Doctoral thesis summary: Research on rainfall - runoff changes and propose scientific methodology to compute designed flood for transportation in northeast moutainous region of

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.

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

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

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

CHAPTER 1 LITERATURE REVIEWS ON CALCULATION OF DESIGN FLOOD FOR TRANSPORTATION WORKS

1.1 Literature reviews on design flood calculation

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

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,

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

o f 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

Calculation of design floods in transportation in Vietnam is summarized and mentioned in Vietnam Standards TCVN 9845:2013; Handbook of calculation

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

each area Figure 1.2 Methods for calculation of

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

supporting and outdated instruments for the calculation that led to unavoidable and undesired tolerance of the results and subjected to experience of the calculators

1.4 Study approach and methodology

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

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 improvement

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

Changes over time:

Mann kendall and

Sen test for trend

Calculation of design rainfall:

- Downscaling daily rainfall to short duration rainfall

- Develop IDF curves

- Calculate design rainfall

Delineati

on and calculatio

subcatch ment characteri stics

Deve lopm ent of

CN maps

Develo pment

of runoff coeffic ient maps

Develop ment of roughness maps

Case studies

- Drainage catchment structures A< 5km 2

- Drainage catchment structures A=5-30 km 2

- Drainage catchment structures A=30-100 km 2

- Drainage catchment structures A>100km 2

Recommended suitable methods for the North-East region

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, r oads have ma n y small

bridges, culverts, and sluices crossing the

(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

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

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

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:

QmaxP = (C.I.A)/3,6 (1-13)

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

Figure 1.4 Diagram of SCS-CN method

for design flood calculation

Figure 1.5 Diagram of rational method for design flood calculation

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:

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 Z

1-α/2 (α=5%)

Trend by Mann- Kenndall

Trend by Sen (mm/year)

Figure 2.11 CV Map of the studied area Figure 2.24 Isohyet map (I-1-100) of the