MINISTRY OF EDUCATION AND
TRAINING
MINISTRY OF AGRICULTURE
AND RURAL DEVELOPMENT
WATER RESOURCES UNIVERSITY
NGUYEN VAN THIN
WAVE OVERTOPPING AT SEA DIKES
WITH CROWNN-WALLS IN THE NORTHERN
COASTAL DELTA OF VIETNAM
Specialization: Hydraulic Engineering
Code No : 62-58-40-01
SUMMARY OF DOCTORAL DISSERTATION
HA NOI, 2014
This scientific work has been accomplished at Water Resources University
Advisor 1: Assoc. Prof. Nguyen Ba Quy
Advisor 2: Prof. Ngo Tri Vieng
Reviewer No. 1 Prof. Dinh Van Uu
Reviewer No. 2 Prof. Tran Dinh Hoi
Reviewer No. 3 Prof. Tran Dinh Hoa
This Doctoral Thesis will be defended at the meeting of the University Doctoral
Committee in room No………… on …….
This dissertation is available at:
- The National Library
- The Library of Water Resources University
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INTRODUCTION
1. Rationale
Viet Nam is a nation that is seriously affected by climate change and sea level
raise. There are many centres of economy and culture along the coastline. In the
north, sea dikes are relatively low with narrow crests, steep seaward and
landward slopes; most dikes are directly exposed to wave attack. Historical
records show that wave overtopping often causes damage to dike crests and
landward slopes. One of the effective measures to reduce overtopping is the use
of (low) crown-walls, because heightening dikes or constructing outer berms are
costly and not feasible, especially dikes with narrow margins. Till now, studies
into the influence of low crown-walls and interaction between wave-wall and
overtopping are limited. A better understanding of the influence of crown-walls
and promenade on overtopping is necessary to improve the present dike design
guidelines in Viet Nam. These facts lend the foundation for this thesis that is to
investigate “Wave Overtopping at sea dikes with crown-walls in the northern
coastal delta of Vietnam”.
2. Research objectives
The thesis aims to investigate the influence of low crown-walls on overtopping
discharge and the behaviour of overtopping flow at sea dikes. By doing so, the
reliability of overtopping estimation is increased to improve the dike design
guidelines currently applied in Viet Nam.
3. Scope of the study
Investigation of wave overtopping at sea dikes with low crown-walls in the north
of Viet Nam.
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4. Research contents
Review on overtopping on sea dikes with low crown-walls; Physical model to
investigate the effects of low crown-walls on wave overtopping at sea dikes;
Numerical and physical examination of the wave-wall interaction and
overtopping flow on sea dikes with low crown-walls; Case study-Overtopping at
Giao Thuy dike, Nam Dinh province
5. Approach and study methods
5.1. Approach
To obtain the objectives, the author carried out a literature study on wave
overtopping at sea dikes with low crown-walls to select an approach that is
inherent and also creative, suitable for Viet Nam.
5.2. Study approaches
Literature review; Physical and numerical modelling; Application.
6. Implications
Building low crown-walls on seadikes to heighten the crest level, reduce wave
overtopping is considered technically and economically viable in Viet Nam.
There exists limited research into overtopping at sea dikes with low crown-walls,
especially the interaction between wave and wall. Therefore, better
understanding of the wall influence on wave overtopping discharge and the
overtopping flow characteristics will help improve the reliability of design for
this type of sea-dikes in Vietnam.
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7. New contributions
- Insights into the influence of low crown-walls on wave overtopping and
the merit of wall promenade through a detailed examination of the wave-
wall interaction;
- Empirical equations to determine the overall influence factor of low
crown-walls for regular waves (Figure 2-12);
- Relationship between splash height and wave parameters and wall
geometry (Figure 2.13);
- Proposal on the use of a new sea-dike cross-section with crown-walls and
promenade, appropriate for the northern coastal detla of Viet Nam (Figure
4.8).
8. Thesis contents
In addition to the Introduction, Conclusions and Recommendations, the thesis
consists of 04 chapters
Chapter 1: Literature study on overtopping on sea dikes with low crown-walls;
Chapter 2: Physical model to investigate the effects of low crown-walls on wave
overtopping at sea dikes;
Chapter 3: Wave-wall interaction and overtopping flow on sea dikes with low
crown-walls;
Chapter 4: Case study-Overtopping at Giao Thuy dike, Nam Dinh province.
CHAPTER 1 REVIEW ON OVERTOPPING ON SEA DIKES WITH
LOW CROWN-WALLS
1.1 Introduction to research into overtopping at sea dikes
Due to significant changes of climate and environment, the frequency and
intensity of natural hazards gradually increase especially storms, tide and sea
level rise. As a result, overtopping at sea dikes remains as a risk to countries with