advisory report_sustainable coastal protection in vietnam.compressed

HZ University of Applied Sciences

ADVISORY REPORT Sustainable coastal protection in Vietnam

“Improving safety, ecology and profits in Soc Trang by using different strategies of coastal protection”

20th July 2015 Shrimp farm property located at the Hinterland of Soc Trang province’s coastline, Vietnam

Document Advisory Report

Research Conclusion 20th July 2015

Document Status Final

Version 4.0 Rev. 09/11/2015

Year 2014/2015, 2nd semester

AUTHORS:

HZ University Department of Applied Sciences

Study Civil Engineering

Course Research Internship

Supervisor João N. Salvador de Paiva

20Th July 2015

ADVISORY REPORT Sustainable coastal protection in Vietnam

Anthony W. V. Meijer

Student ID: 00063496 - Civil Engineering

Email: [email protected]

LinkedIn: https://nl.linkedin.com/in/AnthonyMeijer

Rick P. Kool

Student ID: 00061541 - Civil Engineering

Email: [email protected]

LinkedIn: https://nl.linkedin.com/in/RickKool

© 2015 The Authors.

https://nl.linkedin.com/in/RickKool

https://nl.linkedin.com/in/AnthonyMeijer

Message from the Authors

“With this research our intention is to develop coastal protection solutions for Soc Trang using sustainable soft-

engineering techniques that contribute to enhance the overall

scenario in the region.”

We are glad to present you the summary of months of research and design. It was a joyful time to work and collaborate with so many different parties; in fact, the production of this document would have never been possible without the dedicated effort of all stakeholders and parties involved. Over the time we received valuable input coming from different people such as our mentor in the Hz University in The Netherlands, The Ministry of Agriculture and Rural Development of the Soc Trang Province and our Professors in the Can Tho University. I would like to thank you for all your effort and support.

After all the time spent in Vietnam, experiencing the different characteristics over the different regions of the country, we concluded that one thing is unanimous among all of them: The Mekong Delta has a lot of importance in the lives of the Vietnamese.

With this research our intention is to develop coastal protection solutions for Soc Trang using sustainable soft-engineering techniques that contribute to enhance the overall scenario in the region. This document portraits the thought process carried out during the different phases of the research. The result is a sustainable alternative aimed on improving safety, ecology and profits in Soc Trang by utilizing different methods of Coastal Protection. We hope to make a positive contribution and support the development of this fast-growing country.

Best regards, Anthony Meijer

Anthony Meijer 3rd year Civil Engineering Student in HZ University of Applied Sciences

“The Mekong delta is an emerging, dynamic area that has a lot to offer

and wants to take a venture in development by taking the next step

in water management.”

We are proud to present to you the result of an adventure that took five months to complete. The Mekong delta is an emerging, dynamic area that has a lot to offer and wants to take a venture in development by taking the next step in water management. This shows by all the great support we have received by different stakeholders and parties involved.

I would like to give special thanks to the following persons and parties; their support has made this project happen.

Msc. J.N. Salvador de Paiva, your support for this project before it was even in the current form has been an enormous boost for our interest and enthusiasm and a push to improve continuously. Nghia Phan, for supporting the project pro bono, handling relations with everything from governmental procedures to smoothen the transition and contact with Can Tho University. Dhr. Tran van Ty, for not only supporting our projects, arranging seminars, and giving advice on the project. Also for showing us Can Tho, local delicacies and introducing us to local people. Without the support of the ministry of agriculture and Can Tho University, this would not have been possible.

The result is a study aimed to improve safety, ecology and profits in Soc Trang by using different methods of Coastal protection. We hope this study will give you an insight in complexity of the region, as well as providing thought for your own opinion about the best approach.

Kind Regards, Rick Kool

Rick Kool 3rd year Civil Engineering Student in HZ University of Applied Sciences

Abstract

The Mekong Delta plays an important role as ‘rice bowl’ for the whole of Vietnam. Rapid expansion of shrimp farming in the Mekong Delta has contributed to economic growth and poverty reduction, but has been accompanied by rising concerns over environmental and social impacts. Thousands of hectares of mangrove forest were converted into shrimp farms in the last decade. The lack of an integrated approach to sustainable management, utilization and protection of the coastal zone and economic interests in shrimp farming have led to the unsustainable use of natural resources, thus threatening the protection function of the mangrove forest belt and, in turn, reducing income for local communities.

In our research, we focused on Soc Trang province, which deals with all these issues on an accelerated rate. The coastal zone is also affected by the impacts of climate change, which is predicted to cause increased intensity and frequency of storms, floods and droughts, increased saline intrusion, land subsidence, higher rainfall during the rainy season and rising sea levels. The aim of this research was a design of sustainable coastal protection system that is comprehensive and inclusive. As a starting point, an inventory during an on-site analysis was conducted to determine the status of the study area. In this way it was possible to determine the acceptability and strategy per study location. This was led by development of designs per strategy per study location including calculations, geotechnical verification, technical drawings and budgetary analysis. From there we conducted analytics, which resulted in the discussion and conclusion.

It is concluded that Sustainable coastal protection systems can potentially address these issues. For location A the Traditional strategy was shown to be the most cost-effective. For study area B however, Managed Realignment was the most efficient, both in costs and in sustainability. Therefore being able to improve safety, ecology and profits in the area.

Keywords: Coastal defence; Mekong Delta; Mangroves; Coastal Engineering; Vietnam; Sustainable coastal protection; Managed Realignment;

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Contents

PAGE 1 INTRODUCTION

PAGE 3 BACKGROUND

PAGE 12 PROBLEM DEFINITION

PAGE 14 STUDY AREA

PAGE 16 DISCUSSION OF THE STRATEGIES

PAGE 17 TECHNIQUES

PAGE 19 METHODOLOGY

PAGE 21 STUDY AREA A (PRE-DESIGN)

PAGE 38 STUDY AREA B (PRE-DESIGN)

PAGE 55 GEOTECHNICAL VERIFICATION

PAGE 58 BUDGETARY ANALYSIS

PAGE 63 DISCUSSION AND RECOMMENDATIONS

PAGE 67 CONCLUSION

APPENDIX 1: PARAMETERS FOR DEFINITION OF THE STUDY AREA

APPENDIX 2: 3D SURFACE GRAPH: WAVE RUNUP THROUGH MANGROVE FOREST

APPENDIX 3: BUDGETARY ANALYSIS TECHNICAL TERMS

BIBLIOGRAPHY

AKCNOWLEDGEMENTS

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loods affect the greatest number of people. The number of affected people and economic damages from flooding and especially from extreme floods is raising an alarming bell within the context of climate

change discussions (UN, 1998).

As a developing country located in Southeast Asia, Vietnam has annually suffered natural disasters such as typhoons, tropical storms, floods, inundation, drought, salt penetration, landslides, and earthquakes for

centuries. The Vietnamese people have recently, however, experienced an increase in their numbers. In a summary report of natural disasters from 1995 to 2006, the number of deaths was 9.416 people. The total estimated damage due to storms, floods and drought was VND1 61.479 billion (PDR-SEA, 2008). In view of these data, natural disaster reduction and risk mitigation are currently priority problems of Vietnam’s government.

The Vietnamese Mekong Delta (MD) is an extremely vulnerable and damageable flooding region compared to other countries in Southeast Asia. Mekong Delta people have coped with and adapted to a number of “natural disasters” and “human disasters.” Dyke works can be considered as a potential human disaster in the flooding context of the MD because flood control measures have caused a number of negative impacts for the ecosystem and the inhabitants (University Bonn, 2011). In this regard, a study has been produced aimed to design coastal protection systems able to potentially address these issues.

Two study areas located along the coastline of Soc Trang Province were selected, which account for a total length of 21-Km. These areas were chosen because they deal with two opposite scenarios: Erosion and sedimentation. Thus due to their location facing directly the sea (near the Mekong river mouth), they deal with the problems of sea level increase, damage of existing coastal protection structures and land damage in an accelerated rate. In this way, it is possible to design systems that take into account a wide range of variables, making them possible to fit in any given location along Vietnam’s coast. For ensuring efficient flow and quick response to the scenarios, the process was carried out according to Chart 1.

F

Introduction

“FLOODS HAVE THE GREATEST DAMAGE POTENTIAL OF ALL NATURAL DISASTERS WORLDWIDE” (UN, 1998)

1. On-site analysis

Pp. nr.1.: Traditional Approach

Pp. nr.2.: Managed Realignment Pp. nr.3.: Advancing

2. Calculate current situation

3. Determine acceptability and

strategy

4. Calculate new designs 5. Finalize Proposals

Chart 1: Process Flow Summary

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The Research will be based on the guidelines proposed by the existing Mekong Delta Plan, produced under the cooperation agreement signed in 2010 by the Dutch and Vietnamese governments to collaborate on climate change adaptation and water management related matters. A consortium of Dutch water-expert companies and both governments joint forces for creating this plan.

According to the Mekong Delta plan, the dikes at the Northwest and Eastern coastal area are located to close to the sea. This fact in combination with the destruction of the mangroves – increasingly happening due to the aquaculture expansion - will lead to potential risks regarding flooding and land subsidence.

It is in accordance with the Mekong Delta Plan to increase the wave reduction zone and allow the mangroves to grow naturally, as well as create room for potential aquaculture. For this purpose, Integrated Coastal Zone Management strategies including Managed Realignment were taken into account in the designs proposals in this document.

This Advisory Report is a systematic summary of the thought process taken place during the research. Its aims is giving substantial information about the development of the research. After definition of the problem and the chosen study areas (based on the program of requirements), each area was evaluated and assigned two strategies. These strategies were the foundation for the design of the final proposals, which focus on answering the Main and Sub-questions of the research, stated on the Project Plan and in page 12 of this document. A geotechnical verification and a budgetary analysis was done for each design proposal. This report is finalized by a discussion and recommendations chapter followed by a conclusion (drafted for each study area), where objective is serving as a guideline for future decisions by the stakeholders involved on the administrative level upon the future plans on the areas. Chart 12 illustrates the organizational structure of this report.

Chart 2: Advisory Report Structure

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Mekong Delta Mekong River water is everywhere and is the basis of agricultural livelihood, transportation, communication, fishing and all kind of daily domestic uses of the deltaic people (Käkönen, 2008). As a pure agricultural region, it provides food for at least 18 million residents. The MD plays an important role in guaranteeing national food security and contributes heavily to the economic and social development of the country. Natural conditions in terms of land, water and climate are favorable for agricultural development – and agriculture is still a major component of Vietnam’s economy. Therefore, most of all crops, domestic animals and aquaculture are being raised in this area. Additionally, canalization and river networks have been developed to provide water for agricultural development. Graph 1 portraits the agriculture model present on the Mekong Delta region.

The Mekong Delta plays an important role as ‘rice bowl’ for the whole of Viet Nam. Rapid expansion of shrimp farming in the Mekong Delta has contributed to economic growth and poverty reduction, but has been accompanied by rising concerns over environmental and social impacts (Phan NH, 1993) (JH, 2006). Between 1987 and 1992, for example thousands of hectares of mangrove forest were converted into shrimp farms (TT, 2011). The lack of an integrated approach to sustainable management, utilization and protection of the coastal zone and economic interests in shrimp farming have led to the unsustainable use of natural resources, thus threatening the protection function of the mangrove forest belt and, in turn, reducing income for local communities. The coastal zone is also affected by the impacts of climate change (IPCC, 2013). Climate change is predicted to cause increased intensity and frequency of storms, floods and droughts, increased saline intrusion, higher rainfall during the rainy season and rising sea levels.

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80

Crops Livestock and Fishery Agricutlrural Services

%

Graph 1: Structure of Agriculture in the Mekong Delta

1990 1995 2000 2001 2002

Background

Source: Socio-economic Statistics of Mekong Delta.

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Figure 1: Rivers are an important element of the transportation chain.

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In the MD, rice is still the most important crop. In 2004, the total rice area of the MD was 3.8 million ha, accounting for 86 percent of total crop area. The average rice yield was 4.9 tons/ha and total paddy rice production was 18.5 million tons. In the period of 2000-2004, rice area decreased by 0.8 percent annually whereas the yield and output increased by 3.3 and 2.4 percent per annum respectively. (Economic Development of the Mekong Delta in Vietnam, 2008)

“The MD is currently facing new challenges with the old rice farming systems. Natural resources in the area are being exploited with three annual crops and this is creating serious

consequences for the sustainability of the rice production system” (Robert Lensink, 2008)

The first problem is the efficiency by which water resources are provided for competing crops. That is, it is impossible to fully provide water for multicropping for the entire region. Despite the fact that rice systems have been integrated with the cropping calendar, rice requires a great amount of water in order to develop. Additionally, multicropping in upstream areas is causing a lack of water in downstream which increases saline intrusion and acid sulfate levels during the dry season. The second problem is soil erosion, along with modern input uses; a three crop per year rotation system seriously degrades the soil.

Increased investment in inputs such as modern fertilizers and pesticides, in order to keep decreasing yields constant, has been observed in many places throughout the region. These fertilizers and pesticides create environmental impacts in terms of pollution of water sources, which in turn creates increased health risks for the community.

Aquaculture The current decrease in rice area is due to Project 09/2000/NQ-CP, which requires the transfer of land from low yield rice areas to aquaculture production. In 2005, of the 310,841 ha of land transferred to aquaculture production 297,187 ha was rice area. In total, rice area accounted for 84 percent of total land transferred to aquaculture production.

Graph 2 shows the switch of rice cultivation area to aquaculture production from 1999 to 2005. The most rapid change has occurred since 2000. Specifically in 2000, the rice area transferred to aquaculture area was at a record high of 132,852 ha.

In 2005, Vietnam has 959,945 ha of aquaculture area, of which 685.250 was located in the MD. In this region, 1,004,257 tons of aquaculture is produced with an export value of 1.5 billion $USD. However, the rapid growth of aquaculture production activities has caused many environmental problems including degradation and pollution. Aquaculture production is considered the main contributor to the destruction of ecology systems that were previously very rich and has destroyed coastal forests. New farming models, or so- called “rice-shrimp systems” have led to increased salinity in the rice fields. Consequently, a new environmentally friendly farming system is required for the Delta.

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150000

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2000

2001

2002

2003

2004

2005

Area

(Ha)

Year

Graph 2: The switch of rice cultivation area to aquaculture production (1999-2005)

Vietnam

Mekong Delta

Source: Ministry of Fishery.

Economy in the Mekong Delta

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The current system is highly unsustainable and although aquaculture is highly profitable, the long-term forecast is very negative. Floods that are more impactful are to be expected - which these agricultural practices and the endangered dykes increase the pace – as well as a decrease in availability of lands due to the damage to the soil. To some extend some measures have been taken, however do not meet the expectations and are behind the ideal image of sustainability and profit model of the 21st Century. (Robert Lensink, 2008) Chart 3 summarizes the main problems that take place in the actual scenario.

The next chapter of this report will go more in depth about the aspects and status of the mangrove vegetation along the coastline and highlight its importance and usefulness to efficient coastal protection, achieved by its ability to reduce the outflow of sediment and the wave energy. Thus, a recommendation for new techniques of mangrove restoration, which were used in projects implemented successfully in Bangladesh and Indonesia. Countries where coastlines are very similar to Vietnam, thus dealing with the same problems.

(1) Rice Farming•Fertilizers and Pesticides create

environmental impact•Requires great amount of water

to develop

(2) Aquaculture•Causes Soil degradation and

Pollution•Negative effect over ecology

systems

(1) + (2) Environmental Damage•Destruction of Mangroves•Salt Water intrusion

Chart 3: Problem Summary in Mekong Delta

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Figure 2: The Mekong is an important Delta for the locals and place to the biggest floating market in the World.

https://www.flickr.com/photos/johanders/

https://www.flickr.com/photos/johanders/

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Mangroves are tidal forest ecosystems on muddy soils in sheltered saline to brackish environments. Mangroves are a key-ecosystem laying in the tropical and sub-tropical coastlines. The vegetation possesses special root systems for both water and air supply. Because of the root systems, the trees are adapted to grow in anaerobic and unstable conditions of waterlogged muddy soils (Augustinus, 2004). Its vegetation is composed of trees and shrubs and copes with the harsh conditions in the intertidal: Salinity, tidal flooding and exposure to waves. They

often play a key role in the nutrient cycle in tropical estuarine ecosystems, the sustainability of marine coastal ecological systems, the support of aquaculture and the stabilization of the tropical coastal shoreline.

However, mangrove forests have been destroyed for land reclamation, shrimp farming, timber and charcoal production at an alarming rate throughout the world. Overcutting of mangrove trees often led to a significant impact on the ecological system in mangrove swamps and the nearby coastal waters; this removal of mangroves trees also resulted in coastline erosion. This happens because mangrove forests play an important role in flood defense - by dissipating incoming wave energy and reducing the erosion rates – thus decreasing wave-driven, wind-driven and tidal currents due to the dense network of trunks, branches and aboveground roots of the mangroves, which also contribute to sediment stabilization. (Wave attenuation in coastal mangroves in the Red River Delta, Vietnam, 2006)

Chart 4 highlights the benefits of Mangrove forests to coastal areas thus their potential for coastal protection as a natural structure. During the past years, there has been an increase in interest of governments of different nations in regards to their coastline vegetation. In a world facing evident climate change and the threat of sea level rise threatening lowland countries and littoral areas, it is necessary to take measures that transform the social-economic model present on these areas into a sustainable. Even some measures including change in behaviors that were accepted in the past. The mangrove forest fit well in this scenario. Being an ecosystem that has been victim of pollution and destruction, big parts had been transformed into ashes. The problems generated by the decrease in mangrove forest have not been exclusively in regards to the biodiversity but also a change in flow pattern has been observed. It was only in recent decades that researches about mangroves and their potential to wave attenuation took part. In fact, unravelling the dissipation of wave energy in coastal mangroves by field and laboratory studies has only gained attention since

Mangrove Vegetation

“Coastal mangroves provide an important contribution to reducing risk

from coastal hazards by attenuating incident waves and by trapping and

stabilizing sediments.” (Augustinus, 2004)

Enhance

•Biodiversity•Nutrient circulation•Sediment

stabilization

Reduce

•Erosion rates•Tidal currents•Wave energy

Chart 4: The Benefits of Mangroves

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the late nineties. (Alongi, 2009) Due to the inaccessibility of (natural) mangrove forests, a limited number of field studies have been executed in mangroves in Vietnam, Australia and Japan. These studies emphasize in unison the positive contribution of mangroves to the dissipation of wind and swell waves of limited height and period. Nevertheless, observed wave reduction rates show significant variation with water depth and vegetation characteristics. Bao et al. (2011) in his study about the Effect of mangrove foreststructures on wave attenuation in coastal Vietnam, showed that wave height reduction depends on initial wave height, cross-shore distances, and mangrove forest structures. This relationship is used to define minimum mangrove band (or mangrove belt) width for coastal protection from waves in Vietnam.In 2002, Vietnam had approximately 155 290 ha of mangrove forests left. More than 200 000 ha of mangrove forests have been destroyed over the last two decades as a result of conversion to agriculture and aquaculture as well as development for recreation (VEPA (Vietnam Environment Protection Agency), 2005). Mazda Y., et al., 1997a in their study in the Red River Delta, Vietnam, showed that wave reduction due to drag forced on the trees is significant in high density, six-year-old mangrove forests. The hydrodynamics of mangrove swamps changes over a wide range, depending on their species, density and the overground roots in a mangrove forest present a much higher drag force to incoming waves that the bare sandy surface of a mudflat does. The wave drag force can be expressed as an exponential function (Quartel S., Kroon A., Augustinus P.G.E.F., Augustinus P.G.E.F., Van Santen P., & Tri N.H., 2007). All these research proved that Mangrove forests are an essential part of the coastlines. Via observational, mathematical and computer modelling approaches, mangrove forest’s capacities to reduce wave energy have been quantified. In this research, the proposed designs will make use of data provenient from mangrove studies based on obersvational and mathematical approaches. A spreadsheet have been built up in order to select the best values for calculating the reduced wave heights in Soc Trang province coastline. For more information over the techniques and references please refer to Discussion of Strategies/Techniques chapter.

Mangrove Restoration Projects Many mangrove restoration projects have taken place in the past; however, they all failed due to present insufficient rate of mangrove development. Restoration often fails in areas that suffer from erosion because the sediment balance is disturbed. Due to human presence, the original characteristics of the coastline were changed, resulting in a scenario where the conditions for optimal mangrove development were absent. Besides placing mangrove seeds, it is necessary the right conditions, thus a consistence of these. A successful mangrove restoration technique have been implemented in Indonesia and Bangladesh, resulting in proper growth of mangrove. The project involves the use of "building with nature," using engineering techniques in combination with natural processes via the implementation of permeable brushwood dams. It is Dutch developed technique, very cost efficient and easy to implement, and designed to provide the required conditions for the mangroves to growth. Figure 3 shows an example implemented in the Demak district, Mid-Java, where its coastline share the same problems as the Vietnamese one and coastal erosion over the last decade extends over large areas.

“In 2002, Vietnam had approximately 155 290 ha of mangrove forests left. More than 200 000 ha of mangrove

forests have been destroyed over the last two decades” (VEPA, 2009)

Figure 3: Coastal restoration Demak; left: erosion between 2003 and 2012; right: restoration principle.

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The technical design of the project is to first restore a natural coastal profile with dredged material and sufficient accommodation space for tidal water behind it, thus creating a physiotope (muddy bed, in- and outgoing tide) that is suitable for mangrove. Wave action is damped by permeable brushwood dams (as applied for centuries for land reclamation in the Wadden Sea); such that conditions are favorable for fine sediments to settle. Once these conditions have been created, mangrove is likely to colonize the area spontaneously, and if necessary initial conditions will be enhanced by mangrove planting. (Building with Nature: Mainstreaming the Concept, 2014). The method of permeable brushwood dams has been applied with salt marshes along the coasts of the Netherlands and Germany for centuries and is a suitable, fast and cheap technique that can be used for restoring the Vietnamese with high satisfaction rates. The restoration of the mangroves belts is a high priority task and must be addressed accordingly. Besides the coastal protection aspect, they provide great socio-economic development to the communities where they are inserted. According to studies regarding cost-benefit analysis of mangrove restoration in Vietnam, mangrove restoration generates larger benefits than that of aquaculture: about VN$21 billion compared to VN$10 billion over 22 years. The benefits of mangrove restoration are approximately double that of aquaculture development, from a 5 per cent per cent to a 15 per cent per cent discount rate. (Asian Cities Climate Resilience Working Paper Series: Cost–benefit analysis of mangrove restoration in Thi Nai Lagoon, Quy Nhon City, Vietnam, 2013)

Figure 4: Coastal area in Soc Trang Province. A big amount of the mangroves present in this particular area have been destroyed. Thus these human interventions led to a change in the sediment balance affecting the natural characteristics of the coastline.

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Soc Trang Province is one of 13 provinces in the Mekong Delta region and is located south of the Hau River, which is the southern-most arm of the Mekong. The province covers a total area of 331,176 ha, of which 205,748 ha are used for agriculture, 11,356 ha for forestry and 54,373 ha for aquaculture. The population of the province is 1,285,096 out of which 371,266 are Khmer and 75,421 are ethnic Chinese (Soc Trang Statistics Office, 2009). The coastal zone has a length of 72 km.

The coastline of Soc Trang Province is characterized by a dynamic process of accretion and erosion created by the flow regime of the Mekong River and its sediment load, the tidal regime of the South China Sea (Vietnamese East Sea) and coastal long-shore currents driven by prevailing monsoon winds. In some areas of Soc Trang loss of land, due to erosion, of up to 30 m per year has been recorded, while in other areas land created through accretion can reach up to 64 m per year (Pham TT, 2013; Joffre O, 2013). About 11 km of coastline of Soc Trang are currently subject to erosion. The earth dyke along this stretch of coast, which protects the hinterland from flooding, is in several places endangered by severe erosion, which in turn endangers the people and farmland directly behind the dyke. In several sites, a total of around 300 m of mangrove forest in front of the dyke has been eroded away completely.

The dynamic coastline of Soc Trang Province in the Mekong Delta of Viet Nam is in most parts protected from erosion, storms and flooding by a narrow belt of mangroves. However, the unsustainable use of natural resources and development in the coastal zone is threatening the protection function of this forest belt. This situation is exacerbated by the impacts of climate change, particularly by the increased intensity and frequency of storms, floods and by rising sea levels. Chart 5 summarizes the current problems encountered in the region.

Soc Trang Province

Chart 5: Problem summary in Soc Trang province

Loss of land

Land Subsidence

Salt Water Intrusion

Flooding

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The main function of a dike is to prevent flooding of low-lying coastal hinterland, which means that the height of the dyke is the most important design parameter. However, the dyke must also be able to resist the large forces of waves during extreme events. (Albers, 2014)

Many centuries of experience in dyke design have led to an optimized design. A sea dyke is a system consisting of different parts, starting with the foreshore or floodplain further offshore. The seaward slope ratio was decreased to reduce the wave energy and therefore erosion induced by the run-up and overtopping of waves. That depends on the amount of area available. Nowadays, the seaward slope of the dyke is usually 1:6 or flatter. In some cases, a berm is installed –where possible - to reduce the wave run-up and to simplify the maintenance of the dike after storm surges. The width of the dike crest should be 3 meters or more. This decreases wave overtopping and allows an effective dike defense. Dike defense is defined as the sum of measures to regularly control the condition and the quality of the dike (at least twice a year; before and after the storm season, but also after heavy storms) and to maintain the dyke, to take action in case of smaller or severe damages during extreme events and to eventual repairs in case of such events.

A solid dike toe on the seaward as well as on the landward side is very important for the stability of the dike. On the landward side, a drainage system (I.e.: ditch) must be available to discharge the overtopping waves and to ensure that the dike’s negative pressures - created by the water in its interior - are reduced and the stability is maintained. A dike defense lane is recommended for material transport and maintenance in the case of damage during storms.

Dutch History

“The Dutch are well known for their water management skills. Water is in their genes”

The Dutch windmills (once used to pump out excess water); dikes and levees form a powerful international image. From the early Middle Ages onwards, Dutch people have reclaimed and defended land from the sea. A skill that goes hand in hand with water management, spatial planning, water supply and water quality. A history that revolves around adaptation to water: Histogram 1 illustrates the important milestones and events that happened over the Dutch history in regards to water management.1

1 Source: Dutch Water Sector, 2015

General Aspects of Dike Design

Figure 5: Construction of dike-in-boulevard (Scheveningen), 2013

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1000 •First man-made dike

•The oldest dike in TheNetherlands that we know ofis about 1000 years old andsituated near the villagePeins in Friesland. It was builtby monks and made of piledturf.•In the North of Hollanddifferent villages combinedtheir dikes. They succeededin creating one big living areathat was embanked by theWestfriese Omringdijk. A realpiece of water art of about120 kilometers long and acouple of meters high.

1255 •First Official Water

Board

•The first official WaterBoard in The Netherlandswas founded in 1255 byCount Willem II ofHolland an named the'Hoomheemraadschapvan Rijnland'. NowadaysThe Netherlands counts25 Water Boards. Dutchwater boards (Dutch:waterschappen orhoogheemraadschappen)are regional governmentbodies charged withmanaging water barriers,waterways, water levels,water quality and sewagetreatment in theirrespective regions.

1918 •The Zuiderzee Works

•The Zuiderzee Works (Dutch:Zuiderzeewerken) are amanmade system of dams,land reclamation and waterdrainage works, the largesthydraulic engineering projectundertaken by theNetherlands during thetwentieth century. Theproject involved thedamming of the Zuiderzee, alarge, shallow inlet of theNorth Sea, and thereclamation of land in thenewly enclosed water usingpolders

•Its main purposes are toimprove flood protection andcreate additional land foragriculture. Together withthe Delta Works, theAmerican Society of CivilEngineers declared the worksamong the Seven Wonders ofthe Modern World.

1953 •The flood of 1953

•The 1953 North Sea flood(Dutch, Watersnoodramp,literally "flood disaster") wasa major flood caused by aheavy storm.•The combination of wind,high tide and low pressurehad the effect that the waterlevel exceeded 5.6 metres(18.4 ft) above mean sealevel in some locations. Theflood and wavesoverwhelmed sea defencesand caused extensiveflooding.•As a result of thewidespread damage, theNetherlands particularly, andthe United Kingdom hadmajor studies on means tostrengthen coastal defences.The Netherlands developedthe Delta Works, anextensive system of damsand storm surge barriers.

1958 •Start building the Delta

Works

•The Delta Works is aseries of constructionprojects in the southwestof the Netherlands toprotect a large area ofland around the Rhine-Meuse-Scheldt deltafrom the sea. The worksconsist of dams, sluices,locks, dikes, levees, andstorm surge barriers. Theaim of the dams, sluices,and storm surge barrierswas to shorten the Dutchcoastline, thus reducingthe number of dikes thathad to be raised.•Along with theZuiderzee Works, DeltaWorks have beendeclared one of theSeven Wonders of theModern World by theAmerican Society of CivilEngineers.

2007

-201

0 •Room for the River programme & Preparations for the Future

•Extremely high riverdischarges will occur morefrequently in the future andfor this reason it was decidedto ensure that the riverscould discharge the forecastgreater volumes of waterwithout flooding. For thisreason the DutchGovernment approved theRoom for the Riverprogramme in 2007.

•Moreover, the new-styleDelta Plan has beenstructured so that theNetherlands can put itscurrent safety in order andprepare itself for the next100 years.

•The plan is based on the 5Dutch D's: Delta Act, DeltaProgramme, Delta Fund,Delta Commissioner andDelta Decisions.

Histogram 1: Important events in the Dutch Water Sector

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The main objective of the research is to design a new coastal protection system for Soc Trang province that protects the land from floods and restores the water and land quality of the area. This province was chosen for being the ideal research place as it faces directly the sea and deals with all the issues related to flooding in an accelerated rate. In order to support the research’s objective, different locations had to be selected. This gives the possibility for the researchers to implement different strategies at different locations creating efficient coastal protection designs with a broad workability spectrum, capable of working in any given location.

According to the Mekong Delta Plan (2013), the dikes at the Northwest and Eastern coastal area lay too close to the sea. This fact in combination with the destruction of the mangroves – increasingly happening due to the aquaculture expansion – will lead to potential risks regarding flooding and land subsidence. It is in accordance with the Mekong Delta Plan to increase the wave reduction zone and allow the mangroves to grow naturally as well as create room for potential aquaculture. For this purpose, the designs will take into account concepts of Integrated Coastal Zone Management including Managed Realignment.

Main question The main question that the research aims to answer is stated as follows:

“How can the current situation in the study area comply with the Mekong Delta Plan by using Integrated Coastal Zone Management Strategies in order to increase safety, ecology and profits in the area and create room for mangrove development?”

Sub Questions In order to answer the main question different sub questions are stated. The sub questions read as follows:

� How is the current safety situation and why is it not satisfactory? � How can this be improved with the new solution? � What is the best location for the new inland dike? � What are the dimensions of this new dike? � Which solution is the most cost efficient? � How can the dike be placed to allow for growth of mangroves? � In what way the mangroves can contribute for safety and reduction of costs? � How can this project be implemented as efficient as possible?

Sustainability and flood management measures Given the desired development scenario and the actual vulnerability of the delta as stated in the Mekong Delta Plan, different measures are suggested based on the climate change scenario that the region in question will deal it. Moreover, taking also into account the uncertainties of the future development: In terms of the extremity of possible climate change, in terms of developments to take place in the upstream Mekong and last but not least in terms of the economic development to emerge within the delta. In view of these uncertainties and the long-term impact of infrastructural measures this Mekong Delta Plan distinguishes between "no-regret" measures (fits all scenarios), priority measures (short-term) and more structural measures

to be deferred to the mid and long term.

The Coastal Protection Designs presented and supported in this Advisory Report take into account “no-regret “measures to be taken in the short- to mid-term (2050) that enable: 1) the adaptation of land and water use to the short-term climate change impacts, with emphasis on increasing the sustainable land and water use; and 2) are flexible enough in their structuring of water management and hydrological features to permit differential socio-economic development of the delta's economy in the mid- to long-term. As well as mid- to long-term (2100) measures that are specifically designed to prepare the delta to cope with, and adapt to, the more extreme impacts of climate change. By necessity, these are more structural and large-scale in nature, requiring careful valuation, planning and capital outlay. Table 1 gives more information on these measures.

Problem Definition

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The desired outcome is a coastal protection design that makes use of managed Realignment and integrated Coastal Zone management strategies in order to increase safety and profits in the area.

Table 1: Coastal Zone Measures (Mekong Delta Plan, 2013)

Coastal Zone: Brackish water economy and advanced coastal protection

2050 "no-

regret"

Dual Zone Coastal Management. Brackish economy and dynamic shorelines. Modernization and increased sustainability of aquaculture by adopting poly-culture based systems aligned with mangrove regeneration in the outer coastline. Mangrove regeneration and sedimentation along outer coastline as reinforcement of seashore. Movement of hard-protective sea-dyke to inner-core zone.

Food Production Agro-Business Industrialization Dual Node Industrialization Corridor Industrialization

2050 - 2100

Reinforcement of coastal defense. For non-Dual Zone Coastal Management areas, sea-defense structures (dykes) need to be revamped to keep up with sea level rise. Especially northwest coast and Eastern Delta (Mekong Branch). The routing of the dykes needs to be in line with Dual Zone Coastal Management.

All scenarios Unlinking road system from dyke system. Flexibility in dyke trajectories is required to allow for natural cost effective coastal flood defense strategies. The road function impedes the flexibility for the dyke. Under extreme sea level rise, coastal defense system is upgraded to accommodate rising flood risks. This includes reinforcement of inner protection dykes.

Figure 6: Dr. Tran Van Ty and Mr. Ha Tan Viet , Acting Head of Civil Engineering Department (CTU) and Head of Water Resources Division on the Department of Agriculture and Rural Development of Soc Trang respectively, during the On-Site analysis.

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The first goal of the research was to find a suitable area, where the required conditions are available, maximizing the possibilities and spectrum in regards to the design proposals. The locations had to comply with a list of parameters in order to be in line with the research. This guarantees that the research is feasible and fully executable. The description of the process regarding the selection of these study areas is attached in Appendix 1. This chapter will deal with the description of the selected study areas.

The study areas were selected in Soc Trang province’s coastline. This province was chosen for being directly facing the sea, dealing with all previous mentioned issues in an accelerated rate. The final chosen areas account together for a length of 21-Km and deal with two opposite scenarios. This gives the possibility for the researchers to implement different strategies at different locations creating efficient coastal protection with a broad workability spectrum.

Most Suitable Study Areas Based on the pre-defined criteria, stated in Appendix 1, two locations were selected. The first one lies in an area that suffers from big outflow of sediment, shortening the foreshore and damaging the existing dike. The second location reveals a totally opposite scenario suffering from deposition instead of erosion. The different scenarios supports the research’s objective. The description of these locations will follow on the next subchapters.

Study Area A Study Area A is located along a stretch of 700 meters that lies in a sedimentation area but suffers from erosion due to direct exposure to waves. Different kinds of Revetment have been implemented; nevertheless, the Dike system struggles to keep its original shape. Many breaches were seen - one of them completely divided the dike – and new ones were beginning to form.

Regarding the mangroves, a big chunk of this vegetation was seen being removed due to aquaculture expansion. Most of the hinterland at this location serves as place to Shrimp Farming. Properties.

Study Area B Study Area B is located on the border of Bac Lieu continuing near Vin Chau. It is a stretch of 19 kilometres along the shore. T sections and Mangrove regeneration projects have improved the defence system over the past years. During the visual analysis, it became clear that the dike was a lot better than Location A. Despite these efforts, the dike system is still not sufficient. During an average high tide the toe construction is eroding, rapidly reducing the defensive ability and stability of the structure

.

Study Area

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Study Area A•Erosion•Sediment transport from East to West•Hard-revetment/Soft-revetment•Partly mangroves •Companies [Aquaculture]•Dike has many breaches. Due to collapse

Study Area B•Sedimentation•Hard-revetment/ Soft-revetment•Presence of T-sections for control of sediment flow•Mangroves•Sparse-popullated/

Companies [Aquaculture]•Dike is not sufficient thus Toe-construction is eroding reducing the

stability of the Dike

Chart 6: Overview of the Study Areas

Evaluation of the Current Situation

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Discussion of the Strategies

The definition of the strategy will be based on the way the current situation was evaluated and the results from this analysis. The aim of the research is to answer the main question of the research, stated below:

“How can the current situation in the study area comply with the Mekong Delta Plan by using Integrated Coastal Zone Management Strategies in order to increase safety, ecology and profits in the area and create room for mangrove development?”

For answering the questions, new coastal protection systems were proposed for each study area, considering the aspects of the region and the adequate strategies that best help to enhance the overall situation. Each strategy was set in accordance to the priorities listed in the Program of Requirements. All of them determined on basis of a careful analysis of the area and process, and were carried out according to chart 7. See Strategy Definition chapters for specific information regarding each study area.

The course of action for each study area will be determined by the strategies pointed on the picture on the right.

The decision to choose a strategy is site-specific; depends on pattern of relative sea-level change, geomorphological setting, sediment availability and erosion, as well as a series of social, economic and political factors (HEURTEFEUX., 2011). Each study area was assigned two proposals. The brief description of some techniques implemented in these proposals will follow in the next page.

�� Inaction

� Managed Realignment

� Protection

� Advancing

� Limited intervention

Figure 7: Policy options (Coastal risk management modes: The managed realignment as a risks conception more integrated, 2011)

1. On-site analysis

Pp. nr.1.: Traditional Approach

Pp. nr.2.: Managed Realignment

Pp. nr.3.: Advancing

2. Calculate current situation

3. Determine acceptability and strategy

4. Calculate new designs

5. Finalize Proposals

Chart 7: Process flow

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Techniques

The coastal protection design proposals in this document take into account the traditional approach as well as concepts of Integrated Coastal Zone Management such as Managed Realignment ,taking into account the implementation of a mangrove forest on the foreshore. For the optimal calculation of the wave height/energy reaching the dike through the mangrove forest, two approaches – set after a literary study - were used:

� Observational (Hashim & Catherine, 2013) � Mathematical (S. Quartel, 2006)

In order to ensure the most unfavourable reduction rate, the smallest reduction of these two studies related to the width of the mangrove belt was chosen. The reductions for the design have been categorized in four classes of mangrove width: 50m, 100m, 150m and 200m.

Observational

The observational approach is based on the laboratory study (Hashim & Catherine, 2013) and bases mangrove reduction on the density of the mangrove area and the arrangement. There are two testing arrangements, tandem and staggered. The Density of the mangrove area is divided in dense (0,22 trees/m2), Medium (0,16 trees/m2) and Sparse (0,11 trees/m2). In order to get the most unfavourable reduction rate the sparse density was chosen in combination with a tandem arranged mangrove belt. This is to avoid any uncertainties regarding the mangrove development in relation to the reduction.

Table 2: Observational approach reduction rate (Hashim & Catherine, 2013)

Mathematical

This approach is based on (Quartel S., Kroon A., Augustinus P.G.E.F., Augustinus P.G.E.F., Van Santen P., & Tri N.H., 2007) and calculates the reduction rate per meter of cross-shore mangrove belt. The reduction rate is calculated as following:

Wave height reduction*Mangrove classification*100%

Results are listed in Table 3.

From these two results the most unfavourable value was chosen to ensure a safe design. Over a mangrove width of 150 meters however the reduction value of the mathematical approach reaches more then 1,0 , causing for a negative reduction rate. In other words, a reduction of 100%. Therefore, the results of the observational approach have been used for these mangrove belt widths. However, for the width 50-100 meters the Mathematical approach turned out to be the most unfavourable, therefore reduction table 2 was used for these mangrove belts widths.

Table 3: Mathematical approach reduction height (Quartel S., Kroon A., Augustinus P.G.E.F., Augustinus P.G.E.F., Van Santen P., & Tri N.H., 2007)

Reduction in wave energy by mangroves

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Maintaining a foreshore with a proper slope is one of the approaches used to reduce the height of the wave reaching the dike. In case of Vietnam, Mangroves are particularly important because of their ability to decrease wave energy and trap sediment, as stated in the Mangrove Vegetation chapter.

Based on the results of the literary study stated on the previous page two tables were built up.

Table 4 was drafted on basis of the observational approach. The reduction values of mangrove forests of a certain width taking into account both Tandem and Sparse arrangements were averaged.

The same process was carried out for Table 5, based on the mathematical approach. However on this approach, factors from graphs were selected in order to obtain the reduced wave heights generated by each width of mangrove forest.

Table 6 portraits the final reduction percentages taking into principles the selection of the most unfavourable value in order to increase the safety of the design.

The methodology for calculation of the wave heights will be explained in the following chapter.

Observational Approach Approach: Observational

Density [M2]: 0,11 Trees/m2 Wave Reduction [%]

Mangrove Forest Width [M] Tandem Arrangement Sparse Arrangement Average 50 0,53 0,65 0,59

100 0,76 0,88 0,82 150 0,9 0,95 0,925 200 0,95 0,98 0,965

Table 4: Reduction in wave height by mangrove forest. (Observational approach) (Hashim & Catherine, 2013)

Mathematical Approach Approach: Mathematical Density [M2]: 0,11 Trees/m2 Factors Mangrove Forest Width [M] Significant Wave Height [Hx1] Reduced Wave Height[Hx2] Reduction Rate

50 1,023 0,35805 0,35805 100 1,023 0,7161 0,7161 150 1,023 1,07415 0,05 200 1,023 0 1

Table 5: Reduction in wave height by mangrove forest. (Mathematical approach) (Quartel, Kroon, Augustinus, Van Santen, & Tri, 2006)

Most Unfavorable value

Mangrove forest Width [M] Wave reduction [%]

50 0,35805 100 0,7161 150 0,925 200 0,965

Table 6: Final Reduction rates

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MethodologyThis chapter will explain the calculation process. The first two paragraphs will be about the wave height at the dike. The other paragraphs are about the impact and design choices on the dike due to the wave run-up.

Set-up

Because the slope is very low and there is a long foreshore the case might be that the waves already break on the foreshore. In this case a higher wave as well as set-up might occur. The Wave at the toe-construction of the dike consists of the following components

� Wave Energy from the breaking wave � Wave energy resulting from a new wave over the foreshore, H n

The total wave height at the toe-construction of the dike is given by Formula I

𝐻0 = √𝐻𝐷2 + 𝐻𝑛

2 (I)

𝐻𝑛Will be determined using the book Toegepaste Vloeistofmechanica, Hydraulica voor waterbouwkundigen (1994)

𝐻𝐷 Will be determined using the following Formula II

𝐻𝐷 ≈ 0,5 ∙ ℎ (II)

This formula is of based on the slope, wave height, vegetation and soil

It is not in the interests of the research group to go further in detail into the calculation due to the difference being minimal therefore surpassing the aim of the research.

Additionally, when there is a flat slope like in the above-mentioned situation, set-up will occur. This means that the water level at the toe-construction of the dike will be higher than the actual sea level. To calculate this Formula III is used.

𝑆𝑢 ≈ 0,15 ∙ 𝐻𝐵 (III)

Wave run-up The wave run-up is calculated by the Method of Hunt, given by Formula IV:

𝑧 = √𝐻 ∙ 𝐿0 ∙ tan ∝ (IV)

∝=Slope

Reduction Factor

Aside from the mangroves the following reduction factor for the wave run-up will be used, this are given by Formulas V and VI

� 𝑧 𝑟𝑢𝑤 = 𝑧𝑔𝑙𝑎𝑑 ∙ 𝑓𝑟 (V)

� 𝑓 𝑏𝑒𝑟𝑚 = (1 − 𝑏𝐿 ) (VI)

The first reduction occurs due to the revetment used. Hard revetment with uneven surface will reduce the wave run-up.

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Wave run-down

The wave run-down is important when using hard revetments. Due to the negative pressure under the blocks when the waves are below still water level the blocks might get pushed upwards. For the calculation of the wave-rundown z’, formula VII will be used:

𝑧′ = 0,3 ∙ 𝐻 ∙ 𝜉 (VII)

𝜉 is the breakwater parameter and is defined by:

𝜉 =tan𝛼

√𝐻𝐿0

Revetment The negative pressure plays an important role in the Dike Design. Due to the process of the water infiltrating and being expelled from the dike, “suction “is created. This can cause revetment to be taken out from the dike. This translates into a force that acts in the base of the revetments against them, known as negative pressure. The aim of calculating the negative pressure is to find the minimum weight at which a certain revetment would be safe given the target situation.

The negative pressure calculation differs by the type of construction. This can be:

� Closed construction � Filter construction

Closed construction

Taking into account the current situation the revetment from the old dike can be reused and be directly placed on the new dike together with an asphalt mortar. This leads to a watertight construction (closed construction) that does not let the water in but thus causes the negative pressure influence to increase.

For calculating the negative pressure on a closed construction, the formula of Hudson (VIII) is used.

𝐺 = 𝑐ℎ ∙ 𝐻3 ∙ tan𝛼 (VIII)

� 𝐺 = Weight of the revetment (N) � 𝑐 ℎ = Hudson Coefficient � 𝐻 = Wave height before toe construction � 𝛼 = Slope

𝑐ℎ = 𝜌𝑠𝑡𝑒𝑒𝑛∙𝑔(𝜌𝑠𝑡𝑒𝑒𝑛−𝜌𝑤𝑎𝑡𝑒𝑟

𝜌𝑤𝑎𝑡𝑒𝑟)3∙𝑘𝐷

� 𝑐 ℎ = Hudson Coefficient � 𝜌 𝑠𝑡𝑒𝑒𝑛 = Revetment density � 𝜌 𝑤𝑎𝑡𝑒𝑟 = Water density � 𝑔 = Gravitational force � 𝑘 𝐷 = Stability coefficient �

Filter construction

To calculate the thickness of the revetment, Formula IX.

𝑑 = ( 𝜌𝑤𝑎𝑡𝑒𝑟𝜌𝑠𝑡𝑒𝑒𝑛−𝜌𝑤𝑎𝑡𝑒𝑟

) ∙ ( sin𝛼5 𝑐𝑜𝑠2𝛼

) ∙ √𝐻 ∙ 𝐿0 (IX)

� d = brick thickness � 𝜌 𝑤𝑎𝑡𝑒𝑟 = Density water � 𝜌 𝑠𝑡𝑒𝑒𝑛 = Density bricks � 𝐻 = Wave height at the toe construction of the dike � L 0 = Wave Length in deep water (1,56 𝑇2)

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Analysis of the current situation's results Definition of the strategy Calculation of the design

Chart 8: Pre-design process

Study Area A Pre-Design

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Map 1: Province of Soc Trang

Following the gather of data and evaluation of the current situation, actions were taken for determining the right strategies for the study area.

Study Area A is located along a stretch of 700 meters that lies in the erosion area. (See map). This region characterizes by the presence of big longshore drift, which washes away sediment and shortens the foreshore, making the current dike system endangered. According to the visual analysis, it is evident that the current design is not sufficient. Many sections of the dike are breached and others are due to collapse.

Based on the visual inspection and the evaluation of the current situation, the existing dikes cannot withstand the reality to which they are exposed requiring a redesign of the existing coastal protection system. These designs will be based on the principles stated on Sustainability and Flood Measures chapter.

Study Area A

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Results

The main objective of this chapter is to present concrete evidence of whether or not the actual dike system present in this study area is able to withstand the forces to which it is exposed. For this purpose, mathematical calculations were performed. These calculations took into account the actual heights of the Dike system and the current water and wave heights, which the Ministry of Agriculture and Rural Development of Soc Trang provided. The complete systematic calculation process - in spreadsheet format – is located in Annex B - Appendix 1B. Hereby the final output is presented in Graph 3.

Graph 3 visually portraits the results of the mathematical calculations, executed on basis of the current values for wave, water (level) and dike heights. The calculations shown that the height of the wave run-up overtops the existing dike, as seen in the graph. The calculations considered the height at the crown of the dike.

When analysing both the technical drawings of the current dike system present and the reality, the outer slope was found to be 1:2 (point 2 on the x-axis), which on the calculations - taking into account the current wave attack - generates a Wave Run-up of 1,793 meters. This accounts for the average slope profile of the current dike.

Because of the nonexistence of a structure for reducing wave energy, the values of the wave run-up are very high. In fact, any small variation in the slope of the Dike led to an even bigger change in the height of the wave run-up. This is seen by the relation of the orange curve in the graph, representing the wave run-up, with the blue one, representing the slope of the actual dike.

3,80

3,25

0

1

2

3

4

5

6

1/2 1/6 1/nW

ave

Run-

up (M

)

Slope (Fraction)

Graph 3: Wave Run-up [M] - Current Situation (A)

Total Wave Run-up Height at the Crown of the Dike Wave Run-up (z)

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Strategy Definition

Sediment transport

•Big longshore dritft•Erosion of the foreshore•Erosion of the dike's toe-construction•Sediment transport from East to West

Existing Dike'scondition

•Usage of traditional hard-revetment•Usage of soft-revetment (I.e.: Clay)•Dike is due to collapse•Current dike has many breaches

Vegetation

•Non-optimal growing conditions for the vegetation•Destruction of mangroves for aquaculture purposes

Hinterland

•Mainly ocupied by shrimp farming properties

Wave attack

•Wave attack is classified as small•Current slope of the foreshore leads to an increase in wave power

Chart 9: Results of the Visual Analysis (Study Area A)

The current dike is endangered. The longshore drift washes out sediment and contributes to an increase of wave attack to the dike. Thus, the use of improper construction techniques leads to instability of the overall construction, being an easy target for stronger wave attacks.

The slope of the dike has a big influence on the height that the wave can reach (known as wave run-up). As seen on Graph 3 - the current situation seen at the dike system - the steep dike’s slope (1:2) leads to high wave run-ups causing an overtopping. It is evident that the current protection system needs change in design and implementation.

Recommendation: It is extremely important to update the dike’s height and/or make use of wave reduction structures in order to decrease the wave energy that reaches the dike. A change on the construction techniques is equally important.

The following chapters will discuss the two proposed solutions for study area A.

Figure 8: Dike system’s situation at Study Area A.

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Proposal 1 Location A

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Strategy 1: Traditional Location A

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Traditional approach The first proposed design is drafted on basis of the traditional approach, which regards to heightening the dyke as well as making use of proper construction techniques and materials, which have been used by the Dutch over the years. The design generated on this approach is based on mathematical formulas that ensure that the dyke’s dimensions and design aspects are sufficient - given the situation- as well optimized. The chapter’s structure is illustrated below:

Calculations The calculations performed to design the dike for the traditional proposal took into account the parameters stated in table 7. The sketch below illustrates the design of the dike and its different sections, which dimensions were determined according to the values of the outputs, stated in table 8. In order to better optimize results, all formulas were imported into a spreadsheet, resulting in a better workflow and flexibility. The complete calculation process, which is done in spreadsheet format, is available in Annex B - Appendix 2B.

Input The following parameters and their respective values were taken into account for the calculations of the traditional design proposal.

Table 7: Input General Parameters

Input Parameter Symbol Value

Wave height [M] H 0,55

Deep water wave height [M] H0 0,55

Wave Length [M] L 10,53

Deep water wave Length [M] L0 10,53

Wave period [s] T 2,17

Depth [M] h 1,5

Breaker depth [M] hb NONE

Berm Height

Storm water level [M] Significant wave height (Design wave) [M] Berm Height [M]

2 1,023 2,5115

According to table 7, the generated height for the Berm of the dike was set to a minimum of 2,52 meters. This value was calculated based on the Sum of the max value registered for the high tide and the half of the design wave.

Input

Output

Optimization

CalculationsDiscussion of the final design

Conclusion

Source: THUYÉT MINH THIÉT KÉ CO SO (2010). Vietnamese Dike Design Code

Sketch 1: Traditional Profile Cross-Section. Study Area A

Chart 10: Chapter’s structure

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Output The results of the calculations follow below, in table 8.

Table 8: Output Wave Run-up

Slope H0 L0 Significant Wave Height [H]

Slope α (Decimals)

Wave Run-up (z) [M]

1;3 0,55 10,53 1,023 0,33 1,136439281

Reduced Wave Run-up

Initial Wave Run-up z [M]

Material Revetment Fr

Reduced Wave Run-up [M]

1,136439281 Hard revetment 0,95 1,079617317

Revetment

Filter construction

Design Wave [M] Deep water wave length Slope (α) ρ Revetment ρ Water

Revetment Thickness [M]

1,023 10,53 0,33 2,4 1,025 0,14296623

Open Construction

Design Wave [M] Hudson Coefficient Slope (α)

Minimal Revetment Weight (N)

1,023 46,09875068 0,33 17,08874979 Final Design Values (Dike)

Max High tide [M] Total Wave Run-

up [M] Dike Height

(Crown) [M] Outer Slope

2 2 4 1:3

Optimization Some reduction factors were considered in order to optimize the design. This relates to the following parameters:

� Wave run-up � Revetment

This process had the objective of determining the material that will better absorb the wave energy and their respective dimensions in order to carry sufficiently the external factors that act on the dike. The chosen material was hard-revetment due to the wave impact being too high, which requires a retaining structure that prevents the Dyke from being washed out. The minimum revetment was calculated as 0,15 meters if a filter construction [geotextile/fine riprap/ hard-revetment]. In case of an open construction [i.e.: Brabon2] the minimum weight required – based on the 1:3 slope – is 20,085 Newton, as stated in table 8.

Conclusion Based on this approach a strong dike and dry hinterland are ensured, assuming that the recommended values are taken into account. The calculations and tables previously stated point to an optimal design if an outer slope of 1:3 and a dyke of 4 meters in height (crest level) are considered.

In this design the outer slope can be made of hard revetment of a minimum of 0,15 meters in height – in case of opting for a filter construction – and a weight of 17,1 Newton if an open construction is used. There is even the possibility of using revetment made of asphalt and rip rap-stones, which makes it act as a closed construction type but with the possibility of fast and cheap implementation. In this case calculation of the negative pressure are important as can assure that the revetment remain in place and the dike is stable. Detailed design calculations regarding settlement and stability can be found in the Geotechnical Verification chapter. The budget calculation and feasibility discussion are presented afterwards.

2 Vietnamese designed revetment made up of small riprap stones enclosed in a metal cage, usually placed on the outer slope of a dike.

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Final Concept 3D View Strategy: Traditional

Location A

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Proposal 2 Location A

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Strategy 2: Advancing Location A

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Advancing approach The second proposal for the area consists on advancing into the foreshore, increasing the wave reduction zone in order to keep the modification costs low - regarding the existing dyke - as well as creating a buffer zone for the mangroves to regenerate. This design is composed of a bank of sand (implemented by sand nourishment techniques), a buffer zone and the existing dyke, which may be modified according to the results of the calculations of the wave energy that reaches the Dike.

The objective of this chapter is to present substantial technical data about the design’s aspects as well as a comparison between the two proposals. The chapter is structured according to the illustration below:

Calculations The calculations performed for designing the dike for the advancing proposal took into account the parameters stated in table 9.The sketch below illustrates the design of the dike and its different sections, which dimensions were determined according to the values of the outputs, stated in table 10. As this design is composed by a wave reduction zone, specifications from wave reduction from mangroves were used in order to generate the final values of the wave height. The complete calculation process is attached in Annex B - Appendix 2B.

Input The same parameters used in the previous chapter were used; however, a calculation was performed to check the wave height in case it breaks in the foreshore. This was due to the presence of the sand bank in the design, which requires a determination of its minimum height. This value generates on basis of the summation of the wave let-through and Set-up.


Input Parameter Symbol Value [M]






Depth [M] h 1,5


Sand Nourishment Wave Height Calculation

Wave let-through HD Foreshore developed wave Hn

Wave at the toe-construction Htot Set-up Total H [M]

0,75 NONE 0,75 0,112

5 0,8625

Input

Output

CalculationsReduction in wave energy

Comparison

Discussion of the results

The design considerations

Conclusion

Sketch 2: Advancing Profile Cross-Section. Study Area A


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Output Taking into account the calculations previously executed, the wave-reduction techniques proposed in this design suggest that the existing dyke does not need many modifications, in fact the existing profile can be maintained with a requirement solely of reinforcement of the key areas. These include replacing the revetment and protecting the toe-construction. The reduced wave height was based on a decrease in wave energy based on the specifications of a mangrove forest of 100 meters in width.

Regarding the revetment asphalt didn’t show the smallest reduction in wave run-up, however it is the ideal material for the existing dike due to its cheap and fast implementation. Table 10 summarizes the results. Dike’s Design values section portraits the final values for the key parts of this design variant.

Table 10: Output Wave run-up (Hunt) - Width Mangrove Forest: 100 meters

Slope H0 L0 Reduced Wave Height

Slope α (Decimals) Wave Run-up (z)

Reduction [%]

1;3 0,55 10,53 0,29 0,33 0,605520614 72%

Wave Run-up reduction Initial Wave Run-up (z) [M]


Reduced Wave Run-up (z) [M]

0,605520614 Asphalt 1 0,605520614

Revetment

Filter construction

Reduced Wave height

Deep water wave length Slope (α) ρ Revetment ρ Water


0,29 10,53 0,33 2,4 1,025 0,076175649

Closed Construction

Reduced Wave height

Hudson Coefficient Slope (α)


0,29 46,09875068 0,33 0,39102675

Dike's Design Values

Foreshore Buffer Zone Existing Dyke*

Sand Nourishment

Crest’s height: DTM +1 Meters

Mangrove Forest

Width: 100 [M]

Height at the Crest

Actual dike's crest level (3,5m)

Slope: 1:20 Revetment

Asphalt or Hard-revetment (concrete

blocks)

Comparison Reduction in wave energy In an effort to decrease any necessary modifications to the existing dike, this design variant made use of some techniques. Such as the implementation of structures for wave energy reduction (I.e.: wave breaker, sand bank etc.). As shown in the sketch 2 this design is composed by the following structures:

� Sand bank � Buffer zone with mangrove forest � Permeable brushwood dams

The wave reaching the existing dike will be reduced by the sand-bank and the mangrove forest located on the buffer zone, thus permeable brushwood dams will trap sediment to keep the sediment balance stable, providing the required conditions for the mangroves to regenerate. See Mangrove vegetation chapter for more information regarding techniques and requirements regarding implementation of mangrove forests. Graph 4 shows the effect of a mangrove forest on the height of the wave run-up.

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Graph 4 was generated in order to visually portrait the effects of mangrove forests over the height of the wave Run-up.

Each point on the x-axis was generated on basis of the following parameters:

� Wave Height (meters) � Dike’s slope (decimals) � Wave run-up (meters) � Reduction factor by width of mangrove forest

The reduced wave height is determined based on the factor of reduction specified by the width of the mangrove forest. Each point on the curves is a representation of the wave run-up reaching the dike, after suffering the reduction in energy by the mangrove belt.

It is possible to see the effect that slopes have on the height of the wave run-up. Furthermore, it was shown that mangroves forests up and until 100 meters in width have little effect over the absorption of energy in steep dike slopes. In this case, larger mangrove forests are necessary for appropriate reduction and significant reduction in construction costs.

0

0,4

0,8

1,2

1,6

2

2,4

2,8

3,2

3,6

4

1/2 1/6 1/n

Wav

e Ru

n-up

hei

ght [

M]

Dike's slope [Fraction]

Graph 4: Wave Run-up through mangrove forest

50 meters 100 meters 150 meters 200 meters

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Conclusion Discussion of the Results

The aim of this subchapter is portraying visually the differences in wave run-up height generated by the two different proposals, which were made on basis of the results of the wave run-up tables, available in Annex B - Appendix 2B.

0

1

2

3

4

0

1

2

3

4

Wav

e Ru

n-up

(M)

Graph 6: Final Wave Run-up Comparison between output from final designs

Existing dike's crest height

Wave Run-up Advancing Strategy

Wave Run-up Current Sit.

Wave Run-up Traditional Strategy

The current situation and the traditional proposal generates identical primary wave run-up heights. It is however, of high importance to take into account that the traditional proposal dike’s design uses some optimization techniques to reduce the wave height as well as its guaranteed to support all the forces to which it is exposed. In opposition of the current encountered situation.

In case of the current situation – regarding the total wave run-up - it was found to reach 3,8 meters, overtopping the current dike’s height of 3 meters. On the other hand, the traditional proposal – designed with a slope of 1:3 - led to a reduced wave run-up of 1,079 meters (against the original 1,13 meters) and a total of 3,079 meters in water height.

The implementation of structures that reduce the wave energy into the design makes the advancing proposal have the best output when it comes to wave run-up heights.

Graph 6 shows the final wave run-up heights generated in each proposal. It is evident that the current scenario demands a change of action – for instance, the height of the crest at the current dike is smaller than the actual wave run-up. Furthermore portraits the efficiency of the advancing strategy: The wave run-up generated by the final dike design proposed in this variant is 72% smaller than the original wave run-up.

0

1

2

3

4

5

6

0 1/2 1/3 1/4 1/5 1/6 1/7 1/8 1/9 1/n

Wav

e Ru

n-up

(M)

Slope (Fraction)

Graph 5: Wave Run-upA global overview at the outputs by the different

strategies

Traditional Advancing

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The design considerations Graph 7 illustrates the wave run-up heights reaching a certain dike’s slope through a mangrove forest of 100 meters in width. The best optimal level was found using the design values stated in Table 11.

Table 11: Specifications of the final design

Reduced Wave Height [M] Slope α (Decimals) Wave Run-up (z) [M]

0,29 1:3 0,66

The best reductions in wave energy happen in mangrove forests of 150 and 200 meters in width. This system however proposes a width of 100 meters as being an optimal value. This is because most of the mangrove belts present in the area (which measured around 100 meters in width), showed to be developing well. Thus the implementation feasibility assessment, which assesses the difficulty ant the time span of the implementation process. This result is a system that can carry the reality sufficiently taking into account the required safety margins, while still being easy to implement.

This variant was designed to be in first place land consistent. In other words, to be a system that aims mainly at the land besides preventing flooding of the hinterland. The implementation of this concept into the design has been done in the form of a mangrove forest, which reduces the wave energy that hits the existing dyke as well as acting as a filter and ecosystem stabilizer, resulting in a better water quality as well as increasing the land value.

This system requires low maintenance and very little modifications to the existing dyke as replacement of revetment by riprap stones covered by asphalt and the reinforcement of the toe-construction with high graded riprap stones, making it a very balanced design with a good feasibility rate.

Taking into consideration all the mathematical thought and the respective outputs, the workability of the design – in regards to the ability to withstand all the negative forces and its feasibility –, make it a very good fit for the area and will cause a positive impact on all stakeholders involved.

0

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2,8

3,2

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1/2 1/6 1/n

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n-up

hei

ght [

M]

Dike's slope [Fraction]

Graph 7: Wave Run-upWave Run-up on Advancing's final design.

100 meters

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Final Concept 3D View Strategy: Advancing

Location A

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Analysis of the current situation's results Definition of the strategy Calculation of the design

Chart 12: Pre-design process

Study Area B Pre-Design

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Map 2: Province of Soc Trang

Study area B is located near Bac Lieu continuing near Vin Chau. (See marked area in the Map) It is a stretch of 19 kilometres along the shore. T sections and Mangrove regeneration projects have improved the defence system over the past years. During the visual analysis, it became clear that the dike was a lot better than Location A. Despite these efforts, the dike system is still not sufficient. During an average high tide, the toe construction is eroding, rapidly reducing the defensive ability and stability of the structure. The new design waiting to be implemented will solve the flood height issue, but not the eroding problem. This chapter will explain the pre-design process parameters and results.

Study Area B

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Results

Graph 8 represents the outputs in regards to the calculations of the current situation for study area B

According to the visual analysis the average slope of the dike was found to be 1:3 which generates a total wave run-up of 2, 92 meters against the actual 3 meters at the crown of the dike. The values of the wave run-up are smaller than the ones in study area A due to the presence of mangroves, which help to decrease the wave energy reaching the dike.

Is important to notice that the dike is not sufficient, especially due to the erosion of its toe-construction, which compromises the stability of the whole Dike. Thus the scenario of years to come point to an increase in sea water level, strength of storms and increase inland subsidence. This combination of factors will surely contribute to big flooding’s in the area and an increase on the existing problems if actions are not taken to modify the current coastal protection system.

2,91

3,00

0

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1,5

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2,5

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3,5

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1/2 1/6 1/n

Wav

e Ru

n-up

(M)

Slope (Fractions)

Graph 8: Wave Run-up [M] - Current Situation (B)

Total Wave Run-up Height at the Crown of the Dike Wave Run-up (z)

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Strategy Definition

Sediment transport

•Moderate outflow velocity•Erosion of the foreshore•Usage of T-sections to trap sediment

Existing Dike'scondition

•Usage of soft-revetment (I.e.: Clay)•Dike is damaged•Toe-construction is being washed out and dike's original slope has

been modified

Vegetation

•Mangrove regeneration projects. Minimum of 50 meters

Hinterland

•Mainly ocupied by shrimp farming properties

Wave attack

•Wave attack is classified as small

Chart 13: Results of the Visual Analysis (Study Area B)

Following the results from the visual analysis, shown in chart 13, and the calculations regarding the evaluation of the current situation, supporting the statement regarding insufficient protection, the following strategies were set in order to address the problems in the area:

� Traditional Strategy � Managed Realignment

These strategies are in accordance with the Program of Requirements, which highlights spatial usage and valuable hinterland as two important factors in determining the strategy. Due to the hinterland from study area B being sparsely populated, the soil being salty and dry and mainly occupied by aquaculture properties.

Traditional Approach

Reduction of wave energy is the most important factor for these designs. Location B already has a minimum of 50 meters of mangrove wave reduction in place, as stated in the previous chapter. This is due to successful mangrove regeneration projects and the implementation of T-sections. However, this reduction is not sufficient so alternative ways to reduce the wave Energy will be implemented into the designs. For the traditional variant, this will be hard revetment.

Managed Realignment

There are various approaches to implementing Managed Realignment. This includes:

� Opening of small breaches to the existing dike in order to let sediment flow in the buffer zone.

� Keeping the existing dike as it is and placing a new dike behind. � Removal of existing dike and reuse its revetment and soil for the construction

of the new dike.

This variant will deal initially with creating a natural buffer for increasing vegetation and an optimal design for the new dike because of wave height decrease. Moreover, the vegetation will also increase the water quality going inland.

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Proposal 1 Location B

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Strategy 1: Traditional Location B

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Traditional approach The first proposed design is drafted on basis of the traditional approach, which would be to heighten the dyke as well as making use of proper construction techniques and materials, used by the Dutch over the years. The design generated by this approach is based on mathematical formulas that ensure that the dyke’s parameters are sufficient - given the situation- as well as that they are optimized. This chapter is structured according to the illustration below:

Calculations The sketch below illustrates the design of the dike and its different sections, which dimensions were determined according to the values of the outputs, stated in table 13. All formulas for calculating the different sections and aspects of the dike were imported in a spreadsheet, in order to have a better workflow and be able to quickly optimize results. In the following pages, an explanation about calculations is carried out aiming on giving substantial information about the design’s reliability and serving as a basis for comparisons between current and proposed scenario outputs. The complete set of calculations in spreadsheet format is available in Annex B - Appendix 3B.

Input The following parameters and their respective values were taken into account for the calculations of the traditional design proposal.


Input Parameter Symbol Value






Depth [M] h 1,5


Berm Height

Max High tide [M] Significant wave height (Design wave) [M] Berm Height [M]

2 0,66 2,328357425

Input

Output

Optimization

CalculationsDiscussion of the results

The design considerations

Conclusion


Sketch 3: Traditional Profile Cross-Section. Study Area B


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Output The results of the calculations, executed on basis of the imported general parameters, are located below, in table 13.

Table 13: Output Wave Run-up


Reduction

Reduced Wave Height

Slope α (Decimals)

Wave Run-up (z)

1;3 0,55 10,53 1,023 0,358

05 0,66 0,33 0,910535

407

Reduced Wave Run-up Initial Wave Run-up z [M]


Reduced Wave Run-up [M]

0,910535407 Hard revetment 0,95 0,865008636

Revetment

Filter construction Design Wave [M]

Deep water wave length

Slope (α) ρ Revetment

ρ Water


0,66 10,53 0,33 2,4 1,025 0,114547092

Open Construction

Design Wave [M]

Hudson Coefficient

Slope (α)


1,023 0 0,33 0

Final Design Values Max High tide

[M] Dike's Crown

Height [M] Outer Slope

2 3,5 01:33

Optimization In order to optimize the design, the following reduction parameters were used:

� Wave run-up � Revetment

This process has the objective of determining the material that will better absorb the wave energy and their respective dimensions, in order to carry appropriately the external factors that act on the Dyke.

The chosen material was hard-revetment due to the wave impact being too high, which requires a retaining structure that prevents the dike from being washed out. Based on this, the revetment thickness was determined by crossing values of reduced wave height and the slope with some fixed parameters. The minimum revetment thickness was found to be 0,15 meters in case of usage of a filter construction [geotextile/fine riprap/ hard-revetment]. In case of open construction type (I.e.: Brabon) the minimum weight required – based on the 1:3 slope – is 20,085 Newton.

Conclusion Because this design meets the standards, it will ensure a dry hinterland, allowing the area for further development. The Calculation of the other strategies will show if this is the most suitable variant for this location. This will be determined in the budgetary analysis chapter.

In this design the outer slope can be made of hard revetment of a minimum of 0,15 meters in height – in case of opting for a filter construction – and a weight of 20,085 Newton if an open construction is used. There is also the possibility of using revetment made of asphalt and rip rap-stones, which makes it act as a closed construction type but with the possibility of fast and cost efficient implementation. Detailed design calculations regarding settlement and stability can be found in Geotechnical Verification chapter. The budget calculation and feasibility discussion are presented afterwards.

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Final Concept 3D View Strategy: Traditional

Location B

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Proposal 2 Location B

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Strategy 2: Managed Realignment Location B

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Managed Realignment approach The second proposal for the area will allow the sediment to flow inland, increasing the wave reduction zone. This will keep the modification costs low while creating a buffer zone for the mangroves to regenerate. A new dike will be implemented inland after the buffer zone. The wave attack will be significantly reduced by the buffer zone allowing the new dike to be very cost efficient.

The objective of this chapter is to present substantial technical data about the design’s workability as well as a comparison between the two approaches. The chapter is structured according to the illustration below:

Calculations The calculations were carried out according to the general workflow explained before. The sketch below illustrates the design of the dike and its different sections, which dimensions were determined according to the values of the outputs, stated in table 15. All the parameters regarding the current scenario were imported in order to generate the outputs used in the wave run-up calculations. As this design has a wave reduction zone, specifications by wave reduction from mangroves were used in order to generate the final values of the wave height. The complete calculation process is in Annex B - Appendix 3B.

Input The same parameters used in the traditional approach were used; however, a calculation was performed to check the wave height in case it breaks in the foreshore. This was due to the presence of the sand bank in the design, which requires a determination of its minimum height. This value generates on basis of the summation of the wave let-through and Set-up.

Table 14: Input

General Parameters

Input Parameter Symbol Value [M]

Wave height [M] H 0,55 Deep water wave height [M] H0 0,55

Wave Length [M] L 10,53 Deep water wave Length [M[ L0 10,53


Depth [M] h 1,5


Input

Output

Calculations

Reduction in wave energy

Land use

Comparison

Chosen design

Discussion of the most optimal design

Conclusion


Sketch 4: Managed Realignment Profile Cross-Section. Study Area B


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Managed Realignment Wave Height Calculation

Wave let-through HD Foreshore developed wave Hn

Wave at the toe-construction Htot Set-up Total H

0,75 0,5 0,901387819 0,13520817

3 1,03659599

2

Output Taking into account the calculations previously executed, the wave-reduction techniques proposed in this design suggest that due to the foreshore developed wave there is quite a wave run-up. However due to the mangrove belt in this strategy the wave run-up will be significantly reduced and is in fact minimal compared to the other strategies.

The outputs in the table below give the revetment specification according to the chosen type. The reduced wave height is based on a wave energy decrease caused by a mangrove forest of 200 meters in width.

Table 15: Output Wave run-up (Hunt) - Width Mangrove Forest: 200 meters


Reduced Wave Height Wave Run-up (z)

Reduction [%]

1;4 0,55 10,53 1,036595992 0,04 0,157824743 97%

Wave Run-up reduction Initial Wave Run-up z [M]


Reduced Wave Runup [M]

0,609531113 Grass 0,9 0,548578002

Revetment

Filter construction

Reduced Wave height

Deep water wave length Slope (α) ρ Revetment ρ Water


0,04 10,53 0,25 2,4 1,025 0,021403255

Closed Construction Reduced Wave height

Hudson Coefficient Slope (α)


0,04 46,09875068 0,25 0,000562139

MR Variant Design Values

Foreshore Buffer Zone Existing Dyke*

Permeable brushwood dams Mangrove

Forest Width: 200 [M]

Height at the Crest

Actual dike's crest level (3,0m)

Revetment Maintained Toe-construction Rip-rap Stones

Comparison Reduction in wave energy In an effort to decrease any necessary modifications to the existing dike, this design variant made use of some techniques. Such as the implementation of structures for wave energy reduction (I.e.: wave breaker, sand bank etc.). As shown in the sketch 4 this design is composed by the following sections:

� Existing Dike � Intertidal Buffer zone with mangrove forest � New dike � Permeable brushwood dams

The wave reaching the new dike will be greatly reduced by the existing dike and the mangrove forest located on the buffer zone, thus the permeable brushwood dams will trap sediment to keep the sediment balance stable while providing the required conditions for the mangroves to regenerate. See Mangrove vegetation chapter for more information regarding techniques and requirements regarding implementation of mangrove forests.

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Land use

This coastal protection design makes use of concepts of Integrated Coastal Zone Management that shift from the traditional ‘hold-the-line’ approach of coastal protection towards more flexible soft engineering options.

Managed realignment is a relatively new soft engineering alternative aiming to provide sustainable flood risk management with added environmental and socio-economic benefits by creating space for coastal habitats to develop more dynamically (Esteves, 2014). Managed realignment is able to reduce both coastal flooding and erosion. It is the deliberate process of altering flood defenses to allow flooding of a presently defended area. Managing this process helps to avoid uncertain outcomes and negative impacts.

There are various approaches to implementing Managed Realignment. This includes:

� Opening of small breaches to the existing dike in order to let sediment flow in the buffer zone.

� Keeping the existing dike as it is and placing a new dike behind.

� Removal of existing dike and reuse its revetment and soil for the construction of the new dike.

In this deign it involves setting back the line of the actively maintained defense to a new line, inwards. Doing so should promote the creation of intertidal habitat between the old and new defenses. (See Map 3)

Intertidal habitats attenuate incoming wave energy, meaning that waves reaching the shore are smaller in height and less powerful. This is advantageous, as it require hard structures of reduced height and strength. Reduced incident wave energy is also likely to result in reduced defense maintenance costs. This beneficial for restoring the natural ecosystem and habitats in the area thus improving the water quality.

Map 3: Location Coastal protection System – Managed Realignment approach (B)

1 KM

North

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Conclusion This coastal protection system takes into account many variables, incorporating principles of modern coastal protection in its design. By using strategies of Integrated Coastal Zone management, it is possible to minimize the use of hard construction techniques, which are necessary for implementing the dike. Therefore, the costs of implementation are drastically reduced. Besides the budget factor, the creation of an intertidal buffer zone – between the existing and new dikes – is highly beneficial to the area as it is a proven concept for creation of a sustainable model where costal protection, biodiversity and farmlands are part of the same cycle.

However, according to the Mekong Delta Plan (2013), in the dry season, the flow of fresh water in the coastal areas is limited. This to the extent that increasingly groundwater is being used from deep phreatic aquifers (ca. 110 m) as an additional source of fresh water. Both to control salinity levels in shrimp farming, enable the diversification of production into vegetables, and homestead production (both in rice and shrimp areas). Already today, water pressures drop by 2-5 m in the dry season, forcing farmers to lower their centrifugal pumps into the wells to enable continued pumping as water levels drop to 15-20 m below the surface. There are strong indications that ancient (Pleistocene) deep-water layers are being depleted that are not (or very limited) replenished from Mekong floodwaters. As shown in chart 16, this method is highly unsustainable.

The preservation of coastal mangrove forests, and its gradual regeneration and expansion is of extreme importance as it forms a critical ecological function for the delta – not only in terms of ecology and biodiversity, but also in terms of enabling a natural wastewater treatment capacity for the aquaculture sector and coastal defense capacity. By creation of “waste-water” disposal areas along the intertidal buffer zone, mangroves can be actively planted and regenerated (feeding on nutrient rich brackish water). These new, and regenerated, mangrove areas can be used to actively settle coastal sedimentation and contribute to costal expansion and fortification system. This is possible because the intertidal buffer zone gives room for shorelines to settle while remains open to tidal inundation.

This proven method has the capacity to sustainably improve the brackish water quality, reduce disease occurrences and yield losses, and diversify income. In addition, it meets international certification standards of sustainability and quality, which enables producers to enter higher value markets. The result is illustrated chart 17.

Destruction of

mangroves

Aquaculture farmlands

Salt water intrusion

Wastewater pollution

Groundwater extraction

Depleet of aquifers

Erosion and land

subsidence

Chart 16: In the current scenario, the cycle is highly unsustainable.

Filter process

Use of water by agrictulrure

and aquaculture

Waste water run-off

Mangrove regeneration

Chart 17: This coastal protection design addresses all the problems in the area by creation of a sustainable cycle.

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Final Concept 3D View Strategy: Managed Realignment

Location B

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Soil parameters

Geotechnical Verification

A Geotechnical verification was performed for each dike design in order to determine sections of the dike that are more suitable to pressures, to check the slope stability and the amount of settlement to be expected. For these purposes soil data obtained from Soc Trang province was used. In an effort to optimize the process and accuracy, Plaxis® software was utilized for all calculations. Hereby will follow the tables of parameters used for all calculations and a discussion of the results outputted from the software for each study area. The complete output is available in Annex B - Appendix 4B. This chapter is structured in accordance to chart 18.

Table 16: Soil Properties Property Layer

Material Clay_1 Clay_2 Clay_3 Clay_4

Material model Mohr-Coulomb Mohr-Coulomb Mohr-Coulomb Mohr-Coulomb

Material type Undrained Undrained Undrained Undrained

ϒunsat 15 Kn/m3 15 Kn/m3 16 Kn/m3 16 Kn/m3

ϒsat 18 Kn/m3 18 Kn/m3 18 Kn/m3 18,5 Kn/m3

κx 1,00E-04 1,00E-03 1,00E-02 1,00E-02

κy 1,00E-04 1,00E-03 1,00E-02 1,00E-02

Εref 1000 1000 2000 1,00E+04

ν 0,33 0,33 0,35 0,33

σref 375,94 375,94 740,741 3759,398

Εoed 1482 1482 3210 1,48E+04

Ϲref 2 5,5 2 4

Φ 24 3,6 24 25

Ψ 0 0 0 0

Strength Rigid Rigid Rigid Rigid

Soil Properties table

Soil ParametersModel Geometry

Output

Study Area AModel Geometry

Output

Study Area B

Source: BÁO CÁO DIA CHÁT. Soc Trang Soil Book

The geotechnical verification was done on basis of the soil data obtained from previous surveying on soil properties of Soc Trang province. According to BÁO CÁO DIA CHÁT (Soc Trang Soil Data Book), the soil in Soc Trang coastline is mostly composed by clay layers that differ mostly by their permeability factors and rigidity, varying from muddy to hard plastic.

For modelling the different dike designs, different soil clusters were built and assigned to their respective soil type. The different soil types used for the geotechnical verification are described in the following table.


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Study Area A

Output

For the geotechnical verification the following strategies have been verified:

� Traditional Strategy (Location A+B) � Advancing Strategy (Location A) � Managed Realignment Strategy (Location B)

Input and mesh parameters are constant for both locations. The following input parameters have been maintained during the calculation:

� Plain strain � Finite elements mesh � Medium Coarseness � Stability around point 1

Design steps taken:

1. Initial phase 2. Maximum High tide 3. Storm Surge with Maximum wave run-up

The variant has been verified for the following failure mechanisms:

� Horizontal Settlement � Vertical Settlement � Stability � Bearing Capacity

Figure 9: Geometry models for Study Area A. Traditional and Advancing dike design variants respectively.

The calculations consisted of two phases. First the initial stress was calculated via the input of the initial conditions by means of Gravity loading. Secondly the calculations of the stresses resulting from the increase in water level - originated from the Wave Run-up - were calculated.

The output views are shown in figure 10. Is possible to see the deformations of the embankment due to the change in water level. The plot clearly shows the uplift of the soil layers behind the embankment and the movement of the embankment itself to the left direction as initially predicted.

Thus is evident that the undrained behaviour in the clay layers causes excess pore pressures to develop.

Location A Traditional

� Maximum Extreme displacement 17,51*10 -3m (Capacity) � Maximum Vertical displacement U y = 13,05*10-3m (Settlement) � Total incremental displacements dUtot = 6,26*10 -3m (Stability)

Location A Managed Advancing

� Maximum Extreme displacement 19,45*10 -3m (Capacity) � Maximum Vertical displacement U x =10,42*10-3m (Settlement) � Total incremental displacements dUtot = 1,52*10 -3m (Stability)

The complete output is attached in Annex B - Appendix 4B.

Figure 10: Results of the geotechnical calculation for Study Area A. Visualization of the parameters has been modified by a factor of*200

Clay_1

Clay_2

Clay_2

Clay_3

Clay_4

Clay_4

Clay_1

Clay_2

Clay_3

Clay_2

Clay_4

Clay_4

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Study Area B

Output

The two dike variants and respective soil clusters were modelled as shown in the figure 9. As the dikes are subject to a change in water level, which result in modifications to the pore pressure distributions, the stability of the embankment was crucial to be checked. Is particularly important to check the influence of this change to see the effect in the lowlands behind the embankment, areas that are more subject to the pressures arisen from this effect.

The embankment consists of clay of different strengths, rigidity and permeability factors. The soil type Clay_1 was assigned to the new dike profile as it consists of highly impermeable soil, a requirement for the design of top soil sections of dike embankments. The geometry is modelled with a plain strain geometry model. The finite element mesh is based on the 15-node elements. The units used were meters for length, Kilo Newton for force and day for time. Standard fixities option is used to define the boundary conditions.

For the mesh generation global coarseness was set to medium. In order to model the parts of the embankment more subject to pressure accurately, the mesh generation was refined around point 1. As a result, the element size around that part is modified to half the average element size.

As the geometries contain non-horizontal soil surfaces the stress was calculated by means of “Gravity loading”, therefore pore water pressures from the phreatic level were calculated.

Figure 11: Geometry models for Study Area B. Traditional and Managed Realignment dike design variants respectively.

The output parameters per variant will be discussed in this subchapter.

Output

Location B Traditional

� Maximum Extreme displacement 22,37*10 -3m (Capacity) � Maximum Horizontal displacement U x = 19,99*10-3m (Settlement) � Maximum Vertical displacement U y = 14,98*10-3m (Settlement) � Total incremental displacements dUtot = 14,25*10 -3m (Stability)

Location B Managed Realignment

� Maximum Extreme displacement 1,26*10 -3m (Capacity) � Maximum Horizontal displacement U x =1,21*10-3m (Settlement) � Maximum Vertical displacement U y =1,10*10-3m (Settlement) � Total incremental displacements dUtot = 222,31*10 -6m (Stability)

Due to the flattened inner slope the traditional variant did not have the same stability issues as in location A. The Managed Realignment variant was proven stable as well.

Figure 12: Results of the geotechnical calculation for Study Area B. Visualization of the parameters has been modified by a factor of*200

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Budgetary Analysis

In order to make an accurate comparison between the strategies for each study area, a budgetary analysis has been drafted. The Budgetary analysis has been divided in the following Categories:

� Implementation � Maintenance

The difference in results will be discussed per study area. After this a comparison of both study variants will be drafted to clearly state the most advantageous variant. As conclusion the reason for the difference in costs will be discussed. This results from the different materials used and in the case of the Managed Realignment strategy, for instance, the difference in maintenance and strategy. All results are a direct result from the excel calculations, available in Annex B - Appendix 5B. On Appendix 3 the technical materials are explained. All cost calculations are based upon the Vietnamese design codes.

Comparison of implementation costs Comparison of maintenance costs

Chart 19: Chapter’s Structure

58 | P a g e

Study Area A Comparison of implementation costs

$- $100.000,00 $200.000,00 $300.000,00 $400.000,00 $500.000,00

$-

$20.000,00

$40.000,00

$60.000,00

$80.000,00

$100.000,00

$120.000,00

$140.000,00

$160.000,00

$180.000,00

$200.000,00

Volu

me

NPL

Mat

ress

Rip-

rap

Toe-

cons

truc

tion

Reve

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t

Gran

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Geot

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Wea

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Bind

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Base

laye

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Geot

extil

e

Extr

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ploy

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Build

ing

site

Inci

dent

s (20

%)

Earthworks Foreshore Filter-Construction Berm (+road) General

Graph 9: Implementation costs - Study Area A_Traditional

Total cost CostSource: Ministry of Infrastructure, Vietnam

$- $100.000,00 $200.000,00 $300.000,00 $400.000,00 $500.000,00

$-

$20.000,00

$40.000,00

$60.000,00

$80.000,00

$100.000,00

$120.000,00

$140.000,00

$160.000,00

$180.000,00

$200.000,00

Volu

me

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Mat

ress

Rip-

rap

Toe-

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Reve

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Nour

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Perm

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ms

Extr

a em

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ees

Build

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site

Inci

dent

s (20

%)

Earthworks Foreshore Filter-Construction Sand Nourishment General

Graph 10: Implementation costs - Study Area A_Advancing

Total cost CostSource: Ministry of Infrastructure, Vietnam

A budgetary analysis has been performed for each proposal regarding both study areas. The detailed spreadsheet calculations with the systematic process are available in Annex B - Appendix 5B. Hereby will follow the comparison/discussion of the results of the budgetary analysis. These comparisons are divided between implementation and maintenance costs by study area.

Graph 9 visually portraits the results of the cost calculations ,performed for estimating accurately the implementation costs of the coastal protection design for the first proposed variant of Study Area A.

The results, shown in Graph 9, revealed a total cost of U$334.057, 40, necessary for implementing the traditional dike design. Costs are higher for the foreshore section of the dike design (41,22%), which needs more expensive material (I.e.: heavy concrete revetment blocks) and require specialized machinery for placing these blocks on the toe of the dike. These costs are followed by the general costs, such as building site, extra employees and incidents, which account for 28,57%. The total cost is derived from the following:

- Material (37%) - Machinery + Specialized equipment (22%) - Employees +General (41%)

Graph 10 on the other hand portraits the implementation costs of the second dike design variant proposed for Study Area A. As this dike design is composed by a sand bank - placed on the end-foreshore by sand nourishment techniques – and a buffer zone (for mangroves to grow), the calculated wave attack reaching the existing dike was smaller than the one calculated for the 1st proposal.

As a result, the necessary modifications to the existing dike were fewer. This is seen in the graph at the required earthworks, being much less in volume, impacting directly the total costs as a comparison to the traditional design (0,28% VS 4,22% of total costs),. The Advancing design doesn’t make use of a berm, but the implementation of sand nourishment techniques for creation of the sand bank still keeps the prices high due to the implementation requirements, which include the use of specialized equipment and techniques. Which makes the sand nourishment account for almost 40% of the total costs of U$450.727,20 for implementation of the Advancing proposal. The total cost is derived from the following:

- Material (39%) - Machinery + Specialized equipment (23%) - Employees +General (38,16%)

59 | P a g e

Comparison of maintenance costs

$913,11

$5.465,40

$1.213,03 $550,04 $409,53

$2.379,68

$-

$1.000,00

$2.000,00

$3.000,00

$4.000,00

$5.000,00

$6.000,00

$7.000,00

$8.000,00

$9.000,00

$10.000,00

Cost Total cost

Graph 11: Maintenance costs - Study Area A_TraditionalAccording to Maintenance Planning


Graphs 11 and 12 portrait the maintenance costs by section of construction for the 2 different proposals for Study Area A: Traditional and Advancing proposal. These costs were calculated based on an inflation rate of 4%/year and an interest rate of 6%. As pointed in the implementation costs, the total cost of the advancing design is directly impacted by the sand nourishment, which costs are particularly high in Vietnam, as it requires specialized equipment and techniques for its implementation and maintenance (94,47% of total maintenance costs). The sand nourishment maintenance planning considered maintenance intervals of 2 years for the first 10 years of its lifespan, going to 5 year-intervals from 10 to 20 years of its lifespan and then 10-year intervals from 20 to 50 years of its lifespan. This derives from the principles of mangrove grown rate and sediment balance, which will gradually change the current scenario as the new conditions are created, affecting positively the erosion reduction of the foreshore and the flow velocity. These graphs portrait the individual maintenance prices for each section of the dike design thus their percentage amount in regards to the total costs.

$651,99

$106.464,11

$1.213,03 $472,50

$100.576,25

$3.550,34

$-

$1.000,00

$2.000,00

$3.000,00

$4.000,00

$5.000,00

$6.000,00

$7.000,00

$8.000,00

$9.000,00

$10.000,00

Cost Total cost

Graph 12: Maintenance costs - Study Area A_AdvancingAccording to Maintenance Planning

Earthworks Foreshore Filter-Construction Sand Nourishment General

The maintenance costs of each design were calculated and are based on a forecast of 50 years. This ensures that the coastal protection designs can maintain their structural integrity over their lifespan thus create a basis for proper planning of inspections and repairs. The final maintenance costs, shown in the graph below, were derived from the maintenance planning sheet (available in Annex B - Appendix 5B) and are organized on regular intervals of time and built up according to the difficulty level of the task thus its maintenance costs. The maintenance is divided in two categories: Inspections and Repairs. Repairs are divided by labour, machinery and materials. The description of the materials is attached in Appendix 3.

Source: Ministry of Infrastructure, Vietnam

Source: Ministry of Infrastructure, Vietnam

Chart 20: Illustration of the budget calculation from quantities determination to maintenance costs

17% 22% 10% 7% 44%

0,61% 1,14% 0,44% 94,47% 3,33%

60 | P a g e

Study Area B Comparison of implementation costs

$- $2.000.000,00 $4.000.000,00 $6.000.000,00 $8.000.000,00 $10.000.000,00

$- $250.000,00 $500.000,00 $750.000,00

$1.000.000,00 $1.250.000,00 $1.500.000,00 $1.750.000,00 $2.000.000,00 $2.250.000,00 $2.500.000,00 $2.750.000,00 $3.000.000,00 $3.250.000,00 $3.500.000,00

Volu

me

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Graph 13: Implementation costs - Study Area B_Traditional

Total cost Cost

Graph 13 visually portraits the results of the cost calculations ,performed for estimating accurately the implementation costs of the coastal protection design for the first proposed variant of Study Area B.

The results, shown in Graph 13, revealed a total cost of U$6.100.162,46, necessary for implementing the traditional dike design. As in the traditional proposal for the Study Area A, costs are higher for the foreshore section of the dike design (43,95%), which needs more expensive material (I.e.: heavy concrete revetment blocks) and require specialized machinery for placing these blocks on the toe of the dike. These costs are followed by the general costs, such as building site, extra employees and incidents, which account for 28,57%. The total cost is derived from the following:

- Material (43%) - Machinery + Specialized equipment (16%) - Employees +General (42%)

$- $2.000.000,00 $4.000.000,00 $6.000.000,00 $8.000.000,00 $10.000.000,00

$- $250.000,00 $500.000,00 $750.000,00

$1.000.000,00 $1.250.000,00 $1.500.000,00 $1.750.000,00 $2.000.000,00 $2.250.000,00 $2.500.000,00 $2.750.000,00 $3.000.000,00 $3.250.000,00 $3.500.000,00

Volume Planting ofMangroves

LCC PermeableDams

Wear layer Binder layer Base layer Extraemployees

Building site Incidents (20%)

Earthworks Foreshore Berm (+ road) General

Graph 14: Implementation costs - Study Area B_M

Total cost Cost

Graph 14 illustrates the results of the budgetary analysis performed for the managed realignment proposal regarding implementation costs.

It is evident that this variant makes little use of hard techniques and specialized material. As a consequence the construction costs are low. This design differentiates itself by using concepts of integrated coastal zone management as the implementation of an intertidal buffer zone that will contribute for the mangroves to regenerate resulting in a sustainable cycle of “waste-water use – filter process + nutrient feeding by mangroves – clean water” restoring the land and increasing its land value thus allowing the local farmers to enter higher value markets. For this purpose some farm properties have to be relocated which results in a total LCC (land compensation costs) of U$3.350.973,50. The permeable dams’ technique, used for creating the proper sediment balance required for the mangroves to grow- is very cheap and makes use of natural materials.

The total cost for implementing this design variant is calculated as U$5.284.161,89 and is derived from the following:

- Material (4,24%) - Machinery + Specialized equipment (0,98%) - Employees +General (30,73%) - Land Compensation (63,42%)

61 | P a g e

Comparison of maintenance costs

Cost Total cost PercentageEarthworks USD 8.282,75 USD 83.107,34 10%Foreshore USD 21.252,42 26%Filter-Construction USD 4.622,54 6%Berm (+road) USD 5.398,21 6%General USD 43.551,43 52%

$-10.000,00

$-

$10.000,00

$20.000,00

$30.000,00

$40.000,00

$50.000,00

Graph 15:Maintenance costs - Study Area B_TraditionalAccording to Maintenance Planning


Cost Total cost PercentageEarthworks USD 1.300,24 USD 41.071,20 3,17%Foreshore USD -6.894,41 -16,79%Berm USD 2.595,13 6,32%General USD 44.070,24 107,30%

$-10.000,00

$-

$10.000,00

$20.000,00

$30.000,00

$40.000,00

$50.000,00

Graph 16: Maintenance costs - Study Area B_Managed RealignmentAccording to Maintenance Planning

Earthworks Foreshore Berm General

Graphs 15 and 16 portrait the maintenance costs, by section of construction, for the 2 different proposals for Study Area B: Traditional and Managed Realignment. These costs were calculated based on an inflation rate of 4%/year and an interest rate of 6%. In both situations general costs (I.e.: building site, extra employees and incidental costs) account for more than 50% of the total maintenance cost: 52% in the traditional variant and 73,72% in the managed realignment variant. In the Managed Realignment design variant, the return-rate coming from the profits of extraction were calculated. This is because when mangrove forests get too dense, the tress run out of space for growth, resulting in death. Therefore, extraction of a certain amount of tress was planned on 3-year interval basis from 6 to 15 years of their lifespan, with an increase of this interval as the mangrove forest gets more stable. The profit from extraction result in a return of costs, as seen in the graph in the foreshore column, as a negative value. The reduced use of specialized materials and equipment make the maintenance costs for the managed realignment be significantly smaller: U$41.071,20 VS U$83.107,34.

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Discussion and Recommendations

63 | P a g e

Discussion

Technical Aspects

Traditional Variant

Implementation costs

Maintenance costs Construction time

Benefits

U$334.057,40 U$5.645,40 2 years Flooding control Storm protection

Advancing Variant


Maintenance costs Construction time

Benefits

U$450.727,20 U$106.464,113 2 years Flooding control Storm protection Reduced modification to existing dike Restoration of water quality

USD -

USD 100.000,00

USD 200.000,00

USD 300.000,00

USD 400.000,00

USD 500.000,00

TR A

Graph 1: Implementation Costs

TR VS A

USD -

USD 20.000,00

USD 40.000,00

USD 60.000,00

USD 80.000,00

USD 100.000,00

USD 120.000,00

TR A

Graph: Maintenance CostsTR VS A

For Study Area A, two design variants were proposed. The first one was built up on basis of the traditional approach of “holding-the-line”. The second mixes concepts of Advancing, Integrated Coastal Zone Management and Traditional approaches.

The traditional variant is both in implementation and in maintenance less expensive, making the difference in costs hard to advocate. In terms of costs, the hold the line strategy would be the obvious winner. However, there are some discussion points to be addressed that defend this increase in costs. The entire area is protected through a mangrove protection system filtering the water intake for the aquacultures area inland. It is therefore quite important to keep this mangrove belt in existence. Mainly because the current erosion has not stopped, but is increasing. The mangrove belts are shrinking in both directions along the shoreline. This continuous process needs a sustainable approach. The traditional variant would need to be slowly implemented along the stretch of coastline potentially causing higher costs in the long term. Unfortunately, these costs are not possible to calculate and therefore not included in the research.

Implementing the advancing approach would result in a shift in this natural process using it to an advantage. By breaking the wave energy, it will not reduce the width but increase the size of the current and new mangrove belt. This will have the followings benefits

� Protection against flooding � Improved water Quality intake � Beneficial for mangrove belt behind the dike � Beneficial for the aquaculture behind the dike

The big difference in investment is the Sand Nourishment. This leads to 20x of increase in maintenance costs. In graph 18, it is clear that the biggest maintenance costs in traditional and advancing (excluding the nourishment) is for the riprap in terms of costs, as shown by the orange curve. This is also needed in the advancing variant on top of the nourishment after implementation to prevent washing out before the mangroves can grow. In addition to this, the nourishment is needed however in order to ensure a reduced wave impact and the creation of a wetland which will allow the mangroves to regenerate. In the first years, this will be high maintenance, as the mangroves will not have time to grow and still have to stabilize the sediment. Over the long term, however, the maintenance costs will become cheaper and could be tweaked after monitoring. It is very hard to determine this however beforehand and monitoring will be key. The implementation of permeable dams is relatively cheap. This would result in the long term in the nourishment costs going down and the mangrove beneficiary costs going up, resulting in a sustainable approach.

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1. Soil Interval (Years) 1. Soil Maintenance Costs (VD) 1. Soil Maintenance Costs ($)

64 | P a g e

Technical Aspects

Traditional Variant


Maintenance costs Earthworks

Construction time Benefits

U$6.100.162,56 U$83.107,34 563.315,2 M3 3 years Flooding control Storm protection

Managed Realignment Variant


Maintenance costs Earthworks

Construction time Benefits

U$5.284.161,89 U$41.071,20 42.972,89 M3 3 years Flooding control Storm protection Restoration of water quality Increase of land-value Meets international certification standards of sustainability and quality. Added value to exports (Farmers can enter higher quality markets)

USD 4.500.000,00

USD 5.000.000,00

USD 5.500.000,00

USD 6.000.000,00

USD 6.500.000,00

TR MR

Graph: Implementation Costs

TR VS MR

USD - USD 20.000,00 USD 40.000,00 USD 60.000,00 USD 80.000,00

USD 100.000,00

TR MR

Graph: Maintenance CostsTR VS MR

For Study Area B, two design variants were drafted: Traditional and Managed Realignment. Principles of classic coastal engineering sustain the first proposal, like “holding-the-line”, which consists of heightening and making modifications to the existing dike. This proposal is efficient for flooding control and storm protection. Managed Realignment on the other hand is based on both concepts of classic costal engineering and new concepts of coastal protection, such as Integrated Coastal Zone Management. It is a relatively new soft engineering alternative aiming to provide sustainable flood risk management, increasing socio-economic benefits - by creating space for coastal habitats to develop more dynamically -. For implementation of these concepts into the design, two main guidelines were set:

� Increase the use of soft-engineering techniques � Implement an Intertidal Buffer Zone

By switching the actively maintained defence inwards, an Intertidal Buffer Zone is created, where the mangroves can regenerate. This results in an attenuation to incoming wave energy, meaning that waves reaching the shore are smaller in height and less powerful. This is advantageous, as it require hard structures of reduced height and strength. Reduced incident wave energy is also likely to result in reduced defence maintenance costs. This beneficial for restoring the natural ecosystem and habitats in the area thus improving the water quality. When comparing the budgetary analysis output of the proposals, the integration of concepts of managed realignment techniques result in implementation costs 13, 37% cheaper. By consequence, maintenance costs are cheaper too: 50, 58% from the Traditional design. The Return of Investment (ROI) rates are also higher on this proposal. In fact, the implementation of the coastal habitat generates direct, indirect and non-use values that surpass the implementation costs within 20 years (considering 7 years as the period for restoration of the mangrove forest). This doesn’t count for benefits and the avoided costs of land damage (due to flooding and salt-water intrusion) and current maintenance costs, which when added to the equation, proves Managed Realignment to be an even stronger design proposal for this Study Area. The ROI shown by graph 19, considers cash inflow generated from mangrove forests and cash outflows from implementation and maintenance costs. The complete calculation is attached in Annex B - Appendix 5B.

2017 2018 2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034 2035 2036 2037 2038 2039 2040 2041 2042 2043 2044 2045 2046 2047 2048 2049 2050 2051 2052 2053 2054 2055 2056 2057 2058 2059 2060ROI MR -33% -97% -87% 193 -59% -89% -96% -1 -100 -100 -100 -100 -100 1814 8467 1687 2560 1591 6522 1470 2379 1061 6327 1255 1761 1746 5587 8666 1620 1025 4724 9471 1370 6828 4055 1098 1103 7464 3452 5375 1021 6366 2574 5878

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ROI [%]

YEAR

GRAPH 19 : ROI - MANAGED REAL IGNMENT PROPOSAL

ROI MR 2 per. Mov. Avg. (ROI MR)

Study Area B

Discussion

Period for mangrove regeneration: 7 years (starting from completion of construction) Start of construction: 2020 Start of funding: 2017 Interest rate: 6% Mangrove value estimated with non-parametric method (Tinh, 2013)

In the world of today facing climate change, the emerging desire to provide flood control and storm protection is rising, especially in countries dominated by a large amount of coastline. In this scenario Vietnam is one of the most vulnerable countries due to the already presence of land subsidence, flooding, and salt-water intrusion in its coastline, items that are increasing their rates as the years pass by and climate gets more severe. The Soc Trang Province’s coastline particularly is more affected due to its location, right at the Mekong Delta river mouth and directly facing the sea, dealing with sea level rise, increase in river water level and different current directions.

Most of the problems are getting worse as natural protection habitats – mangroves - are being destroyed, whether by human caused changes to the original situation (resulting in salt water intrusion and/or change in sediment balance) or due to the expansion of aquaculture and agriculture. This is happening mainly due to a lack of information and desire to aim for short-term benefits, which results in many areas of environmental and social development being used for private economic purposes such as agriculture and aquaculture. Such decisions however only benefit certain stakeholders, but not sustain more equitable long-term economic, environmental and social development and resilience in the face of climate change. The desire is that all layers of society benefit by, generating economic, environmental and social development in a way that is compatible with the current and future scientifically forecasted scenarios.

It is important to notice that mangrove habitats are the main source of income for a large proportion of the population, both in direct ways (such as aquaculture, fishing and agro-forestry) and indirect ways (such as nutrient retention, flood control and storm protection). In the context of climate change impacts, the respondents are increasingly acknowledging indirect values and non-use values generated by mangrove habitats.

65 | P a g e

Conclusion

66 | P a g e

Taking into account these conclusions the following recommendations can be set:

� Quick decision-making and implementation is key. Whatever the choice in strategy, actions have to be taken swift and efficiently in order to ensure safety and the stability of the hinterland.

� Advancing is more expensive but is the sustainable approach. When choosing the traditional approach, implementation of permeable dams is still key to reduce the degradation process of the mangrove belts on either side.

� Recommended therefore is a quick and accurate initiative, widely supported by the community, with a mind-set for the future

For the successful implementation of the design proposed on this document, is strongly important that:

� Make use of Permeable Dams techniques during and after the construction phase in order to change the sediment balance of the area and put in place the required conditions for the mangroves to grow.

� Raising local awareness of climate change issues and the importance of mangrove restoration as a climate change adaptation and mitigation measure is an important step to getting local community involvement in protection and restoration of mangroves.

� Making the community and stakeholders aware of the benefits of the project and the importance of aiming for long-term measures as a way to benefit all the community, increase the business value and create a sustainable cycle, well adapted to the future to come, is likely to raise initiative and support.

Wetlands with mangroves provide tangible and intangible benefits for human beings who have direct and even indirect interactions with these dynamic systems. The climate is changing and its induced impacts on local communities have been causing issues in Soc Trang province. Flooding is increasing in size, wave attack is getting stronger, the land is subsiding and salt intrusion is decreasing the land value. Moreover, in the dry season, the flow of fresh water in the coastal areas is limited. As a result, increasingly groundwater is being used from deep phreatic aquifers (ca. 110 m) as an alternative source of fresh water. Both to control salinity levels in shrimp farming enable the diversification of production into vegetables and homestead production (both in rice and shrimp areas). This due to the extent that already deep-water layers are being depleted. What happens today is a highly unsustainable.

In our research, it shown that Managed Realignment and Advancing strategies can potentially address all these issues thus be a tool for restoring the water quality and increasing land value. Furthermore, the use of an intertidal buffer zone is highly beneficial to the area as it is a proven concept for creation of a sustainable model where costal protection, biodiversity and farmlands are part of the same cycle. A cycle in which the mangroves can regenerate faster via the nutrients for the aquaculture, prepare the water inlet for farming and filter the water run-of.

Ultimately, however, it is a conscious choice that has to be taken by the municipality, letting the degradation process continue and try to keep up with the degradation, slowly upgrading the dikes with hard revetment, or implement a sustainable approach that will be beneficiary for the whole area. Advancing and Managed Realignment are solutions that will be sustainable in the long term, letting nature take over reducing the costs every year. Traditional approach would provide flood protection but might ultimately lead to higher implementation and maintenance costs because the degradation does not stop. In this study however, the increase in the destruction of mangroves around this area was not taken into account, as there was neither the time nor resources to achieve this. Therefore, the priority was to focus on the already depredated area prone to failure. Therefore, the following conclusions have been drafted:

� Advancing is more expensive in both implementation and maintenance for Study Area A � Managed Realignment is less expensive in both implementation and maintenance for Study Area B � Traditional approach would still suffice in the short term � Traditional approach would in the long-term mean degradation of the existing infrastructure therefore increasing the amount of

hard infrastructure in the long term. Only way to counter this mechanism is to implement a sustainable design.

Appendix 1: Parameters for Definition of the Study Area

This chapter will portrait the process of determining the study areas along the coast. This included the following steps:

� Parameters � Data � Suitable Location

Parameters The location chosen for this study has to comply with a list of parameters in order to be in line with the research. This guarantees that the research is feasible and fully executable. The stretch of the research area will include an amount of 12, 7 kilometres that belongs to the Soc Trang province.

Based on this stretch different study locations will be determined. This gives the possibility for the researchers to implement different strategies at different locations creating efficient coastal protection designs based on the specific scenario. To do so the different study locations have to comply with the following parameters as stated in the table below.

For achieving the correct choice of locations, a detailed survey will be carried on-site, evaluating all the parameters and choosing the locations, which offers the best balance according to the table above. The objective is finding areas that deal with different issues in order to be able to combine different strategies.

Data Vegetation

On the subject of vegetation, mainly the mangroves will be taken into account. As stated in the introduction, the research area should include the following parameters:

� Dense Mangrove forest � Sparse Mangrove forest � No Mangrove/Endangered Mangrove forest

Sediment transport

Regarding sediment transport, the study locations should offer opportunity to evaluate a design on an erosion scenario and in a sedimentation scenario.

Existing dike

In order to get a diversified solution the existing dike system in the study area should have hard revetment as well as a stretch of soft revetment (I.e.: grass).

Value Hinterland

The hinterland belonging to the study locations should be of different values in order to give the research the possibility of evaluating specific designs and sizing their return in investment over time according to the chosen area.

Vegetation Sediment transport

Existing dike Value of the Hinterland

Mangroves Erosion Hard Revetment Populated Partly Mangroves Sedimentation No Revetment Companies No Mangroves Sparse-populated

Appendix 2: 3D-Surface Graph: Effect of width of mangrove belt over the wave run-up on a certain dike ‘slope

Graph A8 was generated in order to clearly portrait the effects of mangrove forests over the height of the wave Run-up.

Each point on the x-axis was generated on basis of the following parameters:

� A Reduced Wave Height (meters)

� Dike’s slope (decimals)

� Wave run-up (meters)

The reduced wave height is a fixed value (hidden in the graph), which was determined based on the reduction in wave energy by the mangrove forest. The graph is divided by width of mangrove forest (see x-axis)

The output is a representation of the interpolation of the fixed reduced wave height, a certain dike’s slope and its respective wave run-up value.

This process makes it possible to immediately identify the boundaries to what each mangrove forest output is acceptable or not. Via the colour-scale, the values coded in dark orange These are precisely the wave run-up heights generated by mangrove forest of 50 and 100 meters over steep dike slopes.

It is shown however that the dike’s dimensions in this coastal protection proposal, added the buffer zone, led to values within the boundaries of acceptable (0-1,50).

0,00

0,50

1,00

1,50

2,00

2,50

3,00

3,50

4,00

4,50

Wav

e Ru

n-up

(m)

Slope (Decimals)

Graph A8: 3D Surface - Wave Run-up through mangrove forest

0,00-0,50 0,50-1,00 1,00-1,50 1,50-2,00 2,00-2,50 2,50-3,00 3,00-3,50 3,50-4,00 4,00-4,50

50 meters*

100meters*

150meters*

200 meters*

*Width of the mangrove belt

Appendix 3: Budgetary analysis technical terms

Earthworks:

Clay and fill material for the dike construction. Maintenance due to material loss. After the implementation, this is fill volume.

Foreshore:

Rip-rap and mattress designed to prevent washing out of the toe construction.

Filter Construction:

Revetment, granulate and geotextile to prevent revetment being pushed out due to negative pressure. Detailed Calculations can be found in the excel files.

Berm (+Road):

Water asphalt construction to reduce wave run-up in storm conditions while at the same time providing improved infrastructure for transportation. Not applicable for all variants

General

Incidental percentage of 1% for unforeseen maintenance. This can be from unplanned subsidence to washing out of certain constructions of the dike. This has been taken into account with a regular interval.

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Acknowledgements

The research was carried out under cooperation of both institutions. Our university in the Netherlands, HZ University of Applied Sciences, and Can Tho University in Vietnam. Research Supervisor MSc. João Nuno Salvador de Paiva, Civil Engineer and Lecturer, HZ University of Applied Sciences. Research supervisor in country Dr. Tran Van Ty, Acting Head of Civil Engineering Department, College of Technology, Can Tho University. Collaborators in site Mr. Ha Tan Viet, Head of Water Resources Division, Department of Agriculture and Rural Development of Soc Trang Province. Mr. Vo Quoc Tam, Deputy Director of CRSD Project, Soc Trang Province. Responsible for Relationships Netherlands-Vietnam: Mr. Nghia Pham (Lê-Pham).

Knowledge providers HZ University of Applied Sciences. College of Technology, Can Tho University. Building with Nature research group, HZ University of Applied Sciences. Ministry of Agriculture and Rural Development of Soc Trang province.

Supporters

© 2015 The Authors.

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