metadata: authors: 0: author: van Ledden,Mathijs
1: author: Tung,Tran Thanh
2: author: Nguyen,Dzung Huy
3: author: Nguyen,Long Thanh
count: Vietnam
docna: 0: docna: Coastal Development between Opportunity and
            Disaster Risk : An Assessment of the Coastal Protection
            System in Vietnam
docty: Policy Research Working Paper
subtopic: Natural Disasters,Hazard Risk Management,Social Risk Management,Disaster Management,Hydrology,Climate Change and Environment,Climate Change and Health,Science of Climate Change
teratopic: Social Development,Environment,Science and Technology Development,Conflict and Development,Urban Development,Health, Nutrition and Population,Water Resources
abstracts: cdata!: This paper provides a high-level
            assessment of Vietnam's sea dike system and its
            prescribed dike safety standards. The assessment estimates
            that 65 percent of the sea dike system does not meet the
            safety standards and that about $2 billion in capital
            investment is necessary to meet the standards, mainly in the
            Red River Delta. It also shows that current safety standards
            need finetuning, especially in areas with high risk and
            growth. This paper acts as a technical background paper to
            the report Resilient Shores: Vietnam's Coastal
            Development between Opportunity and Disaster Risk
            (Rentschler et al. 2020).
geo_reg_key: 517198,517191
repnme: repnme: Coastal Development between Opportunity and
            Disaster Risk : An Assessment of the Coastal Protection
            System in Vietnam
display_title: Coastal Development between
            Opportunity and Disaster Risk : An Assessment of the Coastal
            Protection System in Vietnam
listing_relative_url: /research/2020/08/32304278/coastal-development-between-opportunity-disaster-risk-assessment-coastal-protection-system-vietnam
topicv3: Water m1326522 137,Disaster Risk Management m1326682 820,Flood Protection m1326683 154,Climate Change m1326829 567,Flood m1503315 3216
publishtoextweb_dt: 2020-08-05T00:00:00Z
historic_topic: Social Development,Environment,Science and Technology Development,Conflict and Development,Urban Development,Health, Nutrition and Population,Water Resources
origu: Climate Change-D1-GFDRR-IBRD (GFDRR)
no_of_pages: 15
author_keys: 0: author_key: 1136160
1: author_key: 1357650
model_extractions: Policy Research Working Paper 9351 Resilient Shores: Vietnam’s Coastal Development between Opportunity and Disaster Risk _Background Paper_ Coastal Development between Opportunity and Disaster Risk An Assessment of the Coastal Protection System in Vietnam _Mathijs van Ledden Tran Thanh Tung Dzung Huy Nguyen Long Thanh Nguyen_ Global Facility for Disaster Reduction and Recovery & Urban, Disaster Risk Management, Resilience and Land Global Practice August 2020
Policy Research Working Paper 9351

# **Abstract**

This paper provides a high-level assessment of Vietnam’s sea dike system and its prescribed dike safety standards. The assessment estimates that 65 percent of the sea dike system does not meet the safety standards and that about $2 billion in capital investment is necessary to meet the standards, mainly in the Red River Delta. It also shows that current safety standards need finetuning, especially in areas with high risk and growth. This paper acts as a technical background paper to the report _Resilient Shores: Vietnam’s Coastal Development between Opportunity and Disaster Risk_ (Rentschler et al. 2020).

This paper is a product of the Global Facility for Disaster Reduction and Recovery and the Urban, Disaster Risk Management, Resilience and Land Global Practice. It is part of a larger effort by the World Bank to provide open access to its research and make a contribution to development policy discussions around the world. Policy Research Working Papers are also posted on the Web at http://www.worldbank.org/prwp. The authors may be contacted at mvanledden@worldbank.org.

_The Policy Research Working Paper Series disseminates the findings of work in progress to encourage the exchange of ideas about development issues. An objective of the series is to get the findings out quickly, even if the presentations are less than fully polished. The papers carry the names of the authors and should be cited accordingly. The findings, interpretations, and conclusions expressed in this paper are entirely those of the authors. They do not necessarily represent the views of the International Bank for Reconstruction and Development/World Bank and its affiliated organizations, or those of the Executive Directors of the World Bank or the governments they represent._ Produced by the Research Support Team
# Coastal development between opportunity and disaster risk: An assessment of the coastal protection system in Vietnam

Mathijs van Ledden<sup>1</sup> , Tran Thanh Tung<sup>2</sup> , Dzung Huy Nguyen<sup>3</sup> , Long Thanh Nguyen<sup>2</sup> _1Global Facility for Disaster Reduction and Recovery, World Bank, Washington DC, USA Contact: mvanledden@worldbank.org_ _2Faculty of Coastal Engineering, Thuyloi University, Hanoi, Vietnam_ _3World Bank, Hanoi, Vietnam_

**Acknowledgements:** This working paper contributes to the report _Resilient Shores: Vietnam’s Coastal Development between Opportunity and Disaster Risk_ (Rentschler et al. 2020). The assessments presented in this paper have benefited from helpful comments, feedback, and inputs by Beatriz Pozueta Mayo, Jun Rentschler, Sophie Anne de Vries Robbé, Johannes Braese, Stephane Hallegatte, Claire Nicolas, Benoit Bosquet, Francis Ghesquiere, and Peter Kristensen.

The result of a collaboration between the government of Vietnam and The World Bank, this report would not have been possible without the inputs, feedback, and support of the government of Vietnam, led by Tran Quang Hoai and Nguyen Truong Son, Director General and Deputy Director General of the Vietnam Disaster Management Authority, and with sectoral consultation inputs of relevant agencies at MARD, the Ministry of Construction, Ministry of Finance, Ministry of Natural Resources and Environment, Ministry of Planning and Investment, and Vietnam Electricity.
# 1. Introduction

Vietnam’s low-lying river flood plains, deltas and coastal margins, frequently exposed to natural hazards, are home to 70 percent of the country’s population and many important economic activities. Due in part to the high concentration of population and level of development, riverine and coastal flooding is a serious problem in the deltas and lowlands of coastal Vietnam. This is particularly so in the Red River and Mekong River Deltas, with their vast low-lying areas around or just above mean sea level. Without artificial protection from embankments and dikes, these areas would flood regularly. With flooding the most serious hazard facing Vietnam, in recent decades, the government has recognized the importance of flood mitigation for the country’s continued development and prosperity, investing significantly in structural and non-structural solutions for each region.

The government of Vietnam has established a clear strategy for disaster risk management and climate change adaptation, with substantially different approaches in the north, central and southern parts of the country. In the Red River Delta and North Central Regions, it aims to radically prevent floods, and take initiatives in prevent and respond to storm, drought and storm surge. In other words, it aims to completely protect these regions from flooding. In contrast, in the Mekong River Delta Region, its natural disaster prevention, response and mitigation approach is one of “living with the flood”, ensuring safety for sustainable development while also taking initiatives to “prevent storm, thunderstorm, whirlwind, salinity intrusion, drought. Its approach in the Central Region combines proactive disaster prevention and adaptation for development. This mixes the two approaches, protecting the population and important economic areas from the flood, while allowing other less important areas to be flooded to a certain level.

Dikes in Vietnam’s coastal zone have been recognized as a central element of coastal defense for several decades.<sup>1</sup> Extensive low-lying regions in the Red River and Mekong River Deltas have a large system of sea and estuary dikes. In these deltas, several provinces — such as Quang Ninh, Hai Phong, Ca Mau and Kien Giang — have over 150 kilometers of sea dikes each to protect the hinterland from coastal flooding. In the Central Region, smaller dike systems provide flood safety for pockets of low-lying areas near the coast. Vietnam’s sea dike system is essential for preventing extensive flooding of livelihoods and assets during high tides and typhoon surge. The total length of the sea dike system in the coastal zone is 2,659 kilometers (figure 1.1).

> **Figure 1.1. Extent of the river and sea dike system in Vietnam’s Delta Regions**

> _a) Dike system in the Red River Delta_

2
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in two phases from Quang Ninh to Quang Nam (phase 1) and from Quang Ngai to Kien Giang (phase 2).<sup>2</sup> This national program was divided into three periods with clear objectives for each:

- 2009–2012: Planting mangrove forests parallel to the sea dike system

- 2013–2016: Upgrading and developing the sea dike system alongside the road network

- 2017–2020: Constructing a sluice system to adapt the sea dike system to sea level rise and operate it for transportation.

It is widely recognized that the sea dike system is below its established grade level in many places and needs further upgrade. The government has introduced a grade level system for sea dikes that reflects the number of people and area protected. The higher the grade level, the higher the return period for which the sea dike should be able to withstand storm surge and waves. It is widely acknowledged in Vietnam that, due to funding constraints, many sea dikes do not comply with these grade levels. Moreover, the rapid growth in the coastal zone also makes it likely that these grade levels will increase in the near future to mitigate the increased risk to assets and livelihoods.

The aim of this technical note is to provide a preliminary assessment of investment needs for Vietnam’s structural coastal protection system — consisting of sea/estuary dikes and revetments — based on the existing data and design standards managed by the Vietnam Disaster Management Authority (VNDMA). The work has been conducted as part of the Increasing Resilience in Vietnam’s Coastal Areas Program<sup>3</sup> under the Vietnam Disaster Risk Management Advisory Services & Analytics. This draft note has been prepared for discussions with representatives from the Ministry of Agriculture and Rural Development (MARD) and other relevant agencies. The assessment and its results have been integrated into the report _Resilient Shores: Vietnam’s Coastal Development between Opportunity and Disaster Risk_ (Rentschler et al. 2020).

# 2. Data collection and dike safety standards

An inventory of all sea and estuary dikes and revetments has been compiled as a basis for this assessment. The dike profile information provided by the VNDMA’s Dyke Management Department was used to produce a detailed list of the characteristics of each stretch of the coastal protection system. Table 2.1 shows an example for Quang Ninh Province. This information is provided for every 1–10 kilometers, and the list includes over 500 stretches of coastal protection, throughout all of Vietnam’s 28 coastal provinces. Where crest height information was not available, this was estimated using the best available data from nearby locations. It is noted that the list provides information about the former flood protection level.<sup>4</sup> A new method of classifying this information has recently been adopted and is used throughout the assessment. It is explained in Section 3.

**Table 2.1. Overview of coastal protection information used in this assessment** _Example of a coastal protection stretch in Quang Ninh province_

4
|**Item**|**Example**|
|---|---|
|Numbering of the province TT (I–XXVIII), numbering for<br>each stretch(1,2,etc)|I.1|
|Province and location|Quang Ninh, dike system in Quang Yen<br>town: Ha An dyke|
|Location bykilometer|K0–K8+500|
|Length(in kilometers)|8.5|
|Flood protection level according to QĐ 58 (Grades 9–12,<br>Tide 5%)|Grade 9, Tide 5%|
|Floodprotection level based on new design(Grades I–V)|Grade IV|
|Type(sea dike,estuarydike,revetment)|Estuarydike|
|Current crest height(in meters)|+4.5 ÷ +5.0|

The Technical Standards in Sea Dike Design (MARD 2012) have been used to extract relevant information, including the sea dike grade classification (table 2.2). This document provides guidance for the design and rehabilitation of various types of sea dike and other relevant structures in Vietnam and includes information on the grading classification system. The grade determines the safety standard, which depends on the area and population the section protects: the larger the protected area and number of people; the higher the safety standard. In areas of industrial or economic importance, the safety level can be upgraded on a case-by-case basis. The classification system is used to set the safety standard for each stretch of the coastal protection system. Grade I offers protection for a 150-year return period; Grade V for 10–30 years. This assessment has applied a 20-year return period for Grade V as a starting point.

**Table 2.2 Sea dike grade classification**

|**Area**|**Protected area**<br>**(hectares, thousands)**|**Population**<br>**(thousands)**|**Safety standard**<br>**(years)**|
|---|---|---|---|
|Developed industrial urban<br>area|Over 100|Over 200|150|
|Rural areas with developed<br>industryand agriculture|50–100|100–200|100|
|Developed rural and<br>agricultural area|10–50|50–100|50|
|Medium developed rural<br>and agricultural area|5–10|10–50|30|
|Underdeveloped rural and<br>agricultural area|Below 5|Below 10|10<SS<30|

# _Source:_ MARD 2012.

_Notes:_ Developed industrial and agricultural areas are determined on the percentage of economic structure in the protected area. Areas with a greater industrialization are classified as a developed industrial area and so on. The protected areas are first classified according to industrial/agricultural development. The criteria about size and population size then determine the safety standard. If the protected area meets only one criterion, the level is lowered by one. Spatial planning must consider the country’s socioeconomic development plan for 2016–2020 and Vision to 2030.

Sea dike grading, introduced relatively recently in Vietnam, is an important step in putting an explicit risk-based grade system in place. Most sea dike designs were originally based on a typical protection level against storm surge and waves with a 20 to 25-year return period (Mai et al. 2008). The current sea dike grade classification system differentiates between areas of high and 5
low risk, directing more investment into protecting areas with a higher risk profile. These differentiated protection levels follow the same logic applied in other countries with extensive dike systems, like the Netherlands.

However, it is striking that the difference in protection levels between the areas distinguished in the classification scheme is relatively small in Vietnam. For example, there is factor 5 difference in protection levels between a rural and agricultural area with medium-level development (Grade IV) and a developed industrial area (Grade I), but the difference in number of people and area size is factor 60. This results in an uneven distribution of risk, disadvantaging more urbanized areas. Various studies also show that providing a 100–1,000-year protection level along Vietnam’s coast is justified from a cost-benefit perspective (see, for example, Mai et al. 2008; Hillen et al. 2008). This is much higher than the current protection levels of the sea dike classification system.

It is therefore recommended that the government undertake further analysis and potential finetuning of its grade classification system, with more detailed assessments to optimize investments in the dike system. In particular, the analysis should consider:

- **Consistency:** The safety standards of the dikes protecting low-lying areas are not always consistent, even within the same area. For example, a detailed analysis for Tien Lang in the Red River Delta shows that the dike system surrounding this polder has significant differences in safety standards for different stretches of the sea and river dikes. These inconsistencies are potential weak links in the polder’s protection system.

- **Level of protection:** As outlined above, the existing safety standard framework has a limited bandwidth in terms of protection levels, despite the large differences in area characteristics; and higher safety standards are economically justifiable in Vietnam.

- **Socioeconomic and climate change:** Rapid growth along the coast and the effects of climate change will likely require higher safety standards in the future. An exploratory analysis of how safety standards may change in time and what this implies for setting existing standards is essential.

6
# 3. Methodology of the sea dike system assessment

Using the information presented in the previous section, a methodology — outlined below — was set out to preliminarily define potential investment levels for Vietnam’s sea dike system. The focus of this assessment is to define the difference between the actual and required crest height of each coastal stretch, and to translate this into an investment level using a common practice unit cost for upgrading dikes (per meter of crest height and per kilometer of dike length). This approach is used only for policy analysis, to assess investment needs and define priorities, and has been used globally in other countries, such as the Netherlands. The approach has several limitations, since it does not include any geotechnical or structural assessment of the dike system, inter alia. Nevertheless, this level of analysis is considered sufficiently accurate for gaining a better understanding of the order of magnitude and geographical distribution of investment needs in Vietnam’s coastal protection system.

The methodology consists of three steps. First, the hydraulic boundary conditions of the coastal stretch are defined. Second, the required crest height for each stretch is determined. Finally, based on the obtained information, the investment needs per dike stretch are determined. These steps are explained in detail below.

## Step 1: Defining the hydraulic boundary conditions for each coastal stretch

The design water levels for each stretch of the coastal protection system have been directly adopted from the MARD’s dike design standards. These numbers represent the best possible information available in Vietnam. Frequency curves are available for more than 120 coastal locations, providing water levels for return periods ranging from 1–100 years. In this assessment, each stretch of the coastal protection system has been assigned a design water level from the frequency curve of the nearest point. If necessary, the design water level has been interpolated or extrapolated from the frequency curve.

Apart from design water levels, wave information is also necessary to define required crest heights. The MARD’s dike design guidelines also provide detailed information about waves. However, design wave heights at the dike toe are not available and have to be calculated from offshore wave heights using wave transformation modelling on the most updated bed topography. The wave information used in this assessment has therefore been estimated in a simplified way, as described in the next two paragraphs.

During storms, wave conditions near the dike toe will be severe due to strong winds, and the depth will most likely limit certain wave characteristics such as the maximum wave height that can exist during these conditions. Therefore, a constant wave height (Hs)/water depth (d) ratio has been applied, herein: Hs/d = 0.6. This ratio is considered to be a good first-order estimate of the maximum wave height at a certain water depth, based on coastal engineering practice. This ratio has also been verified and confirmed by analyzing the detailed wave computation results in the current dike standards.

The toe of the embankments is set at -0.25 meters with respect to the reference level in Vietnam. This number has been estimated based on wave and water depth information near the toe from the current sea dike standards. Using the toe and design water levels, a design water depth has 7
been estimated for this assessment. For example, a design water level of 2 meters results in a total water depth of 2.25 meters. The wave height/water depth ratio is applied to determine the design wave height for the dike stretch. In this example, the design wave height is then equal to 0.6 x 2.25 meters = 1.35 meters.

# Step 2: Defining the required crest height for each dike segment

The required embankment crest height is defined by meeting an allowable/design wave overtopping, using the dike geometry and hydraulic boundary conditions. The allowable overtopping rate is not a constant and can vary depending on the quality of the dike’s landward slope. The landward side of dikes in Vietnam is often unprotected but has grass cover. Hence, a maximum allowable overtopping rate of 10 liters per second per meter has been used as an initial estimate for this assessment. This maximum allowable overtopping rate originates from the current sea dike standards. Actual overtopping depends on many factors, including the magnitude of hydraulic boundary conditions, the obliqueness of the waves, dike geometry, and the use of friction elements such as blocks on the seaward-facing slope. The presence of a wave berm — an additional step on the seaward-facing side of dike that dissipates some of the wave energy — can be included in the design geometry to reduce the required crest height.

A simplified approach has been chosen to define the required crest height, by estimating the required freeboard — that is, the difference between water level and crest height — to meet the overtopping criterion mentioned above. This freeboard is generally expressed relative to the wave height at the dike toe. The assumption is made that a wave berm is generally applied for most of Vietnam’s sea dikes and some friction elements are in place at the seaward-facing slope to reduce wave overtopping. The seaward-facing slope is generally built at a 1:3–1:4 gradient with a wave berm present. The typical freeboard required is then about equal to the wave height to limit the overtopping below 10 liters per second per meter. This approximation of the required freeboard is applied throughout the assessment.

The required crest level also includes a safety height increment and provision for sea level rise and settlement. The safety height increment, established based on guidance from the MARD’s sea dike design standards, varies from 0.3–0.5 meters, depending on the grade level. A provision for sea level has been included in the crest height in accordance with the design guidance, calculated by using the lifetime of the construction (which depends on grade level) and the projected average sea level rise during that lifetime, which is around 5–6 millimeters per year using a medium climate change and sea level rise scenario (MONRE 2016).<sup>5</sup> The provision for sea level rise in the required crest height is 0.2–0.7 meters. No allowance for settlement has been included in this assessment.

# Step 3: Defining the dike system’s investment needs

Potential investment needs are determined using a dike raise unit price. For this purpose, the difference between the required and actual crest height for each dike stretch (determined using Steps 1 and 2) gives a potential deficiency in crest height. This is then translated into an investment cost using a unit price for dike reinforcements from literature reviews of $0.7–1.2 million per kilometer dike stretch and per meter dike raise (Hillen 2008; see also Mai et al). Based on reviews of dike reinforcement programs in Hai Phong and Nam Dinh, this unit price is set at $1 million per kilometer dike stretch and per meter dike raise for the time being. It is noted that 8
<!-- Start of picture text --> Investment need<br>determined by required<br>height increase between<br>actual height and Required height<br>required height including sea level rise and<br>safety increment to meet<br>lifetime<br>; safety standard during its<br>Actual height at this<br><!-- End of picture text -->
<!-- Start of picture text --> Protects against coastal surges with<br>a return period of<br>Grade | 150 years<br>Grade II 100 years<br>Grade III 30 years<br>Grade IV 30 years<br>Grade V < 30 years<br><!-- End of picture text -->
**Figure 4.2. Assessment of existing sea dike system in Vietnam**

<!-- Start of picture text --> Dike length (km)<br>0 50 100 150 200<br>Quang Ninh 33% 56% 11%<br>Hai Phong City 73% 27%<br>Thai Binh 77% 23%<br>Nam Dinh 20% 35% 44%<br>Ninh Binh 53% 47%<br>Thanh Hoa 3% 76% 21%<br>Nghe An 11% 52% 37%<br>Ha Tinh 76% 7% 17%<br>Quang Binh 41% 33% 26%<br>Quang Tri 17% 83%<br>Thua Thien - Hue 1% 99%<br>Da Nang City 100%0% 0%<br>Quang Nam 38% 62%<br>Quang Ngai 67% 33%0%<br>Binh Dinh 100%<br>Phu Yen 0%5% 95%<br>Khanh Hoa 82% 0%18%<br>Ninh Thuan 100%<br>Binh Thuan 96% 4%<br>Ba Ria-Vung Tau 13%30% 57%<br>Ho Chi Minh City 100%<br>Tien Giang 46% 54%<br>Ben Tre 100%<br>Tra Vinh 90% 10%<br>Soc Trang 68% 32%<br>Bac Lieu 100%<br>Ca Mau 54% 46%<br>Kien Giang 40% 60%<br>Meets Safety Standard < Safety Standard << Safety Standard<br><!-- End of picture text --> The analysis suggests that several billions of dollars are required to upgrade the existing system to the established safety standard. Although this is a first-order estimate, it provides direction on likely required investments per province (figure 4.3). In total, about $2 billion is needed to bring the system up to the established safety standard (CAPEX), and some provinces require investments of several hundreds of millions of dollars. Hai Phong, Nam Dinh and Thai Binh Provinces in the north and Ben Tre Province in the south have the highest investment needs per kilometer of dike length.

These results are based on a minimum scenario analysis. If the population and economy grow at likely rates in the coming years and decades, the investment need will be much higher, since the necessary safety standards will also rise. A further assessment of investment needs for the dike system and other interventions is recommended once more details are known about the geographical distribution of current and future flood risk. This assessment focuses on the dike 11
system only, which contain many hydraulic structures such as sluice gates and sometimes road crossings. Upgrading these structures and special objects generally requires significant additional investment, which will be further assessed in more detailed analyses.

**Figure 4.3. Assessment of dike investment need in Vietnam**

||<br> <br> <br> <br> <br> <br> <br>Dike upgrade cost|<br> <br>s ($, millions)|
|---|---|---|
||$-<br>$50<br>$100<br>$150<br>$200<br>$250<br>$300|$350<br>$400|
|Quang Ninh<br>|118||
|Hai Phong City||354|
|Thai Binh|201||
|Nam Dinh|218||
|Ninh Binh|43||
|Thanh Hoa|132||
|Nghe An|27||
|Ha Tinh|52||
|Quang Binh|52||
|Quang Tri|107||
|Thua Thien - Hue|206||
|Da Nang City<br>Quang Nam|0<br>25||
|Quang Ngai<br>Binh Dinh<br>Phu Yen<br>Khanh Hoa<br>Ninh Thuan<br>Binh Thuan|16<br>17<br>91<br>12<br>2<br>2||
|Ba Ria-Vung Tau|39||
|Ho Chi Minh City|34||
|Tien Giang|87||
|Ben Tre|209||
|Tra Vinh|20||
|Soc Trang<br>Bac Lieu|36<br>39||
|Ca Mau|170||
|Kien Giang|101||

1 The focus is on sea and estuary dikes. Vietnam also has an extensive river dike system, especially along the Red and Mekong Rivers, which extend into the delta regions. These river dikes in the coastal zone are not considered in this assessment due to the lack of comprehensive data sets at national level.

2 Decree No. 667/QÐ-TTg, 2009.

3 TF0A4573.

4 According to Prime Minister’s Decision #58/2006/QĐ-TTg dated March 14th, 2006 12