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Riverbank Erosion Risk Assessment Under Impact of Climate Change on Ho Chi Minh City, Pham Ngoc
1. RIVERBANK EROSION RISK ASSESSMENT
UNDER IMPACT OF CLIMATE CHANGE ON
HOCHIMINH CITY
Presenter: A/Prof. PHẠM NGỌC
Organization: International University
Quater 6, Linh Trung Ward, Thủ Đức
District, Hochiminh City
Phone: (08) 372 44270; Fax: (08) 37244271
Email: info@hcmiu.edu.vn
Website: http://www.hcmiu.edu.vn/
Hochiminh City, 9 March 2017 1
2. CONTENTS:
I. Introduction
II. Research framework and
methodologies
III. Results and discussions
IV.Conclusions and recommendations
2
Riverbank erosion risk assessment under impact of
climate change on Hochiminh City
3. I. INTRODUCTION
3
- However, beside of
benefits, many water-
related disasters from river,
including: river bank
erosion. For example:
Lower DongNai river
basin; dense river
network, with 975km
of river for navigation,
cary 145 Mil.tons of
goods/year
- 1997-2007: Economic loss
caused by water related-
disaster in HCMC is 202 Bill.
VND (10 Mil.$), in which river
bank erosion damage is 24.6
Mil. VND.
- In 2009, 114 severe erosion
positions were recorded in
HCMC (City transportation
Department)
1.1. Needs of study
4. Generally, Climate and Hydrologic regime of river are
strong factors influencing bank erosion.
Currently, they are dramatically changed
4
Does CC increase risk of river bank erosion?
Observed max-rainfall intensity at Tan Son
Hoa gauging station
Observed water level at Phu An gauging
station, loacted in Sai Gon River
Riverbank erosion risk assessment under impact of
climate change on Hochiminh City
5. 1.2. Objectives and studied areas
a) Objectives:
- To assess current situation, development of river bank
erosion (RBE) in HCMC;
- To identify main driving factors of RBE relevant to
specific river reach;
- To assess the risk of CC on RBE
b) Study area:
- Main rivers flowing through HCMC:
5
Riverbank erosion risk assessment under impact of
climate change on Hochiminh City
Saigon
Dongnai
Soairap
Longtau
Cầu Binh
Phuoc
Cầu Dong
Nai
Hiep Phuoc
Port
An Nghia
Canal
Cape of Red
Light Cat Lai Ferry
Station
7. Hazard VulnerabilityExposure
Direct risk
Disaster
Risk
Exposure
Disaster
Risk
Exposure
Reducing Risk & Increasing
Resilience (or adaptation)
Indirect Risk
Definition: the probability (likely, ‘chance’) of harmful consequences, or expected
losses/damage (injuries, property, livelihood, economic activity disrupted or environment
damaged, deaths) resulting from interaction between natural or human-induced hazards
and vulnerable exposure units.
Hazard - Mitigation = Vulnerability
Concept of risk assessment
7
Riverbank erosion risk assessment under impact of
climate change on Hochiminh City
8. 8
Current situation assessment and
main driving factor identification
Collection of
secondary data
Field investigation
and measurement
Location and
magnitude of erosion
Water levels,
discharges, TSS
Questionnaire to
Local communities
Mike models
(NAM, HD, ST)
Fuzzy Logic
(ArcGIS)
Calibration &
Verification
Set up CC/SLR
Scenarios
Risk assessment
and mapping
Research frame work: A risk
based approach
Riverbank erosion risk assessment under impact of
climate change on Hochiminh City
9. 9
3.1. Situation assessment of river bank erosion in
HCMC and main driving factors
- Recently, developmet of RBE in investigated rivers tends to
more complex, no reduction recorded; eventhough there are
many protection structures constructed (20 projects completed
until 2011). For example:
III. RESULTS AND DISCCUSION
Sông Sài Gòn: number of
erosion positions seem to
be increased, and move to
downstream (district 2)
instead ot Thanh Da island
in previous.
Resons: human activities,
such as: navigation,
construction in protected
river-corrodor, or un-
suitable structures
10. Sai gon
river
Factors influencing erosion
Flow
Ship
generated
wave
Sand
minning
Ship
parking
Human
occupation
Bình Phước
- Bình Triệu
bridge
x x x x
Bán đảo
Thanh Đa
x x x
Cầu Sài
Gòn đến
mũi Đèn Đỏ
x x x x
10
Dong Nai
River
Factors influencing erosion
Flow
Ship
generated
wave
Sand
minning
Ship parking
Human
occupation
Đồng Nai
bridge to Ba
Sang island
x x x x x
Ba Sang
island Tắc
juntion
x x x x
Tắc junction
to Cát Lái
ferry
x x x x x
Nha Be river
Factors influencing erosion
Flow
Ship
generated
wave
Sand
minning
Ship
parking
Human
occupation
Mũi Đèn Đỏ to Nhà Bè
junction
x x x x
Ngã ba sông Nhà Bè đến
cảng Hiệp Phước
x x x x x
Long Tau
River
Factors influencing erosion
Flow
Ship
generated
wave
Sand
minning
Ship parking
Human
occupation
Nhà Bè
junction to
Ông Kèo
harber
x
x x
Ông Kèo
harber Tam
Thôn Hiệp
junction
x x
x x
Tam Thôn
Hiệp to Tắc
An Nghĩai
x x x
- Natural cherateristic of river: weak foundation, breaded river...
- Other social activities in upper river basin:
Forest destruction: can be improved but need to collabration among
provices
Construction of reservoirs: Dau Tieng, Tri Anreservoirs trap sediment
(about 2,65 Mil. M3/year in Dau tieng, VKHTLMN, 2013).
Riverbank erosion risk assessment under impact of
climate change on Hochiminh City
11. 11
Riverbank erosion risk assessment under impact of
climate change on Hochiminh City
3.2. Impact of
CC/SLR on
hydrodynamic in
river system
NAM
(rainfall-
runnof
modeling)
Reservoir
operation
scenarios
Downstream
boundary conditions:
SLR scenarios, 2012
Version
MIKE 11-HD
for scenarios
Mike 21
HD/ST
model
Simulation
and scenarios
analysis
Initial, boundary
conditions
River network,
cross-sections
Upper
boundaries
for 2D model
Topo. data
Hazard
maps
Initial
parameters
12. SIMULATED DOMAIN FOR MIKE 21 MODEL
Thủ Dầu Một Biên Hòa
Thị Vải
Vàm Cỏ
Riverbank erosion risk assessment under impact of
climate change on Hochiminh City
13. Division of Sub-basin of upstream region for NAM model
MÔ HÌNH NAM
Riverbank erosion risk assessment under impact of
climate change on Hochiminh City
14. ĐA GIÁC THIESSEN
Weighted factor for input of rainfall data
MÔ HÌNH NAM
Riverbank erosion risk assessment under impact of
climate change on Hochiminh City
15. R2 = 0.816
KẾT QUẢ HIỆU CHỈNH CỦA MÔ HÌNH NAM
Calibration results of discharge hydrograph at Dầu tiếng and Phước Hòa gauging station,
from 01/01/1995 to 31/12/2005
Calibration results of discharge hydrograph at Trị An gauging station from 01/01/2013 to
31/12/2013
Riverbank erosion risk assessment under impact of
climate change on Hochiminh City
16. HIỆU CHỈNH MÔ HÌNH ĐIỀU TIẾT HỒ CHỨA
Observed and simulated discharge released from Trị An reservoir in 2013
Riverbank erosion risk assessment under impact of
climate change on Hochiminh City
17. Observed and simulated discharge released from Dầu Tiếng reservoir , 1989 to 12/2005
HIỆU CHỈNH MÔ HÌNH ĐIỀU TIẾT HỒ CHỨA
Riverbank erosion risk assessment under impact of
climate change on Hochiminh City
18. Observed and simulated discharge released from Phước Hòa resevoir, in 2013
HIỆU CHỈNH MÔ HÌNH ĐIỀU TIẾT HỒ CHỨA
Riverbank erosion risk assessment under impact of
climate change on Hochiminh City
19. Simulated river network in MIKE 11 model
MÔ HÌNH MIKE 11
Riverbank erosion risk assessment under impact of
climate change on Hochiminh City
20. Calibration results of discharge and water level hydrograph at some gauging stations : (a)
Phú Cường, (b) Phú An và (c) Nhà Bè, 20/9/2013 9:00 - 22/9/2013 9:00
(a) (b) (c)
HIỆU CHỈNH MÔ HÌNH MIKE 11
Riverbank erosion risk assessment under impact of
climate change on Hochiminh City
21. Verification results of discharge and water level hydrograph at some gauging stations(a)
Phú Cường, (b) Phú An và (c) Nhà Bè từ 19/10/2013 9:00 - 21/10/2013 9:00
(a) (b) (c)
HIỆU CHỈNH MÔ HÌNH MIKE 11
Riverbank erosion risk assessment under impact of
climate change on Hochiminh City
22. Calibration and verification of Mike 21 – HD/ST
VT1
VT2
VT3
VT4
Riverbank erosion risk assessment under impact of
climate change on Hochiminh City
23. Discharge: 4 & 9/2015 at
VT2
Water levels: 4 & 9/2015 at
VT2
Riverbank erosion risk assessment under impact of
climate change on Hochiminh City
24. 24
Calibration and verification for
estuaries region (Can Gio
biosphere)
Kết quả so sánh mực nước tại trạm Đồng Tranh từ ngày 19/10 –
21/10/2013
Kết quả so sánh vận tốc tại trạm Đồng Tranh từ ngày
9/10 – 21/10/2013
25. 25
Các kịch bản tính toán
SC1 Real hydrologic situation in
2013
SC 2 CC & SLR to 2020
SC 3 CC & SLR to 2030
SC 4 CC & SLR to 2050
SC 5 CC & SLR to 2070
SC 6 CC & SLR to 2100
SC 7 Release flood, P = 5%
SC 8 Release flood, P = 1%
Scenarios for simulation and analysis
Riverbank erosion risk assessment under impact of
climate change on Hochiminh City
36. Simulated results after 3 months in flood season
Erosion 0.3
m
erosion 0.13
m
2100 2013
To 2100: + Erosion reduced about 0.17m
+ Deposition increased to 0.06m, and deposited area also increased
Deposition 0.06
m
Deposition
0.08 m
38. TĐ 1%
TĐ 5%
Vmax = 2.1m/s
Vmax = 1.8 m/s
Vmax = 0.5-0.6 m/s
Vmax = 0.7-0.8 m/s
Thanh
Đa
island
Thanh
Đa
island
In comparison with SC1-
2013
SC7: V increase ≈ 40%
SC8: V increase ≈ 60%
39. In summary of hydrodynamic part:
• In comparison with current situation: CC/SLR not affect
much on hydrodynamic condition in river system (lower
discharge, higher water level); therefore, tendency or
erosion is reduced but higher deposition.
• However, flood release from 2 upstream reservoirs cause
serious change of hydraulic situation in rivers: velocity
higher from 40% to 70%.
Riverbank erosion risk assessment under impact of
climate change on Hochiminh City
40. 3.3. Risk assessment relevant to scenarios
40
Bank materials
Bank protection
Bank
vegetation
Hydraulic (v, H)
Rainfall pattern
Bank
occupation
Navigation
FUZZY LOGIC
Risk
assessment
and mapping
GIS tool
41. 41
modules in river bank risk assessment
Riverbank erosion risk assessment under impact of
climate change on Hochiminh City
50. Conclusions
(1) River bank erosion in HCMC is not mitigated in
comparision with previous data. Main reason now is
human activities instead of natural factors (soft soils,
river morphology…)
(2) Integrated Fuzzy logic and traditional hydrodynamic
modeling is reliable method for risk assessment
because many qualitative and quantitative factors can
be included. The model predicted that:
• CC not affect much on hydrodynamic regime in river
system; but
• Flood water released from 2 upstream reservoirs make
severe change of velocity in river (40% - 80% higher);
therefore, potentially cause higher bank erosion.
50
51. Conclusions (con’t)
• Under current situation, 56% length of river banks
is at high risk level, 32% at high to very high;
only 12% at safe (low to moderate level);
• In relative comparison, it is found that CC make
incensement of high risk area from 12% to 13%;
meanwhile flood released from reservoirs increase
from 6% to 8% areas at extreme risk level.
Therefore, urgent need to protect these regions to
cope with CC
51
52. Recommendations
• Effect of sedimentation change on erosion shout
be further studied.
• When application of fuzzy logic, several key
factors should be included, not consider all of
them
• Try to make membership function and fuzzy rules
more realistic basing on quantitative relationship
and expert consultancy.
• Need to determine thresh hole level which trigger
erosion of river bank (may be in Lab experiment).
52
