Eco -engineering in the Dollart - Hanze...Climate (Ex) Change – Eco-engineering in the Dollart 2 Title: Eco-Engineering in the Dollart Authors: J.J. Punter 296441 C.A. Gerbers 294255

Climate (Ex) Change – Eco-engineering in the Dollart

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2010

J.J. Punter, C.A. Gerbers, J.M Luursema

Hanze University of Applied Sciences

Groningen

7-6-2010

Eco-engineering in the Dollart


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Title: Eco-Engineering in the Dollart

Authors: J.J. Punter 296441

C.A. Gerbers 294255

J.M. Luursema 292262

Date: 07-06-2010, Groningen

Teachers & Lecturers:

O.M. Akkerman

D. Krol

J. Postma

H. Revier

T. Van de Maarel

Cooperating companies

and institutes: Waterschap Hunze en Aa’s

Jade Hochschule

Ingenieurs- en adviesbureau Tauw

Waterschap Noorderzijlvest

Deichacht Rheiderland

Provincie Groningen

Hogeschool Van Hall Larenstein

Stenden Hogeschool

Internationaal Waddenzee

Secretariaat

Waddenacademie

Openbaar Lichaam Eems Dollart

Regio

Groninger Landschap

National Wattenmeer


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Foreword

The report “Eco-engineering in the Dollart” that lies in front of you is the results of five months

graduation by three 4th year students at the Hanze University of applied sciences in Groningen, at

the faculty of Civil Engineering. During the research, that took place between February 2010 and June

2010, we attempted to find solutions for the coastal defense in the Dollart region. The solutions

should give a new vision how to change the current embankment to improve safety and also increase

the value for nature development and recreation.

We would like to thank the following people who helped with our investigation. Ton van de Maarel

and Hans Revier from “Kenniscentrum Gebiedsontwikkeling Noorderruimte”; Olof Akkerman,

Doutzen Krol and Jaap Postma as supervisors and assessors and finally Kampe Lentz from

“Waterboard Hunze en Aa’s”. Besides that we would like to thank the following institutes:

Waterboard Hunze en Aa’s, Province Groningen, Ministery of Transport, Public works and Water

management and “Technische Adviescommissie voor de Waterkeringen”

We hope that the results will give a good vision of the alternative dike revetments and -designs

available today and the applicability for the Dollart region.

Jelmer Punter

Christiaan Gerbers

Jeroen Luursema


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Summary

After reading this report, you will get to know more about ecological engineering in the Dollart

region. An investigation is performed on how to combine the safety of dikes with nature

development. The main question of the research:

What are the possibilities of applying ecological dike concepts in the Ems Dollart region?

This question is divided in five sub-questions.

• What are the properties of the current coastline in the Dollart?

• In what way are the dikes constructed?

• What are the loads on the dikes at this moment and in 2100?

• Do the existing dikes meet the current safety requirements and what are the safety

requirements in 2100?

• Which new ecological concepts are available on the market?

Properties of the Dollart coast

The coast is homogeneous in its properties besides the trajectory along polder Breebaart. This is the

only part of the Dollart coast without marshes in front of the coast. The embankment is designed at

10,20 m +NAP, but the current crest height is lower everywhere along the coast. On the West side

the crest height is lowest, with a minimum of 7,3 m + NAP. This could be contributed to gas

extraction and local subsidence but this is not investigated.

Dike construction

The current dikes are constructed with a sand core, and an outer layer of 0,8 m with clay and a grass

revetment. The old clay dike is used on the land side of the dike and incorporated in the core. The

crest height is determined using the following steps:

Determining a reference level with an exceedance probability corresponding to the legal standards.

Adding the sea level rise during the design period

Adding the soil subsidence during the design period

Adding additions for shower oscillations, storm blows, seiches1 and local storm surges

Adding the expected crest subsidence due to settlement of the embankment and its foundation

during the design period.

Adding the height for wave run up or wave overtopping.

Loads

The loads on the current dikes are determined in 1960. The highest wave height is 1,25 m and the

review level deviates between 6,5 and 6,7 m +NAP. Since then there has been no research

publication about the hydraulic boundaries. In this research the calculation for the crest height is

made manually and with computer software CRESS. This resulted in needed crest heights Cx for three

normative profiles (x) in the future with the expected sea level rise of 1,20 m:

C4 = 10,84 m

C10 = 10,17 m

C14= 10,15 m

1 A seiche is a standing wave in an enclosed or partially enclosed body of water


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Safety requirements

The Dollart region is an estuary with specific properties. During this research it became clear that

during a storm the water level can increase dramatically. Were the normal high tide is 1.5 m +NAP

do the hydraulic conditions say that a water level can be as high as 6.8 meter + NAP at Nieuwe

Statenzijl. This extreme high water level is caused by the fact that storm surges occur in the Dollart.

The fact that the Dollart is a bay also contributes to the extreme high water, water is enclosed and

the only way is up. Waves in the Dollart a relative low when compared to the Dutch and German

coast. The waves are according the hydraulic condition on the Dutch Dollart coast 0.9 meter at Punt

van Reide and up to 1.25 meter at Nieuwe Statenzijl. The wave height at the German dikes is

unknown but is to be expected be higher than 1.25 meter.

Ecological concepts

The ecological concepts that are most interesting are those without the use of ecological hard

revetments. The revetments aren’t useful because the Dollart dikes aren’t wet. Changing the shape

of the dike could be interesting because slope changes can result in decreased wave run-up and

overtopping. Raising the crest height has similar results. The Dollart coast is divided in four sections

and for each section this research gives a recommended concept. These concepts are not final

designs, they have to be worked out further.

Conclusion

The use of ecological materials only doesn’t contribute to nature development. Other ways have to

be found to combine nature development with coastal safety.


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Index

1 INTRODUCTION 10

1.1 MOTIVATION 10

1.2 PROBLEM DEFINITION AND RESEARCH QUESTIONS 11

1.2.1 MAIN RESEARCH QUESTION 12

1.2.2 SUB-QUESTIONS 12

1.2.3 RESEARCH GOALS 12

1.2.4 RESEARCH RESULTS 12

1.2.5 RESEARCH AREA 13

1.2.6 REPORT STRUCTURE 14

2 ANALYSIS OF THE DOLLART COAST 15

2.1 ANALYSIS FORESHORE 17

2.2 ANALYSIS EMBANKMENT 17

2.2.1 THE REVETMENT OF THE CURRENT DIKES 18

2.2.2 CREST HEIGHT 18

2.2.3 MANUAL CALCULATION WAVE OVERTOPPING 22

2.2.4 CREST HEIGHT CALCULATION WITH COMPUTER PROGRAM CRESS 30

2.2.5 REVIEW LEVEL AND ALLOWANCE 33

2.2.6 ROAD TYPES AND MANAGEMENT 35

2.2.7 DUTCH DIKE STRUCTURE 35

2.2.8 LOADS , SIGNIFICANT WAVE HEIGHT & TIDES 36

2.2.9 GERMAN DOLLART DIKES 36

2.3 CONCLUSIONS CHAPTER 2 ANALYSIS OF THE DOLLART COAST 37

3 ECO ENGINEERING 39

3.1 INTRODUCTION 39

3.2 OVERVIEW INVESTIGATED ECO MATERIALS & METHODS 39

3.2.1 EVALUATION CRITERIA 40

3.3 ECO MATERIALS 41

3.3.1 PILE BUNDLES 41

3.3.2 ECO XBLOC’S 42

3.3.3 ARMORFLEX 44

3.3.4 C-STAR® COASTAL ELEMENTS 45

3.3.5 VETIVER 47

3.3.6 ELASTOCOAST 49

3.3.7 HYDROTEX 50

3.3.8 SMART GRASS REINFORCEMENT 52

3.3.9 ROAD SURFACING MATERIALS 53


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3.4 ECO METHODS 56

3.4.1 INCREASED OVERTOPPING 56

3.4.2 ADJUSTMENTS OF DIKE SLOPE 58

3.5 MULTI-CRITERIA ANALYSIS 59

3.5.1 CONCLUSIONS MCA’S 62

3.6 CONCLUSIONS CHAPTER 3 ECO ENGINEERING 63

4 CONCEPTS 64

5 CONCLUSIONS 71

6 RECOMMENDATIONS 73

7 DEFINITIONS 74

8 BIBLIOGRAPHY 76

APPENDIX 1: HYDRAULIC CONDITIONS EMS-DOLLART REGION 78

APPENDIX 2: TIDE TABLE NIEUWE STATENZIJL 79

APPENDIX 3: CALCULATION OF THE OVERTOPPING CAPACITY OF THE RETENTION BASIN 80

APPENDIX 4: OVERTOPPING CALCULATIONS WITH CRESS 82

CALCULATION DIKE PROFILE 4 CURRENT HYDRAULIC CONDITIONS 82


CALCULATION DIKE PROFILE 10 FUTURE HYDRAULIC CONDITIONS 84


CALCULATION DIKE PROFILE 14 FUTURE HYDRAULIC CONDITIONS 86

CALCULATION DIKE PROFILE 14 FUTURE HYDRAULIC CONDITIONS WITH SLOPE 1:6 87

CALCULATION DIKE PROFILE 14 FUTURE HYDRAULIC CONDITIONS WITH SLOPE 1:8 88

APPENDIX 5: CALCULATION WAVE PERIODS 89

APPENDIX 6: MANUAL CALCULATION WAVE OVERTOPPING 91

APPENDIX 7: MULTI CRITERIA ANALYSIS 99

APPENDIX 8: DRAWINGS CROSS-SECTION 4, 10, 14 103


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Figures

Figure 1: Overview of the research area, red line shows dike trajectory ________________________________ 13

Figure 2: Overview of cross sections of the Dutch Dollart coast ______________________________________ 15

Figure 3: Additions to the reference level to determine the height of the dikes __________________________ 19

Figure 4: Relation between crest height and overtopping after sea level rise of 1,20m ____________________ 22

Figure 5: Relation between the volume of wave overtopping and the crest height _______________________ 24

Figure 6: Determination of the characteristic slope for a cross section consisting of different slopes _________ 25

Figure 7: Relation between wave run-up and length of the “average” slope of the dike ___________________ 25

Figure 8: Relation between the volume of overtopping waves and the length of the “average”slope ________ 26

Figure 9: Relation between the wave run-up and the bermwidth _____________________________________ 26

Figure 10: Relation between the volume of overtopping waves and the bermwidth ______________________ 27

Figure 11: Relation between the angle of wave attack and volume of overtopping waves _________________ 28

Figure 12: Relation between SWL and the wave run-up ____________________________________________ 29

Figure 13: Relation between the volume of overtopping waves and review level ________________________ 29

Figure 14: Relation between the volume of overtopping waves and the significant wave height ____________ 30

Figure 15: Crest height and review level of the Dutch embankment ___________________________________ 33

Figure 16: Soil subsidence in the North of Groningen (‘Daling’ means subsidence in Dutch) ________________ 34

Figure 17: Freeboard (distance between the review level and the crest) _______________________________ 34

Figure 18: Dutch Dollart dike structure with seaside on the right. ____________________________________ 35

Figure 19: German construction methods _______________________________________________________ 37

Figure 20: Current German dike structure _______________________________________________________ 37

Figure 21: pile bundles _______________________________________________________________________ 41

Figure 22: Eco Xbloc's _______________________________________________________________________ 42

Figure 23: Revetment of Armorflex _____________________________________________________________ 44

Figure 24: A revetment of C-star elements _______________________________________________________ 45

Figure 25: Vetiver used as slope protection in Vietnam _____________________________________________ 47

Figure 26: Mixing ingridients, application and final result of an Elastocoast revetment ___________________ 49

Figure 27: Hydrotex Enviromat Lining (left) and Hydrotex Articulating Blocks ___________________________ 50

Figure 28: Picture of the smart grass reinforcement _______________________________________________ 52

Figure 29: Drawing of grass concrete blocks _____________________________________________________ 54

Figure 30: Baked clinkers made from clay _______________________________________________________ 54

Figure 31: Plastic grass stones, type slimblock ____________________________________________________ 55

Figure 32: Schematic overview of the wave overtopping simulator ___________________________________ 56

Figure 33: Test results from simulator test; left picture is the dike without reinforced grass and the right with

reinforcement _____________________________________________________________________________ 57

Figure 34: Influence of a gentle slope on the crest height ___________________________________________ 58

Figure 35: The Dollart coast divided in different sections ___________________________________________ 60

Figure 36: MCA for the materials and methods applied in section 1 ___________________________________ 61




Figure 40: Concept 1.1: A gentle slope and raised crest height in combination with a Elastocoast revetment on

the berm. _________________________________________________________________________________ 65

Figure 41: Concept 2.1: No other material used, slope changes and increased overtopping ________________ 66

Figure 42: Cross section of the dike, SGR is installed under the grass revetment _________________________ 67

Figure 43: Cross section of the dike with retention basin installed in the crest ___________________________ 68

Figure 44: Top view of the Ems Dollart estuary, red line indicates the estuary ___________________________ 75

Figure 45: Top view, red line indicates The Ems Dollart region _______________________________________ 75

Figure 46: Picture were the freeboard is indicated (free crest height for wave overtopping) _______________ 91


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Figure 47: Definition angle of wave attack, red line indicated the angle of attack ________________________ 92

Figure 48: Left picture; determination of the characteristic slope for a cross section, right picture; The situation

for the manual calculation of the Dollart dikes ___________________________________________________ 95

Tables

Table 1: Analysis of the cross sections __________________________________________________________ 16

Table 2: Legend ____________________________________________________________________________ 16

Table 3: Results for the relation between crest height, materials and the volume of wave overtopping ______ 24

Table 4: Results calculation profile 4 with current hydraulic conditions ________________________________ 31

Table 5: Results calculation profile 10 with current hydraulic conditions _______________________________ 31

Table 6: Results calculation profile 10 with future hydraulic conditions ________________________________ 32

Table 7: Results calculation profile 14 with current hydraulic conditions _______________________________ 32

Table 8: Results calculation profile 14 with future hydraulic conditions ________________________________ 32

Table 9: Overview with possible combinations for the discharge pipes. ________________________________ 69


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1 Introduction

This research is part of the project Climate (ex)change, initiated by water board Hunze and Aa’s,

Hanze University Groningen and Jade Hochschule Oldenburg. The project focuses on the Ems Dollart

region, the estuary of the river Ems in the North of the Netherlands and Germany.

Climate (ex)change is initiated to find solutions for the reinforcement of the coastal zone in

combination with nature development. An issue that’s getting more complex due to a rising sea level,

soil subsidence and changing views on nature development and protection. Several researches in the

area are conducted, looking at possibilities to apply progressive dike designs and the development of

marshes and sand flats. All with one goal:

Integrating a reinforcement of coastal protection with nature development in an international

environment.

Fresh meets salt water in this transition zone between a river and the Wadden Sea environment. The

Ems Dollart provides a habitat for a lot of endangered animals and plants. It acts as a stoppage point

for birds from the North during their winter travel to the South. They find food and shelter on the

marshes and sand flats. This research focuses on different materials that can be used on the outer

layer of the dike. Manufacturers of dike covering are developing new materials in order to meet the

demand for nature friendly dike design.

This trend is a result of the increasing human intervention in the coastal zone, which started in the

second half of the 50’s after the storm flood of February 1953. The Delta plan was initiated. For the

first time, a real statistical risk analysis was carried out to establish an acceptable small chance of a

new major flood disaster. The reaction time of the natural system to large-scale projects like the

closing of the Zuiderzee and the Delta project is in the order of decades (50-100 years). This means

we begin to see the influences of our interventions 50 years ago. With other words: it takes almost

50 years for an ecosystem to totally adjust to human intervention. This time can be shortened when

more nature friendly designs are used. The interventions like the Delta works show that it is

important for nature development to be combined with coastal engineering and that is why building

method’s are adjusted to combine nature development with coastal protection. This is called eco-

engineering (or ecological engineering).

Ecology is the interdisciplinary scientific study of the interactions between organisms and their

environment.2

K. R. Barrett from the State University of New Jersey defined eco-engineering as follows: ‘‘Eco-

engineering is the design, construction, operation and management (that is, engineering) of

landscape/aquatic structures and associated plant and animal communities (that is, ecosystems) to

benefit humanity and, often, nature.’’

1.1 Motivation

Because the Ems Dollart is a Natura2000 area3 and part of the National Ecological Network (NEN)

reinforcement of the coast has to be combined with nature development. This combination could

2 Begon, M.; Townsend, C. R., Harper, J. L. (2006). Ecology: From individuals to ecosystems. (4th ed.). Blackwell.


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also contribute to a rising economic value, provided that the increased natural values attract

significantly more visitors and there are enough facilities to accommodate those visitors. One could

think of parking facilities and restaurants. According to Elles Bulder with the homonymous

investigation bureau, a way to attract more visitors could be accomplished by organizing large events

in the region to place the Dollart on the map.

Nature development can be developed by using new materials on the embankment. These so called

“eco-materials” can be defined as materials that are used in eco-engineering. They are designed to

fulfill multiple purposes and serve nature as well as humanity. The manufacturers thought of the

response of nature on new (civil) works and the best way to make these civil works fit in the natural

environment.

Which materials can be used best has to be investigated. There are different eco-materials available.

Before this report goes into detail, a definition of the word eco-material has to be given. Eco, derived

from ecology, tells us something about the properties of the material.

The Coastal zone of the Ems Dollart estuary forms a sharp boundary between agricultural land and a

Natura2000 area. It also forms a zone were three types of policy and law apply: the German, the

Dutch and the European law. The estuary forms a transition zone between a river environment, the

Wadden Sea and the North Sea. These three aspects are a motivation to apply eco engineering in the

Ems Dollart estuary.

The dikes are a form of human intervention. They are build to keep the ocean from our land and out

of our houses. The primary role of the dikes is coastal protection. Secondly, the dikes can fulfill the

role of transition zone between different environments. A coastal environment has a lot of potential

for nature development, especially in a transition zone like an estuary. That is why it is important to

investigate in which ways eco-engineering can help us unite these different elements in our coastal

defenses. And that is where eco-materials can be used. The different laws that apply are out of the

scope of this research.

New insights makes the society want to combine the reinforcement of coastal defenses with nature

development to create recreation and nature on and around the dikes. So, every environment asks

for different solutions, the best way to do this in the Ems Dollart region is yet unknown and has to be

investigated. Eco-engineering and eco- materials could provide solutions for this complicated

problem.

1.2 Problem definition and research questions

Due to a rising sea level all dikes in the Netherlands have to be reinforced. The Ems Dollart estuary

faces higher water levels at high tide compared to normal coastal area’s because of its shape, which

result in water level set up to fifty centimeter. When flood-control dam in the Ems is closed during a

storm, the water gets a second set up and rises another 10 centimeters4. The Netherlands assume

the sea level to rise 120 centimeters over the next 100 years. This has unknown negative effects on

the water set up due to the estuary shape and the Emsperwerk. Besides the rising water level the

surface level will locally decrease with 35 centimeter due to gas extraction.

3 Natura2000: An EUwide network of nature protection areas established under the 1992 habitats directive.

4 F.J. Sytsma, 2006, Evaluation of the German Emssperwerk: The value of more scale levels


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1.2.1 Main research question

What are the possibilities of applying ecological dike concepts in the Ems Dollart region?

The definition of the ecological dike concept can be described as follows: A conceptual design of the

considered cross section of the dike. The considered area includes the foreshore or marshes, the dike

body and the seepage zone, which is assumed to run to the seepage ditch on the land side.

1.2.2 Sub-questions

These sub questions are answered in different chapters in this report. The chapters in which the sub

questions can be found are listed below. The sub questions can be found in the conclusion of the

chapter.

• What are the properties of the current coastline in the Dollart? Chapter 2

• In what way are the dikes constructed? Chapter 2

• What are the loads on the dikes at this moment and in 2100? Chapter 2

• Do the existing dikes meet the current safety requirements

and what are the safety requirements in 2100? Chapter 3

• Which new ecological concepts are available on the market? Chapter 4

1.2.3 Research goals

• Creating design requirements by determining the loads on the dikes at this moment and in

2100 and the way the existing dikes are constructed.

• Determine if the existing dikes meet the current safety requirements and determining the

safety requirements for the situation in 2100.

• Determine what type of ecosystem exists in the Ems Dollart estuary and what habitats exist

in the region.

• Investigating which eco materials are on the market and which of them are suited for the

Ems Dollart region.

• Defining the eco-engineering philosophies and their applicability in the Dollart region.

1.2.4 Research results

• Analysis of the fotreshore, embankment and hinterland, to get an idea of the situation in

which the ecological dike concepts (the subject of this report) have to be applied.

• Hydraulic conditions in the Dollart, because every cross section has slightly different

hydraulic conditions.

• A investigation about wave overtopping with CRESS software, because wave overtopping is

very important for the choice of ecological materials

• A sensitivity analysis of the manual calculation method for wave overtopping to investigate

the importance of all variables in the formulae.

• A multi criteria anaylsis of all investigated ecological materials.

• Several ecological dike concepts based on the outcome of the research.

• A conclusion in which the different ecological dike concepts are applied on certain cross

sections in the Dollart.


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1.2.5 Research area

The research is focused on the dike trajectory of the Dollart. This includes the dikes on the Dutch and

German part of the Dollart. The Dutch dikes start in Punt van Reide to Nieuwe Statenzijl and the

German dikes from Nieuwe Statenzijl to Pogum, see red line in Figure 1 . The total length of the dike

trajectory is 26 kilometers. The investigated trajectory is in a way unilateral. The conditions of the

sea, presence of marshes, crest height, width and the use of the hinterland differ only slightly. This

makes the results of the research applicable on similar trajectories elsewhere. This research focuses

on the Dutch calculation and design methods, which are also applicable on the German dikes.

The research area is the dike trajectory annotated with the red line. This line is chosen due to a

presence of marshes along the coast. In the West at the Punt van Reide the end of the marshes

define the end of the research area. In the East the mouth of the river Ems defines the end of the

research area. The trajectory is chosen because it is the same as in the foundation of Dutch water

boards, see Figure 1.

Figure 1: Overview of the research area, red line shows dike trajectory


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1.2.6 Report structure

Chapter 2 � Analysis of the Dollart coast. This chapter includes a description of the Dollart

coast, the hinterland and the embankment. The major part of this chapter is

about wave overtopping and includes a sensitivity analysis, the current crest

heights and a calculation for the crest height

Chapter 3 � This chapter contains the investigation of materials. This aren’t all available

materials, but the selection gives a overview of the different kinds of

available materials. The selection is based on availability only, so the

suitability and/or applicability are not in this selection.

Chapter 4 � This chapter describes ecological concepts. The results of chapter 2 and 3

are used in combination with specific locations on which the ecological

concepts can be used best. The concepts include a location and a design

adjusted to the local conditions.

Chapter 5 � This chapter contains conclusions.

Chapter 6 � This chapter gives recommendations


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2 Analysis of the Dollart coast

This analysis is focused on the Dutch part of the Dollart coast. The analysis is made of nineteen cross

sections of the embankments, satellite images of the geographical situation and additional

information derived from literature. The cross sections form a representative image of the Dutch

Dollart coast. The emphasis in the analysis lies on safety and design of the embankment.

The method of using the cross sections for the analysis is chosen because the information from the

waterboard is also in this form. The cross sections have a distance of approximately 700 m between

them. The position of the cross sections is determined by the distance between them and the line of

cross sections runs along the research area.

Figure 2: Overview of cross sections of the Dutch Dollart coast

Figure 2 shows the nineteen cross sections that are considered for the analysis. They also mark the

research area for the Dutch part of the Dollart. The German part will be treated at the end of this

chapter. The comparison of the cross sections is made in Table 1. The foreshore, embankment and

hinterland is taken into account. Table 2 shows the legend properties and used symbols of Table 1.

Information about the German part is difficult to obtain. Therefore the Dutch part is analyzed

thoroughly and the German part needs to be investigated further. A comparison is made in

Paragraph 2.2.9 which gives a conclusion about the Dollart coast as a whole.


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1 Foreshore 2

Seaside

1.1 1.2 1.3 2.1 2.2 2.3 2.4 2.6 2.7 2.8 2.9 3.1

Cross section

1 0 m N,C PP GC, CS 7,25 6,5 0,75 G As SH 1,00 N



4 100 m N,C PP GC, CS 7,50 6,5 1,00 G As SH 0,90 A








12 1100 m N,C SHGL GC, CS 8,04 6,6 1,44 G As SH 1,00 A








Table 1: Analysis of the cross sections

Legend properties

1. Foreshore

1.1 Width of marshes, measured

right angled from cross

section

1.2 Utilization foreshore

1.3 Management

2. Embankment

2.1 Revetment materials

2.2 Crest height

2.3 Review level

2.4 Allowance: distance between

crest height and review level

2.6 Vegetation

2.7 Road types on the

embankment

2.8 Management type

2.9 Significant wave height Hs [m]

Ag Agriculture

As Asphalt

C Cattle breeding

CS Copper Slag

G Grass

GC Grass Concrete Blocks

N Nature development

PP Private property

SH Sheep

SHGL Stichting Het Groninger

Landschap

Table 2: Legend


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2.1 Analysis foreshore

The investigated properties:

• Width of the marshes

• Utilization of the land

• Management

These three properties are chosen because they are necessary for the ecological dike concepts.

Different concepts can be used in different locations and the width of marshes, utilization of the

marshes and the owners determine the characteristics of the foreshore and the cross section at a

certain point.

The latter two are logically related. The utilization of the marshes in the Dollart goes with

management. Strangely this cannot be seen in the utilization alone, because the whole area is used

for agriculture and cattle breeding without regard of the owner. The part where Stichting het

Groninger Landschap (SHGL) is the owner, the cattle is present, but with another cause, namely to

maintain the vegetation instead of reproduction.

The factor safety is missing and that is because recent research5 shows that the influence of marshes

on coastal safety is negligible. The research concluded that wave period and height are relatively

small because of the bowl shaped estuary. Because of the same reason water boost occurs, resulting

in water level rises up to circa 5,00 m +NAP while mean high water is about 1,50 m +NAP. The ratio

between the level of the marshes and the water depth is too high. Entire breaking of waves6 does not

occur. The width of the marshes is an unimportant factor when it comes to safety, but gives an idea

of the surface of land that stretches along the coast. The role of marshes in safety is not further

addressed in this research.

An important fact that becomes clear when the foreshore is considered, is the fact that a large area

in front of the sea side of the revetment stays dry during regular weather conditions. This means the

water doesn’t reach the toe of the dike, not even at high tide. It doesn’t even come close to the dike.

The marshes flood a couple of times a year in the winter season when the storms are most powerful.

The storm season is between October and April.

2.2 Analysis embankment

The embankment forms the primary sea defense and is important for coastal protection. Tests point

out that the embankment or dike in the Dollart doesn’t meet the new safety requirements because

the outer layer which is build out of grass at this moment, is insufficient to counter wave attacks. The

conclusion that the outer layer wouldn’t suffice can be contradicted by the Waterboard, because the

standards with which the embankments are tested assume a rectangular wave and wind direction on

the dikes. In practice, this never occurs in the Dollart, making the tests too heavy. Nonetheless new

ways have to be found to protect the embankment from the rising sea level and combine this

increased protection with nature development and safety. Chapter 3 treats the different ecological

concepts available. This chapter focuses on the current situation. In this paragraph the following

properties are investigated:

5 G. Drijfhout, 2010, Grensoverschrijdende kansen voor kwelders in de Dollart

6 Entire breaking of waves is defined here as the breaking of waves higher or equal to the average wave height

(not significant wave height)


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• Revetment

• Crest height

• Review level

• Allowance

• Significant wave height (Hs)

• Road types

• Management

• Dike structure

• Overtopping

• Wave run up

This information is needed to determine the needed crest heights in the future and to determine

which ecological materials can be used on the dike.

2.2.1 The revetment of the current dikes

The revetment of the embankment in the Dollart is very constant. The dikes are mainly covered with

a mixture of grass. Copper slag is used at the point where the waves strike during storm surges. Grass

concrete blocks are used above the copper slag, under the first meters of grass to increase stability.

The revetments have to withstand wave attacks with a significant wave height between Hs=0,90 m

and Hs=1,25 m. As mentioned above, new tests indicate that the current revetments are insufficient

to withstand the expected wave attacks when the sea level rises. Grass is a good way of protection

against medium and small wave attacks like those in the Dollart. Because of shallow waters the

waves won’t be higher than 1,25 m. Also overtopping can be resisted as recent tests show7. These

tests, conducted on a couple of other Wadden Sea dikes showed that the force a grass revetment

can withstand is higher than assumed. The result of these tests is that the permissible amount of 0,1

l/m/s overtopping will be changed to 1 l/m/s and probably to 5 l/m/s, an increase of 5000%. This is

the same for all cross sections.

2.2.2 Crest height

This paragraph calculates the needed crest height for three different profiles in the Dollart. Wave run

up and overtopping are important criteria for new ecological concepts, especially when the criteria

for these two parameters are changed. To investigate the differences in crest height, the wave run

up and wave overtopping will be calculated manually and tested to the hydraulic boundaries. To

make sure a representing part of the dikes is investigated, profiles 4 (low crest height), 10 (medium

crest height) and 14 (high crest height) are investigated. The crest height is taken as criterion because

the height of the dike determines for the most part the amount of overtopping waves. The wind

direction is taken into account. Profile 4 is situated in the lee and profile 10 and 14 are situated in a

trajectory with the highest significant wave heights. The location of these three profiles can be seen

in Figure 2 and the drawings can be found in Appendix 8: Drawings cross-section 4, 10, 14

7 Van der Meer, Schrijver, Hardeman, Van Hoven, Verheij and Steendam, 2010, Guidance on erosion resistance of inner slopes

of dikes


19

The crest height C is defined as C=a+b+c+d+e+f8. variable e and f can be influenced, a through d

cannot be influenced and depend on hydraulic and geographic conditions.

Figure 3: Additions to the reference level to determine the height of the dikes

The variables a through f can be seen in Figure 3 and are defined as follows:

a. A reference level with an exceedance probability corresponding to the legal standards.

The review level is given by the hydraulic preconditions and are composed by the Ministry of

Transport, Public Works and Water Management. The review level is almost constant in the Dollart

as can be seen in Figure 11. The Dollart dikes are part of the primary water retaining structures

category A and according to the legal standards the exceedance probability is 1/40009.

Profile 4: a=6,5 m +NAP



b. The sea level rise during the design period

The sea level rise is difficult to predict. The Delta commission predicts a sea level rise of 0,65 to 1,30

meter in 2100 and 2 to 4 meter in 2200. Because these predictions are based on a lot of uncertainties

they have to be used with precision. Because insight in sea level rise and other loads like wave

attacks change every year, the design period of embankments is mostly 50 years. The current dikes

are designed on a level of 10,20 m +NAP10

. In that time it was believed to be high enough to

withstand the highest water levels and storm surges. At this moment we use the expected sea level

rise of 1,20 m.

Profile 4: b=1,20 m

Profile 10: b=1,20 m

Profile 14: b=1,20 m

c. The soil subsidence during the design period

Due to gas extraction, the soil will subside locally with 18 centimeters in 2050. In this figure, a safety

margin of 1,25 is added because of uncertainties; the embankment is situated on the edge of the gas

extraction fields. In Figure 16 can be seen that the Dollart area is only partly influenced by gas

8 Technical Advice committee on Flood defense, Delft, 2002, Technical report wave Run-up and overtopping at

dikes 9 Ministry of transport, public Works and Water management, 2006, Hydraulic boundaries 2006

10 Kampe Lentz, Waterboard Hunze en Aa’s


20

extraction. That is why an average of 18 centimeters is used to calculate the crest height of cross

section 1 to 12 and an average of 3 centimeter for cross sections 13 to 19. The Delta commission

calculated the soil subsidence in the sea level rise.

Profile 4: c= 0,18

Profile 10: c=0,18 m

Profile 14: c=0,03 m

d. Additions for shower oscillations, storm blows, seiches11

and local storm surges

The Emssperwerk in the River Ems results in water boost at high tides in combination with storms.

Dutch calculations show a boost of 8 cm at Delfzijl, at Nieuwe Statenzijl this figure is higher. Recent

German calculations show a boost of 20 centimeters at Delfzijl.12

It means the addition for water

boost due to the Emssperwerk will be higher than expected and calculations concerning this subject

have to be investigated again. In this report we apply the worst case and in this case that is the

German figure of 0,20 m. The calculation is made for the whole Dollart so different additions for

variable f can’t be used.

Profile 4: d= 0,20 m

Profile 10: d=0,20 m

Profile 14: d=0,20 m

e. the expected crest subsidence due to settlement of the embankment and its foundation

during the design period.

The embankments are build out of clay and have a sand core. The subsidence of this type of

embankments is difficult to calculate. In a design period of 50 years, the subsidence can reach 1

meter. When the crest heights at the West side of the Dollart are contemplated again, the

subsidence can be estimated on 2 meters for profile 4 and 1 meter for profile 10 and 14. These

values are based on the current crest heights and differences between them. Profile 4 has subsided

the most (2m) profiles 10 and 14 have subsided less, around 1m.

Profile 4: e= 2,00 m

Profile 10: e=1,00 m

Profile 14: e=1,00 m

f. The height for wave run up or wave overtopping.

According to the Technical Advice Committee on Flood Defence (TAW) this can be calculated using

the following procedure:

1. Determine wave conditions at toe of dike: Hm0, Tm-1,0

2. Calculate influence factor for angle of wave attack γβ

3. Adjust wave conditions if ß>80°

4. Calculate average slope, tan α

5. Calculate z2%,smooth (smooth: for γb=1 and γf=1)

6. Calculate influence factor for roughness on slope γf

7. Calculate z2%,rough (rough for: γb=1)

8. Calculate influence factor for berms γb

11

A seiche is a standing wave in an enclosed or partially enclosed body of water 12

Berekening hoogte zeedijken Groningen klopt niet meer, Heijbrock F., 08-04-2010, Cobouw


21

9. Calculate 2% wave run-up

10. Calculate γβ for wave overtopping

11. Calculate wave overtopping with above γb and γf

12. Calculate overtopping volumes per wave

Symbols:

Hm0= significant wave height at the toe of the dike

Tm= average wave period

Tm-1,0= Tspectral= spectral wave period

ß= angle of wave attack

γβ= influence for the angle of wave attack

tan α= (1,5Hm0 + z2%) / (Lslope-B) with B=broad of berm

γb= influence of a berm

γf= influence factor for roughness elements on slope

Another method is the computer program CRESS (Coastal and River Engineering Support System).

More information about this program can be found on www.cress.nl.

The calculation is done manually and with the computer program CRESS. The manual calculation and

an analysis of the different factors can be found in paragraph 2.2.3. The calculation of variable (f)

with the computing program CRESS can be found in paragraph . In the calculation of the crest height

the values from CRESS are used for (f).

Values of (f) with an overtopping flow rate of 0,1 l/m/s (Current standard)

f4=1.461 m

f10=1.87 m

f14=1.83 m

Resulting crest heights at current standard:

C4= a+b+c+d+e+f =6,5+1,20+0,18+0,20+2,00+1.461=11,54 m

C10= a+b+c+d+e+f =6,6+1,20+0,18+0,20+1,00+1.87=11.05 m

C14= a+b+c+d+e+f =6,7+.1,20+0,03+0,20+1,00+1.83=11.00 m

Values of (f) with an overtopping flow rate of 5 l/m/s (future standard)

f4=0,76 m

f10=0,99 m

f14=0,98 m

Resulting crest heights at future standard:

C4= a+b+c+d+e+f =6,5+1,20+0,18+0,20+2,00+0,76=10,84 m

C10= a+b+c+d+e+f =6,6+1,20+0,18+0,20+1,00+0,99=10,17 m

C14= a+b+c+d+e+f =6,7+1,20+0,03+0,20+1,00+0,98=10,15 m

The value for overtopping (variable f) is lowest at profile 4. This is odd because profile 4 has the

lowest crest height. The reason for this deviation can be found in the shape of profile 4, which has a

gentler slope. Another reason is the fact that the waves at profile 4 are the lowest.

Climate (Ex) Change

Figure 4: Relation between crest height and overtopping after sea level rise of 1,20m

Figure 4 shows the relation between the calculated crest height and the overtopping flow rates for

the three considered cross sections. The graph clarifi

rates. The current standard of 0,1 l/m/s gives much higher needed crest heights in comparison with a

flow rate of 5 l/m/s. The difference is almost a meter. Tests which investigated the effect of

increased overtopping on a grass revetment show that flow rates of up to 50 l/m/s cause no

problems for the current revetments so this graph gives an indication of the needed crest height at a

certain overtopping flow rate and a sea level rise of 1,20 m.

Note: the crest height is calculated using assumptions for the sea level rise, settlements of the dike

body and settlement due to gas extraction.

2.2.3 Manual calculation wave overtopping

In this part an explanation will be given about the wave

investigation is done to get a better

region. This information is relevant because the crest height of the dikes

overtopping (see Figure 3 and Figure

influence factors that cause overtopping need to be investigated.

The manual calculation is done to make an approach and to get view of the input paramet

results will be analyzed and compared. The

wave overtopping the most.


: Relation between crest height and overtopping after sea level rise of 1,20m

shows the relation between the calculated crest height and the overtopping flow rates for

the three considered cross sections. The graph clarifies the influence of increases overtopping flow



rtopping on a grass revetment show that flow rates of up to 50 l/m/s cause no


certain overtopping flow rate and a sea level rise of 1,20 m.

t height is calculated using assumptions for the sea level rise, settlements of the dike

body and settlement due to gas extraction.

Manual calculation wave overtopping

In this part an explanation will be given about the wave overtopping in the Ems Dollart

investigation is done to get a better image of the overtopping volume of the waves in the Dollart

region. This information is relevant because the crest height of the dikes depends

Figure 4). The current loads on the inner slope are important and the

overtopping need to be investigated.

The manual calculation is done to make an approach and to get view of the input paramet

and compared. The analysis should make clear which parameters influence

22

shows the relation between the calculated crest height and the overtopping flow rates for

es the influence of increases overtopping flow



rtopping on a grass revetment show that flow rates of up to 50 l/m/s cause no


t height is calculated using assumptions for the sea level rise, settlements of the dike

overtopping in the Ems Dollart region. The

image of the overtopping volume of the waves in the Dollart

depends on the wave

he current loads on the inner slope are important and the

The manual calculation is done to make an approach and to get view of the input parameters. The

r which parameters influence


23

For the calculation the three profiles mentioned in paragraph 2.2.2 are worked out:

• Profile 4 � Crest height 7.51m



The results can be seen in Table 3. For the fourth calculation an average profile is used in with an

average crest height and that calculation is used to analyze the variables. It can be found in Appendix

6: Manual calculation wave overtopping. This chapter gives a summary of the calculation in the

appendix and consists mostly out of tables and graphs with explanations.

For the calculation of the wave overtopping the following things need to be determined:

1. The wave conditions at the toe of the dike � Tm-1,0, Hm0

2. Influence factor for the angle of wave attack � γβ

3. The average slope of the dike � tan(α)

4. The 2% wave run-up � z2%

5. Influence factor for berms � γb

6. The average wave overtopping discharge � q

7. The volume of overtopping waves per meter � V

The following results were found (The average height of all the 19 profiles is used with a slope of 1:3

and the dike is covered in grass):

1. The highest significant wave height was found on Hm0=1,25m and the spectral period of the

waves on Tm-1,0=3,25s

2. The influence factor for the angle of wave attack γβ=1, This is because the angle for the wave

attack needs to be zero. So all waves strike the dike perpendicular. This is set in the test

(Voorschrift Toetsen op veiligheid primaire waterkeringen). In reality the waves strike the

dikes under an angle.

3. The representative angle of the dike is tan(α)=0,4 with a slope of 1:3 and an estimate of the

wave run-up because this was not yet determined. In this case the wave run-up was set on

1,5x Hm0=1.9m. The calculated wave run-up should be put back in the equation for the

calculation of tan(α) for a better idea of the average slope. In this case the z2% > 1,5x Hm0.

If the wave run-up is bigger than the freeboard between the crest height and the SWL, the

freeboard height needs to be used instead of the z2% or the 1,5x Hm0.

4. The final wave run-up z2%=2,5m, see that the run-up is bigger than 1,5 the significant wave

height and so also bigger as the freeboard from crest to SWL (Crest height-SWL=1.7m, hk <

z2%).

5. The influence factor for the berm of the dike γb=1. So the berm has no effect on the wave

run-up of the waves. In this calculation is assumed that the influence of the dike is negligible.

Normally this need to be taken into account. The influence by the width of the berm and the

position of the berm in respect to the waterline is important.

6. The average overtopping discharge for a grass revetment, q=0,04m2/s. Also said as m

3 / m

per second. This average wave overtopping discharge is above the current requirements for

wave overtopping (current requirement is set on q=0,0001m2/s also written as q=0,1 l/s/m ).

Research is ongoing to get a better view on the relationship between wave overtopping and

Climate (Ex) Change

the capacity of the inner slope. The requirements for wave overtopping change, because of

the already performed research

7. Volume of overtopping wave per linear meter of the crest V=4,77m

that goes over the crest per meter during a storm event. Therefore the total amount of

waves that strike against the dike during a storm event and the ac

need to be determined. In the calculation, the storm event was estimated on 5 hours. This is

similar to 358 waves that go over the dikes.

At first the relationship between the use of different revetments, the crest height and the v

wave overtopping will be explained. In

and volume can be seen.

Profile Hcrest

[m]

Grass

q

[m2/s]

V

[m3/m]

4 7,51 0,16 10,65

10 8,35 0,0088 4,49

14 9,37 0,00535 1,11

Table 3: Results for the relation between crest height, materi

Figure 5: Relation between the volume of wave overtopping and the crest height

0

2

4

6

8

10

12

7 7,5

V [

m3

/m]

-->

Relation between the volume of wave overtopping and the crest height



ed research.

Volume of overtopping wave per linear meter of the crest V=4,77m3/m. So the total volume


waves that strike against the dike during a storm event and the actual overtopping waves


similar to 358 waves that go over the dikes.

At first the relationship between the use of different revetments, the crest height and the v

wave overtopping will be explained. In Table 3 and Figure 5 the results for the overtopping discharge

Armorflex Elastocoast

V

[m3/m]

q

[m2/s]

V

[m3/m] q [m2/s]

V

[m3/m]

10,65 0,136 10,38 0,08 9,6

4,49 0,005 3,95 0,024 2,67

1,11 0,00304 0,83 0,000603 0,34

Results for the relation between crest height, materials and the volume of wave overtopping

: Relation between the volume of wave overtopping and the crest height

8 8,5 9 9,5

Hcrest [m] -->


24


/m. So the total volume


tual overtopping waves


At first the relationship between the use of different revetments, the crest height and the volume of

the results for the overtopping discharge

als and the volume of wave overtopping

9,5


Grass

Armorflex

Elastocoast

Climate (Ex) Change

• If the height of the crest increases, the volume o

height is sensitive for the outcome of the overtopping.

• The volume of overtopping waves is less for Armorflex and Elastocoast compared to the

grass revetment. This is because the

revetments. Grass has a smooth surface whi

• So in this case, Elastocoast would be the best option for the top layer of the dike

• Other revetments are not worked out. The roughness factor for these revetments are

unknown. But the outcome for other revetments w

• The yellow line indicates the average height of the dikes in the Dollart region. The

intersection between the yellow line and the green is at 4,77 m3 / m.

• By this calculation (for an average profile) the discharge of water is ab

The current requirement for the discharge of water is 0,1 l/m/s.

In this part the relation between the length of the slope and the bermwidth are investigated. Both

factors are needed to determine the average slope of the dikes. The

The average slope is needed to determine the wave run

overtopping. The formula is an approach of the characteristic slope of the dike. The outcome for the

volume of wave overtopping can be seen in

Figure 6: Determination of the characteristic slope

Figure 7: Relation between wave run-up and length of the “average” slope of the dike

12,47

3,86

0

2

4

6

8

10

12

14

0 5 10

Z2

% [

m]

-->

Relation between wave run

"average" slope of the dike


If the height of the crest increases, the volume of overtopping waves decreases. The crest

ive for the outcome of the overtopping.

The volume of overtopping waves is less for Armorflex and Elastocoast compared to the

grass revetment. This is because the surface roughness of grass is less than the other

revetments. Grass has a smooth surface while Elastocoast has an open rough surface.

So in this case, Elastocoast would be the best option for the top layer of the dike

Other revetments are not worked out. The roughness factor for these revetments are

unknown. But the outcome for other revetments would not deviate as much.

The yellow line indicates the average height of the dikes in the Dollart region. The

intersection between the yellow line and the green is at 4,77 m3 / m.

By this calculation (for an average profile) the discharge of water is above the requirements.

The current requirement for the discharge of water is 0,1 l/m/s.


factors are needed to determine the average slope of the dikes. The formula can be seen in

The average slope is needed to determine the wave run-up and eventually the volume of wave


e of wave overtopping can be seen in Figure 7 until Figure 10.

: Determination of the characteristic slope for a cross section consisting of different slopes

up and length of the “average” slope of the dike

3,86

2,05 1,34 0,98

15 20 25 30

L slope [m] -->

Relation between wave run-up and length of the

"average" slope of the dike

25

f overtopping waves decreases. The crest

The volume of overtopping waves is less for Armorflex and Elastocoast compared to the

surface roughness of grass is less than the other

le Elastocoast has an open rough surface.

So in this case, Elastocoast would be the best option for the top layer of the dike

Other revetments are not worked out. The roughness factor for these revetments are

ould not deviate as much.

The yellow line indicates the average height of the dikes in the Dollart region. The

ove the requirements.


formula can be seen in Figure 6.

up and eventually the volume of wave


for a cross section consisting of different slopes

Climate (Ex) Change

• If the length of the slope increases the wave run

• The slope of the dike decreases when the length of the slope increases. In other words the

slope becomes gentler.

Figure 8: Relation between the volume of overtopping waves and the length of the “average”slope

• If the length of the average slope increases also the volume of wave overtopping decreases.

In other words, when the dike slope becomes more gentle the volume of overtopping

increases.

• The volume increases exponential when the length of the slope increases. In other words,

the more gentle the slope, the more water will flow

• The relation between the length of the slope and the overtopping discharge is not shown in a

graph. This is because for the determination of the overtopping discharge, the shape of the

dike is not taken into account, only the freeboard between the crest and the SW

Figure 9: Relation between the wave run

• If the bermwidth increases the wave run

• The increase of the wave run

• This is the opposite compared to the length of

1,47 3,77

0

10

20

30

40

50

0 5 10

V [

m3

/m]

-->

L slope [m]

Relation between the volume of overtopping waves

and the length of the "average" slope of the dike

3,18 3,694,35

5,24

0

2

4

6

8

10

12

14

16

18

0 2

Z2

% [

m]

-->

B [m]

Relation between the wave run

bermwidth


If the length of the slope increases the wave run-up decreases

The slope of the dike decreases when the length of the slope increases. In other words the

: Relation between the volume of overtopping waves and the length of the “average”slope

If the length of the average slope increases also the volume of wave overtopping decreases.

when the dike slope becomes more gentle the volume of overtopping

The volume increases exponential when the length of the slope increases. In other words,

slope, the more water will flow over the crest of the dike.

tion between the length of the slope and the overtopping discharge is not shown in a


dike is not taken into account, only the freeboard between the crest and the SW

: Relation between the wave run-up and the bermwidth

If the bermwidth increases the wave run-up increases as well.

The increase of the wave run-up increases exponential.

This is the opposite compared to the length of the slope.

3,77

9,18

20,76

41,28

15 20 25 30

L slope [m] -->


and the length of the "average" slope of the dike

5,246,49

8,35

11,26

16,3

4 6 8

B [m] -->

Relation between the wave run-up and the

bermwidth

26

The slope of the dike decreases when the length of the slope increases. In other words the

: Relation between the volume of overtopping waves and the length of the “average”slope

If the length of the average slope increases also the volume of wave overtopping decreases.

when the dike slope becomes more gentle the volume of overtopping

The volume increases exponential when the length of the slope increases. In other words,

over the crest of the dike.

tion between the length of the slope and the overtopping discharge is not shown in a


dike is not taken into account, only the freeboard between the crest and the SWL.

Climate (Ex) Change

Figure 10: Relation between the volume of overtopping waves and the bermwidth

• When the width of the berm increases the influence on the wave overtopping decreases.

• The line shows a sharp drop in the beginning. So the

volume of overtopping is

• In the equations the influences of the berm itself is neglected because the berm of the dikes

in the Dollart are under the SWL. Therefore we say the berm has no influence on the

overtopping. In fact this needs to be investigated. The position of the berm and the

bermwidth are important for determination of the influence factor.

The volume of wave overtopping i

decreases. It can be explained by the formula in

significant wave height is divided by the difference between the length and the width (L

slope and berm. If L gets larger and B st

therefore the angle tan(α) will decrease. If the tan(α) decreases, the volume of wave overtopping will

increase and the wave run-up decrease. If L has the same value and B is increased, the height

divided by a smaller number and therefore the tan(α) will increase.

It is hard to explain why the volume of overtopping waves increases when the slope becomes gentler

or the berm smaller and the crest height of the dikes is the same. If

for wave run-up it could be logical. The berm is almost horizontally and therefor

transfer its kinetic energy as much to the level energy. However

influences the water as well. This influence

Based on this calculation the length of the slope shows opposite results for the volume of wave

overtopping. If the slope of the dike becomes gentler, the volume of wave overtopping increases.

This observation sounds so unlikely that more research need

mistake has been made in the manual calculation. Therefore the calculation has to be done with the

program of PC-overtopping.

4,773,98

3,31

2,75

0

1

2

3

4

5

6

0 2

V [

m3

/m]

-->

B [m]


and the bermwidth


: Relation between the volume of overtopping waves and the bermwidth

When the width of the berm increases the influence on the wave overtopping decreases.

The line shows a sharp drop in the beginning. So the influence of the berm width on the

volume of overtopping is significantly.

In the equations the influences of the berm itself is neglected because the berm of the dikes


ertopping. In fact this needs to be investigated. The position of the berm and the

bermwidth are important for determination of the influence factor.

The volume of wave overtopping increases when the slope length increases and the bermwidth

can be explained by the formula in Figure 6. The height between the wave run

significant wave height is divided by the difference between the length and the width (L

slope and berm. If L gets larger and B stays the same, the height is divided to a bigger number and


up decrease. If L has the same value and B is increased, the height

divided by a smaller number and therefore the tan(α) will increase.


or the berm smaller and the crest height of the dikes is the same. If the width of the berm accounts

logical. The berm is almost horizontally and therefore the water won’t

kinetic energy as much to the level energy. However the roughness of the berm

influences the water as well. This influence is so big that the volume of overtopping waves decreases.



s observation sounds so unlikely that more research needs to be performed. It


2,752,28

1,891,56 1,29

4 6 8

B [m] -->


and the bermwidth

27

When the width of the berm increases the influence on the wave overtopping decreases.

influence of the berm width on the

In the equations the influences of the berm itself is neglected because the berm of the dikes


ertopping. In fact this needs to be investigated. The position of the berm and the

increases and the bermwidth

. The height between the wave run-up and

significant wave height is divided by the difference between the length and the width (Lslope-B) of the

ays the same, the height is divided to a bigger number and


up decrease. If L has the same value and B is increased, the height will be


of the berm accounts

e the water won’t

the roughness of the berm

is so big that the volume of overtopping waves decreases.



to be performed. It is possible that a



28

But it can be said (if the outcome is correct), that the idea of using a wider berm on the dikes is a

good option for decreasing the volume of wave overtopping. The problem for using a wider berm is

the location. The berm needs to be at the right level of the dike to influence the volume of

overtopping water. The top of the berm comes probability very high. So a lot of soil is needed and

the consequences for nature development should also be investigated. In most cases, the slopes

under and above the berm of the dike are sharp.

Figure 11: Relation between the angle of wave attack and volume of overtopping waves

• In Figure 11 the relation between the angle of wave attack (direction of the waves) and the

volume of overtopping water can be seen

• The volume of wave overtopping decreases linear to the increase of the β. So in other words,

V will become the largest when the wave direction is perpendicular to the dike. Therefore

the angle of wave attack is set to 0 degrees

• The angle of wave attack stops when the angle reaches 80degrees. After the wave direction

becomes 80 degrees from the perpendicular, the wave run-up and overtopping almost

become zero. But in the Dollart region this can mean that the waves can strike the

surrounding dikes in a straight line. The fetch will be less compared to the main wind

direction.

• The determination of β would not influence the outcome of the volume of wave overtopping

as much. Even if β changes for 80 degrees away from the dike, the V will only be reduced

with 1 m3/m of water. So β is not very sensitive in this calculation.

0

1

2

3

4

5

6

0 20 40 60 80 100

V [

m3

/m]

-->

β -->

Relation between the angle of wave attack and

volume of overtopping waves

Climate (Ex) Change

Figure 12: Relation between SWL and the wave run

• Figure 12 shows the relation between the SWL and the wave run

• When the SWL increases the wave run

• It can be concluded that the wave run

Note: for the result of this graph the fact that the wave run

calculation of the average slope is left out of consideration. Also, the increase of the significant wave

height [Hs ] is neglected.

Figure 13: Relation between the volume of overtopping waves and review level

0

0,5

1

1,5

2

2,5

3

3,5

5 5,5 6

Z2

% [

m]

-->

Relation between SWL and the wave run

0

2

4

6

8

10

12

14

16

4 5

V [

m3

/m]

-->

Relation between the volume of overtopping waves and review


: Relation between SWL and the wave run-up

shows the relation between the SWL and the wave run-up

When the SWL increases the wave run-up stays constant

It can be concluded that the wave run-up is not depending on the SWL.

Note: for the result of this graph the fact that the wave run-up exceeds the freeboard for the


: Relation between the volume of overtopping waves and review level

6 6,5 7 7,5 8

SWL [m] -->

Relation between SWL and the wave run-up

6 7 8 9

SWL [m] -->

Relation between the volume of overtopping waves and review

level

29

up exceeds the freeboard for the



30

• Figure 13 shows the relation between the review level and V. The yellow line indicates the

average review level that fluctuates from 6,5m until 6,7.

• The graph has an odd shape. In the beginning the graph is quite flat, then it increases

exponential and after the SWL comes above the 7m it will flatten. So if the freeboard

between the crest and the review level becomes bigger, the V will eventually be zero.

If the freeboard becomes almost zero, the influence of the dike becomes less, and the water

will just flow over the dike. The volume of overtopping will increase linear. But it can be sad

that the determination of the review level is important. Therefore it is important to predict

the right hydraulic boundaries by measurements.

Figure 14: Relation between the volume of overtopping waves and the significant wave height

• In Figure 14 the relation between the volume of wave overtopping and the significant wave

height is given. The yellow line indicates the normative value of the significant wave height in

the Dutch region of the Dollart.

• The significant wave height is very sensitive for the outcome of the V

2.2.4 Crest height calculation with computer program CRESS

In this part the input and outcome for the calculation of wave overtopping with computer program

CRESS is given.

The first calculation is made with the current hydraulic conditions and dike profiles and the second

with hydraulic conditions that can be expected in 100 years. The assumption is made that the review

level in 100 Years will be 120 cm higher than in the current situation. The location of the profiles can

be seen in Figure 2.

This program calculates the overtopping height needed for a required overtopping discharge. This

height is used to determine the final crest height of the dike. In the manual calculation this height

wasn’t found. Therefore the outcome of this calculation is used to determine the crest height. The

results are given bold.

0

5

10

15

20

25

30

35

0 0,5 1 1,5 2 2,5 3 3,5

V [

m3

/m]

-->

Hm0 [m] -->

Relation between the volume of overtopping waves and the

significant wave height


31

Profile 4

Current hydraulic conditions

Input Result

Hm0 :0,9 m

Requirement

q [l/s/m]

Required

height f [m] z2%

[m]

Tp :3,1 s 0.1 1.461

1,35

β :0o 1.0 1.046

SWL :6,5 m 5.0 0.756

10 0.632

100 0.217

Table 4: Results calculation profile 4 with current hydraulic conditions

Note: The 2%-wave run-up is higher than the dike freeboard.

Future hydraulic conditions

The hydraulic condition contain several values. The main values are the wave height and the review

level. In the future will the wave height be the same, however because of the sea level rise will the

review level also need to rise. That fore a calculation with future review level will be conducted. The

future review level is the current review level +1,20 m sea level rise.

However this part of the dike is lower than the future review level. The dike has a crest height of

7,51+NAP and the future review level has a height of 7,7 +NAP. In this case was it not possible to

make the calculation. The future review level is too high for the dike. This means that the dike

according the future review level must be heightened to protect the land behind the dike, or other

innovative measures must conducted.

Profile 10


This dike profile is the south side of the Ems Dollart region. Figure 2 is a schematic drawing of the

dike profile used for the calculation. The main input data are:

Input Result

Hm0 :1,0 m

Requirement

q [l/s/m]

Required

height f [m] z2%

[m]

Tp :3,3 s 0.1 1,87

1,7

β :0o 1.0 0,99

SWL :6,6 m 5.0 1

10 0,84

100 0,32



32


Input Result

Hm0 :1,0 m

Requirement

q [l/s/m]

Needed

height f [m] z2%

[m]

Tp :3,3 s 0.1 1,87

1,7

β :0o 1.0 1,35

SWL :7,8 m 5.0 0,99

10 0,84

100 0,32

Table 6: Results calculation profile 10 with future hydraulic conditions

Note: The 2%-wave run-up is higher than the dike.

Profile 14


This dike profile is the south side of the Ems Dollart region. Figure 2 is a schematic drawing of the

dike profile used for the calculation.

Input Result

m0 :1,1 m

Requirement

[l/s/m]

Needed

height [m] z2%

[m]

Tp :3,4 s 0.1 1,83

1,64

β :0o 1.0 1,33

SWL :6,7 m 5.0 0,98

10 0,83

100 0,33



Input Result

Hm0 :1,1 m

Requirement

[l/s/m]

Needed

height [m] z2%

[m]

Tp :3,4 s 0.1 1,83

1,64

β :0o 5.0 1,33

SWL :7,9 m 1.0 0,98

10 0,83

100 0,33

Table 8: Results calculation profile 14 with future hydraulic conditions

Note: The 2%-wave run-up is higher than the dike.

Climate (Ex) Change

2.2.5 Review level and allowance

Figure 15: Crest height and review level of the Dutch embankment

The figure above shows the crest height and the review level derived from the Hydraulic Boundaries

2006 (HR2006). The numbers 1 till 1

the Dollart. Big differences can be seen in crest height. In the 70’s when the current embankments

were build, the height of the crest was the same along the coast: 10,20m +NAP

the embankments body subsided

could be concluded that at the West side of the Dollart

dike body has settled the most. In the South, set

with 1 to 2 meters in 40 years. The soil subsidence can be seen in

13

K. Lentz, 2010, Waterboard Hunze en Aa’s


Review level and allowance

: Crest height and review level of the Dutch embankment

he figure above shows the crest height and the review level derived from the Hydraulic Boundaries

2006 (HR2006). The numbers 1 till 19 represent the 19 considered cross sections

differences can be seen in crest height. In the 70’s when the current embankments

were build, the height of the crest was the same along the coast: 10,20m +NAP13

subsided with different speeds, resulting in the different crest heights. It

at the West side of the Dollart, where wind and wave attacks are lowest, the

dike body has settled the most. In the South, settlements are less, but still the crest height lowered

The soil subsidence can be seen in Figure 16.

K. Lentz, 2010, Waterboard Hunze en Aa’s

33

he figure above shows the crest height and the review level derived from the Hydraulic Boundaries

9 represent the 19 considered cross sections in the Dutch part of

differences can be seen in crest height. In the 70’s when the current embankments 13

. Due to settlement,

with different speeds, resulting in the different crest heights. It

, where wind and wave attacks are lowest, the

tlements are less, but still the crest height lowered

Climate (Ex) Change

Figure 16: Soil subsidence in the North of Groningen (‘Daling’ means su

Another factor that plays a role in the settlement of the dikes is gas extraction, of which the center is

situated Southwest of the Dollart

Dollart, which is situated in the range of influence of the gas extraction point, where t

parts of the Dollart are just outside that range. The exact settlement due to g

Dollart region is difficult to predict, but ranges between 5 and 20 centimeters.

the settlement stops in the year 2050. They assume the ground structure will be strong enough

around that time.14

The review level and allowance can be seen in the graph below. The

between the review level and the crest height. The graph shows big differences in allowance but the

review level is almost the same, differing between 6,5 m +NAP and 6,7 m +NAP. This graph clearly

shows the influence of gas extraction and settlements

cross section 1 till 10 (horizontal).

Figure 17: Freeboard (distance between the review level and the crest)

14

J.E. Pôttgens, 1991, Land Subsidence Due to Gas Extraction in the Northern

,00

,500

1,00

1,500

2,00

2,500

3,00

0 2 4

Fre

eb

oa

rd [

m]

-->

Freeboard (distance between the review level and the crest of the dike)


: Soil subsidence in the North of Groningen (‘Daling’ means subsidence in Dutch)


lart. This also clarifies the increase in settlement on the Westside of the

d in the range of influence of the gas extraction point, where t

are just outside that range. The exact settlement due to gas extraction in the

region is difficult to predict, but ranges between 5 and 20 centimeters. Expectations are that


The review level and allowance can be seen in the graph below. The allowance is the difference

and the crest height. The graph shows big differences in allowance but the


shows the influence of gas extraction and settlements on the West side of the Dolla

cross section 1 till 10 (horizontal).

: Freeboard (distance between the review level and the crest)

ôttgens, 1991, Land Subsidence Due to Gas Extraction in the Northern Part of The Netherlands

4 6 8 10 12 14

Profiles -->


34


t on the Westside of the

d in the range of influence of the gas extraction point, where the Southern

as extraction in the

Expectations are that


llowance is the difference

and the crest height. The graph shows big differences in allowance but the


on the West side of the Dollart, which covers

Part of The Netherlands

16 18 20



35

2.2.6 Road types and management

The roads form a large surface along the Dollart coast. This surface can be optimized by using

ecological materials. The roads on the dikes are made of tarmac and don’t have a long design period.

They need a lot of maintenance because tarmac has a relatively short design period and don’t offer a

lot of chances for vegetation or water retention. The material of which the roads are constructed

could be changed to increase nature development and decrease maintenance costs. Possibilities are

an element surfacing with concrete blocks or baked clinkers.

The management of the embankment is in hands of Waterboard Hunze en Aa’s with head office in

Veendam. They are responsible for the trajectory along the Dollart. Sheep and mowing machines

maintain the grass revetment.

When a storm threats the embankment and the water level at Delfzijl reaches a certain point a

special guard force starts patrols along the Dollart to inspect the dike body on possible failure

mechanisms.

2.2.7 Dutch Dike structure

After 1953, the Delta commission decided that al dikes had to be raised. The Dollart dikes were

initially raised with a small wall that was build on the crest. It took another 20 years before the dike

got to its current height. In the 70’s the dikes where raised to 10,20 m +NAP. The old dike which was

totally made of clay, was used in the construction of the current dikes. The contractor dumped a new

sand core against the sea side of the old dike. A new clay layer with a thickness of 0,8 m was

constructed to protect the core. This thickness was needed because the outer layer is almost always

dry. That means small cracks can form in the outer clay layer because of drought.

On the landside the old clay dike acts as a strong outer layer and the crest wall is incorporated in the

outer layer as well. The dike is constructed with a norm frequency of 1/4000 years. More details

about loads can be found in paragraph 2.2.8. The picture below shows the dike structure, with the

old clay dike, the new outer clay layer and a grass revetment. This is the same for all cross sections.

Figure 18: Dutch Dollart dike structure with seaside on the right.


36

2.2.8 Loads , significant wave height & tides

The norm frequency of 1/4000 means the review level probably will be exceeded once in 4000 years.

The rising water level caused by onshore blowing storms and low atmospheric pressure is called a

positive storm surge. The tides and high water levels caused by storm surges are recorded by the

ministry of transport, public works and Water management (Rijkswaterstaat). The top 5 water

heights in Nieuwe Statenzijl since 1900 are given below:

483 cm +NAP 01 November 2006

453 cm +NAP 28 January 1901

451 cm +NAP 13 March 1906

448 cm +NAP 04 February 1944

446 cm +NAP 16 February 1962

These high water levels are used to determine the review levels. The significant wave height in the

Dutch Dollart fluctuates between 0,90 m and 1,25 m. The highest waves on the Dutch side of the

Dollart can be found at Nieuwe Statenzijl, where the fetch is longest. Higher waves cannot exist

because the water is rather shallow. At high tide the water is only a couple of meters deep, which

isn’t enough for waves to develop. They reach the bottom and stop growing in size. Even when the

sealevel rises the average wave height will not increase dramatically.

The Dutch dikes are tested with the average wave heights rectangular on the dike. This test is

theoretical, because in a worst case, the highest waves will always reach the dikes under an angle

when the wind comes from the Northeast and the Dollart is blown full with water from the Wadden

Sea. With other wind directions, the worst case won’t occur because the highest water doesn’t occur.

An important load is wave attack. Wave attacks are characterized by the following factors

• The Ems-Dollart region is relative shallow, this restricts the development of wave height

• The Ems-Dollart is sheltered, big waves from the North Sea can’t enter the area directly

• The fetch distance in the Ems-Dollart is restricted

In Appendix 1: Hydraulic conditions Ems-Dollart region, hydraulic conditions for the Ems-Dollart

region can be found. The most important factors for the design are the review level (based on the

highest water levels) and the significant wave height.

2.2.9 German Dollart dikes

The German Dollart dikes are constructed with slightly different hydraulic boundaries. As can be seen

in the overview of the Dollart, the German dikes are situated on the Eastside and suffer from a bigger

fetch and thus higher water set up. The construction has a different shape: the dikes are lower, with

an average crest height of 8 m +NAP. The slopes on the seaside are more gentle. The Dutch dikes are

build with outer slopes of 1:4. The German ones with a slope of 1:6. On the landside the dikes are the

same with a slope of 1:3. The gentle slope in Germany causes a reduction in wave run up and

overtopping. Because of that reduction the crest height can be lower. In the beginning of the 60’s

the German dikes were raised to the current level. Figure 19 shows the method used by the Germans

to increase the crest height. Figure 20 shows the current German dike design with an average crest

height of 8 m +NAP.

Climate (Ex) Change

Figure 19: German construction methods

Figure 20: Current German dike structure

2.3 Conclusions Chapter 2

Conclusion 2.1: The coastline is homogeneous in its properties.

A lot of them don’t change. The ones that do change are related to the position of the

embankments. Some parts of the embankment suffer from greater settlement or higher swell due to

soil properties and wind directions with a deviating crest height as result.

• The Embankment has a broad foreshore, water doesn’t reach the dike often

• The crest height deviates al

• The embankment is uniform in design.

• The Western shoreline is more subsided because its situated closer to the center of gas

extraction


: German construction methods

Current German dike structure

Conclusions Chapter 2 analysis of the Dollart Coast

The coastline is homogeneous in its properties.


arts of the embankment suffer from greater settlement or higher swell due to

soil properties and wind directions with a deviating crest height as result.

The Embankment has a broad foreshore, water doesn’t reach the dike often

The crest height deviates along the coast.

The embankment is uniform in design.

The Western shoreline is more subsided because its situated closer to the center of gas

37


arts of the embankment suffer from greater settlement or higher swell due to

The Embankment has a broad foreshore, water doesn’t reach the dike often

The Western shoreline is more subsided because its situated closer to the center of gas


38

• The review level is almost uniform along the coastline

• The significant wave height deviates between 0,95 m and 1,20 meter

Conclusion 2.2: The seaside of the dike can be considered dry.

Because of the marshes in front of the embankment, the water doesn’t reach the embankment very

often, only a couple of times in the storm season from October till April. Especially the dike trajectory

rectangular to the wind and dominant wave direction has a broad foreshore (up to 1100 m).

The only place where the water reaches the dike is along polder Breebaart. This trajectory of 2500 m

is potential for the use of hard ecological materials.

Conclusion 2.3: The West side of the Dollart is subjected to high subsidence.

The embankment is designed with a review level deviating from 6,5 to 6,7 m +NAP, a difference of

0,2 meter. The crest height deviates between 7,25 and 9,37 m +NAP, a difference of 2,12 m. This is a

factor 10 and implicates local subsidence. According to K. Lentz from waterboard Hunze en Aa’s, the

crest heights where designed to be equal along the Dollart coast, with an average height of 10,20 m

+NAP.

The influential zone of gas extraction can partly clarify this subsidence. This means that the

subsidence locally amounts to almost 3 meters. According to the NAM, the maximum subsidence

that can be attributed to gas extraction is 0,20 m on the Westside of the Dollart. This means that the

amount of subsidence due to settlement of the dike body is 2,80 m in the last 40 years.

Conclusion 2.4: Conclusion of the manual calculation of overtopping

• The review level and the significant wave height are important values for the outcome of the

volume of wave overtopping

• The angle of wave attack is not sensitive for the outcome of the volume of overtopping

• Using rougher revetments decreases the volume of overtopping.

• If the berm of the dike becomes wider, the wave run-up increases and the volume of

overtopping decreases.

• If the length of the slope increases the wave run-up and the volume of overtopping

decreases.

Recommendations

• The soil structure has to be investigated further by comparing CPT’s taken from the Westside

and from the Southside. This to determine the cause of settlements and subsidence.

• The use of ecological materials with a high roughness factor like Elastocoast is

recommended.

• The outcome for the influence factors of the bermwidth and the length of the slope need

further investigation.


39

3 Eco engineering

3.1 Introduction

The use of eco-materials and methods is becoming more and more popular. The society realizes that

it has to “live” with nature and everyone has to be careful with it. When the modern dikes were built

nobody realized the important role of those dikes in nature development. Especially in wet areas at

sea sides of dikes with a hard revetment a lot of nature developed. Small plants and animals found a

new habitat created by men.

This chapter investigates the possibilities of ecological dike concepts in the Dollart. An ecological dike

concepts is defined here as the combination of a material, a method and a location.

• Material tells something about the revetment of the dike.

• Method tells something about the shape of the dike.

• Location tells something about the dike trajectory on which the concept is recommended to

use.

Paragraph 3.2 and Paragraph 3.3

These paragraphs treat the eco materials and methods that are available today to create a ecological

dike concept. It can be seen as an inventory of the possibilities in the field of eco engineering. The

materials are divided in a part for the seaside (paragraph 4.2) and the landside (paragraph 4.3) of the

dike.

Paragraph 3.4

This paragraph treats the different methods that can be combined with a material and used to create

a ecological dike concept.

The different ecological dike concepts are given in chapter 4.

3.2 Overview investigated eco materials & methods

Because the dikes need to be adapted to the sea level rise in the future and nature becomes a more

and more important factor, new ecological materials and methods are being developed. These

materials and methods have a positive influence on specific plants and animals and still protect the

dikes against incoming waves. The materials/methods which will investigated in this chapter are

listed below. These materials are mainly suitable for the use at the seaside to protect the dikes

against incoming waves. The armor layers at the seaside protect the dikes against erosion caused by

the motion of water. Besides the land side revetment, a couple of materials for the roads on the

dikes is treated as well. The chapter covers the following materials:

Materials

• Bundle of piles (palenbos) � Piles in front of the coast to break waves

• Eco-Xblocks® Large concrete armor units

• Armorflex® � Concrete mats

• C-star® coastal elements � Small C-fix elements that can be used as

revetment

• Vetiver � Tropical grass

• Elastocoast � Gravel bound together with polyurethane.


40

• Increased overtopping � The flow rate of water that is allowed to overtop the

crest of the dike.

• Smart grass reinforcement � A reinforcing mat beneath the grass to give

the roots more strength.

• Road surfacing materials � The material of which the roads are

constructed can be changed to increase

nature development and the appearance of the dike.

Methods

• Changes in dike slope � Using the effect of a gentler slope to reduce

wave run up and overtopping

• Increased overtopping � A method where the allowed flow rate of

overtopping is increased.

3.2.1 Evaluation criteria

The materials and methods will be evaluated using the same criteria. The criteria are explained here.

Nature development � This criteria tells something about the contribution to nature

development.

Safety � This criteria tells something about the contribution to safety.

Recreation � This criteria tells something about the effect on

recreation.

Needed surface Natura 2000 � This material tells something about amount of Natura 2000

area needed.

Applicability � This criteria tells something about the applicability of the

material or method in the Dollart. The aspect of the hydraulic

boundaries are important here because the hydraulic

boundaries determine the strength of the dike. For some

materials the factor climate also plays a role.

Costs � This criteria tells something about the ratio

costs/benefits of the material or method.

Origin � This criteria tells something about the origin of the material

because the origin determines transport costs and the way it

fits in the environment of Groningen.

Experience � This criteria tells something about the experience the

Netherlands has with application of the material. This is

important because there can be differences between

theoretical and practical use.

Innovation � By using an innovative ecological material or dike concept,

the Dollart can get positive attention in the Netherlands and

the world.


41

3.3 Eco materials

3.3.1 Pile bundles

Figure 21: pile bundles

The use of wooden piles to stop or decrease waves is used for a long time. To stop waves wooden

piles are not very effective. The piles have to be placed closely next to each other in order to stop

waves effectively or the wave energy slips between them, but the piles are a good option if the wave

height has to be reduced. If a wave hits the pile, part of the energy from the wave is lost which

results in a lower wave.

The ministry of Transport, Public works and Water management (Rijkswaterstaat) is conducting a

research on the effect of bundles of piles on the protection of the coast and are investigating if they

have a positive effect on ecology. The piles they are testing are made out of wood and concrete of

which the surface is treated to increase adhesion by algal. The piles are wrapped in thick rope to give

algal an even better chance of settling on the pile bundles. The algal species are a good breeding

ground for certain worms, lobsters and shrimps.

Another advantage of the pile bundles is that the area in which they are placed silts up. Sediment

deposits between the bundles and provides the new habitat with food and increases the water

quality. The research takes place in the Nieuwe Waterweg in Rotterdam. The salinity of that water

fluctuates a lot which creates a difficult habitat for flora and fauna. The research has to conclude if

the bundles of piles have a positive effect on ecosystems and make it more easy for flora and fauna

to settle in those environments. In the Dollart, the piles have to be very high to have a positive effect

on wave height.

Evaluation Pile bundles

Nature development � Bundles of piles can be a way to develop natural values if

they are placed in the water in front of the marshes.

Safety � Because the difference between high tide and low tide is

extremely high in the Dollart, the piles have to be very high to

make a contribution to coastal safety (3 to 4 meters above

the normal water level).


42

Recreation � The use of pile bundles won’t have a significant effect on

recreation, because the ecosystem that would be created by

using the piles would be situated far from the embankment.

Needed surface Natura 2000 � The needed Natura 2000 area is large because the bundle of

piles will have to be placed in the Wadden Sea.

Innovation � Pile bundles are an innovative solution, but not very

attractive for tourists because of pollution of the horizon.

Experience � Bundles of piles have been used before, but not with the

needed height in the Dollart.

Origin � Bundles of piles can be made from hardwood or concrete,

both not especially originating from the Dollard Area. If

materials from the Dollart area are used to make the piles,

the design period of the piles will decrease.

Costs/benefits � The costs of pile bundles are low.

Applicability � Bundles of piles have no effect on coastal safety and

recreation. Besides that they will cause horizon pollution and

will need a lot of Natura 2000 area. Bundles of piles aren’t

suited for application in the Dollart area because the costs

outweigh the benefits.

3.3.2 Eco Xbloc’s

Figure 22: Eco Xbloc's

Xbloc’s are a variant on the normal Xbloc’s and form a single layer of armor which can be used for

the protection of piers, seawalls and other coastal object against wave attacks. Eco Xbloc’s are quit

new however they already proved their use. Because of the special design they have a very high

stability coefficient and use less concrete compared to other armor layers (cubes, tetrapods, etc.).

From the ecological aspect Eco Xbloc’s are interesting. The rough concrete surface provides a very

good habitat for flora and fauna. The armor layer has a lot of space where water can be retained.


43

Tests were performed in Ijmuiden using these bloc’s and after three years the Eco Xbloc’s were

totally overgrown by flora.

Besides the function as revetment, the Eco Xbloc’s can be used as artificial reefs as well. These reefs

can be made in front of the coast where they will reduce wave heights. A reef stimulates nature

development in two ways:

• The Artificial reef made from Eco Xbloc’s will create a habitat for fish and plants. This is

caused by the space between the bloc’s and the high porosity of the Eco Xbloc’s. The reef

environment offers protection and shelter and a place that will be silted up and provide food.

• Because the wave height is reduced, a sheltered area between the reef and the coast is

created which is good for nature development.

Evaluation Eco Xbloc’s

Nature development � Eco Xbloc’s can contribute to nature development with their

rough surface or by using them to build artificial reefs.

Safety � Eco Xbloc’s are build to withstand high wave heights of 3,5 m

or more. They are used in extreme conditions. When they are

used to build artificial reefs they will also help breaking waves

and reducing wave attacks.

Recreation � The effect of Eco Xbloc’s on recreation will be negative

because they are very big and make the sea side of the dike

inaccessible for tourists.

Needed surface Natura 2000 � There is no loss of Natura 2000 area when Eco Xbloc’s are

used.

Innovation � The use of Eco Xbloc’s is not innovative. They are being used

for years.

Experience � There is little experience of using Eco Xbloc’s in the

Netherlands, but the normal Xbloc’s, without the rough

surface, are used around the world.

Origin � Eco Xbloc’s are made from concrete, the origin is not specific

from the Dollart region.

Costs/benefits � The costs of Eco Xbloc’s are very high. It costs a lot of work to

install them in a correct way.

Applicability � The Eco Xbloc’s are meant for heavy wave attacks. In the

Dollart those high waves won’t occur. A lot of value of the

Eco Xbloc’s is in safety, so in order to make application of

them feasible, there have to be heavy wave attacks. When

they are used for building artificial reefs, the visual of the

Dollart will decrease.


44

3.3.3 Armorflex

Figure 23: Revetment of Armorflex

Armorflex blocks are developed in the United states by the company Armortec. The bloc’s are

specially designed to protect all kind of structures against flowing water and wave attacks. Armorflex

armor layer are suitable to protect:

• Ditches

• Channels

• Dikes

• Estuaries

• Breakwaters

• Piers

• Groins

To avoid the sight of grey concrete, the bloc’s have an open texture and are shaped conically at one

side. The opening on the inside and the special shape gives vegetation enough space to grow

between the bloc’s. Another advantage of the special shape is that the can follow settlement

contours and that the bloc’s have a high water permeability. All this without losing hydraulic stability,

also caused by the special shape of the bloc’s. The bloc’s are made from concrete, which has a rough

surface and is a good living habitat for algal. The armorflex bloc’s are already used in the Netherlands

on several places under which the Ijsselmeer. They can withstand high wave heights.

Evaluation of Armorflex

Nature development � Armorflex can contribute to nature development with its

rough surface when the sea reaches the it. In the Dollart this

is not always the case.

Safety � Armorflex are designed to withstand heavy wave attacks and

is used on several dikes in the Netherlands along the

Ijsselmeer coast.

Recreation � The effect of Armorflex on recreation will be small because

the sight of them is not very special.


45

Needed surface Natura 2000 � There is no loss of Natura 2000 area when Eco Xbloc’s are

used.

Innovation � Armorflex is not very innovative, it is used all over the world.

Experience � There is a lot of experience with Armorflex.

Origin � Armorflex bloc’s are made from concrete, the origin is not

specific from the Dollart region.

Costs/benefits � The costs of using Armorflex are normal, but the benefits that

can be achieved when the dike is situated directly to the

water won’t be achieved when marshes are present.

Applicability � The applicability of Armorflex depends on the presence of

marshes. When marshes are present, the use of armorflex is

not recommended.

3.3.4 C-star® coastal elements

Figure 24: A revetment of C-star elements

C-star elements are elements made from C-fix. C-fix is a material made from sand, fillers, aggregates

and are bound together with a visco-elastic binder. C-fix has some advantages in comparison with

the standard building materials like concrete:

• 100% recyclable

• Impermeable to liquids

• Resistant to chemicals, salt and acids

• Strong, hard , high tensile stresses possible

• Resistant to dynamic loads, no brittle behavior, no breaking of units.

• A significant reduction of CO2

emissions in comparison with use of concrete.

C-start elements have sort of triangular shape of which the edges are rounded. Furthermore the top

of the C-star elements can be provided with various ecological top layers to stimulate the flora and

fauna in the flood zone. The C-stars can be used to protect all kind of structures like:


46

• Dikes (sea and river)

• Groins

• Revetments

• Embankments

• Shore protections (as an alternative to Standard rock and concrete breakwater armor units)

C-stars are a good option for protection of coastal structures because of the high hydraulic stability.

Economical the C-stars can also be very attractive. A relatively thin layer is necessary to protect a

coastal structure. Other materials need a thicker layer to protect the coastal structure, like rock or

concrete armor.

Evaluation C-star elements

Nature development � C-star elements can contribute to nature development with

its rough surface when the sea reaches the it. In the Dollart

this is not always the case. The top layer of C-stars can be

customized with different ecological materials to create more

diversity in the revetment. Besides these advantages, C-stars

are made from C-fix, which is 100% recyclable.

Safety � C-star elements are designed to withstand heavy wave

attacks and is used on several dikes in the Netherlands along

the Ijsselmeer coast.

Recreation � The effect of C-star elements x on recreation will be small

because the sight of them is not very special.

Needed surface Natura 2000 � There is no loss of Natura 2000 area when C-star elements

are used.

Innovation � C-star elements are not very innovative, they are used all

over the world.

Experience � There is a lot of experience with C-star elements.

Origin � Because the top layer of C-star elements can be customized,

materials from the Dollart region could be used. Which

materials could be used has to be investigated.

Costs/benefits � The costs of using C-stars are normal, but the benefits that

can be achieved when the dike is situated directly to the

water won’t be achieved when marshes are present.

Applicability � The applicability of C-stars depends on the presence of

marshes. When marshes are present, the use of C-stars is

not recommended.

Climate (Ex) Change

3.3.5 Vetiver

Figure 25: Vetiver used as slope protection in Vietnam

An effective and efficient way of protecting the outer slope is to apply the grass specie

combination of Vetiver and hard revetment. The grass can cover t

crown and inner slope.

Important aspects of Vetiver grass:

• The grass can grow up to 1,5meter high and the grass fast

reaching between 2 and 4meter deep in 12 months.

• Good tolerance to extreme

temperature (from -15ºC to +55ºC)

• Vetiver can re-grow very quickly after being affected by frosts or salinity

• High tolerance level for soil pH, pesticides and heavy metals

• Medium growth in salty environm

• Intolerant to shading

• It’s a typical tropical grass. Best pe

• Vetiver hedges are a natural soft eco

• Application of Vetiver on the slope of a dike has

technologies

• Long-term maintenance costs are low

Evaluation Vetiver

Nature development �

Safety �


: Vetiver used as slope protection in Vietnam

An effective and efficient way of protecting the outer slope is to apply the grass specie

and hard revetment. The grass can cover the dike surface

grass:

The grass can grow up to 1,5meter high and the grass fast-growing root system capable of

reaching between 2 and 4meter deep in 12 months.

Good tolerance to extreme climate variations. For example drought and extreme

15ºC to +55ºC)

grow very quickly after being affected by frosts or salinity

High tolerance level for soil pH, pesticides and heavy metals

um growth in salty environment

It’s a typical tropical grass. Best performance in a warm environment

hedges are a natural soft eco-engineering and a good alternative to hard structures

on the slope of a dike has lower costs compared to many other

term maintenance costs are low

� Vetiver can contribute to nature development because it

creates a new environment with vegetation which provides

shelter and food for specific plants and animals. No artificial

materials have to be used.

� Vetiver is a grass species that grows in tropical climates. It

has long roots that make the soil more adhesive and increase

stability more than the usual grass species used as

revetment. Vetiver gives the slope of dikes a high roughness

47

An effective and efficient way of protecting the outer slope is to apply the grass species Vetiver or a

he dike surfaces like the berm,

growing root system capable of

climate variations. For example drought and extreme

engineering and a good alternative to hard structures

ed to many other

Vetiver can contribute to nature development because it

creates a new environment with vegetation which provides

ific plants and animals. No artificial

Vetiver is a grass species that grows in tropical climates. It

has long roots that make the soil more adhesive and increase

ecies used as

revetment. Vetiver gives the slope of dikes a high roughness


48

factor and decreases wave run-up and overtoppingl It can

withstand high wave attacks.

Recreation � Vetiver causes a natural look and is attractive for tourists.

Needed surface Natura 2000 � There is no loss of Natura 2000 area when Vetiver is used.

Innovation � Application of Vetiver in the Netherlands would be very

innovative. The species only grows in Asia, so it is never used

in the Netherlands before.

Experience � There is a lot of experience with Vetiver as revetment in Asia.

Studies are performed by technical Universities like Technical

University of Delft to investigate the strength of this grass15

.

The outcome was positive.

Origin � Vetiver originates from Asia, making it a foreign species and

less attractive to use in the North of the Netherlands when

the culture and historical values of the Dollart area have to

remain.

Costs/benefits � Vetiver has a low price, especially compared to hard

revetments (concrete or C-fix)

Applicability � Applicability of Vetiver in the Netherlands is not possible at

this time. It can’t resist periods of high frost. Genetically

improving the species to make it resistant to strong cold

could be an option. Another option could be to look for

similar indigenous species with similar properties.

The following result are the outcome from the test of H.J. Verhagen , D.J. Jaspers Focks, A. Algera

and M.A. Vu, performed for the Technical University of Delft.

• Vetiver grass is a suitable and innovate solution for the protection of sea dikes

• Vetiver protects earth structures more effectively

• Vetiver grass can be used at SWL as well as on the dikes were the water table can be low

• Vetiver barrier reduces 45% of the total overtopping discharge, with a grass density of 200

steams per square meter. The value is higher when grass density increases.

• The roughness coefficient of Vetiver grass varies from 0.33 to 0.41, depending on grass

density

• A Vetiver barrier is successful to reduce wave run-up. Wave run-up reduction increases up to

60% at density of 200 steams per meter.

15

H.J. Verhagen , D.J. Jaspers Focks, A. Algera and M.A. Vu,

THE USE OF VETIVERS IN COASTAL ENGINEERING, Dubai, 2008


49

3.3.6 Elastocoast

Figure 26: Mixing ingridients, application and final result of an Elastocoast revetment

A new type of revetment is called Elastocoast. This protection system combines gravel with a 2-

component polyurethane (PU). The polyurethane glues the gravel together resulting in a stable

structure. A small amount of PU is used to keep the structure porous, which results in a reduced

wave run-up. The material consists of approximately 50% vegetable acids, i.e. renewable raw

materials. The production process is given in Appendix 2. The stones need to be clean and dry before

they can be processed. Simple measures regarding handling and logistics eliminate this obstacle.

The porous revetment offers a lot of advantages. If water runs up on the porous surface of

Elastocoast part of the hydraulic energy will be absorbed by friction in the volume of the pores. The

wave masses will be transformed into thermal energy and that will result in a lower wave run-up.

Two tests were performed and analyzed during the storm season in the Netherlands (wind speeds

above 17 m/s). The test results gave the following outcome:

• Negligible damages to the Elastocoast revetments

• Even layer with a thickness of only 10 centimeter performed as a stable construction

The high porosity has another advantage. Revetments are saturated with water when the water level

is against the dike and therefore subject to overpressure. When the height of the water drops the

overpressure can lead to destabilization. The decrease of water pressure is faster with porous

revetments. Tests show that Elastocoast is much more resistant to erosion and abrasion compared to

Open Stone Asphalt. Projects showed that Elastocoast is cost effective. The basic costs in the

realization of the coastal protection structure are transport, prices for raw material, simple

installation and the process of the materials. The high porosity and load bearing result in a thinner

layer of Elastocoast on the dike. This may rise to 50% compared to a conventional revetment.

Tests in the field and in a laboratory gave a positive outcome of the growth of biotic live. A couple of

species that found a habitat on the Elastocoast revetment can be found in Appendix 2. Elastocoast is

already in use or being tested in Canada, France, Germany, Great Britain and the Netherlands. The

best example is a reference project in Emden – Germany. Near the Ems sperwerk a 15m2 area with


50

Elastocoast is set into place. The revetment is built on granite gravel (thickness between 30 and

60mm) and Elastocoast on gravel core with a geotextile base.

Evaluation Elastocoast

Nature development � Elastocoast forms a rough and open surface and a habitat for

specific plants. A prequisit is that the revetment is build next

to the seas and water can reach it. In the Dollart this is not

always the case.

Safety � Elastocoast forms a strong layer and can resist high wave

attacks.

Recreation � The Elastocoast revetment looks like tarmac and when the

dike is not overgrown with specific plants, the dike won’t look

very attractive.

Needed surface Natura 2000 � There is no loss of Natura 2000 area when Elastocoast is

used.

Innovation � Application of Elastocoast is an innovative solution of

creating a revetment with an open texture. The material is

not used a lot.

Experience � There is not much experience with Elastocoast revetments

but tests have proven its strength and are still conducted to

investigate the exact properties.

Origin � Elastocoast is a combination of gravel and PU and is not

specifically from the Dollart area.

Costs/benefits � Elastocoast has the advantage of an open texture where

specific plants can grow if sea water flows over the

revetment at high tide. In the Dollart this is not always the

case, so the benefits of Elastocoast can only be achieved at

places without marshes.

Applicability � Elastocoast can be applied in the Dollart but only on places

where there are no marshes present.

3.3.7 Hydrotex

Figure 27: Hydrotex Enviromat Lining (left) and Hydrotex Articulating Blocks


51

This is a fabric formed armoring system usable on different types of water constructions. The

manufacturer has different types of products for different applications. We will describe two of the

products.

• Enviromat Lining

• Articulating blocks

Enviromat Lining

Enviromat Lining is a big mattress (woven double-layer fabric joined together by large interwoven

areas) with different compartments. These compartments will be filled with a mixture of Portland

cement, fine aggregate and water. The result is a solid structure. Approximately 20% of the total area

of the mats is opened by cutting the fabric. After the installation vegetation can be planted within

the open structures. Within a growing season a vegetated cover will normally extend over the lining.

The result is an erosion control system with the hydraulic and ecological features.

The Enviromat Lining is a new type of revetment that provides protection against periodic high flows

and is subject to heavy run-off. It is used in drainage ditches and on the upper slopes of canals,

channels, lakes, reservoirs, rivers and other water courses. So it is not really suitable as a revetment

on the dike. But this type of revetment is mentioned because the added value for natural

development is high.

Articulating Blocks

As a revetment for the dikes in the Ems Dollart region the Articulating blocks are more suitable when

the revetment is exposed to frontal attack by wave action. The Blocks differ from the Enviromats.

They are strengthened with reinforced concrete. The average thickness, mass per unit, area and

hydraulic resistance of each concrete lining withstands high wave attacks.

Evaluation Hydrotex Articulating Blocks

Nature development � Hydrotex Articulating Blocks form a very rough but hard

surface which retains water in the open surface and forms an

ideal surface for algal to grow on. This only works when

Hydrotex Articulating Blocks are applied on a dike next to the

open water.

Safety � Hydrotex Articulating Blocks can withstand high wave attacks

and are suitable for hydraulic conditions in the Dollart.

Recreation � The open texture attracts specific plants and animals which

make the outer layer of the dike attractive to the eye.

Needed surface Natura 2000 � There is no loss of Natura 2000 area when Hydrotex

Articulating Blocks are used.

Innovation � The use of Hydrotex Articulating Blocks is not very innovative.

Experience � Hydrotex Articulating Blocks have been used before with

success.


52

Origin � The material is made from concrete and aggregates and

doesn’t originate specifically from the Dollart area.

Costs/benefits � The costs of Hydrotex Articulating Blocks are medium, and

the benefits will only be achieved when the material is used

in the presence of open water.

Applicability � Applicability of Hydrotex Articulating Blocks depends on the

presence of marshes along the coastline and the average

wave height. For trajectories of the coast without marshes it

could be a good choice for the revetment.

3.3.8 Smart grass reinforcement

Figure 28: Picture of the smart grass reinforcement

Smart Grass Reinforcement (SGR) is an idea from Royal Haskoning and Imfram. They made a

functional analysis of possible reinforcement systems. Finally, the Fortrac 3D-120 system from

Heusker was chosen as the most suitable erosion prevention system. The Fortrac 3D-120 system is a

synthetic gauze which can be used on slopes to prevent erosion. SGR was also used with the

overtopping tests and proven to be very helpful to prevent erosion when overtopping occurs. The

SGR protects the dike in three ways against erosion:

• Fotrec 3D-120 gives the grass extra holding power in the ground, because the roots and the

system weave in together

• The system gives extra protection to the underlying clay layer

• The system prevents shear of the slope because it pulled over the crest of the dike and

anchored

SGR can also be used at the seaside of the dike where it can be used for protection against erosion.

How much protection it will give is not known, but it probably gives extra protection against waves.

Tests have to point out the exact addition of SGR to the strength of a grass revetment. Installing SGR

is quite easy and large surfaces are also not a problem. The top layer is cut away and then the system

is installed. After the system is installed the grass can be put back in place. After some time the grass

stronger than before and ready to handle future storms.


53

Evaluation SGR

Nature development � The current natural values are preserved because SGR is

applied beneath the current grass revetment.

Safety � The resistance against overtopping increases by applying

SGR. The current standard of 1 l/m/s can be raised up to 50

l/m/s. Also the resistance against wave attacks increases.

Recreation � The revetment of grass with SGR doesn’t change the

appearance of the dike. This material won’t have an effect on

recreation.

Needed surface Natura 2000 � There is no loss of Natura 2000 area when SGR is used.

Innovation � The increased overtopping is innovative. This can be achieved

with SGR without changing the appearance of the dike. The

standards of allowed flow rate of overtopping are not

changed yet. If this happens it could mean that the crest

height won’t have to be raised.

Experience � There is not much experience with the use of SGR. Research

is still performed to determine the exact properties of this

material.

Origin � The material does not origin from the Dollart area, but the

grass revetment like it exists now will remain, and will give

the dike an authentic look.

Costs/benefits � The costs of SGR are low, but it has to be applied under the

current grass revetment. The current revetment has to be

removed and replaced. This can’t be done in the storm

season. The benefits of SGR are that the appearance doesn’t

change but strength increases.

Applicability � SGR can be applied in the Dollart region. It can guarantee

safety and the costs are low.

3.3.9 Road surfacing materials

The maintenance road at the landside are now made from tarmac which doesn’t give the dikes a

naturally appearance. The road’s primary goal is to give access to the embankment for water boards

when maintenance or inspections have to be done. A secondary function of the road is the access for

tourists who visit the area. There are a lot of cyclist and walkers who use the dike to enjoy the sight

of the landscape and sea. This paragraph treats materials that could be used to replace the existing

road, with the primary reason to make the dike more attractive for tourists.


54

Grass concrete block’s

Figure 29: Drawing of grass concrete blocks

Grass concrete block’s can be an alternative for tarmac on the dikes in the Ems-Dollart region. It’s a

concrete surfacing that allows grass to grow between the block’s and in that way a natural look is

created. There are different types of grass concrete block’s manufactured by different manufactures.

The most Grass concrete blocks are suitable for cars to drive. However not all block’s are suitable for

bicycle’s and sheep. Not suitable blocks are to open or too rough too use for a bicycle road. The block

shown in Figure 29 is a type of block that can be used to construct a green road on the dike.

Baked clinkers

Figure 30: Baked clinkers made from clay

Clinkers baked from clay are used since the Middle Ages and still very popular in gardens and

driveways. The use of baked clinkers in road construction has decreased. An interesting feature for

the roads on the dike is the fact grass can grow between the stones because they all slightly differ in

shape and size. That makes a road of baked clinkers an element surfacing with a lot of space for grass

and weeds to grow, resulting in a very green appearance. The clinkers aren’t very suitable for roads

with heavy traffic loads, but for the dikes in the Dollart they would be very suitable. A disadvantage

could be the price of this element surfacing.


55

Plastic grass stones

Figure 31: Plastic grass stones, type slimblock

Plastic grass stones are made parking spaces and roads which have to fit in the surroundings. Plastic

grass stones are suitable for roads and places with a low traffic density. The stones are strong enough

for cars and heavy trucks to drive over. The fact the plastic grass stones are open for 86% gives grass

the opportunity to grow between the stones. There are all kind of plastic grass stones but the type

seen in Figure 31 is manufactured by Three Ground Solutions. The plastic stones are made from

recycled plastic and available in green or black. All the stones are mounted together to get a strong

and even surface. Plastic grass stones can be suitable for the maintenance roads with a very light

traffic density. A disadvantage could be the fact that the plastic grass stones probably aren’t

comfortable for cyclist. Besides that it could be difficult to see the road on a dike that is totally

covered with grass.

Evaluation road surfacing materials

Nature development � The contribution to nature development by using a nature

friendly road surfacing material can be neglected.

Safety � n/a

Recreation � The use of nature friendly road surfacing materials can

contribute to recreation because it makes the dike more

attractive.

Needed surface Natura 2000 � n/a

Innovation � n/a

Experience � There is a lot of experience with these road surfacing

materials

Origin � Materials originating from the Dollart area can be used for

road surfacing.

Costs/benefits � the costs of replacing the surface road aren’t high when its

combined with the replacement of the revetment. The

benefits can be an attractive appearance of the dike.


56

Applicability � Nature friendly road surfacing materials can be applied in the

Dollart region.

3.4 Eco methods

3.4.1 Increased overtopping

Because of the rising sea level a lot dikes in the Netherland need to be raised according to the

current guidelines. This means a lot of money has to be spent on the coastal defenses. Rough

estimates say no less than 2000 billion Euro’s are needed to bring the dikes to the desired height.

That money has to be spent in the next century. To bring back the high costs for dike raising, tests are

being conducted that investigate an increase in permissible overtopping. The current standards only

allow an overtopping flow rate of 0.1 l/m/s. Dike administrators are very cautious with overtopping

because the effects of it on the revetment on the land side are not very clear. The guidelines are not

based on scientific evidence but on personal feelings. Nobody exactly knew what would happen if

large amounts of water washed over the crest and the land side of the dike.

In 2007 the ministry of transport, public works and water management started researching what

would happen when larger amounts of water overtopped the crest. The focus was to investigate

what would happen with the inside slope and the toe of the dike. Different tests were conducted on

different locations.

Figure 32: Schematic overview of the wave overtopping simulator

The most of the tested dikes have the same properties as the dikes in the Dollart. The outer layer of

the dike is made from clay and covered with grass. This means that the landside of the dike has no

armor layer which protects the dike against water. Besides testing the actual existing dikes

“reinforced” grass and clay without grass was also tested. In total there were 3 tests.

The overtopping simulator has the capacity to simulate overtopping up to 50 l/s/m over a width of 4

meter. Every test series last for six hours in which a “storm” becomes more and more intense. Every

two hours all damages, speed of the waves and the wave height were being determined. The first

test was the dike with grass. These tests were carried out very smoothly and there was no real

damage on the dike, even with a flow rate of 50 l/s/m. The fact that the tests were more successful

than expected the engineers decided to create some damage to the dike and look what would

happen.

The second test was the dike with the “reinforced” grass. Just like the normal dike no damage

occurred when the storm of 6 hours was imitated. When artificial damage to the dike was made, and

water came over the dike no damage occurred.


57

Figure 33: Test results from simulator test; left picture is the dike without reinforced grass and the right with

reinforcement

The third and last test investigated the strength of a dike without any revetment. The strength of the

clay layer determined the strength of the dike. It turned out that a dike without a revetment like

grass can survive a storm with an overtopping flow rate of 10 l/m/s, but little damage will occur in

that case. The test pointed out that a grass revetment makes a dike many times stronger.

Usability in the Dollart

The overtopping tests had a very positive outcome and better than the most experts expected. At

this moment the tests are being reviewed and is it expected that new regulations for overtopping are

ready in 2011. This means that from 2011 there probably will be an increase in the allowed

overtopping flow rate. The sea level rise makes an increased crest height necessary, but with an

increase in overtopping flow rates, the amount with which the current dikes have to be raised could

be less than expected.

Evaluation of increased overtopping

Nature development � The method of increased overtopping doesn’t directly

influence nature development.

Safety � This method doesn’t increase safety but redefines it, making

it possible that the current dike height is safe enough for sea

level rise in the future.

Recreation � n/a

Needed surface Natura 2000 � n/a

Innovation � The increased overtopping method is very innovative. First it

was believed that water flowing over a dike was dangerous.


58

At this time experiments are conducted to determine the

amount of overtopping can be allowed, resulting in

overtopping flow rates of up to 50l/m/s. This means that the

definition of safety is redefined with this method.

Experience � The only experience with this method is derived from

experiments.

Origin � n/a

Costs/benefits � The benefits of this method is that the crest height doesn’t

need to be raised when the sea level rises. This means this

method reduces the costs of coastal safety.

Applicability � Because the Dollart isn’t densely populated and there is

enough space behind the dike, this method is applicable in

the Dollart.

3.4.2 Adjustments of dike slope

The slope of the dike determines the amount of wave run up and overtopping. A gentle slope causes

earlier breaking of waves and therefore reduces wave run up and overtopping. In the Dollart, where

the waves aren’t higher than 1,25 m, the dikes can be kept lower if the slope is made gentler. Figure

34 shows the influence of the slope and the overtopping flow rate on the crest height.

Figure 34: Influence of a gentle slope on the crest height

Evaluation of adjusting the dike slope

Nature development � When the dike slopes are made gentler, the sharp line

between the embankment and the marshes or the sea

becomes broader. The result could be an increase in specific

animals and plants on the sea side of the dike. But on the

other hand, the sharp line still exists on the crest, whith the

land side of the dike being as steep as before. The exact

influence from this method on nature development has to be

investigated further.

Safety � As can be seen in Figure 34 a gentler slope has a positive

effect on the needed crest height. The contribution to safety

depends on the reduction of steepness.


59

Recreation � A gentle slope can have a positive effect on recreation when

the slope is made accessible for visitors.

Needed surface Natura 2000 � The amount of Natura 2000 area needed for this method is

high. This means that a lot of nature values are lost and have

to be retrieved elsewhere. In the Dollart area this can’t be

done.

Innovation � A gentle slope is not innovative. Germany already has a more

gentle slope of 1:6 instead of 1:4 in the Netherlands.

Experience � There is a lot of experience with gentle slopes of

embankments, but not in a nature reserve like the Wadden

Sea. The effects on nature development have to be

investigated further.

Origin � n/a

Costs/benefits � The costs of making a slope more gentle is very high. There is

a lot of material needed to stretch the dike core and also the

needed revetment materials which are the most expensive,

increase. Besides that the lost nature value of the Natura

2000 area have to be regained, with the corresponding costs.

The benefits are uncertain, besides the fact that the crest

height doesn’t have to be raised.

Applicability � Because the Dollart is a Natura 2000 area, this method will

cause a loss of nature value. Besides this the costs of applying

this method are very high because of the needed material.

These reasons make applicability of this method difficult in

the Dollart.

3.5 Multi-criteria analysis

To determine the best suitable material and method per section, 4 multi criteria analysis are made,

one for each section.The Dollart dikes aren’t the same along the coast, so the coast has to be divided

in different sections. The trajectories are based on the presence of marshes, the crest height, and the

dike slope, because that are the main characteristics of the embankment. The different sections can

be found in Figure 35.

Red section 1 (2500 m) � No salt marsh in front of the dike, the influence of

wave (representative for profile 4) wave attack is almost negligible and the crest height

is the lowest. The water stands against the toe of the

dike.

Green section 2 (8000 m) � Salt marsh in front of the dike, an average influence

of (representative for profile 10) wave attack and an average crest height compared to

the other sections. Under normal weather conditions,

the water doesn’t reach the dike.


60

Bleu section 3 (4250 m) � Salt marsh in front of the dike, an average influence

of (representative for profile 14) wave attack and an high crest height compared to

the other sections. Under normal weather conditions,

the water doesn’t reach the dike.

Yellow section 4 (11000 m) � Salt marsh in front of the dike, assumed that the

influence of wave attack is the highest, because the

fetch is the longest (The value of the significant wave

height is unknown). Assumed that the water doesn’t

reach the dike under normal weather conditions.

Figure 35: The Dollart coast divided in different sections

The materials and methods have to be classified to determine the best and the least suitable

solution. This is done by the same criteria as were used in the evaluation of the materials and

methods:

• Nature development

• Safety

• Recreation

• Needed surface Natura 2000

• Innovation

• Experience

• Origin

• Costs/benefits

• Applicability

Climate (Ex) Change

The criteria are of different importance. That is why different weighing factors are assigned to each

of them. The scores of a material per criteria are multiplied with the weighing factor and the total is

divided with the addition of the weighing factors resulting in a score per material.

The weighing factor varies from 1 to 5 where 1 equals very unimportant and 5 equals very important.

The scores of each material vary from

effect.

The header materials analyses the situation where the only change in design is the material on the

outer layer of the primary embankment.

change in design is the use of one of the two methods described in this chapter (an increase in

allowable overtopping and a more gentle slope).

The materials that can be used for road surfacing

because they don’t have a significant ef

development.

Analyzed materials

1. No different material used

2. Bundle of piles

3. Eco Xbloc’s

4. Armorflex

5. C-star elements

Analyzed methods

1. No changes

2. Increased overtopping

3. Slope changes

4. Raising the crest height

Figure 36 till Figure 39 indicate the scores of the materials and method mentioned above. The

numbers on the x-axis correspond with the numbers mentioned above for the materials and the

methods.

Figure 36: MCA for the materials and methods applied in section 1




with the addition of the weighing factors resulting in a score per material.


The scores of each material vary from 1 to 5 where 1 equals a negative effect and

analyses the situation where the only change in design is the material on the

outer layer of the primary embankment. The header methods analyses the situation where the only

of one of the two methods described in this chapter (an increase in

allowable overtopping and a more gentle slope).

for road surfacing are not included in the multi-criteria analysis

because they don’t have a significant effect on the most important issues: safety and nature

material used 6. Vetiver

7. Elastocoast

8. Hydrotex Articulating Blocks

9. Smart Grass Reinforcement

indicate the scores of the materials and method mentioned above. The

nd with the numbers mentioned above for the materials and the

: MCA for the materials and methods applied in section 1

61



with the addition of the weighing factors resulting in a score per material.


t and 5 equals a positive

analyses the situation where the only change in design is the material on the

The header methods analyses the situation where the only

of one of the two methods described in this chapter (an increase in

criteria analysis

fect on the most important issues: safety and nature

Hydrotex Articulating Blocks

Smart Grass Reinforcement

indicate the scores of the materials and method mentioned above. The

nd with the numbers mentioned above for the materials and the

Climate (Ex) Change

Figure 37: MCA for the materials and methods applied in sectio



3.5.1 Conclusions MCA’s

• Hard revetments score high on nature developm

4. That is because section 1 is the only section without marshes in front of the coast. In

section 2, 3 and 4 the hard revetments lo

• Smart Grass Reinforcement scores

appearance of the dike, but improves strength, is easy to apply and relatively cheap.

• ‘No different material used’ scores high in every MCA and in the last three it even comes at

the second place. This is because it is the cheapest method and in MCA 2, 3 and 4 the hard

revetments lose their advantage of contributing to nature development.


and methods applied in section 2



Hard revetments score high on nature development in section 1, but low in sections 2,3 and


section 2, 3 and 4 the hard revetments loose their contribution to nature development.

Smart Grass Reinforcement scores high in every section. This is because it doesn’t change the


‘No different material used’ scores high in every MCA and in the last three it even comes at

. This is because it is the cheapest method and in MCA 2, 3 and 4 the hard


62

ent in section 1, but low in sections 2,3 and


se their contribution to nature development.

high in every section. This is because it doesn’t change the


‘No different material used’ scores high in every MCA and in the last three it even comes at

. This is because it is the cheapest method and in MCA 2, 3 and 4 the hard



63

• Vetiver has good results in these MCA’s, but this material is not suitable for the Dutch

climate. Vetiver is in the MCA because it would be the best nature friendly material to use.

More research has to be done to the use of Vetiver on Dutch dikes.

• The method of increased overtopping scores highest in every MCA. This is because it’s no

real method, but a change in standards. It has the advantages of a ecological method, but

not the disadvantages like application problems or costs.

• The method of raising the crest height scores highest in section 1 because the West bank of

the Dollart is subjected to higher subsidence and has a lower average crest height.

• The scores of methods are similar in every MCA. This is because the criteria with the highest

weighing factor are the same along the Dollart coast (See Appendix 7: Multi criteria analysis)

3.6 Conclusions Chapter 3 Eco engineering

Conclusion 3.1: The use of ecological materials only, doesn’t contribute to an increase of both nature

development and coastal safety

If marshes are present in front of the dikes, the problem of combining nature development with

coastal safety cannot be solved by using one specific method or material. The most of the available

materials are only applicable in situation where seawater reaches the toe of the dike continuous. In

the Dollart this is only the case in section 1.This can be seen in Figure 36. Ecological materials used as

revetment have to be covered with water at least one period a day to create more natural value. If

not, they only cause higher protection.

Conclusion 3.2: The most ecological materials focus on vegetation and animals that live in a wetland

area, not in a relatively dry environment like the Dollart dike.

Most materials are developed to be wet for a certain amount of time a day. Especially in brackish

water nature develops very well on these materials. However when the materials are being used in a

mainly dry environment almost no nature will develop.

Conclusion 3.3: Section 1 is the only trajectory where eco materials could be useful.

Section 1 is the only trajectory where water reaches the toe of the dike during high tide. In front of

the other part of the Dollart coast marshes are present, limiting the use of eco materials to their

safety function.


64

4 Concepts

With the MCA’s from chapter3 and the trajectories that can be seen in Figure 35, concepts are made

for each section. A concept is a combination of a method, a material and a location. The location is

the considered trajectory and its most important properties are length, type of foreshore and a wet

or dry embankment. Per section the properties of the location are given as well as the best suitable

materials and methods. These are derived from the corresponding MCA’s (see paragraph 3.5).

Section 1

Location Length trajectory � 2500 m

Foreshore � No marshes, Natura 2000 area

Wet/dry embankment � Wet

Material Material 1(MCA 1) � Armorflex

Material 2 � C-star elements

Material 3 � Elastocoast

Method Method 1 � Increased overtopping

Method 2 � Slope changes

Method 3 � Raising the crest height

Concept 1.1: Elastocoast + gentle slope + Raised crest height + Increased overtopping

Motivation:

Section 1 is situated along polder Breebaart which is used as a nature reserve. The sea reaches the

dike so a hard eco material can be used as revetment. The revetment material can vary. The three

materials have almost the same score. There are two methods chosen with different scores. The

allowed overtopping can be raised because there is no agriculture on the land side of the dike. The

slopes have to be made gentler because section 1 has a low crest height. An increase of overtopping

has no negative effects on the hinterland and both methods are chosen for concept 1.1. The crest

height has to be raised because the review level will become higher in the future than the current

crest height. The loss of nature value has to be investigated further.


65

Figure 40: Concept 1.1: A gentle slope and raised crest height in combination with a Elastocoast revetment on the berm.

Advantages

• Increasing coastal safety

• Increase in nature value on the dike

Disadvantages

• Loss of Natura 2000 area

• High costs

Section 2


Foreshore � Marshes, Natura 2000 area

Wet/dry embankment � Dry

Material Material 1 � No other material

Material 2 � SGR


Method 2 � Slope changes

Concept 2.1: No other material + Slope changes + Increased overtopping

Motivation:

The embankment is dry so hard revetments aren’t useful. The area suffers from medium hydraulic

conditions because it is mostly situated in the lee. The Slopes can be made more gentle to increase

nature development on the dike and increase safety. Increased overtopping can be allowed, the

agriculture has to adapt to the increase of salinity. The costs of a higher crest height/slope changes to

minimize overtopping have to be compared with the costs for agriculture to adapt to the increased

salinity.


66

Figure 41: Concept 2.1: No other material used, slope changes and increased overtopping

Advantages

• Increasing coastal safety

• Increase in nature value on the dike

Disadvantages

• Loss of Natura 2000 area

• High costs

• Increased salinity of agricultural hinterland

Section 3


Foreshore � Marshes, Natura 2000 area


Material Material 1 � SGR


Concept 3.1: SGR + Increased overtopping

Motivation:

The embankment is dry under normal conditions, so hard eco-materials aren’t useful. The area

suffers from medium hydraulic conditions and the crest height of the dike is high compared to the

other sections on the Dutch side. In other words the waves in this section are only 1.25m and the

embankment is only several times a year under water. Therefore overtopping will be less compared

to section 1 and 2. SMR and increased overtopping come out as best. The fact the dike is still relative

high is a gentle slope to reduce waves and overtopping not necessary.


67

Figure 42: Cross section of the dike, SGR is installed under the grass revetment

Advantages

• Current nature value will be maintained

• The current image of the dike is preserved

• Costs are relatively low

Disadvantages

• No increased value for nature development

• Not much practical experience

• Loads on the inner slope will be increased

Alternative: Overtopping with retention basin

Another option for this section is using a retention basin. Comcoast came up with a new design for

increasing the overtopping over the crest of the dike. In this part an alternative for the increase of

overtopping will be worked out. As mentioned before the requirements for the volume of wave

overtopping will change. More overtopping will be allowed during a storm event. The result is a

greater effect of erosion on the inner slope of the dike. But with this new concept the inner slope will

be less disturbed.

A concrete construction will be installed in the crest of the dike. This concrete construction has an U-

shaped profile and acts as a retention basin. Most of the overtopping water will be caught by the

retention basin and discharged to the inner side of the dike. So for this concept, a retention basin is

used instead of the SGR. The function of the SGR is negligible.

The crest width of the dikes in the current situation should be enlarged to fit the construction.

Further investigation is needed to determine how width the construction has to be, to catch all


68

overtopping water.

Figure 43: Cross section of the dike with retention basin installed in the crest

Less amount of water will run over the inner slope, because the retention basin will catch a large

amount of overtopping water. The result is a reduction of the loads on the inner slope. In extreme

conditions it is possible that the retention basin is not able to discharge all the water, so water will

run over the inner slope. But the energy of the water is decreased by the retention basin compared

to the smooth crest right now. The construction and the drainage pipes must be placed in clay to

prevent instability.

Discharge

The allowable amount of wave overtopping depends on the capacity of the retention basin with the

discharge pipes. Comcoast calculated with a wave overtopping of 15 l/s/m during their investigation

to apply a retention basin.

In Table 9an overview is given of the possible combinations of pipe diameters and their capacities.

The results from the table are determined by the Darcy-Weisbach formula, see Appendix 3:

Calculation of the overtopping capacity of the retention basin. With the current height of the dikes

the discharge capacity of the dikes is approximately 250l/s for a pipe diameter of 250mm. A pipe

needs to be installed every 17m to discharge all the water from a wave overtopping of 15l/s/m. The

result is not very satisfying. The cost will be too high for the installation and purchase of the pipes.

But for the calculation, the worst scenario is taken into account. If the height of the dike is enlarged

and the distance from the trench to the crest is shortened, the discharge capacity increases

significantly. In this section of the Dollart the dikes are relatively high compared to the other location.

This would be the best location if you want to use a retention basin.

The fact that the pipe will never be totally filled with water is neglected in the calculation. Based on

this calculation can be concluded that the use of a retention basin with discharge pipes will be a bad

solution for the Dollart dikes. The possibility of using an open drain instead of a discharge pipe looks

as a good alternative. This is not investigated. Further study is needed for the overtopping and

discharge of water at the crest.


69

Pipe

diameter

[mm]

Pipe capacity

[m3/s]

Pipe

frequency

Catch-off

capacity crest

[l/s/m]

200 0,14 Every 100m 1

200 0,14 Every 50m 3

200 0,14 Every 25m 6

250 0,25 Every 100m 2,5

250 0,25 Every 50m 5

250 0,25 Every 25m 10

300 0,40 Every 100m 4

300 0,40 Every 50m 8

300 0,40 Every 25m 16

Table 9: Overview with possible combinations for the discharge pipes.

Durability

The durability of the construction should not be considered as a problem. The working live of this

construction is around 80 years. The working live of the retention basin on the dike is expected to be

less, 50 years.

Environment

The concept is mentioned because it minimizes the environmental effects. At the crest of the dike

the construction doesn’t allow nature development but because of the construction the grass

revetment can be preserved at the inner slope of the dike. Nature development can be maintained at

the inner slope of the dike and there is no negative influence on the landscape values within the dike

area.

Maintenance road

The retention basin can also be used as a maintenance road beside its function as drain. In the

current situation the maintenance roads are located at the bank of the dike. It is a good option to

investigate:

• If the landside road of the dike can be placed on top of the dike. This increases the landscape

value.

• If the seaside road can be removed. That would be helpful for the concept of changing the

slopes of the dikes at the seaside. See concept changing the slopes. The problem could be

the accessibility to the salt marshes.


70

Section 4


Foreshore � Marshes


Material Material 1 � SGR


Concept 4.1: SGR + Increased overtopping

Motivation:

Section 4 is the dike trajectory in Germany from which not much information is available yet. During

our research was it difficult to get contact with the different German authorities, which have the

dikes in management. There was also no information about the hydraulic conditions of the German

dikes. However looking to the Dutch hydraulic conditions it looks plausible that the waves and the

review level will increase at the German dike when going more to the north. This is because the dike

there is more in line of sight with the Ems, were waves from the North Sea are. The German dike has

already a gentle slope compared to the Dutch dike. Therefore the method of changing the slope is

not chosen here. Based on this motivation concept 4.1 is chosen.

It can be said that the development of the concepts for dike trajectory 4 is based on assumptions.

Advantage:

• Current nature value will be maintained

• The current image of the dike is preserved

• Costs are relatively low

Disadvantages

• No increased value for nature development

• Not much practical experience

• Loads on the inner slope will be increased


71

5 Conclusions

The main goal of this research is trying to find out if application of ecological dike concepts in the

Dollart can contribute to a combination of coastal safety and nature development. An ecological dike

concept is defined in this research as a location, a revetment material and a change in the shape of

the dike (method). The use of no material is also defined as a material and for method the same

applies. This can be seen as the situation with no changes at all.

The Dollart region is an estuary with specific properties. During this research it became clear that

during a storm the water level can increase dramatically. Were the normal high tide is 1.5 m +NAP

do the hydraulic conditions say that a water level can as be high as 6.8 meter + NAP at Nieuwe

statenzijl. This extreme high water level is caused by the fact that storm surges occur in the Dollart.

The fact that the Dollart is a bay also contribute to the extreme high water, water is enclosed and the

only way is up. Waves in the Dollart a relative low when compared to the Dutch and German coast.

The waves are according the hydraulic condition on the Dutch Dollart coast 0.9 meter at Punt van

Reide and up to 1.25 meter at Nieuwe Statenzijl. The wave height at the German dikes is unknown

but is to be expected be higher than 1.25 meter.

The philosophy behind this research goal is that the dike and the sea are in contact with each other.

When hard revetments are used or special techniques like water retaining structures on the outer

slope, a habitat is created for specific plants and animals. This is a form of eco engineering and

contributes to nature development and coastal safety. These two features make eco materials very

useful in some places.

The use of ecological materials only, doesn’t contribute to an increase of both nature development

and coastal safety. The most ecological materials focus on vegetation and animals that live in a

wetland area, not in a relatively dry environment like the Dollart dike. The Dollart coast can be

considered dry except the trajectory along polder Breebaart. The marshes in front of the dike hinder

the water of reaching the dike. At high tide there is still a couple of hundreds of meters between the

water and the dike. The average high water is 1,50 m +NAP and the height of the marshes deviates

between 1,50 m +NAP and 2,00 m +NAP. Section 1 is the only trajectory where eco materials could

be useful.

The west side of the Dollart along polder Breebaart is probably subjected to higher subsidence. The

reason for this can be the gas extraction and local soil properties. However it is clear that the dike

along the Breebaart the lowest in the Dollart and not high enough is. The settlement in that side is

not investigated but the expected review level will be higher than the current crest height. This

means the West side of the Dollard has to be raised to withstand the expected sea level rise. By using

methods like overtopping, gentle slope and materials SGR can the heightening of the dike be reduced

to a minimum.

The dikes at the south of the Dollart have salt marshes in front of them and the length of these salt

marshes vary from 500 to 100 meter. The crest height at the south side of the Dollart varies from 8

meters in the West and up to 9 meters on the East side. With methods like increased overtopping

and SGR and creating gentle slopes it is possible to increase the safety.

The dikes on the East side in Germany, have a gentle slope of 1:6. This means they suffer from less

wave run-up and overtopping. The German trajectory suffers from the highest wave attacks and

water boost due to the Ems sperwerk. The average crest height is 8 m +NAP. Possibly the crest height

has to be raised, but this depends on the German hydraulic boundaries. Also here, methods and

materials like overtopping and SGR could help to keep the increase of the crest height to a minimum.


72

In this research it becomes clear that there are no easy ecological solutions for the dike. With the

materials and methods that are available today it is not possible to find a solution to increase safety

and increase nature development together. When nature development must be created in the

Dollart region it is recommended to find solutions in front of the dike or behind it.


73

6 Recommendations

• Research has to be done on different ways to increase nature development besides using

ecological materials as revetment. This research shows that the possibilities to create nature

development on the Dollart dikes is marginal. The Natura 2000 area in front of the coast

makes nature development on the sea side difficult, but the chances of nature development

are highest on the marshes on the border of water and land. The hinterland could be used

like the way polder Breebaart is developed. This will result in high costs and resistance of

local inhabitants. Further research has to be done to investigate the possibilities.

• The use of ecological materials is not directly useful but the chances of those materials with

regard to safety are interesting. The dikes might have to be reinforced with future hydraulic

conditions and although nature development is not directly increased by using ecological

materials, the use of them should be investigated further for section 1.

• The Dollart is divided in four sections based on hydraulic conditions, crest height and the

presence of marshes. The recommended concepts that could be worked out further:

Section 1: Elastocoast + gentle slope + Raised crest height + Increased overtopping

Section 2: No other material + Slope changes + Increased overtopping

Section 3: SGR + Increased overtopping

Section 4: SGR + Increased overtopping

• The soil structure has to be investigated further by comparing CPT’s taken from the Westside

and from the Southside. This to determine the cause of settlements and subsidence. This

could affect the needed crest height.

• The hydraulic boundaries in front of the German coast have to be investigated further. This

will lead to more insight in adaption of the German dikes to sea level rises

• The eco system in the Dollart determines which ecological materials are most suitable. A

research on the eco systems has to be done to get a better fine tuning between the existing

nature and the dike design.

• Investigation should be done on nature development with materials for a dry environment.

This research focuses on dike revetments but other materials have to be investigated and

their applicability on the Dollart dikes.

• Research has to be done on dikes with incorporated marshes and the conflicts that would

have with regulations in the Dollart


74

7 Definitions

Eco-engineering: The design, construction, operation and management (that is,

engineering) of landscape/aquatic structures and associated plant

and animal communities (that is, ecosystems) to benefit humanity

and, often, nature.

Ecological dike concept: A conceptual design of the considered cross section of the dike. The

considered area includes the foreshore or marshes, the dike body

and the seepage zone, which is assumed to run to the seepage ditch

on the land side.

Eco- materials: Materials used in eco engineering that serve human and natural

development purposes.

Fetch: The unobstructed area wind can blow over water to create waves

Negative storm surge: Exceptionally low tides caused by wind blowing offshore and high

atmospheric pressure

Natura 2000 Area: Nature reserve area where the European nature laws are in order.

NAP: NAP stands for “Normaal Amsterdam Peil”, the reference height used

in the Netherlands.

NN: NN stand for “Normal null”, The reference height used in Germany,

the same height as NAP

Positive storm surge: Exceptionally high tides caused by wind blowing ashore and low

atmospheric pressure

Revetment: Sloping structures placed on banks in such a way as to absorb to

energy of incoming water

Sea level rise: An increase in sea level with approximately 120 centimeters in the

next 100 years excluding a decreasing ground level.

The Dollart: The pelvis found in the South of the Ems Dollart estuary.

The Ems Dollart estuary: The estuary that includes the Dutch and German Wadden Sea and

the salt marshes.


75

Figure 44: Top view of the Ems Dollart estuary, red line indicates the estuary

The Ems Dollart region: The region that includes the Ems Dollart estuary, the coastal

defenses and the hinterland.

Figure 45: Top view, red line indicates The Ems Dollart region

The Tide Rise and fall of the water in the sea caused by moon and sun

and other influences

Wave overtopping: The flow of water over a dam or embankment

Wave run-up: The ultimate height reached by waves after running up to a

coastal barrier, f.e. a dike


76

8 Bibliography (TAW), T. A. (2002). Technical report wave run-up and wave overtopping on dikes. Retrieved from

www.helpdeskwater.nl.

Anh, V. M. (n.d.). Wave overtopping reduction through Vetiver grass. Retrieved from www.tudelft.nl.

B.V., V. d. (n.d.). Information wave overtopping simulator. Retrieved from

www.vandemeerconsulting.nl.

BASF, T. c. (n.d.). Information revetment type Elastocoast. Retrieved from www.elastocoast.com.

C-fix. (n.d.). Information revetment type C-star. Retrieved from www.c-fix-coastalelements.com.

Comcoast. (n.d.). Technical solutions for wave overtopping resistant dike. Retrieved from

www.comcoast.org.

Deichacht, R. (n.d.). Information German dikes. Retrieved from www.rheider-deichacht.de.

Deltacommissie. (2008). Deltaplan: Samen werken met water. Retrieved from

www.deltacommssie.com.

Ecomare. (n.d.). Information about the vegetation and animals in the Wadden Sea. Retrieved from

www.ecomare.nl.

Fabriform. (n.d.). Information revetment type Enviromat. Retrieved from www.fabriform1.com and

www.greenbanks.nl.

Huesker. (n.d.). Smart grass reinforcement products. Retrieved from www.huesker.com.

International, T. V. (n.d.). Information Vetiver grass. Retrieved from www.vetiver.org.

Rijkswaterstaat. (n.d.). Report Eco-engineering "Harde werken met zachte trekken". Retrieved from

www.rijkswaterstaat.nl.

Secretariat, C. W. (n.d.). Information about ecosystems in the Wadden Sea. Retrieved from

www.waddensea-secretariat.org.

Van de Maarel, i. A. (2009). Climate (Ex)Change, Klimaatbewuste verdediging en natuurontwikkeling.

Vekeer&Waterstaat, M. v. (n.d.). Instruction manual for safety requirement 2006. Retrieved from

www.helpdeskwater.nl.

Verkeer&Waterstaat, M. v. (2006). Hydraulic Boundaries 2006. Retrieved from

www.verkeerenwaterstaat.nl.

Verkeer&Waterstaat, M. v. (n.d.). Pictures from the Dutch coastline. Retrieved from www.kustfoto.nl.

Waterkeringen, T. A. (1999). Leidraad Zee-en Meerdijken. Retrieved from www.enwinfo.nl.

Xbloc's. (n.d.). Information about Xbloc's. Retrieved from www.xbloc.com.


77


78

Appendix 1: Hydraulic conditions Ems-Dollart region


79

Appendix 2: Tide table Nieuwe Statenzijl


80

Appendix 3: Calculation of the overtopping capacity of the

retention basin

In this annex a calculation is performed for the discharge capacity of the PP pipes for the retention

basin. In this simple equation is assumed that the quantity of wave overtopping depends on the

capacity of the discharge from the crest.

A pipe of 200mm and the average height of the dikes is used in the next calculation.

Flow velocity in the pipe

The negative flow is negligiblev 4.6

m

s:=

1

λ L⋅ D+( )2

1

2⋅ λ L⋅ D+( ) dH⋅ D⋅ g⋅

1

2⋅

1−

λ L⋅ D+( )2

1

2⋅ λ L⋅ D+( ) dH⋅ D⋅ g⋅

1

2⋅

4.6

4.6−

m

s=

dH λL

D⋅

v2

2 g⋅⋅

v2

2g+

Gravitational acceleration g 9.807m

s2

=

Length of the pipe

Longest distance from the crest to the trench, landside of the dike. L 81m:=

Natural drop pipe line

Average height of the dikes at the Dutch side of the Dollart regiondH 8.3m:=

Determine the flow velocity in the pipe under normal drop

λ 0.017=

Friction factor

Depends on the wall roughnessλ

0.25

log 3.7D

k⋅

2:=

k 0.1 103−

⋅ m:=Factor for the wall roughness

Discharge pipes will be made from synthetic Poly Propyleen pipes

Diameter of the pipeD 0.2m:=

Determine the friction factor

Model for determining the discharge capacity of the pipes.Representative for the

discharge of the water in the retention basin

Darcy - We isbach e quation


81

Freqpipe2 101

m=Freqpipe1 29

1

m=

Freqpipe2Q

Requirement2:=Freqpipe1

Q

Requirement1:=

Requirement2 15 103−

⋅m

3

s

m

⋅:=Requirement1 5 103−

⋅m

3

s

m

:=

Determine the frequency of the pipe for a wave overtopping of 5 and 15 l/s/m

Q100m 1.4liter

s=Q100m

Q

100:=

Q50m 2.9liter

s=Q50m

Q

50:=

Q25m 5.8liter

s=Q25m

Q

25:=

Discharged water through PP pipe when the pipes will be installed every 25,50 and

100m

Q 0.145m

3

s=

Flow capacity of the PP pipeQ v A⋅:=

Discharged water through PP pipe per meter of the dike

A 0.031m2

=Surface of the pipe

A1

4πD

2⋅:=

Determine the capacity of the pipe


82

Appendix 4: overtopping calculations with CRESS

Calculation dike profile 4 current hydraulic conditions

Input data

g : 9.81 m/s2

wave height : 0.9 m

Peak period : 3.087 sec

Wave direction : 0o

Horizontal water level : 6.5 m

X-position toe :0 m

Y-position toe : 2.254 m

Accuracy : 1%

Storm duration : 21600 sec

Average wave period : 3 sec

admissible over topping : 0.005 m3/m/s

Percentage volume : 5%

Aantal dijkprofielen : 4

X-co-ordinaat : 1.399

Y-co-ordinaat : 2.59

Roughness factor : 1










Output data

Needed crest height 5.0 l/s/m : 0.756 m


Needed crest height 1.0 l/s/m : 1.046m

Needed crest height 10 l/s/m : 0.632 m


Volume overtopping wave exceed in x : 0.117 m3/m

Volume overtopping wave exceed 1% : 0.208 m3/m



Volume of highest overtopping wave : 0.344 m3/m

2%-wave run-up height : 1.35 m

Remark: The 2%-wave run-up is higher than the dike.


83


Input data

g : 9.81 m/s2

wave height : 1.0 m


Wave direction : 0o


X-position toe :0 m


Accuracy : 1%





Aantal dijkprofielen ` : 3

X-co-ordinaat : 3.226 m

Y-co-ordinaat : 2.988 m

Roughness factor : 1 m







entage volume : 5%

Output data












Remark:


84

Calculation dike profile 10 future hydraulic conditions

Input data

g : 9.81 m/s2

wave height : 1.0 m


Wave direction : 0o


X-position toe :0 m


Accuracy : 1%















Output data














85


Input data

g : 9.81 m/s2

wave height : 1.1 m


Wave direction : 0o


X-position toe :0 m


Accuracy : 1%















Output data












Remark:


86

Calculation dike profile 14 future hydraulic conditions

Input data

g : 9.81 m/s2

wave height : 1.1 m


Wave direction : 0o


X-position toe :0 m


Accuracy : 1%















Output data














87

Calculation dike profile 14 future hydraulic conditions with slope 1:6

Input data

g : 9.81 m/s2

wave height : 1.1 m


Wave direction : 0o


X-position toe :0 m


Accuracy : 1%















Output data






Volume overtopping wave exceed in x : 0 m3/m

Volume overtopping wave exceed 1% : 0 m3/m



Volume of highest overtopping wave : 0 m3/m


Remark: The 2%-wave run-up is higher than the dike


88

Calculation dike profile 14 future hydraulic conditions with slope 1:8

Input data

g : 9.81 m/s2

wave height : 1.1 m


Wave direction : 0o


X-position toe :0 m


Accuracy : 1%





Aantal dijkprofielen : 3 m










Output data






Volume overtopping wave exceed in x : 0 m3/m




Volume of highest overtopping wave : 0 m3/m


Remark: The 2%-wave run-up is higher than the dike


89

Appendix 5: Calculation wave periods

Wave period 0.9 m

Wave period 1.0 m

Calculation peak period

Hi 0.9m:=

Tp

2 π⋅ Hi⋅( )0.05g⋅

:=

Tp 3.396s=

Calculation spectral wav e period

Tm_1.0

Tp

1.1:=

Tm_1.0 3.087s=

Calculation peak period

Hi 1.0m:=

Tp

2 π⋅ Hi⋅( )0.05g⋅

:=

Tp 3.58s=

Calculation spectral wav e period

Tm_1.0

Tp

1.1:=

Tm_1.0 3.254s=


90

Wave period 1.1

Calculation Piek period

Hi 1.1m:=

Tp

2 π⋅ Hi⋅( )0.05g⋅

:=

Tp 3.754s=

Calculation spectral wave period

Tm_1.0

Tp

1.1:=

Tm_1.0 3.413s=


91

Appendix 6: Manual calculation wave overtopping

Figure 46: Picture were the freeboard is indicated (free crest height for wave overtopping)

Solve wave overtopping at the Dollart dikes

(Technisch rapport golfoploop en golfoverslag bij dijken)

Determine the freeboard at the crest•

SWL 6.6m:= Average sea water level

Hprofile4 7.51m:=Crest height of the Dutch profiles used for the comparison

Hprofile10 8.35m:=

Hprofile14 9.37m:=

Hcrest 8.3m:= Average height of the crest, of all 19 Dutch profiles

Rc Hcrest SWL−:=

Rc 1.7m= Freeboard at the crest, with respect to the Sea water level (SWL)

Hm0 1.25m:= Significant wave height at the toe of the dike

Influence factor for the roughness of the top layers of the dike revetment during wave •overtopping [-]

γf.grass 1:= For grass revetments, the grass has no influence on the roughness

γf.armorflex 0.9:= For Armorflex

γf.elastocoast 0.7:= Lowest roughness factor for elastocoast products

Influence factor for the angle of wave attack, the wave impact •will be less when the waves strike the dike under an angle

β 0:= Angel of wave attack (degrees)

γβ 1 0.0022β⋅−:=

γβ 1= Influence factor for the angle of wave attack


92

Figure 47: Definition angle of wave attack, red line indicated the angle of attack

g 9.81m

s2

= Gravitation

Note:

The crest height is too low based on the current overtopping discharge requirement

because qgrass > qcurrent.

But this conclusion is too quick because not all waves go actually over the top of the crest

Possible requirement for wave overtopping dischargeqnew.maybe 5.0 103−

⋅m

2

s:=

New requirement for wave overtopping dischargeqnew 1.0 103−

⋅m

2

s:=

Current requirements for wave overtopping dischargeqcurrent 1 104−

⋅m

2

s:=

This average wave overtopping discharge is above the current requirements for wave

overtopping.Research is ongoing to get a better view on the relationship between wave

overtopping and the capacity of the inner slope. The requirements for wave overtopping

change, because of the already performed research

The average overtopping discharge, m3 / m per secondqgrass 0.04m

2

s=

qgrass .20 exp 2.3−Rc

Hm0 γf.grass γβ⋅⋅⋅

⋅ g Hm03

⋅

1

2

⋅:=

For grass

Solve the wave overtopping

q

g Hm03

⋅

0.2 e

2.3−Rc

Hm0

⋅1

γ f.gras γβ⋅⋅

⋅

With the maximum:

Emperical formula TAW formula for wave overtopping at dikes

Calculate the wave overtopping


93

For Armorflex

qarmorflex .2 exp 2.3−Rc

Hm0 γf.armorflexγβ⋅⋅⋅

⋅ g Hm03

⋅

1

2

⋅:=

qarmorflex 0.027m

2

s= The average overtopping discharge, m3 / m per second

For Elastocoast

qelastocoast .2 exp 2.3−Rc

Hm0 γf.elastocoast γβ⋅⋅⋅

⋅ g Hm03

⋅

1

2

⋅:=

qelastocoast 0.01m

2


Determine overtopping volumes per wave

The calculation is only the made for the grass revetment because it is the top layer of the

current dikes in the Dollart region

Tm 1s:= Average wave period

qgrass 0.038m

2


hk Rc:=freeboard, crest height with respect to the SWL

hk 1.7m=


94

s0 0.08=

Wave steepness [no dimension]

s0

2 π⋅ Hm0⋅

g Tm_1.02

⋅

:=

Calculation of the wave steepness•

Tm_1.0 3.25s=

Spectral wave periodTm_1.0

Tp

1.1:=

Calculation spectral period•

Peak periodTp 3.58s=

Tp

2 π⋅ Hi⋅( )0.05g⋅

:=Formula to calculate the wave piek period

Hi 1.0m:=

Calculation piek period•

Influence factor for the berm of the dike. In this calculation is

assumed that the influence of the berm is negligible. Normally this

needs to be taken into account.

The width of the berm and the position of the berm in respect to the

waterline influence is important

γb 1:=

Influence factor for grass revetmentsγf.grass 1=

Influence factor for the angle of wave attackγβ 1=

Determine the wav e run-up


95

Figure 48: Left picture; determination of the characteristic slope for a cross section, right picture; The situation for the

manual calculation of the Dollart dikes

The tan(α) is the average angle in the zone between the sea water level minus 1,5Hm0 and the wave

run-up. The berm should not be taken into account. So the representative berm is depending on the

water level.

Determine the representative angle of the upper slope of the •dike at the seaside

Hm0 1.25m= Significant wave height at the toe of the dike

Horizontal length between two points 1,5xHm0 above and

under the review level on a slope of 1:3Lslope 11.3m:=

B 0m:= Width of the crest

There is a berm on the dike, but the berm is lower then the

review level. Therefore it is not taken into account, so zero.

The width of the lower berm seaside is 3meters

Normally the wave run-up needs to be taken into

account. Only the wave run-up is not yet determined.

For z2%, 1,5xHm0 can be taken into account for a first

estimate.

tan α( )1.5 Hm0⋅ 1.5 Hm0⋅+( )

Lslope B−( )

α1 1.− atan 3.Hm0

1.− Lslope⋅ B+( )⋅

⋅:=

α1 0.32= Angle of the average slope

tan α1( ) 0.33=


96

Determine the breaker parameter•

ξ0

tan α1( )s0

:=Breaker parameter

ξ0 1.21=

Determine the wave run-up•

z2% is the wave run-up height, that is exceeded by 2% of the waves

General formula for the wave run-upz2%

Hm0

1.75γb⋅ γf⋅ γβ⋅ ξ0⋅

z2%1 1.75γb⋅ γf.grass⋅ γβ⋅ ξ0⋅( ) Hm0⋅:=Wave run-up above the sea water level

z2%1 2.64m=

Second estimate: Improved approach for the average slope of the dike


tan α( )1.5 Hm0⋅ z2%1+( )

Lslope B−( )

α2 1.− atan .503. Hm0⋅ 2. z2%1⋅+( )

1.− Lslope⋅ B+( )⋅

⋅:=

α2 0.38=

Angle of the average slopetan α2( ) 0.4=


ξ0

tan α2( )s0

:=Breaker parameter

ξ0 1.45=


z2%2 1.75γb⋅ γf.grass⋅ γβ⋅ ξ0⋅( ) Hm0⋅:=Wave run-up above the sea water level

z2%2 3.178m=


97

The wave run-up is higher than the freeboard at the crest. For this calculation this fact is neglected.

So for the further calculation the Z2%3 is used.

Determine the chance of overtopping per wave•

Rayleigh equation

Pov e

ln 0.02( )−hk

z2%3

⋅

2

−

:=

So a possibility of wave overtopping of:

Pov 0.07=

(If Pov=0,1 that means 10% of the incoming waves go over the top)

z2%3 2.517m=

Wave run-up above the sea water levelz2%3 1.75γb⋅ γf.grass⋅ γβ⋅ ξ0⋅( ) Hm0⋅:=


ξ0 1.15=

Breaker parameterξ0

tan α3( )s0

:=


tan α3( ) 0.316=

Angle of the average slopeα3 0.306=

α3 1.− atan .503. Hm0⋅ 2. hk⋅+( )

1.− Lslope⋅ B+( )⋅

⋅:=

tan α( )1.5 Hm0⋅ hk+( )Lslope B−( )


In this case the wave run-up exceeds the freeboard at the crest. Therefore 3th estimate

for the average slope and wave run-up:

For the determination of the average slope

and also the wave run-upz2%2 hk:=than z2%2 hk>So if

Because the run-up needs to be smaller than the freeboard for the determination of the

average slope

Check if the wave run-up is smaller then the freeboard from the SWL to the crest•


98

N 5.028 103

×=

Total amount of waves that strike against the dike during a

storm period

NTimestorm

Tp

:=

Estimate of storm duration of 5hoursTimestorm 18000s:=

Tp 3.58s=

For a first estimate of the maximum volume of one wave that can be expected at a certain

moment, can be calculated with the total number of overtopping waves

V a ln 1 P−( )−( )

4

3

⋅

The formula to calculate the volume at a certain probability of exceedance

P 1 e

V

a

0.75

−

−

Weibull equation

The average wave overtopping doesn't say much about the amount of water that

instantaneous will flow over the crest of the dike at a particular overtopping wave.

With the information of the wave-overtopping the probability for wave overtopping volume

per wave is calculated.

Determine the chance that wave overtopping per wave V is greater than or same as V •

a 0.453m2

=

a 0.84Tm⋅qgrass

Pov

⋅:=

This scale factor is needed for the Weibull equation,

Determine the scale factor•

Pov

Nov

NThe possibility of wave overtopping, already determined

Nov Pov N⋅:=

Nov 358= Number of overtopping waves

So the volume of the overtopping waves will be:

Alternative formula to calculate the maximum volume. This

can be used for a first estimateV a ln Nov( )( )1.33⋅:=

V 4.77m

3

m= Volume of the overtopping waves


99

Appendix 7: Multi criteria analysis

Multi criteria analysis section 1

Multicriteria–analysis of applicable ecological materials and methods

Features tarjectory 1: no marshes

low crest height (+/- 7 m +NAP)

slope 1:4

Weight criteria from 1–5 5 5 4 3 1 1 3 2 4 28

Score per criteria on a scale of 1 to

5

contribution

to nature

development

contribution

to coastal

safety

contribution

to recreation

needed

surface

Natura2000 innovation experience origin

costs/

benefits Applicability Overall score materials

materials

1. No different material 1 1 1 5 1 5 3 5 5 No different material 2,64

2. Bundle of piles 3 2 1 2 4 2 4 4 1 Bundle of piles 2,32

3. Eco-Xblocks 4 4 1 5 1 5 1 2 2 Eco-Xblocks® 2,86

4. Armorflex 3 4 1 5 2 3 2 4 5 Armorflex® 3,32

5. C-star coastal elements 4 2 1 5 2 4 3 4 5 C-star® coastal elements 3,29

6. Vetiver 3 3 2 5 3 4 1 4 1 Vetiver 2,68

7. Elastocoast 4 3 1 5 3 3 2 5 4 Elastocoast 3,29

8. Hydrotex Articulating Blocks 4 4 1 5 3 2 2 3 4 Hydrotex 3,29

9. Smart grass reinforcement 1 4 1 5 4 2 3 4 5 Smart grass reinforcement 3,11

Methods Overall score concepts

1 No changes 1 1 1 5 1 5 3 3 2 No changes 2,07

2 Increased overtopping 2 5 1 5 4 2 3 5 5 Increased overtopping 3,54

3 Slope changes 1 3 2 3 2 3 3 1 3 Slope changes 2,32

4. Raising dike height 1 5 1 2 1 5 3 2 3 Raising dike height 2,54


100

Multi criteria analysis section 2

Multicriteria–analysis of applicable ecological materials and

methods

Features tarjectory 1: marshes

medium crest height (+/- 8 m +NAP)

slope 1:4


Score per criteria on a scale of 1 to 5

contribution

to nature

development

contribution

to coastal

safety

contribution

to

recreation

needed

surface


costs/


materials






6. Vetiver 2 2 3 5 3 4 1 3 1 Vetiver 2,39



9. Smart grass reinforcement 1 5 1 5 4 2 3 4 4

Smart grass

reinforcement 3,14







101

Multi criteria analyisis section 3



high crest height (+/- 9 m

+NAP)

slope 1:4



contribution

to nature

development

contribution

to coastal

safety

contribution

to recreation

needed

surface


costs/


materials

1. No different material 1 1 1 5 1 5 3 5 5 No different material

2. Bundle of piles 2 2 1 2 4 2 4 4 1 Bundle of piles

3. Eco-Xblocks 1 4 2 5 1 5 1 1 1 Eco-Xblocks®

4. Armorflex 1 4 1 5 2 3 2 1 1 Armorflex®

5. C-star coastal elements 1 4 1 5 2 4 3 1 2 C-star® coastal elements

6. Vetiver 2 2 3 5 3 4 1 3 1 Vetiver

7. Elastocoast 1 4 1 5 3 3 2 1 1 Elastocoast

8. Hydrotex Articulating Blocks 1 3 1 5 3 2 2 2 1 Hydrotex

9. Smart grass reinforcement 1 5 1 5 4 2 3 4 4 Smart grass reinforcement


1 No changes 1 1 1 5 1 5 3 3 2 No changes

2 Increased overtopping 2 5 1 5 4 2 3 5 5 Increased overtopping

3 Slope changes 1 3 2 1 3 3 3 1 3 Slope changes

4. Raising dike height 1 3 1 2 1 5 3 2 2 Raising dike height


102

Multi criteria analyse section 4



medium crest height (+/- 8 m +NAP)

slope 1:6



contribution

to nature

development

contribution

to coastal

safety

contribution

to

recreation

needed

surface


costs/


materials






6. Vetiver 2 2 3 5 3 4 1 3 1 Vetiver 2,39



9. Smart grass reinforcement 1 5 1 5 4 2 3 4 4 Smart grass reinforcement 3,14







103

Appendix 8: Drawings cross-section 4, 10, 14


104


105

Documents

Eco -engineering in the Dollart - Hanze...Climate (Ex) Change – Eco-engineering in the Dollart 2 Title: Eco-Engineering in the Dollart Authors: J.J. Punter 296441 C.A. Gerbers 294255