MINISTRY OF EDUCATION AND TRAINING
MINISTRY OF AGRICULTURE AND RURAL DEVELOPMENT
WATER RESOURCES UNIVERSTY DOAN THI NOI RESEARCH ON RAINFALL - RUNOFF CHANGES AND PROPOSE SCIENTIFIC METHODOLOGY TO COMPUTE DESIGNED FLOOD FOR TRANSPORTATION IN NORTHEAST MOUTAINOUS REGION OF VIET NAM
Specialization: Hydrology Code No: 62-44-02-24
DOCTORAL THESIS SUMMARY HA NOI, 2016
Research has been completed at Water Resources Universty
Advisor 1: Assoc. Prof Ngo Le Long
Advisor 2: Assoc. Prof Hoang Thanh Tung
Reviewer No. 1 : Prof Tran Thuc
Reviewer No. 2 : Assoc. Prof Tran Dinh Nghien
Reviewer No. 3 : Dr. Nguyen Lap Dan
This Doctoral thesis will be defended at the meeting of the Universty Doctoral
Committee in Room No … on… ............................................................................................................................... ...............................................................................................................................
This dissertation is available at:
- The National Library
- The Library of Water Resources University
INTRODUCTION
1. Rationale
Transportation plays a significantly role in national development, it is
necessary to complete and modernize transportation system. The country has
largely invested annually in new construction, upgradation and expansion of
transportation system for commercial, cultural and economical intercourses
both locally and internationally. In Vietnam, with more than 2/3 area is
mountainous area, but more than 70% road length is in this area.
Mountainous roads are mainly III-V grades while design and construction of
drainage works (bridge, culverts and ditch) have not been paid attention to as
well as limitation on calculation of hydrological and hydraulic features. Under
the effect of tropical monsoon climate with increasing extreme rainfall that
heavily damaged the transportation works. One of the main courses
significantly affecting sustainability and resilience of the drainage and
causing falling of negative and positive talus, floating of bridge and
culverts, and damage of bridge piers is effect of extreme rainfall in which
incorrect or improper calculation of design flood is the main cause. Vietnam
Standard TCVN 9845:2013 (based on QP.TL C-6-77) introduces a number of
methods for calculation of design flood based on rainfall such as: Intensity
limits and Xokolopxky originated from Russian authors of which many
parameters are not suitable with Vietnam conditions and their verification is
difficult therefore, results of the calculation may not be suitable to the actuality
and lead to dissatisfaction of apertures of the highway drainage structures. The
lack of rainfall and flow data, especially shorter period data, also causes
difficulty during calculation of design flood. Therefore, dissertation “Research
on rainfall - runoff changes and propose scientific base for calculation of
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design flood for transportation in North-East mountainous Region of Viet nam”
is urgently needed.
1. Research objectives
To study rainfall-runoff changes, to downscale rainfall and surface over time
and space, and to establish scientific base for calculation of design flood for
transportation structures.
2. Scope of the study
- Scope of study: Bac Kan and Lang Son provinces in the Northeast
mountainous areas of VietNam;
- Object of study: design rainfall and design flood for drainage structures on
National Highway QL3, 3B, 279, 3, 4A, 4B, and 1A in the studied area.
3. Study approach and methodology
3.1. Approach
To achieve the proposed target, necessary documents, general studies on
rainfall-runoff changes, methods for calculation of design flood for
transportation locally and internationally are collected to further select
appropriate approaches that are inheritable and yet ensure creativity in research.
3.2. Methodology
Methods used in the dissertation include: i) analysis, statistics, and selective
inheritance of related studies; ii) remote sensing and GIS has been used to
establish basins in mathematical models and to develop maps as scientific
base for proposal of methods for design flood calculation; iii) mathematical
models and case studies have been carried out to propose suitable methods
for design flood calculation transportation structures in the Northeast region
of Vietnam.
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4. Scientific and practical meanings
Results achieved from the dissertation has high practical meaning for having
partially solved the current difficulties in calculation of highway hydrology.
The study on rainfall-runoff changes in the Northeast region and
establishment of scientific base for calculation of design flood for
transportation structures have scientific meaning in approaching modern
calculation methods and is premise for development of calculation
procedure, which is suitable to Vietnam conditions.
5. New contributions
- Improved current methods for design flood calculation for drainage
structures in transportation taking into account of rainfall - runoff
changes and of detailed ground surface conditions by application of
modern techniques such as hydrological models and GIS;
- Developed calculation program for design floods for drainage
structures in transportation.
6. Contents of the dissertation
In addition to the Introduction, Conclusions and Recommendations, the
dissertation consists of 03 chapters:
Chapter 1: Literature reviews on calculation of design flood for transportation
works.
Chapter 2: Development of scientific base for calculation of design floods for
transportation works in the Northeast region of Vietnam.
Chapter 3: Case studies and recommendation of design flood methods for
transportation works.
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CHAPTER 1 LITERATURE REVIEWS ON CALCULATION OF DESIGN FLOOD FOR TRANSPORTATION WORKS.
1.1 Literature reviews on design flood calculation
1.1.1 Studies in the World
Calculation of design flood spanned a long period of study is inheritable,
developed, refined and modernized to serve construction of safety works in
rainy season, especially in the condition of climate change. A number of
typical studies on design floods can be mentioned are Chow and Shaw (1964),
Chow and Maidment (1988), Vijay (2002), Raghunath (2006) studies and
others. Basically, methods for calculation are based on principle theory of
runoff and efficient transformations of rainfall into runoff. However, from the
last two decades, outstanding development of computer, remote and GIS
technology has allowed scientists to analyze, experiment, and update modern
technology for refinement of parameters that had not been able to be developed
by earlier methods.
1.1.2 Studies in Vietnam
Studies for calculation of design floods in Vietnam are mentioned in standards,
norms, text book, projects and dissertation such as: QP.TL C-6-77 (1977);
Engineering Hydrology of Do Cao Dam et al (1990), Doctorate dissertation - a
study on extreme rainfalls and floods in Vietnam by Le Dinh Thanh (1997);
Principle of Hydrology and Design hydrology calculation of Le Van Nghinh
(2000 & 2003); Ministerial scientific study report “study on forecast and
warning on exceeding design flood – additional spillway solution” of Pham Ngoc
Quy et al (2005), Text book on Engineering hydrology of Ha Van Khoi et al
(2012); National scientific project on “Study on proposed scientific base for
flood and sea wall design standards in the conditions of climate change and sea
level rise in Vietnam and solutions for disaster risks mitigation and resilience”
chaired by Ngo Le Long. The studies present methods for calculation of
current design flood, hydrographical models for flow calculation,
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development of computer program for calculation of design flood or
proposal of method for calculation of design flood for reservoirs in
consideration climate change ‟s impacts.
1.2 Literature reviews on design flood calculation for transportation works
1.2.1 Studies in the World
Calculation of design flood for transportation works in the world is
summarized in guideline and design standards namely: Technical guideline for
planning and design (flood control section) in Japan; Guideline on bridge and
road design -technical standards of national road transportation agent in
England; Guideline on drainage structure calculation of American
Association of State Highway and Transportation Officials (AASHTO) in US;
HEC introduction of hydrological model; Highway hydrology (FHWA);
Technical guideline (TR55) or design standards; “ Guideline on and standards
of bridge design” in Columbia; Procedures BCH 63-67- procedures on survey
and design of railway and highway crossing river in Russia and other
documents.
Based on general results,
it is possible to classify
calculation methods into
two main groups: i)
Methods used in Western
countries, Japan and US
and ii) methods used in
Eastern Europe and
Russia (Figure 1.1).
Figure 1.1 Methods for calculation of design flood for transportation works
1.2.1 Studies in Vietnam Calculation of design floods in transportation in Vietnam is summarized and
mentioned in Vietnam Standards TCVN 9845:2013; Handbook of calculation
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of hydrology and hydraulic in bridge and road (2006) of Ministry of Transport;
Studies of Mai Anh Tuan (2003), Tran Dinh Nghiên (2003), Nguyen
Quang Chieu & Tran Tuan Hiep (2004), Nguyen Xuan Truc (2009), Doan Nhu
Thai Duong (2012), Nguyen Tien Cuong (2012), and most recently in doctorate
dissertation of Nguyen Anh Tuan (2014).
Methods for calculation of design
flood in Vietnam are subject to
area, status of hydrological data
and importance of works (level of
works). It is possible to classify
into two groups: i) statistics
analysis and ii) caused and
effected analysis (Figure 1.2)
based on researches of Russia for Figure 1.2 Methods for calculation of each area. design flood in transportation in Vietnam
1.3 Limitations in design flood calculation in transportation in Vietnam
From studying, analysis and assessment, it can be seen that limitations in design
flood calculation for transportation works in Vietnam as the followings: i) At
present, selection of frequency is based on levels of road but not consideration
of other negative conditions such as natural and hydrometeorological conditions
of drainage catchment area that led to unqualification and/or the works had been
damaged in monsoon; ii) Calculation of design flood is only paid attention to
the peak discharge but not consideration to the flood volume that led to
overflow of drainage works because of improper design, flow accumulation in
upper pool will cause formation of air pressure damaging drainage
tails/supports and breakdown of drain-body of the road; Consultation tables as
scientific base for calculation of design floods for transportation works are old
and based on old Russian studies and developed from limited data in Vietnam
(small scale maps and short time-series data), in addition to traditional
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supporting and outdated instruments for the calculation that led to unavoidable
and undesired tolerance of the results and subjected to experience of the
calculators.
Study approach and methodology 1.4
From limitations in calculation of design flood in transportation in Vietnam
and pre-eminence of a number of methods for calculation of design flood
used in Western countries, Japan and US, the dissertation chooses approach
as illustrated in figure 1.3 including:
i) Studies on selected methods, applied conditions, data requirements, and
scientific base; ii) Study on characteristics of rainfall: weather formations
causing heavy rains in the Northeast region and historical floods with statistical
damages of transportation have been presented for urgent needs of the study.
The study on changes of rainfalls over space and time has been carried out
using statistical methods, remote sensing and GIS, in which Mann-Kendal and
Sen have been used for assessment of rainfall changes over time, frequency and
recurrent analysis have been used for development of IDF curves for different
sub-area/regions in the studied region as well as downscaling daily rainfall to
smaller duration rainfall such as hourly rainfall. Remote sensing and GIS have
been used to update information and to develop rainfall intensity, Cv contour
maps; iii) Study on analysis of ground surface conditions of the Northeast
region: spatial data from maps and remote sensed data have been used to
delineate and calculate characteristics for more than 40 drainage sub-
catchments in the studied areas, to develop CN, runoff coefficient, and
roughness coefficient maps for flood design calculation; iv) Experimental
calculation and assessment of the results: analysis on base and conditions of
application of each selected method to propose appropriate methods for each
type of works and in complying with characteristics of the studied areas; v)
Development of computer program in order to integrate all achieved results
and procedures for guidance on calculation of design flood for
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transportation works in the Northeast region with the hope that such
program solves a number of limitations in current calculation methods and
at the same time leave it open for the researchers‟ further update and
Literature reviews
recurrent
improvement.
SCS-CN method - CN map; - Catchment area A - DU
Regional equation method - Catchment area A - Catchment slope S - Mưa
Study on catchment surface factors
Study on rainfall factors
of
Develop ment of roughness maps
IDF
Deve lopm ent of CN maps
Changes over space: - Changes of CV; Changes over time: Mann kendall and Sen test for trend
Develo pment of runoff coeffic ient maps
Delineati on and calculatio of n subcatch ment characteri stics
Calculation design rainfall: - Downscaling daily short to rainfall duration rainfall - Develop curves - Calculate design rainfall
Rational method: - Runoff coefficient C - Rainfall intensity I - Catchment area A
Case studies
Recommended suitable methods for the North-East region
- Drainage catchment structures A< 5km2 - Drainage catchment structures A=5-30 km2 - Drainage catchment structures A=30-100 km2 - Drainage catchment structures A>100km2
Figure 1.3 Diagram of study approach
1.5 Introduction of Studied Areas
The Northeast region of Vietnam (figure 2.1) is next to China, southeast looks
into Northern Bay, South is limited by Tam Dao Mountain and Red River
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Delta. This is an area with mountainous, slope and abyss topography strongly
divided and located in large rainfall centers. In rainy season, occurrence of
landslides, road cuts, floating of bridge are quite severe. Two provinces of
Lang Son and Bac Kan in the Northeast with 80% of mountainous area is
spring upper of large rivers with complicated slopes and is area with large
rainfall centers nationwide such as Bac Quang, Mong Cai, and Dinh Lap. Rainy season from May to September, with total rainfall covers 75 - 80% of
total annual rainfall. Months with largest rainfall are July and August with
total rainfall of more than 300mm/month. National Highways running through
the Northeast area include: QL1A, QL4A, QL4B, QL31, QL3, and QL3B
Drainage works on the roads include:
large and medium bridge (Lc>25m);
small bridge and culverts (Lc<25m);
ditch; spillway; and low water crossing.
In the two provinces of Bac Kan and
Lang Son, roads have many small
bridges, culverts, and sluices crossing the
roads.
Figure 2.1 Map of studied area (The Northeast area)
1.6 Conclusion of Chapter I
Methods for calculation of design flood in the world and Vietnam are divided
into two groups: direct methods (gage data) and indirect based on rainfall and
buffer surface (ungauged data). Existing issues of current methods in
Vietnam (TCVN 9845:2013) cause difficulty in making calculation and
providing rationality of results.Therefore, it is necessary to study and
approach methods used in advanced countries with the support of computer
technology, remote sensed data and GIS technology for elaboration and
refinement of database to apply selected methods for calculation of design
flood for transportation works.
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CHAPTER 2 DEVELOPMENT OF SCIENTIFIC BASE FOR CALCULATION OF DESIGN FLOOD FOR TRANSPORTATION WORKS IN THE NORTHEAST REGION OF VIETNAM
2.1 Theoretical base of of methods for calculation of design flood
2.1.1 SCS-CN method
This method was developed by Soil Conservation Service (SCS) and officially
enlisted in American Handbook of Technique 2004 that is currently used
worldwide. SCS-C method includes two main parts: loss part (effective
rainfall, from C) and efficient conversion of rainfall part into flow by SCS unit
hydrograph. Input data of the method includes: rainfall, type of soil,
topography, humidity, and land used.
2.1.2 Rational Method
Rational method (or Q = C.I.A) is mentioned in most of Standards for
transportation designs all over the world, based on relation between the flow
and basic characteristics of the basin, average intensity of rainfall and area of
the catchment. Formula for calculating design flood peak is in the form of:
(1-13) QmaxP = (C.I.A)/3,6
Figure 1.4 Diagram of SCS-CN method for design flood calculation
Figure 1.5 Diagram of rational method for design flood calculation
In which: QmaxP is peak discharge of design flood (m3/s); C is runoff coefficient; I is rainfall intensity corresponding to time of concentration (mm/h); A is catchment area (km2). Steps of calculation of rational method is summarized in diagram 1.5.
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2.1.3 Regional recurrent Equation
Regional recurrent equation is one of the methods often used in planning or
initial design estimation for drainage works in un-gage areas. Scientific base
of this method is the summary of basin characteristics, ground surface and
design rainfalls to develop regional recurrent equations under relation
between modules or peak flood flows and basin area for different areas in the territory (example: Qm = a.An).
2.2 Database of methods for calculation of design flood
To apply selected methods (item 1.5), it is necessary to develop database on
rainfall and ground surface as the followings:
2.2.1 Development of rainfall database
Rain is important factor deciding the formation of flood flow in the catchment.
Study on rain includes: rainfall, duration, intensity, distribution (fluctuation)
over space and time. Collection of weather formations causing heavy rains in
the studied areas and changes of rainfall over space and time, downscaling
(elaboration) of daily rainfall to short-period rainfall, development of IDF
(Intensity - Duration - Frequency) curves, maps on rainfall variation coefficient
(CV), rainfall accumulation curves of different locations in the studied area. A number of typical results are illustrated and summarized in the following
tables and figures:
Table 2.3 Result of trend of maximum daily rainfall
Station
n
Test Z
Z1- α/2(α=5%)
Trend by Mann- Kenndall
57 39 39 39 39 55 52 47
1,20 0,33 1,72 -0,93 -0,80 1,79 1,10 -1,70
Increase Increase Increase Decrease Decrease Increase Increase Decrease
1,96 1,96 1,96 1,96 1,96 1,96 1,96 1,96
Trend by Sen (mm/year) 176,0 28,0 143,0 -78,0 -67,0 247,0 141,0 -189,0
Xmax Bac Kan Xmax Bac Son Xmax Cho Ra Xmax Dinh Lap Xmax Huu Lung Xmax Lang Son Xmax Ngan Son Xmax That Khe
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Figure 2.11 CV Map of the studied area Figure 2.24 Isohyet map (I-1-100) of the studied area
T = 5
T = 10
T = 25
Trạm
a
n
a
n
a
n
Bac Kan
50,9
-1,25
63,0
-1,25
79,1
-1,25
Bac Son
59,3
-1,32
74,9
-1,38
95,9
-1,45
Cho Ra
38,2
-1,18
47,5
-1,17
59,9
-1,16
Đinh Lap
54,8
-1,14
71,1
-1,14
93,8
-1,14
Lang Son
46,9
-1,24
56,2
-1,24
68
-1,24
That Khe
58,2
-1,32
72,5
-1,31
91,5
-1,29
Ngan Son
57,7
-1,25
71,8
-1,27
89,6
-1,3
Huu Lung
67,5
-1,36
83,9
-1,39
105,9
-1,41
Figure 2.25 Mass 24h rainfall curves at Bac Kan and Bac Son stations
Figure 2.23 IDF curves at Lang Son and Dinh Lap stations Table 2.6 Coeficients of IDF curves, I=a.Dn
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Results of the study shows that if consideration of the Northeast area as one of
the 18 zones of Vietnam using reduction factor and a maximum daily rainfall
for calculation of design flood in transportation, results are unreasonable due to
large fluctuation of rainfall both in space and time among the areas (table 2.9 and
figure 2.17). Therefore, downscaling (elaboration) of daily rainfall into hourly
rainfall and development of daily rainfall distribution map, and IDF curves for
different locations in the studied area are necessary.
2.2.2 Development of surface database
Development of surface database for calculation of design flood for
transportation in the studied area includes catchmentdelineration, determination
of catchment characteristics (area, length, slope..etc), preparation of CN, runoff
coefficient, roughness coeficient maps (tables). In this research, remote
sensing and GIS were applied for updating of information, for spatial analysis,
and for development of the above mentioned maps and tables for flood
calculation.
Figure 2.29 Diagram for development of CN map
2.2.2.1 Development of Curve Number Map
Development of Curve Number Map for the studied areas is performed
according to diagram 2.29. The result is illustrated in Figure 2.32.
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Figure 2.32 Curve Number map of the Bac Kan - Lang Song region
2.2.2.2 Development of runoff coefficient map
Development of runoff coefficient map for the studied areas is performed
Figure 2.33 Diagram for development of roughness coefficient map
according to diagram 2.33. The result is illustrated in figure 2.34.
Figure 2.34 Runoff coefficient map of Bac Kan and Lang Son provinces
2.2.2.3 Development of roughness factor coefficient (Manning n) map
Development of n roughness factor map for the studied areas is performed
Figure 2.35 Diagram for development of roughness coefficient map
Hình 2.36 Roughness coefficient map of Bắc Kạn và Lạng Sơn provinces
according to diagram 2.35. The result is illustrated in figure 2.36
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2.2.2.4 Delineation and determination of catchment features from DEM
It is very necessary to calculate characteristics of catchment such as averaged
elevation, runoff direction are used to estimate time of concentration,
catchment area. More than 40 drainage catchments of the Northeast Region of
Vietnam have been delineated and its characteristics have been determined.
Sample results are briefly shown in Figure 2.37 and Table 2.17.
Figure 2.37 Map of Bac Khuong bridge catchment
Bảng 2.17 Characteristics of cầu Bắc Khương bridge catchment
No. 1 2 3 4 5 6 7 8 9
Characteristics of Bac Khuong Bridge Design probability Catchment area Main flow length Total flow length Catchment length Catchment averaged width Catchment roughness Catchment averaged slope River bed slope
Unit % km2 km km km km2/km
Value 506,5 27,3 40,1 56,2 9,0 2,0 23,6 0,4
Symbol P F L ∑Li Llv B n J(Sb) % Js(Sr)%
2.3 Conclusion of chapter II
It has been seen from the research results that if the North - East Region is
assumed as one of 18 rainfall regions in Vietnam as specified in TCVN
9845:20013, is not suitable in calculation of design floods because of large
changes of rainfall over space. Thus, for calculation of design floods for small
drainage catchments in transportation, it is suitable to downscale daily to
hourly rainfall, to develop IDF curves, to develop 24 hour accumulation rainfall
distribution curves and to develop rainfall contour maps. In addition, the
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downscaling and updating of catchment surface such as catchment delineation
and characteristics determination, development of CN, runoff coefficient,
roughness coefficient grid maps are also important in establishing scientific
base (database) for application of selected flood design calculation method in
this dissertation.
CHAPTER 3 CASE STUDIES AND RECOMMENDATION OF DESIGN FLOOD METHODS FOR TRANSPORTATION
3.1 Classification of drainage structures in calculation of design floods
Drainage structures are classified based on the followings:
+ Applied condition of calculation method: the rational method is applied for catchments with area less than 65 km2; SCS method is applied for catchments with area range from 2 to 500 km2; while the regional recurrent method is applied based on the data details;
+ Data collection on drainage structures (location, route, quantity);
+ Calculation parameters (soil types, land cover, land used, CN, runoff
coefficient, roughness coefficient, slope...etc)
This research has classified drainage catchments for calculation of design flood
into 3 groups:
The first group: structures having small drainage catchment area (A<5km2)
includes sluice, small bridge (about 50% of drainage structures on road). This
group has very simple soil type, land used, thus design flood can be calculated
fast; The second group: structures having drainage catchment areas from 5 to 30 km2 (about 40% of drainage structures on road). This group has more complete soil type and land used. The third group: remaining drainage structures with catchment area more than 30 km2. This group has more complete conditions of soil type, land cover and land used and need to be
divided into subcatchments.
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Case study implementation: The dissertation has carried out calculation of
design flood for more than 40 drainage structures using 3 selected methods and
2 methods specified in TCVN 9845:2013. Results are presented in the Annex
of this report, Table 3.14 below briefly summarizes calculation results for the
Can Bridge (representative for drainage structures having catchment area less than 5 km2), the Ban Chat Bridge (representative for drainage structures having catchment areas from 5 to 30 km2); Pac Vang Bridge (representative for drainage structures having catchment areas from 30 to 100 km2); and the Ky Lua Bridge (representative for drainage structures having catchment areas larger than 100 km2).
Results shown in the above table are different because of differences in
approach and database used. The three dissertation selected methods used
database with updated and downscaled rainfall and catchment surface with
advance technology such as hydrological models and GIS, thus calculation is
faster and with more suitable results than these two methods specified in the
TCVN 9845:2013 that assume the same parameters for the whole region of
Northeast (1 of 18 regions of Viet Nam); thus some parameters in the region
are tendency higher while other parameters are tendency lower in calculations
and in addition, the database was developed long time ago in limited data
condition and has not been updated.
Recommendation of suitable methods: With database of downscaled rainfall
and surface developed as scientific base and with simple theory, this
dissertation recommends to use these 3 methods for calculation of design flood
for drainage structures of transportation as summarized in Table 3.15.
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Table 3.14 Design flood calculations of 5 methods
Design flood discharge Qp% (m3/s)
No.
Recommended in the Dissertation
TCVN 9845:2013
Name of bridge
A (km2)
CIA
SCS
Recurrent Xokolosky CDGH
1
Can
3,16
95,8
74,6
87,8
93,0
71,0
2
Ban Chat
25,2
327,5
276,0
281,9
362,1
252,9
3
Pac Vang
129,2
652,2
610,9
707,4
712,5
711,9
4
Ky Lua
1559,9
2170,1
3420,0
3325,4
3960,0
3856,8
Duty
Method
Structure
Implementation contents
No.
Small sluice
Catchment size (km2) A < 5
5 < A < 30
Rational method Q=C.I.A
Sluice and small bridge
Design
- Define C from map -Define A from map of catchment - Calculate Tc from catchment characteristics - Define I from the IDF curves
1
5 < A < 30
Sluice and small bridge
SCS-CN
Medium bridge
30 < A < 100
-Define CN from map - Define A from map of catchment - Calculate Tc from catchment characteristics
Big bridge
A > 100
A < 400
2
Planning and project development
Regional recurrent method
Sluice Small bridge Medium bridge Bid bridge
- Define A from map of catchment - Select probability - Define parameters of equation Q=f(A)
Table 3.15 Recommeded methods for calculation of design flood for drainage structurers of transportation
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3.2 Development of flood design calculation program for drainage structures of transportation in the North -East Region of VN
3.2.1 General introduction to the program
Based on the results achieved in chapter I and II such as calculation method,
applied conditions, database of downscaled rainfall and catchment surface, this
dissertation has developed a program for design flood calculation for drainage
structures in the North -East Region of Vietnam.
The program is developed by using oriented programing language of Visual
Basic and is integrated on Google Map, thus taking the advantage of updated
information of high resolution remote sensing data regularly (IKONOS -1m)
and of Google based maps with ability to zoom in for more detailed study of
area while computation. Source code of the program is given in the Annex of
this dissertation; initial interface of the program is presented in the Figure 3.19
below:
Figure 3.19 Initial interface of the program (satelite interface)
3.2.2 Program structure
Program structure is presented in Figure 3.20. In this figure, it can be seen that
the program is divided into 2 main modules: i) calculation module including
the development of subroutines for the 3 recommended methods (the first 4
pages of the program source code); ii) database management for data import,
export and for display of calculation results (the remaining pages of the
program source code).
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Figure 3.20 Diagram of calculation program
All maps and database (CN, runoff coefficient C, Cv, rainfall intensity,
subcatchments and its characteristics), curves (IDF, accumulated rainfall
distribution), tables, and regional recurrent equations have been integrated into
GEO-database and into Google Map interface. The GEO-database is special
database that have 2 main parts: i) spatial part for describing location, shape,
and dimension of oriented object, and they can be in vector or raster formats
(These are maps of CN, C, N, Cv...etc) and attribute part for describing values
and information of the spatial part, they can be matric format.
Program user guide, The calculation program has been developed with the
purpose for fast calculation and updating parameters when needed in the North
-East region and it can be extended to other region of Vietnam. The program is
integrated on the Goole Map thus having users friendly interface with simple
calculation procedure. Calculation procedure can be summarized as the
followings:
Step 1: Open the program: if your computer is connected to the Internet, you
can type in the address of the program, a window as shown in Figure 3.21
appears, click on button “bản đồ” or “vệ tinh” on the top left corner to display
map or satellite interface of the calculation area.
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Step 2: Selection of calculation method: based on your calculation purpose and
drainage catchment area of the calculated structure (following recommendation
in Table 3.22), a method should be selected. Figure 3.22 illustrates a window
for the rational method.
Figure 3.21 Initial interface of the program (map interface)
the GEO-database for calculation such as
Step 3: Input information for calculated structure: user needs to input name, probability, location (lat, long), drainage catchment area, the program will move and zoom in to the studied area of the drainage structure and define time of parameters from concentration Tc, averaged catchment slope, runoff coefficient C, design rainfall intensity (see Figure 3.22). User can click on the button “Tính toán” on the top right corner of the window, or can change parameter based on latest land used map of Google (IKONOS -1m). After pressing button “Tính toán”, the program will display the calculation result such as design flood discharge and design hydrograph. User can print or export results to a table and a figure for the report. Procedure for other method is similar to this method.
Figure 3.22 Calculation results of design flood for the Can bridge using rational method (satellite interface)
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3.3 Conclusion of chapter III
With database developed from chapter II, case studies for more than 40
structures of 4 types have been carried out using 5 methods (3 dissertation
recommended methods and 2 methods specified in TCVN9845:2013). Case
study results have been analysed for recommendation of suitable methods for
each type of structures and for each calculation conditions. A calculation
program has also developed and integrated into Google map which allow user
to fast calculate and upgrade information as well as to improve the program
because of its open source code program.
CONCLUSIONS AND RECOMMENDATIONS
1. Performed contents in the dissertation
The dissertation has collected a large number of information and data related to
the studied subject and has carried out literature reviews in order to select
suitable approach and methodology which inherit advantages of previous
researches but still ensure new issues and ideas for the dissertation:
The dissertation has collected data and information (structures, hydro-
meteorological data, soil maps, land used maps, DEM, etc) and developed
scientific base for application of the recommended methods for calculation of
design flood for drainage structures of transportation:
Theory of these 3 recommended methods, applied conditions, data
requirements and application procedure have been introduced:
+ In term of rainfall factor, weather formations causing heavy rains in the
Northeast region and historical floods with statistical damages of transportation
have been presented for urgent needs of the study. The study on changes of
rainfalls over space and time has been carried out using statistical methods,
remote sensing and GIS, in which Mann-Kendal and Sen have been used for
assessment of rainfall changes over time, frequency and recurrent analysis have
been used for development of IDF curves for different sub-area/regions in the
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studied region as well as downscaling daily rainfall to smaller duration rainfall
such as hourly rainfall. Remote sensing and GIS have been used to update
information and to develop rainfall intensity, Cv contour maps.
+ In term of catchment surface, spatial data from maps and remote sensed data
have been used to delineate and calculate characteristics for more than 40
drainage sub-catchments in the studied areas, to develop CN, runoff coefficient,
and roughness coefficient maps for flood design calculation.
2) The dissertation have carried out case studies for different type of structures
(classified by drainage catchment area) and have recommended suitable
methods for design flood calculation for transportation drainage structures :
- In design works: Rational method should be used for drainage catchment area of less than 5 km2; for drainage catchment areas from 5 to 30 km2, SCS-CN method should be used; and for drainage catchment areas of more than 100 km2, SCS-CN in combination of other methods should be used;
- In planning and project development : Regional recurrent method can be used
for fast estimation and assessment of drainage capacity for old bridges and
sluices.
From case studies of more than 40 structures in the studied area, it can be seen
that three recommended methods are very easy to use with the developed
database, and modern techniques such as hydrological models and GIS can be
used when more detailed studies and more information on catchment surface
are needed.
3) The dissertation has integrated all data and scientific base (CN, runoff
coefficients, Cv, sub-catchment„s characteristics, IDF curves, regional recurrent
equations, etc..) into GEO-database for development of a program written on
Google Map. This is an open source code program which allows user to update
data of all types into GEO-database.
2. Limitations of the dissertation
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Rainfall changes have been assessed but flood flow changes have not been
assessed due to some reasons.
Developed program has only accounted design flood peaks with theory
hydrographs (triangle and trapezium shapes); actual design flood hydrographs
have not been considered due to lack of flood flow observations.
3. New contributions of the dissertation
The dissertation has 2 contributions (see Introduction).
4. Future development of the dissertation
Results achieved from the dissertation are considerated to be at initial stages,
more studies need to be carried out: i) to continue upgrading data and
information into the GEO-database; ii) to improve the developed program and
to share this program on the Google Map for having more contributions from
scientists with more useful methods; iii) to extend the study to other regions of
Vietnam.
5. Recommendations
More detailed studies need to be carried out in order to upgrade the existing
National Standards/Guidelines for calculation of design floods for
transportation drainage structures and the guidelines should be easy to use and
modern techniques can be applied similar to the Standards/Guidelines in
developed countries.
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PUBLICATIONS OF THE AUTHOR
1. Doan Thi Noi, Ngo Le Long and Hoang Thanh Tung (2016). ''Research for
recommendation of designed flood calculation methods for transporation in the
Northeast region of Viet Nam''. Journal Water Resources & Environmental
Engineering. Issue 6 - 2016;
2. Doan Thi Noi, Hoang Thanh Tung and Nguyen Hoang Son (2015). ''
Estalishment of IDF curves for lack of short - term data regions in the Northeast
- Viet Nam''. Proceedings of the annual conference on water resources. Issue
11-2015. Pp 369-371;
3. Doan Thi Noi (2015). ''Research on calculating flood of medium and small
basin by SCS-CN with land use change''. Transportation and communications
science journal. Issue 9 - 2015. pp 48-52;
4. Doan Thi Noi and Nguyen Hoang Son (2015). ''Establishment of IDF curves
for calculating design flood of transport works in the Northeastern provinces-
Viet Nam''. Transportation and communications science journal. Issue 8 - 2015.
pp 84-90;
5. Doan Thi Noi and Le Thi Hai Yen (2015). '' Application of hydrologic
mathematical modeling HEC-HMS for Thac Gieng Bridge''. The Transport
journal. Issue 6-2015. pp 52-55.
