2010 Eco -engineering in the Dollart
J.J. Punter, C.A. Gerbers, J.M Luursema Hanze University of Applied Sciences Groningen Climate (Ex) Change – Eco-engineering in the Dolla7-6-2010rt
1
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
Climate (Ex) Change – Eco-engineering in the Dollart
2
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
Climate (Ex) Change – Eco-engineering in the Dollart
3 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, seiches 1 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 Climate (Ex) Change – Eco-engineering in the Dollart
4 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.
Climate (Ex) Change – Eco-engineering in the Dollart
5 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
Climate (Ex) Change – Eco-engineering in the Dollart
6 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 CURRENT HYDRAULIC CONDITIONS 83 CALCULATION DIKE PROFILE 10 FUTURE HYDRAULIC CONDITIONS 84 CALCULATION DIKE PROFILE 14 CURRENT HYDRAULIC CONDITIONS 85 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
Climate (Ex) Change – Eco-engineering in the Dollart
7 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 37: MCA for the materials and methods applied in section 2 ______62 Figure 38: MCA for the materials and methods applied in section 3 ______62 Figure 39: MCA for the materials and methods applied in section 4 ______62 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 Climate (Ex) Change – Eco-engineering in the Dollart
8 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
Climate (Ex) Change – Eco-engineering in the Dollart
9 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 area 3 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.
Climate (Ex) Change – Eco-engineering in the Dollart
10 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 centimeters 4. 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 Climate (Ex) Change – Eco-engineering in the Dollart
11 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.
Climate (Ex) Change – Eco-engineering in the Dollart
12 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
Climate (Ex) Change – Eco-engineering in the Dollart
13 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
Climate (Ex) Change – Eco-engineering in the Dollart
14 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.
Climate (Ex) Change – Eco-engineering in the Dollart
15
Legend properties 1. Foreshore 1 Foreshore 2 1.1 Width of marshes, measured Seaside right angled from cross 1.1 1.2 1.3 2.1 2.2 2.3 2.4 2.6 2.7 2.8 2.9 3.1 section 1.2 Utilization foreshore Cross section 1.3 Management 2. Embankment 1 0 m N,C PP GC, CS 7,25 6,5 0,75 G As SH 1,00 N 2.1 Revetment materials 2 0 m N,C PP GC, CS 7,32 6,5 0,82 G As SH 1,00 N 2.2 Crest height 3 0 m N,C PP GC, CS 8,17 6,5 1,67 G As SH 0,90 N 2.3 Review level 4 100 m N,C PP GC, CS 7,50 6,5 1,00 G As SH 0,90 A 2.4 Allowance: distance between 5 200 m N,C PP GC, CS 8,15 6,5 1,65 G As SH 0,90 A crest height and review level 2.6 Vegetation 6 400 m N,C PP GC, CS 7,81 6,5 1,31 G As SH 0,90 A 2.7 Road types on the 7 400 m N,C PP GC, CS 7,95 6,6 1,35 G As SH 0,90 A embankment 8 500 m N,C PP GC, CS 7,86 6,6 1,26 G As SH 0,95 A 2.8 Management type 9 450 m N,C PP GC, CS 7,87 6,6 1,27 G As SH 0,95 A 2.9 Significant wave height H s [m] 10 550 m N,C PP GC, CS 8,63 6,6 2,03 G As SH 0,95 A Ag Agriculture 11 850 m N,C PP GC, CS 8,52 6,6 1,92 G As SH 0,95 A As Asphal t 12 1100 m N,C SHGL GC, CS 8,04 6,6 1,44 G As SH 1,00 A C Cattle breeding 13 900 m N,C SHGL GC, CS 8,34 6,7 1,64 G As SH 1,10 A CS Copper Slag 14 1000 m N,C SHGL GC, CS 9,37 6,7 2,67 G As SH 1,10 A G Grass GC Grass Concrete Blocks 15 1000 m N,C SHGL GC, CS 9,09 6,7 2,39 G As SH 1,10 A N Nature development 16 900 m N,C SHGL GC, CS 9,04 6,7 2,34 G As SH 1,10 A PP Private property 17 800 m N,C SHGL GC, CS 9,04 6,7 2,34 G As SH 1,10 A SH Sheep 18 450 m N,C SHGL GC, CS 9,22 6,7 2,52 G As SH 1,15 A SHGL Stichting Het Groninger 19 0 m N,C SHGL GC, CS 9,22 6,7 2,52 G As SH 1,15 A Landschap Table 2: Legend Table 1: Analysis of the cross sections
Climate (Ex) Change – Eco-engineering in the Dollart
16 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 research 5 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 waves 6 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) Climate (Ex) Change – Eco-engineering in the Dollart
17
• Revetment • Crest height • Review level • Allowance
• Significant wave height (H s) • 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 show 7. 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 Climate (Ex) Change – Eco-engineering in the Dollart
18
The crest height C is defined as C=a+b+c+d+e+f 8. 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 1/4000 9.
Profile 4: a=6,5 m +NAP Profile 10: a=6,6 m +NAP Profile 14: a=6,7 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 +NAP 10 . 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 Climate (Ex) Change – Eco-engineering in the Dollart
19 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, seiches 11 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: H m0 , T m-1,0 2. Calculate influence factor for angle of wave attack γ β 3. Adjust wave conditions if ß>80° 4. Calculate average slope, tan α
5. Calculate z 2%,smooth (smooth: for γ b=1 and γ f=1) 6. Calculate influence factor for roughness on slope γ f 7. Calculate z 2%,rough (rough for: γ b=1) 8. Calculate influence factor for berms γ b
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 Climate (Ex) Change – Eco-engineering in the Dollart
20 9. Calculate 2% wave run-up
10. Calculate γ β for wave overtopping 11. Calculate wave overtopping with above γ b and γ f 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= (1,5H m0 + z 2% ) / (L slope -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 – Eco-engineering in the Dollart
21
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 es the influence of increases overtopping flow 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 ove rtopping 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 cres t 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 overtopping in the Ems Dollart region. The 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 on the wave overtopping (see Figure 3 and Figure 4). T he current loads on the inner slope are important and the 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 ers. The results will be analyzed and compared. The analysis should make clea r which parameters influence wave overtopping the most.
Climate (Ex) Change – Eco-engineering in the Dollart
22 For the calculation the three profiles mentioned in paragraph 2.2.2 are worked out:
• Profile 4 Crest height 7.51m • Profile 10 Crest height 8.35m • Profile 14 Crest height 9.37m
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 T m-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 H m0 =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 z 2% > 1,5x H m0 . 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 z 2% or the 1,5x H m0 . 4. The final wave run-up z 2% =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=0,04m 2/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=0,0001m 2/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 – Eco-engineering in the Dollart
23 the capacity of the inner slope. The requirements for wave overtopping change, because of the already perform ed research . 7. Volume of overtopping wave per linear meter of the crest V=4,77m 3/m. So the total volume 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 tual overtopping waves 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 olume of wave overtopping will be explained. In Table 3 and Figure 5 the results for the overtopping discharge and volume can be seen.
Grass Armorflex Elastocoast Hcrest Profile [m] q V q V V q [m2/s] [m2/s] [m3/m] [m2/s] [m3/m] [m3/m]
4 7,51 0,16 10,65 0,136 10,38 0,08 9,6
10 8,35 0,0088 4,49 0,005 3,95 0,024 2,67
14 9,37 0,00535 1,11 0,00304 0,83 0,000603 0,34
Table 3: 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 12
10
8
6 Grass Armorflex V [m3/m] --> [m3/m] V 4 Elastocoast 2
0 7 7,5 8 8,5 9 9,5 Hcrest [m] -->
Figure 5: Relation between the volume of wave overtopping and the crest height
Climate (Ex) Change – Eco-engineering in the Dollart
24 • If the height of the crest increases, the volume o f overtopping waves decreases. The crest height is sensit 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 whi 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 unknown. But the outcome for other revetments w ould 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 ab ove the requirements. 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 formula can be seen in Figure 6. The average slope is needed to determine the wave run -up and eventually the volume of wave overtopping. The formula is an approach of the characteristic slope of the dike. The outcome for the volum e of wave overtopping can be seen in Figure 7 until Figure 10.
Figure 6: Determination of the characteristic slope for a cross section consisting of different slopes
Relation between wave run -up and length of the "average" slope of the dike 14 12 12,47 10 8 6
Z2% [m] [m] --> Z2% 4 3,86 2,05 2 1,34 0,98 0 0 5 10 15 20 25 30
L slope [m] -->
Figure 7: Relation between wave run-up and length of the “average” slope of the dike
Climate (Ex) Change – Eco-engineering in the Dollart
25 • 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 slope becomes gentler.
Relation between the volume of overtopping waves and the length of the "average" slope of the dike 50 41,28 40
30 20,76 20 9,18 V [m3/m] [m3/m] --> V 10 1,47 3,77 0 0 5 10 15 20 25 30
L slope [m] -->
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 over the crest of the dike. • The rela tion 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 L.
Relation between the wave run -up and the bermwidth 18 16 16,3 14 11,26 12 10 8,35 8 6,49 5,24
Z2% [m] [m] --> Z2% 6 4,35 3,18 3,69 4 2 0 0 2 4 6 8
B [m] -->
Figure 9: 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.
Climate (Ex) Change – Eco-engineering in the Dollart
26 Relation between the volume of overtopping waves and the bermwidth 6 5 4,77 3,98 4 3,31 2,75 3 2,28 1,89 2 1,56 1,29 V [m3/m] V --> 1 0 0 2 4 6 8 B [m] -->
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 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 in the Dollart are under the SWL. Therefore we say the berm has no influence on the ov 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 i ncreases when the slope length increases and the bermwidth decreases. It can be explained by the formula in Figure 6. The height between the wave run -up and significant wave height is divided by the difference between the length and the width (L slope -B) of the slope and berm. If L gets larger and B st ays the same, the height is divided to a bigger number and 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 will be 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 the width of the berm accounts for wave run-up it could be logical. The berm is almost horizontally and therefor e the water won’t transfer its 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. 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. Thi s observation sounds so unlikely that more research need s to be performed. It is possible that a mistake has been made in the manual calculation. Therefore the calculation has to be done with the program of PC-overtopping.
Climate (Ex) Change – Eco-engineering in the Dollart
27 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.
Relation between the angle of wave attack and volume of overtopping waves 6
5
4
3
V [m3/m] [m3/m] --> V 2
1
0 0 20 40 60 80 100
β -->
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.
Climate (Ex) Change – Eco-engineering in the Dollart
28 Relation between SWL and the wave run -up 3,5 3 2,5 2 1,5 Z2% [m] --> [m]Z2% 1 0,5 0 5 5,5 6 6,5 7 7,5 8
SWL [m] -->
Figure 12 : Relation between SWL and the wave run -up
• Figure 12 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 calculation of the average slope is left out of consideration. Also, the increase of the significant wave height [H s ] is neglected.
Relation between the volume of overtopping waves and review level 16 14 12 10 8 6
V [m3/m] [m3/m] --> V 4 2 0 4 5 6 7 8 9
SWL [m] -->
Figure 13 : Relation between the volume of overtopping waves and review level
Climate (Ex) Change – Eco-engineering in the Dollart
29 • 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.
Relation between the volume of overtopping waves and the significant wave height 35 30 25 20 15
V [m3/m] [m3/m] --> V 10 5 0 0 0,5 1 1,5 2 2,5 3 3,5
Hm0 [m] -->
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.
Climate (Ex) Change – Eco-engineering in the Dollart
30 Profile 4
Current hydraulic conditions Input Result Requirement Required z2%
Hm0 :0,9 m q [l/s/m] height f [m] [m]
Tp :3,1 s 0.1 1.461 β :0 o 1.0 1.046 SWL :6,5 m 5.0 0.756 1,35 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
Current hydraulic conditions 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 Requirement Required z2%
Hm0 :1,0 m q [l/s/m] height f [m] [m]
Tp :3,3 s 0.1 1,87 β :0 o 1.0 0,99 SWL :6,6 m 5.0 1 1,7 10 0,84 100 0,32 Table 5: Results calculation profile 10 with current hydraulic conditions
Climate (Ex) Change – Eco-engineering in the Dollart
31
Future hydraulic conditions Input Result Requirement Needed z2%
Hm0 :1,0 m q [l/s/m] height f [m] [m]
Tp :3,3 s 0.1 1,87 β :0 o 1.0 1,35 SWL :7,8 m 5.0 0,99 1,7 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
Current hydraulic conditions 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 Requirement Needed z2%
m0 :1,1 m [l/s/m] height [m] [m]
Tp :3,4 s 0.1 1,83 β :0 o 1.0 1,33 SWL :6,7 m 5.0 0,98 1,64 10 0,83 100 0,33 Table 7: Results calculation profile 14 with current hydraulic conditions
Future hydraulic conditions Input Result Requirement Needed z2%
Hm0 :1,1 m [l/s/m] height [m] [m]
Tp :3,4 s 0.1 1,83 β :0 o 5.0 1,33 SWL :7,9 m 1.0 0,98 1,64 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 – Eco-engineering in the Dollart
32 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 9 represent the 19 considered cross sections in the Dutch part of 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 13 . Due to settlement, the embankments body subsided with different speeds, resulting in the different crest heights. It could be concluded that at the West side of the Dollart , where wind and wave attacks are lowest, the dike body has settled the most. In the South, set tlements are less, but still the crest height lowered with 1 to 2 meters in 40 years. The soil subsidence can be seen in Figure 16.
13 K. Lentz, 2010, Waterboard Hunze en Aa’s Climate (Ex) Change – Eco-engineering in the Dollart
33
Figure 16 : Soil subsidence in the North of Groningen (‘Daling’ means su bsidence in Dutch)
Another factor that plays a role in the settlement of the dikes is gas extraction, of which the center is situated Southwest of the Dol lart . This also clarifies the increase in settlemen t on the Westside of the Dollart, which is situate d in the range of influence of the gas extraction point, where t he Southern parts of the Dollart are just outside that range. The exact settlement due to g as extraction in the Dollart region is difficult to predict, but ranges between 5 and 20 centimeters. Expectations are that 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 allowance is the difference 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 on the West side of the Dolla rt, which covers cross section 1 till 10 (horizontal).
Freeboard (distance between the review level and the crest of the dike) 3,00 2,500 2,00 1,500 1,00
Freeboard--> [m] ,500 ,00 0 2 4 6 8 10 12 14 16 18 20 Profiles -->
Figure 17 : Freeboard (distance between the review level and the crest)
14 J.E. P ôttgens, 1991, Land Subsidence Due to Gas Extraction in the Northern Part of The Netherlands Climate (Ex) Change – Eco-engineering in the Dollart
34 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.
Climate (Ex) Change – Eco-engineering in the Dollart
35 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 – Eco-engineering in the Dollart
36
Figure 19 : German construction methods
Figure 20: Current German dike structure
2.3 Conclusions Chapter 2 analysis of the Dollart Coast
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 p 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 al ong the coast. • The embankment is uniform in design. • The Western shoreline is more subsided because its situated closer to the center of gas extraction Climate (Ex) Change – Eco-engineering in the Dollart
37 • 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.
Climate (Ex) Change – Eco-engineering in the Dollart
38 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.
Climate (Ex) Change – Eco-engineering in the Dollart
39 • 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. Climate (Ex) Change – Eco-engineering in the Dollart
40 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).
Climate (Ex) Change – Eco-engineering in the Dollart
41 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.
Climate (Ex) Change – Eco-engineering in the Dollart
42 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.
Climate (Ex) Change – Eco-engineering in the Dollart
43 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.
Climate (Ex) Change – Eco-engineering in the Dollart
44 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 CO 2 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: Climate (Ex) Change – Eco-engineering in the Dollart
45
• 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 – Eco-engineering in the Dollart
46 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 s Vetiver or a combination of Vetiver and hard revetment. The grass can cover t he dike surface s like the berm, crown and inner slope.
Important aspects of Vetiver 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 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 • Medi um growth in salty environm ent • Intolerant to shading • It’s a typical tropical grass. Best pe rformance in a warm environment • Vetiver hedges are a natural soft eco -engineering and a good alternative to hard structures • Application of Vetiver on the slope of a dike has lower costs compar ed to many other technologies • Long-term maintenance costs are low
Evaluation Vetiver Nature development Vetiver can contribute to nature development because it creates a new environment with vegetation which provides shelter and food for spec ific plants and animals. No artificial materials have to be used.
Safety 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 sp ecies used as revetment. Vetiver gives the slope of dikes a high roughness
Climate (Ex) Change – Eco-engineering in the Dollart
47 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 grass 15 . 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 Climate (Ex) Change – Eco-engineering in the Dollart
48 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 15m 2 area with
Climate (Ex) Change – Eco-engineering in the Dollart
49 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 Climate (Ex) Change – Eco-engineering in the Dollart
50
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. Climate (Ex) Change – Eco-engineering in the Dollart
51 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.
Climate (Ex) Change – Eco-engineering in the Dollart
52 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.
Climate (Ex) Change – Eco-engineering in the Dollart
53 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.
Climate (Ex) Change – Eco-engineering in the Dollart
54 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.
Climate (Ex) Change – Eco-engineering in the Dollart
55 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.
Climate (Ex) Change – Eco-engineering in the Dollart
56
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.
Climate (Ex) Change – Eco-engineering in the Dollart
57 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.
Climate (Ex) Change – Eco-engineering in the Dollart
58 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. Climate (Ex) Change – Eco-engineering in the Dollart
59 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 – Eco-engineering in the Dollart
60 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 1 to 5 where 1 equals a negative effec t and 5 equals a positive effect.
The header materials 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 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 are not included in the multi-criteria analysis because they don’t have a significant ef fect on the most important issues: safety and nature development.
Analyzed materials 1. No different material used 6. Vetiver 2. Bundle of piles 7. Elastocoast 3. Eco Xbloc’s 8. Hydrotex Articulating Blocks 4. Armorflex 9. Smart Grass Reinforcement 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 correspo nd with the numbers mentioned above for the materials and the methods.
Figure 36 : MCA for the materials and methods applied in section 1
Climate (Ex) Change – Eco-engineering in the Dollart
61
Figure 37: MCA for the materials and methods applied in sectio n 2
Figure 38: MCA for the materials and methods applied in section 3
Figure 39: MCA for the materials and methods applied in section 4
3.5.1 Conclusions MCA’s • Hard revetments score high on nature developm ent in section 1, but low in sections 2,3 and 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 ose their contribution to nature development. • Smart Grass Reinforcement scores high in every section. This is because it doesn’t change the 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.
Climate (Ex) Change – Eco-engineering in the Dollart
62 • 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.
Climate (Ex) Change – Eco-engineering in the Dollart
63 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.
Climate (Ex) Change – Eco-engineering in the Dollart
64
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 Location Length trajectory 8000 m
Foreshore Marshes, Natura 2000 area
Wet/dry embankment Dry
Material Material 1 No other material
Material 2 SGR
Method Method 1 Increased overtopping
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.
Climate (Ex) Change – Eco-engineering in the Dollart
65
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 Location Length trajectory 3500 m
Foreshore Marshes, Natura 2000 area
Wet/dry embankment Dry
Material Material 1 SGR
Method Method 1 Increased overtopping
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.
Climate (Ex) Change – Eco-engineering in the Dollart
66
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
Climate (Ex) Change – Eco-engineering in the Dollart
67 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.
Climate (Ex) Change – Eco-engineering in the Dollart
68 Pipe Catch -off diameter Pipe capacity Pipe capacity crest [mm] [m 3/s] frequency [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.
Climate (Ex) Change – Eco-engineering in the Dollart
69 Section 4 Location Length trajectory 11000 m
Foreshore Marshes
Wet/dry embankment Dry
Material Material 1 SGR
Method Method 1 Increased overtopping
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
Climate (Ex) Change – Eco-engineering in the Dollart
70 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. Climate (Ex) Change – Eco-engineering in the Dollart
71
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.
Climate (Ex) Change – Eco-engineering in the Dollart
72 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
Climate (Ex) Change – Eco-engineering in the Dollart
73
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.
Climate (Ex) Change – Eco-engineering in the Dollart
74
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
Climate (Ex) Change – Eco-engineering in the Dollart
75 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.
Climate (Ex) Change – Eco-engineering in the Dollart
76
Climate (Ex) Change – Eco-engineering in the Dollart
77 Appendix 1: Hydraulic conditions Ems-Dollart region
Climate (Ex) Change – Eco-engineering in the Dollart
78 Appendix 2: Tide table Nieuwe Statenzijl
Climate (Ex) Change – Eco-engineering in the Dollart
79 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. Darcy - We isbach e quation
Model for determining the discharge capacity of the pipes.Representative for the discharge of the water in the retention basin
Determine the friction factor
D:= 0.2m Diameter of the pipe
− 3 Factor for the wall roughness k:= 0.1⋅ 10 m Discharge pipes will be made from synthetic Poly Propyleen pipes
0.25 λ := Friction factor 2 D Depends on the wall roughness log 3.7 ⋅ k
λ = 0.017
Determine the flow velocity in the pipe under normal drop
dH:= 8.3m Natural drop pipe line Average height of the dikes at the Dutch side of the Dollart region
L:= 81m Length of the pipe Longest d istance from the crest to the trench, landside of the dike.
m g= 9.807 Gravitational acceleration 2 s
2 2 L v v dH λ⋅ ⋅ + D 2⋅ g 2g
1 1 1 2 2 ⋅2 ⋅() λ⋅L + D ⋅dH ⋅D⋅g ()λ⋅L + D 4.6 m = 1 1 −4.6 s −1 2 2 ⋅2 ⋅() λ⋅L + D ⋅dH ⋅D⋅g ()λ⋅L + D
m v:= 4.6 Flow velocity in the pipe s The negative flow is negligible
Climate (Ex) Change – Eco-engineering in the Dollart
80 Determine the capacity of the pipe
1 2 A := ⋅πD 4
2 Surface of the pipe A= 0.031m
Discharged water through PP pipe per meter of the dike
Q:= v⋅ A Flow capacity of the PP pipe 3 m Q= 0.145 s
Discharged water through PP pipe when the pipes will be installed every 25,50 and 100m
Q liter Q := Q = 5.8 25m 25 25m s
Q liter Q := Q = 2.9 50m 50 50m s
Q liter Q := Q = 1.4 100m 100 100m s
Determine the frequency of the pipe for a wave overtopping of 5 and 15 l/s/m
3 3 − 3 m − 3 m Requirement1:= 5⋅ 10 Requirement2:= 15⋅ 10 ⋅ s s m m
Q Q Freq := Freq := pipe1 Requirement1 pipe2 Requirement2
1 1 Freq pipe1 = 29 Freq pipe2 = 10 m m
Climate (Ex) Change – Eco-engineering in the Dollart
81 Appendix 4: overtopping calculations with CRESS
Calculation dike profile 4 current hydraulic conditions
Input data g : 9.81 m/s 2 wave height : 0.9 m Peak period : 3.087 sec Wave direction : 0 o 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 X-co-ordinaat : 4.42 Y-co-ordinaat : 2.85 Roughness factor : 1 X-co-ordinaat : 16.071 Y-co-ordinaat : 7.011 Roughness factor : 1 X-co-ordinaat : 22.01 Y-co-ordinaat : 7.509 Roughness factor : 1
Output data Needed crest height 5.0 l/s/m : 0.756 m Needed crest height 0.1 l/s/m : 1.461 m Needed crest height 1.0 l/s/m : 1.046m Needed crest height 10 l/s/m : 0.632 m Needed crest height 100 l/s/m : 0.217 m
Volume overtopping wave exceed in x : 0.117 m 3/m Volume overtopping wave exceed 1% : 0.208 m 3/m Volume overtopping wave exceed 10% : 0.082 m 3/m Volume overtopping wave exceed 50% : 0.016 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.
Climate (Ex) Change – Eco-engineering in the Dollart
82 Calculation dike profile 10 current hydraulic conditions
Input data g : 9.81 m/s 2 wave height : 1.0 m Peak period : 3.254 sec Wave direction : 0 o Horizontal water level : 7.8 m X-position toe :0 m Y-position toe : 2.034 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 ` : 3
X-co-ordinaat : 3.226 m Y-co-ordinaat : 2.988 m Roughness factor : 1 m X-co-ordinaat : 6.042 m Y-co-ordinaat : 3.38 m Roughness factor : 1 m X-co-ordinaat : 26.985 m Y-co-ordinaat : 8.351 m Roughness factor : 1 m entage volume : 5%
Output data Needed crest height 5.0 l/s/m : 0.991 m Needed crest height 0.1 l/s/m : 1.869 m Needed crest height 1.0 l/s/m : 1.353 m Needed crest height 10 l/s/m : 0.836 m Needed crest height 100 l/s/m : 0.319 m
Volume overtopping wave exceed in x : 0.588 m3/m Volume overtopping wave exceed 1% : 1.044 m3/m Volume overtopping wave exceed 10% : 0.414 m3/m Volume overtopping wave exceed 50% : 0.017 m3/m Volume of highest overtopping wave : 2.351 m3/m
2%-wave run-up height : 1.688 m
Remark:
Climate (Ex) Change – Eco-engineering in the Dollart
83 Calculation dike profile 10 future hydraulic conditions
Input data g : 9.81 m/s 2 wave height : 1.0 m Peak period : 3.254 sec Wave direction : 0 o Horizontal water level : 6.6 m X-position toe :0 m Y-position toe : 2.034 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 : 3
X-co-ordinaat : 3.226 m Y-co-ordinaat : 2.988 m Roughness factor : 1 m X-co-ordinaat : 6.042 m Y-co-ordinaat : 3.38 m Roughness factor : 1 m X-co-ordinaat : 26.985 m Y-co-ordinaat : 8.351 m Roughness factor : 1 m
Output data Needed crest height 5.0 l/s/m : 0.991 m Needed crest height 0.1 l/s/m : 1.869 m Needed crest height 1.0 l/s/m : 1.353 m Needed crest height 10 l/s/m : 0.836 m Needed crest height 100 l/s/m : 0.319 m
Volume overtopping wave exceed in x : 0.123 m3/m Volume overtopping wave exceed 1% : 0.219 m3/m Volume overtopping wave exceed 10% : 0.087 m3/m Volume overtopping wave exceed 50% : 0.017 m3/m Volume of highest overtopping wave : 0.224 m3/m
2%-wave run-up height : 1.688 m
Remark: The 2%-wave run-up is higher than the dike.
Climate (Ex) Change – Eco-engineering in the Dollart
84 Calculation dike profile 14 current hydraulic conditions
Input data g : 9.81 m/s 2 wave height : 1.1 m Peak period : 3.413 sec Wave direction : 0 o Horizontal water level : 6.7 m X-position toe :0 m Y-position toe : 2.454 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 : 3
X-co-ordinaat : 1.896 m Y-co-ordinaat : 2.973 m Roughness factor : 1 m X-co-ordinaat : 5.074 m Y-co-ordinaat : 3.435 m Roughness factor : 1 m X-co-ordinaat : 33.402 m Y-co-ordinaat : 9.372 m Roughness factor : 1 m
Output data Needed crest height 5.0 l/s/m : 0.981 m Needed crest height 0.1 l/s/m : 1.834 m Needed crest height 1.0 l/s/m : 1.332 m Needed crest height 10 l/s/m : 0.830 m Needed crest height 100 l/s/m : 0.328 m
Volume overtopping wave exceed in x : 0.000 m3/m Volume overtopping wave exceed 1% : 0.000 m3/m Volume overtopping wave exceed 10% : 0.000 m3/m Volume overtopping wave exceed 50% : 0.000 m3/m Volume of highest overtopping wave : 0.000 m3/m
2%-wave run-up height : 1.64 m
Remark:
Climate (Ex) Change – Eco-engineering in the Dollart
85 Calculation dike profile 14 future hydraulic conditions
Input data g : 9.81 m/s 2 wave height : 1.1 m Peak period : 3.413 sec Wave direction : 0 o Horizontal water level : 6.7 m X-position toe :0 m Y-position toe : 2.454 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 : 3
X-co-ordinaat : 1.896 m Y-co-ordinaat : 2.973 m Roughness factor : 1 m X-co-ordinaat : 5.074 m Y-co-ordinaat : 3.435 m Roughness factor : 1 m X-co-ordinaat : 33.402 m Y-co-ordinaat : 9.372 m Roughness factor : 1 m
Output data Needed crest height 5.0 l/s/m : 0.981 m Needed crest height 0.1 l/s/m : 1.834 m Needed crest height 1.0 l/s/m : 1.332 m Needed crest height 10 l/s/m : 0.830 m Needed crest height 100 l/s/m : 0.328 m
Volume overtopping wave exceed in x : 0.133 m3/m Volume overtopping wave exceed 1% : 0.237 m3/m Volume overtopping wave exceed 10% : 0.094 m3/m Volume overtopping wave exceed 50% : 0.019 m3/m Volume of highest overtopping wave : 0.317 m3/m
2%-wave run-up height : 1.64 m
Remark: The 2%-wave run-up is higher than the dike.
Climate (Ex) Change – Eco-engineering in the Dollart
86 Calculation dike profile 14 future hydraulic conditions with slope 1:6
Input data g : 9.81 m/s 2 wave height : 1.1 m Peak period : 3.413 sec Wave direction : 0 o Horizontal water level : 6.7 m X-position toe :0 m Y-position toe : 2.454 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 : 3
X-co-ordinaat : 1.896 m Y-co-ordinaat : 2.973 m Roughness factor : 1 m X-co-ordinaat : 5.074 m Y-co-ordinaat : 3.435 m Roughness factor : 1 m X-co-ordinaat : 40.732 m Y-co-ordinaat : 9.372 m Roughness factor : 1 m
Output data Needed crest height 5.0 l/s/m : 0.759 m Needed crest height 0.1 l/s/m : 1.437 m Needed crest height 1.0 l/s/m : 1.038 m Needed crest height 10 l/s/m : 0.639 m Needed crest height 100 l/s/m : 0.241 m
Volume overtopping wave exceed in x : 0 m3/m Volume overtopping wave exceed 1% : 0 m3/m Volume overtopping wave exceed 10% : 0 m3/m Volume overtopping wave exceed 50% : 0 m3/m Volume of highest overtopping wave : 0 m3/m
2%-wave run-up height : 1.30 m
Remark: The 2%-wave run-up is higher than the dike
Climate (Ex) Change – Eco-engineering in the Dollart
87 Calculation dike profile 14 future hydraulic conditions with slope 1:8
Input data g : 9.81 m/s 2 wave height : 1.1 m Peak period : 3.413 sec Wave direction : 0 o Horizontal water level : 6.7 m X-position toe :0 m Y-position toe : 2.454 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 : 3 m X-co-ordinaat : 1.896 m Y-co-ordinaat : 2.973 m Roughness factor : 1 m X-co-ordinaat : 5.074 m Y-co-ordinaat : 3.435 m Roughness factor : 1 m X-co-ordinaat : 52.186 m Y-co-ordinaat : 9.372 m Roughness factor : 1 m
Output data Needed crest height 5.0 l/s/m : 0.557 m Needed crest height 0.1 l/s/m : 1.069 m Needed crest height 1.0 l/s/m : 0.767 m Needed crest height 10 l/s/m : 0.466 m Needed crest height 100 l/s/m : 0.164 m
Volume overtopping wave exceed in x : 0 m3/m Volume overtopping wave exceed 1% : 0 m3/m Volume overtopping wave exceed 10% : 0 m3/m Volume overtopping wave exceed 50% : 0 m3/m Volume of highest overtopping wave : 0 m3/m
2%-wave run-up height : 0.99 m
Remark: The 2%-wave run-up is higher than the dike
Climate (Ex) Change – Eco-engineering in the Dollart
88 Appendix 5: Calculation wave periods
Wave period 0.9 m Calculation pe ak pe riod
Hi := 0.9m ()2 π⋅ ⋅Hi T := p 0.05g⋅
Tp = 3.396s
Calculation spectral wave period
Tp T := m_1.0 1.1
T = 3.087s m_1.0
Wave period 1.0 m Calculation pe ak pe riod
Hi := 1.0m ()2 π⋅ ⋅Hi T := p 0.05g⋅
Tp = 3.58s
Calculation spectral wave period
Tp T := m_1.0 1.1
T = 3.254s m_1.0
Climate (Ex) Change – Eco-engineering in the Dollart
89 Wave period 1.1 Calculation Piek period
Hi := 1.1m ()2 π⋅ ⋅Hi T := p 0.05g⋅
Tp = 3.754s
Calculation spectral waveperiod
Tp T := m_1.0 1.1
T = 3.413s m_1.0
Climate (Ex) Change – Eco-engineering in the Dollart
90 Appendix 6: Manual calculation 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
Average height of the crest, of all 19 Dutch profiles Hcrest := 8.3m
Rc := Hcrest − SWL Freeboard at the crest, with respect to the Sea water level (SWL) Rc = 1.7m
Significant wave height at the toe of the dike Hm0 := 1.25m
Figure 46: Picture were the freeboard is indicated (free crest height for wave overtopping)
• Influence factor for the roughness of the top layers of the dike revetment during wave overtopping [-] For grass revetments, the grass has no influence on the roughness γf.grass := 1 For Armorflex γf.armorflex := 0.9
γ := 0.7 Lowest roughness factor for elastocoast products f.elastocoast
• 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− 0.0022 β⋅ Influence factor for the angle of wave attack γβ = 1
Climate (Ex) Change – Eco-engineering in the Dollart
91
Figure 47: Definition angle of wave attack, red line indicated the angle of attack
m g= 9.81 Gravitation 2 s
Calculate the wave overtopping
Emperical formula TAW formula for wave overtopping at dikes
With the maximum:
Rc 1 − 2.3 ⋅ ⋅ q Hm0 γf.gras ⋅γβ 0.2⋅ e 3 g⋅ Hm0
Solve the wave overtopping
For grass
1 R 2 c 3 qgrass := .20⋅ exp − 2.3 ⋅ ⋅ g⋅ Hm0 Hm0 ⋅γf.grass ⋅γβ 2 m q = 0.04 The average overtopping discharge, m3 / m per second grass 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
2 − 4 m q := 1⋅ 10 Current requirements for wave overtopping discharge current s 2 − 3 m q := 1.0⋅ 10 New requirement for wave overtopping discharge new s 2 − 3 m q := 5.0⋅ 10 Possible requirement for wave overtopping discharge new.maybe s
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
Climate (Ex) Change – Eco-engineering in the Dollart
92
For Armorflex
1 R 2 c 3 qarmorflex := .2⋅ exp − 2.3 ⋅ ⋅ g⋅ Hm0 Hm0 ⋅γf.armorflex⋅γβ
2 m The average overtopping discharge, m3 / m per second qarmorflex = 0.027 s
For Elastocoast
1 R 2 c 3 qelastocoast := .2⋅ exp − 2.3 ⋅ ⋅ g⋅ Hm0 Hm0 ⋅γf.elastocoast ⋅γβ
2 m The average overtopping discharge, m3 / m per second qelastocoast = 0.01 s
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
Average wave period Tm := 1s
2 m q = 0.038 The average overtopping discharge, m3 / m per second grass s
hk := Rc freeboard, crest height with respect to the SWL h = 1.7m k
Climate (Ex) Change – Eco-engineering in the Dollart
93
Determine the wave run-up
Influence factor for the angle of wave attack γβ = 1 Influence factor for grass revetments γf.grass = 1
Influence factor for the berm of the dike. In this calculation is γb := 1 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
• Calculation piek period
Hi := 1.0m
()2 π⋅ ⋅Hi Formula to calculate the wave piek period T := p 0.05g⋅
Peak period Tp = 3.58s
• Calculation spectral period
Tp T := Spectral wave period m_1.0 1.1
Tm_1.0 = 3.25s
• Calculation of the wave steepness
2 π⋅ ⋅Hm0 s := 0 2 g⋅ Tm_1.0 Wave steepness [no dimension] s = 0.08 0
Climate (Ex) Change – Eco-engineering in the Dollart
94 • Determine the representative angle of the upper slope of the dike at the seaside
Significant wave height at the toe of the dike Hm0 = 1.25m Horizontal length between two points 1,5xHm0 above and Lslope := 11.3m under the review level on a slope of 1:3
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 ()1.5⋅ Hm0 + 1.5⋅ Hm0 tan ()α account. Only the wave run-up is not yet determined. ()Lslope − B For z2%, 1,5xHm0 can be taken into account for a first estimate.
Hm0 α1 := −1. ⋅atan 3. ⋅ ()−1. ⋅Lslope + B
α1 = 0.32 Angle of the average slope
tan α = 0.33 ()1
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.
Climate (Ex) Change – Eco-engineering in the Dollart
95 • Determine the breaker parameter
tan ()α1 ξ0 := 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 z2% General formula for the wave run-up 1.75 ⋅γb⋅ γf⋅ γβ⋅ ξ0 Hm0 z2%1 := ()1.75 ⋅γb⋅ γf.grass ⋅ γβ⋅ ξ0 ⋅Hm0 Wave run-up above the sea water level z = 2.64m 2%1
Second estimate: Improved approach for the average slope of the dike
• Determine the representative angle of the upper slope of the dike at the seaside
()1.5⋅ Hm0 + z2%1 tan ()α ()Lslope − B
()3.⋅ Hm0 + 2.⋅ z2%1 α2 := −1. ⋅atan .50 ⋅ ()−1. ⋅Lslope + B
α2 = 0.38 Angle of the average slope tan ()α2 = 0.4
• Determine the breaker parameter tan ()α2 ξ0 := s0 Breaker parameter
ξ0 = 1.45
• Determine the wave run-up z2%2 := ()1.75 ⋅γb⋅ γf.grass ⋅ γβ⋅ ξ0 ⋅Hm0 Wave run-up above the sea water level z = 3.178m 2%2
Climate (Ex) Change – Eco-engineering in the Dollart
96 • Check if the wave run-up is smaller then the freeboard from the SWL to the crest
Because the run-up needs to be smaller than the freeboard for the determination of the average slope
So if than For the determination of the average slope z2%2 > hk z2%2 := hk and also the wave run-up
In this case the wave run-up exceeds the freeboard at the crest. Therefore 3th estimate for the average slope and wave run-up: • Determine the representative angle of the upper slope of the dike at the seaside
()1.5⋅ Hm0 + hk tan ()α ()Lslope − B
()3.⋅ Hm0 + 2.⋅ hk α3 := −1. ⋅atan .50 ⋅ ()−1. ⋅Lslope + B
α3 = 0.306 Angle of the average slope tan ()α3 = 0.316
• Determine the breaker parameter
tan ()α3 ξ0 := Breaker parameter s0
ξ0 = 1.15
• Determine the wave run-up
z2%3 := ()1.75 ⋅γb⋅ γf.grass ⋅ γβ⋅ ξ0 ⋅Hm0 Wave run-up above the sea water level z = 2.517m 2%3
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
2 hk Rayleigh equation − − ln() 0.02 ⋅ z2%3 Pov := e
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)
Climate (Ex) Change – Eco-engineering in the Dollart
97 • Determine the scale factor This scale factor is needed for the Weibull equation,
qgrass a:= 0.84T⋅ m⋅ Pov 2 a= 0.453m
• Determine the chance that wave overtopping per wave V is greater than or same as V 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.
0.75 V − Weibull equation a P 1− e
The formula to calculate the volume at a certain probability of exceedance
4 3 V a⋅()− ln() 1− P 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
Tp = 3.58s
Time storm := 18000s Estimate of storm duration of 5hours
Time storm N := T Total amount of waves that strike against the dike during a p storm period 3 N= 5.028× 10
Nov P The possibility of wave overtopping, already determined ov N Nov := Pov ⋅ N Number of overtopping waves Nov = 358 So the volume of the overtopping waves will be:
1.33 Alternative formula to calculate the maximum volume. This V:= a⋅() ln() Nov can be used for a first estimate
3 m V= 4.77 Volume of the overtopping waves m
Climate (Ex) Change – Eco-engineering in the Dollart
98 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 contribution contribution needed Score per criteria on a scale of 1 to to nature to coastal contribution surface costs/ 5 development safety to recreation Natura2000 innovation experience origin 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
Climate (Ex) Change – Eco-engineering in the Dollart
99 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
Weight criteria from 1–5 5 5 4 3 1 1 3 2 4 28 contribution contribution contribution needed to nature to coastal to surface costs/ Score per criteria on a scale of 1 to 5 development safety recreation Natura2000 innovation experience origin 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 2 2 1 2 4 2 4 4 1 Bundle of piles 2,14 3. Eco-Xblocks 1 3 2 5 1 5 1 1 1 Eco-Xblocks® 2,07 4. Armorflex 1 2 1 5 2 3 2 1 1 Armorflex® 1,82 5. C-star coastal elements 1 2 1 5 2 4 3 1 2 C-star® coastal elements 2,11 6. Vetiver 2 2 3 5 3 4 1 3 1 Vetiver 2,39 7. Elastocoast 1 2 1 5 3 3 2 1 1 Elastocoast 1,86 8. Hydrotex Articulating Blocks 1 2 1 5 3 2 2 2 1 Hydrotex 1,89 Smart grass 9. Smart grass reinforcement 1 5 1 5 4 2 3 4 4 reinforcement 3,14
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 4 2 1 3 3 3 1 3 Slope changes 2,32 4. Raising dike height 1 4 1 2 1 5 3 2 2 Raising dike height 2,21
Climate (Ex) Change – Eco-engineering in the Dollart
100
Multi criteria analyisis section 3
Multicriteria–analysis of applicable ecological materials and methods Features tarjectory 1: marshes high crest height (+/- 9 m +NAP) slope 1:4
Weight criteria from 1–5 5 5 4 3 1 1 3 2 4 28 contribution contribution needed to nature to coastal contribution surface costs/ Score per criteria on a scale of 1 to 5 development safety to recreation Natura2000 innovation experience origin benefits Applicability Overall score materials 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
Methods Overall score concepts 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
Climate (Ex) Change – Eco-engineering in the Dollart
101 Multi criteria analyse section 4
Multicriteria–analysis of applicable ecological materials and methods Features tarjectory 1: marshes medium crest height (+/- 8 m +NAP) slope 1:6
Weight criteria from 1–5 5 5 4 3 1 1 3 2 4 28 contribution contribution contribution needed to nature to coastal to surface costs/ Score per criteria on a scale of 1 to 5 development safety recreation Natura2000 innovation experience origin 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 2 2 1 2 4 2 4 4 1 Bundle of piles 2,14 3. Eco-Xblocks 1 3 2 5 1 5 1 1 1 Eco-Xblocks® 2,07 4. Armorflex 1 2 1 5 2 3 2 1 1 Armorflex® 1,82 5. C-star coastal elements 1 2 1 5 2 4 3 1 2 C-star® coastal elements 2,11 6. Vetiver 2 2 3 5 3 4 1 3 1 Vetiver 2,39 7. Elastocoast 1 2 1 5 3 3 2 1 1 Elastocoast 1,86 8. Hydrotex Articulating Blocks 1 2 1 5 3 2 2 2 1 Hydrotex 1,89 9. Smart grass reinforcement 1 5 1 5 4 2 3 4 4 Smart grass reinforcement 3,14
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 1 3 3 3 1 3 Slope changes 2,14 4. Raising dike height 1 4 1 2 1 5 3 2 2 Raising dike height 2,21
Climate (Ex) Change – Eco-engineering in the Dollart
102 Appendix 8: Drawings cross-section 4, 10, 14
Climate (Ex) Change – Eco-engineering in the Dollart
103
Climate (Ex) Change – Eco-engineering in the Dollart
104
Climate (Ex) Change – Eco-engineering in the Dollart
105