i o n b y e n g i n e e r
S t a t e o f p u m p s : i n i t i a t i o n / s t a n d b y / o f f l i n e
Conclusions Chapter. 4
50 Chapter 4. Conclusions
AWARENESS:
– High disastrous risks in Taiwan, because of the characteristics of natural environment.
– Risks increase under the impacts of climate change.
ACTIONS: Taiwan government has taken the action programs
– Integrate the national spatial planning to rethink the development philosophy in the urban and rural area.
– Integrate green and grey engineering.
– Apply technology to improve early warning and preparedness efficiently.
GOAL: Build a resilient home.
Source: Taijiang National Park
52 Chapter 3. How we do
Test the mobile flood barrier. Apply the light and fast combination barrier as the second prevention line.
Taking the Maming Village in Yunlin County as an example, it raises the protection standard to 50 year recurrence interval without disturbing citizens’ daily life.
Mobile flood barrier: 50 years recurrence interval
SOBEK flood simulation
Current situation: 50 years recurrence interval
SOBEK flood simulation
Pumping station
Heighten the levee
21.4 ha flood, 0.52 m depth
No flood
Mobile flood barrier
Mobile flood barrier
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