Master Project Ð Rehabilitation of Holwerd
Written by: Alba Jiménez Moreno 4537750 Arefin Syed Shamsil 4536517 Attman Kar 4537211 Bruna de Queiroz 4535146 María Belén Rada Mora 4475623 Sanduni S. J. Disanayaka Mudiyanselage 4536363
CIE4061-09 Ð Multidisciplinary Project
Delft University of Technology
Document title Rehabilitation of Holwerd Date 6th of June, 2016
Students Alba Jiménez Moreno 4537750 Arefin Syed Shamsil 4536517 Attman Kar 4537211 Bruna de Queiroz 4535146 María Belén Rada Mora 4475623 Sanduni S. J. Disanayaka Mudiyanselage 4536363
Supervision Dr. ir. B. Hofland Ir. M. A. Burgmeijer
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Preface
This report titled “Rehabilitation of Holwerd” is written and submitted by our group consisting of Alba Jiménez Moreno, Arefin Syed Shamsil, Attman Kar, Bruna de Queiroz, María Belén Rada Mora and Sanduni Disanayaka Mudiyanselage.
This document summarizes our research study during the complete project, undertaken in the light of CIE4061-09 Ð Multidisciplinary Project.
We want to sincerely thank Dr.ir. Bas Hofland for his support and are grateful for the help received by the Architecture students following AR1LA050.
This report was written entirely by our group members and has not received any previous academic credit at this or any other academic institution.
Delft, 6th of June, 2016
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Executive Summary
Holwerd is a village located at the coast of the Wadden Sea. Decisions made in the past have affected the town in a negative manner leading to an impoverishment of the region. Therefore, we were tasked with rehabilitating the city of Holwerd by establishing the connection with the sea and making the goal (Holwerd aan Zee) of the inhabitants come into a reality. In order to prioritize the different actions required to achieve the objective, a survey was conducted. Hence, a clearer view of what people are attracted to when choosing a destination is obtained. It was found that the most attractive option is the one that includes recreational elements (proximity to the sea restaurants and bars, hotels...), natural elements (parks, open spaces...) as well as cultural elements (museums, architecture…). Due to the high cost of this alternative, the project is divided into phases. In addition, an Environmental Impact Assessment was conducted to ensure a well-balanced project implementation. In this multidisciplinary project, the focus is mainly on the construction of the navigational channel through the dike connecting to a buffer lake. Together with the channel, the implementation of a sluice in the opening of the dike is also analysed. Through a multi-criteria evaluation each alternative of channel alignment and gates is assessed. These multi-criteria analyses determined that the optimal solution is to connect the navigational channel to a fresh water source where a canal and a small marina were already present. Regarding the type of gate, it resulted that the folding gate made of timber was the most suitable to be installed both in the dike side and in the inner side blocking the salt water flowing further into the fresh water. The design of the channel was developed in such a way that an ebb-dominance tendency is present. The exporting of sediment was checked by using a one-dimensional model with a sinusoidal symmetric tide. The gate prototype was also modelled to ensure the structure can resist the different water levels. Regarding the dredged material of the channel, two proposals are evaluated in order to find a beneficial use of the remaining volume. A nourishment and development of salt marshes in Visbuurt (adjacent town of Holwerd) as well as the creation of the silt islands and development of salt marshes in Holwerd are studied. The dredging operation is also described. Finally, additional research and data collection are recommended prior to further action.
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Table of Contents Preface ...... iii Executive Summary ...... iv List of Figures ...... viii List of Tables ...... xi 1. Introduction ...... 1 1.1. Problem Definition ...... 1 1.2. Holwerd aan Zee Project ...... 2 1.3. Main Objective ...... 4 1.4. Design Approach ...... 4 2. Site Review and Stakeholder Analysis ...... 5 2.1. Site Review ...... 5 2.1.1. Overview ...... 5 2.1.2. Topography ...... 5 2.1.3. Land Use ...... 6 2.1.4. Soil Characteristics ...... 7 2.1.5. Infrastructure ...... 8 2.2. Stakeholder Analysis ...... 8 3. Preliminary Research ...... 11 3.1. Astronomical Tide ...... 11 3.2. Wind ...... 11 3.3. Currents ...... 12 3.4. Waves ...... 13 3.5. Sea Level Rise Ð Estimation from IPCC AR5 ...... 14 3.6. Design Ship ...... 14 3.7. Traffic Analysis ...... 15 4. Conceptual Design ...... 17 4.1. General objective ...... 17 4.2. Possible Alternatives ...... 17 4.2.1. Survey ...... 17 4.2.2 Alternatives ...... 17 4.3. Evaluation of Alternatives ...... 19 4.3.1. Analysis of Results ...... 20 4.4. Master Plan and Phasing ...... 20 4.4.1. A Door to the Wadden Sea ...... 20
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4.4.2 Phasing ...... 22 5. Overview of the main elements ...... 28 5.1. General Objective ...... 28 5.2. Boundary Conditions ...... 29 5.3. Channel ...... 29 5.3.1. Alternatives ...... 29 5.3.2. Evaluation of Alternatives ...... 32 5.3.3. Multi Criteria Analysis (MCA) ...... 33 5.4. Sluices ...... 41 5.4.1. Navigational Lock ...... 41 5.4.1 Guard Lock/Storm Surge Barrier ...... 42 5.4.2 Canal Lock ...... 42 5.4.3 Types of Locks Selected ...... 42 5.4.4 Alternatives for Guard Lock ...... 43 5.4.5 MCA for Guard Lock Gate ...... 45 5.4.6 Alternatives Canal Lock ...... 47 5.4.7 MCA Canal Lock Gate ...... 48 6. Channels ...... 50 6.1. Basis of Design ...... 50 6.2. Design of Channel Elements ...... 50 6.2.1. Embankment of the Channel ...... 50 6.2.2. Width of Channels ...... 52 6.2.3. Depth of Navigational Channel ...... 57 6.2.4. Selection of Embankment ...... 59 6.2.5. Dimensions of the Outer and Inner Channel ...... 59 6.2.6. Water Level in the Outer and Inner Channel ...... 64 6.2.7. Storage Area Approach ...... 65 6.2.8. Wind Induced Wave Growing ...... 67 6.2.9. Velocity in the Channel ...... 67 7. Sluices ...... 71 7.1. Design of the Lock ...... 71 7.2. Basis of Design ...... 72 7.3. Closure of Gates ...... 73 7.4. Material and sections ...... 74 7.5. Analysis of Forces ...... 74 7.5.1. Storm Surge Scenario ...... 75
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7.5.2. Flushing Scenario ...... 78 7.6. Foundation of the Lock ...... 80 8. Dredging Operation ...... 81 8.1. Alternative 1 ...... 81 8.2. Alternative 2 ...... 83 8.3. Dredging Operation Ð Alternative 1 ...... 85 9. Environmental Impact Assessment ...... 87 9.1. Wadden Sea Conservation Area ...... 87 9.2. Potential Impacts ...... 89 9.2.1. Physical Impacts ...... 89 9.2.2. Biological Impacts ...... 90 9.2.3. Socio-economic Impacts ...... 90 9.3. Mitigation Measures ...... 91 9.4. Quantification of Environmental Impacts ...... 92 9.4.1. Environmental Importance (I) ...... 93 9.5. Evaluation of the Chosen Alternative ...... 93 10. Further Recommendations ...... 95 11. Conclusion ...... 97 12. References ...... 98 Appendix A. Field Report ...... 101 Appendix B. Table of Harmonic Components of Holwerd’s Area ...... 105 Appendix C. Master Plan Poster Ð A Door to the Wadden Sea ...... 108 Appendix D. Types of Gates ...... 109 Appendix E. Calculation of the Channels’ Dimensions ...... 119 Appendix F. Risk of Overtopping for Inner Dike ...... 121 Appendix G. Management Survey ...... 125 Appendix H. Timber as a Construction Material for Hydraulic Gates ...... 131 Appendix I. Salt Marshes ...... 133 Appendix J. PoT Analysis ...... 134 Appendix K. Consultation fees ...... 136
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List of Figures
Figure 1: Location of Holwerd...... 1 Figure 2: Project interventions...... 3 Figure 3: Project Approach ...... 4 Figure 4: Population characteristics around Holwerd area (Spotzi Nederland, 2016)...... 5 Figure 5: Bathymetry (m NAP) map of the Pier/outer channel area (webapp.navionics.com). 6 Figure 6: Topography referenced to NAP map of buffer lake area (Cadastre, Geoinformation, Zwolle, [2016])...... 6 Figure 7: Land use around Holwerd (PDOK, 2016)...... 7 Figure 8: Soil characteristics around Holwerd (Cadastre, Geoinformation, Zwolle, [2016]). .... 7 Figure 9: Infrastructure around Holwerd (PDOK, 2016)...... 8 Figure 10: Key Stakeholders for 'Rehabilitation of Holwerd'...... 9 Figure 11: Tide Prediction for Holwerd...... 11 Figure 12: Detailed Wind Speed Data around Holwerd...... 12 Figure 13: Wind Rose diagram around Holwerd...... 12 Figure 14: Tidal currents velocities, wind-driven currents, and extreme wind-currents velocities...... 13 Figure 15: SLR estimation ...... 14 Figure 16: Type of vessels arriving/departing Ameland’s port ...... 15 Figure 17: Average arrivals and departures by hour of Ameland Port ...... 16 Figure 18: Evaluation results ...... 19 Figure 19: Regional scale of the proposal ...... 20 Figure 20: Local scale of the proposal ...... 21 Figure 21: Ecological scheme ...... 21 Figure 22: Recreational scheme ...... 22 Figure 23: Plan made by one of the Architecture Groups: A door to the Wadden Sea ...... 24 Figure 24: Possible harbor, market square and camping sites ...... 24 Figure 25: Intended ecological wet network ...... 25 Figure 26: Blue network ...... 25 Figure 27: Schematic section of saltmarshes ...... 26 Figure 28: Interventions to strengthen the ecological network ...... 26 Figure 29: Mild slope for flora and fauna to flourish ...... 27 Figure 30: Otter and its relation to food chain ...... 27 Figure 31: Alternative 1 ...... 30 Figure 32: Alternative 2 ...... 31
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Figure 33: Alternative 3 ...... 32 Figure 34: Main criteria and corresponding alternatives ...... 34 Figure 35: Schematic figure of selected Alternative ...... 41 Figure 36: Channel with a sloping embankment...... 51 Figure 37: Channel with vertical hard embankment...... 52 Figure 38: Width of the maneuverability lane...... 53 Figure 39: Impact of the environmental factors on the vessel path...... 54 Figure 40: Passing distance...... 55 Figure 41: Dimensions of width of the channel in Alternative 1...... 56 Figure 42: Dimensions of channel in Alternative 2...... 57 Figure 43: Fully Restricted Channel...... 57 Figure 44: Cross- section inner channel...... 61 Figure 45: Cross-section outer channel (zoom close to the opening)...... 62 Figure 47: Storage area sketch ...... 65 Figure 48: Water Levels in Channels ...... 66 Figure 49: Water Level (left axis) and velocity (right axis) in the inner channel...... 69 Figure 50: Velocity in the outer channel ...... 69 Figure 51: Modified initiation of motion Shields diagram (Parker, 2006). Obtained from lecture notes of Sediment Dynamics course...... 70 Figure 52: Flow chart of the design of a barrier...... 71 Figure 53: Probability of exceedance of water level from the database of Rijkswaterstaat. .. 74 Figure 54: Storm surge scenario ...... 74 Figure 55: Flushing scenario ...... 75 Figure 56: Water pressure distribution ...... 76 Figure 57: Maximum momentum ...... 76 Figure 58: Maximum shear stress ...... 77 Figure 59: Deformed shape ...... 77 Figure 60: Hydrostatic pressure distribution ...... 78 Figure 61: Shear stresses ...... 79 Figure 62: Forces ...... 79 Figure 63: Schematization of ecological zones for Alternative 1 ...... 82 Figure 64: Alternative 1 for disposal - Nourishment and development of salt marshes in Visbuurt...... 83 Figure 65: Alternative 2 for disposal Ð 2 Silt islands and development of salt marshes in Holwerd...... 84 Figure 66: Conservation area of the Wadden Sea ...... 87
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Figure 67: Scheme opening of the gates ...... 95 Figure 68: Scheme of a cofferdam. Source:http://www.sepa.org.uk/media/150997/wat_sg_29.pdf ...... 96 Figure 69: Wooden Piles in the Intertidal Area of Outer Channel Embankments ...... 96 Figure 70: Canal with a gate in Dokkum ...... 101 Figure 71: The Pier Showing the Water Level (left) and The Pier Top (rigth)...... 102 Figure 72: Salt Marsh and Old dike near the pier ...... 103 Figure 73: Salt Marsh formation near the Dike of Holwerd ...... 103 Figure 74: Existing Dike for protection of Holwerd ...... 104 Figure 76: Mitre gates scheme...... 109 Figure 77: Single-leaf gate scheme...... 110 Figure 78: Sector gate scheme...... 111 Figure 79: Tainter gate scheme...... 112 Figure 80: Lift gate scheme...... 113 Figure 81: Submersible lift gate scheme...... 114 Figure 82: Rolling or sliding gate scheme...... 115 Figure 83: Inflatable barrier scheme...... 116 Figure 84: Folding gate scheme...... 117 Figure 85: Gelsluis scheme (yellow part represents the gel)...... 118 Figure 86: Operation with a Gelsluis scheme (yellow part represents the gel)...... 118 Figure 87: Preferred travel season ...... 127 Figure 88: Basis of the decision ...... 127 Figure 89: Importance of the cost ...... 128 Figure 90: Importance of environmental aspects ...... 128 Figure 91:.Attractiveness of a destination ...... 129 Figure 92: Favorite destination ...... 130 Figure 93: Pile Groyne near Holwerd, From field trip (12/02/16) ...... 131 Figure 94: Pile Groyne near Holwerd (another view), From field trip (12/02/16) ...... 132 Figure 95: Gumbel distribution for water level ...... 134
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List of Tables
Table 1: Evolution of Holwerd's population. Source: CBS ...... 1 Table 2: Recreational craft dimensions (According to ECEIRVW2011)...... 14 Table 3: Summary of Alternatives ...... 19 Table 4: Project Requirements ...... 29 Table 5: Boundary Conditions ...... 29 Table 6: Multi- Criteria Analysis for selection of channel ...... 40 Table 7: Multi Criteria Analysis of the gates possibilities for the Guard Lock of Holwerd ...... 46 Table 8: Multi Criteria Analysis of the gates possibilities for the canal lock...... 49 Table 9: Definition of the elements in the equation...... 55 Table 10: Statistical properties of water level data from Holwerd station from Rijkswaterstaat ...... 73 Table 11: Calculations for the dredging operation for the inner channel ...... 85 Table 12: Details of calculation for the dredging operation in the outer channel ...... 86 Table 13: Cost Estimation of dredging and disposal operations ...... 86 Table 14: Targets to maintain and enhance the conserved area ...... 89 Table 15: Summary of the potential effects ...... 90 Table 16: Mitigation measures ...... 91 Table 17: Criteria for Conesa method ...... 92 Table 18: Evaluation of criteria ...... 92 Table 19: Importance of impacts ...... 93 Table 20: Method’s result ...... 94 Table 21. Harmonic components ...... 107 Table 22: Equations 1-6 variables ...... 121 Table 23:1 in 2000-year event wind direction dependent variables ...... 122 Table 24: Significant wave height ...... 122 Table 25: Wind direction independent Inputs ...... 123 Table 26: Wind direction dependent variables ...... 123 Table 27: Overtopping discharge ...... 123 Table 28: Probability of failure ...... 124 Table 29: Statistics of PoT analysis ...... 134 Table 30. Consultation fees ...... 136
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1. Introduction
1.1. Problem Definition Holwerd is a village in the northern Netherlands that belongs to the municipality of Dongeradeel in the province of Friesland. It is one of the largest towns of Dongeradeel and it covers an area of 0.47 km². Holwerd is located at the southern coast of the Dutch Wadden Sea (Figure 1).
Figure 1: Location of Holwerd. Decisions and plans made in the past have affected the town in a negative way leading to an impoverishment of the region. People’s tendency to move to bigger cities looking for more attractive job opportunities and the lack of attractions in the zone has led to a decrease in population, especially due to youth leaving the town. Table 1 shows the evolution of Holwerd’s population. The last estimation of population (2014) indicates that only 1475 habitants are living in the town.
1999 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 1687 1762 1778 1620 1600 1530 1500 1480 1490 1500 1500 1495 1520 1475 Table 1: Evolution of Holwerd's population. Source: CBS
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Besides, the lack of attention to welfare and habitability of the zone has affected negatively the quality of life and the properties are too deteriorated to be sold.
Summarizing, the main problems that are found in Holwerd nowadays are: • Increasing unemployment • Youth going to larger cities • Decrease in quality of life • Services are disappearing • House vacancy and property's deterioration • Becoming a "ghost town"
Nowadays, Holwerd is merely a connection to the Wadden Sea’s island. Approximately, half a million people (per year) pass through Holwerd in order to take the ferry to Ameland Island. However, there is no attraction to make them stay in the town. In order to overcome this negative tendency, a group formed by local agricultural business and local stakeholders had the idea of connecting back the city with the sea by opening the present dike and therefore creating room for recreation and hence attracting people. Their ideas are outcome in the project Holwerd aan Zee.
1.2. Holwerd aan Zee Project Holwerd aan Zee is an innovative and unique project. Not only because the plan provides a great advance for local people and nature, but also because it breaks all established patterns. It is a project initiated by local people and all the stakeholders (municipalities, landowners, farmers, etc.) participate actively in the project.
The main objective of the project Holwerd aan Zee is to revitalize the city by making several changes based on connecting Holwerd to the Wadden Sea by letting the salt water go in to the inner part of the dike. This project is not only an economic opportunity for the town and region but also an ecological opportunity for the marshes present in the area. Birds, fishes and other species will benefit from the higher diversity created by the fresh-salt connection (Figure 2).
The local work team considers the following interventions essential for the good development of the project:
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• Open the dike and install a lock • Design a navigational channel • Establish a new pumping station • Create a multiuse area in the wide green dike • Improve the marshes by building flood refuges, muddy banks and breeding islands • Design a harbor promenade, build a hotel near the coastline, improve the existing pier’s conditions to push the economic development
Figure 2: Project interventions.
Programma naar een Rijke Waddenzee (PRW) has carried on several studies to analyze the feasibility of the Holwerd aan Zee. According to PRW, the plan is "promising valuable to guide the nature, in synergy with the experience economy, flood protection and landscape." Holwerd aan Zee has several challenges to achieve a synergy between humans and nature. Therefore, the client has some requirements we need to fulfill: • Preserve as much as possible the nature and agricultural lands; • Maintain the fairway used by reaching Ameland Island; • Reutilization of the capital dredging material, for instance for the construction of dikes and embankments, and • Limited maintenance dredging in the new channel.
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1.3. Main Objective The main objective of the project is to revive the city of Holwerd by connecting it with the sea. The connection will be attained by opening the present dike and connecting it to a navigation channel and a buffer lake.
1.4. Design Approach In dealing with the main objective, a plan of action comprising different hierarchies is considered. This hierarchical order is depicted in Figure 3. In the first tier, a conceptual design covering a broader perspective is discussed incorporating the architectural inputs into the design. In the second tier, a narrower perception is utilized on the connection between Wadden Sea and land, which concentrates on the navigational channel and the gates. In the third tier, subdivision of the second tier into two main parts namely channel and gate is done and an extensive design procedure is carried out for both channel and gates.
Conceptual Design
Overview for main elements
Channels Gates
Outer Channel Guard Lock
Inner Channel Canal Lock
Figure 3: Project Approach
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2. Site Review and Stakeholder Analysis
2.1. Site Review A site review was conducted to better understand how the existing conditions of Holwerd could impact the project. We examined the basic demographic and geological characteristics of the site. The field visit to Holwerd done on February 12th, 2016, is attached to this report as an appendix (Appendix A).
2.1.1. Overview Holwerd covers an area of 0.47 km2. Some of the neighboring towns are Ternard, Blija, Brantgum, Hantum and Wierum. Holwerd’s population, according to the last statistical data obtained from Centraal Bureau voor de Statistiek (CBS), is 1475. Populations of towns near Holwerd area are in Figure 4 shown below.
Figure 4: Population characteristics around Holwerd area (Spotzi Nederland, 2016).
2.1.2. Topography The topographic variation within the area of the Holwerd aan Zee project does not represent any more difficulties for the design of, neither the channels (inner and outer), nor the guard
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and canal lock. Elevations are shown in Figure 5 and Figure 6 and have values of 1.2 m [NAP] for the buffer lake area and 2.1 m to 3.4 m [NAP] for the outer channel area.
Figure 5: Bathymetry (m NAP) map of the Pier/outer channel area (webapp.navionics.com).
Figure 6: Topography referenced to NAP map of buffer lake area (Cadastre, Geoinformation, Zwolle, [2016]).
2.1.3. Land Use Several uses for the land are found around the city of Holwerd. Agriculture is the predominant occupation of the residents and potato is the main cultivated product. A forest is also present southeast of Holwerd. Also some industries are located along the road from Holwerd to the pier. In Figure 7 is presented a map of the land use of the region of Holwerd.
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Figure 7: Land use around Holwerd (PDOK, 2016).
2.1.4. Soil Characteristics An important factor in any engineering project is understanding the soil characteristics of the project site. The project location is predominantly made up of light and heavy clays and heavy loam as it can be seen in Figure 8. In the Holwerd area, these characteristics impact from the sedimentation constraints in the buffer lake, to the foundations of hydraulic structures, such as locks. The dredging equipment, and methodologies will be affected as well but the impact in this area will not create any boundary condition, only restrictions.
Figure 8: Soil characteristics around Holwerd (Cadastre, Geoinformation, Zwolle, [2016]).
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2.1.5. Infrastructure The purpose of this project, among other things, is to rehabilitate Holwerd by creating new infrastructure. Existing infrastructure not only keeps the city well connected but helps it develop further as well. The main elements of infrastructure taken into account for this project were roads, major highways, and shipping navigation channels/harbors. Nowadays, there are no existing highways around Holwerd, but there are important connecting roads such as N356 Ð main road from Dokkum (Dongeradeel municipality capital), N357 Ð road to Leeuwarden (Friesland provincial capital), and N358, road to the province of Groningen. The pier of Holwerd provides a ferry service to Ameland Island for half a million passengers, which makes it one of the most important infrastructures of Holwerd. Drainage ditches, irrigation canals and rural access roads can also be found throughout the city. Figure 9 provides an overview of the area’s infrastructure.
Figure 9: Infrastructure around Holwerd (PDOK, 2016).
2.2. Stakeholder Analysis It is imperative to consider all the parties associated with the project in order to make it more effective and beneficial to everyone involved. In fact, one of the main aims of this project is to make the all parties involved satisfied while making Holwerd a lively city. Moreover, without the acceptance of general public, no plan would be successful irrespective of its technical
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proficiency and adaptability. In order to come up with the most optimal plan, a thorough stakeholder’s analysis with respect to their respective roles, responsibilities, and the nature of interest towards the project scope has to be performed. It is always probable that the interests of different stakeholders’ conflict with each other as well as with the proposals of the project. In such a scenario, identification of the conflicting cases in advance would invariably lead to effective compromises. In the project of ‘Rehabilitation of Holwerd’, the number of stakeholders can be identified as follows (Figure 10):
Stakeholders
Farmers Tourism Municipality of Regulatory around Local people authorities, Environmental Dokkum authorities in Holwerd agencies Holwerd Tourists
Figure 10: Key Stakeholders for 'Rehabilitation of Holwerd'.
With this analysis, it is expected to anticipate the likely reactions and opinions of the above- mentioned stakeholders and build the plan of action accordingly. The Municipality of Dokkum acts as the main client of this project. So it is one of the most influential stakeholder parties involved in the project. Their opinions regarding the project will definitely be useful in shaping the project scope during the early stage. Further, by incorporating their views and suggestions the quality of the project outcome will be enhanced. Under the category of regulatory authorities, there are quite a few governmental agencies that carry certain interest on the project. With their decision making power, these regulatory authorities will influence the project during all its phases such as planning, design, construction and operation. For instance, the water board of the Holwerd has interests on safety, specially flood safety, water circulation systems around the Holwerd city and the project’s impact on the existing canal systems etc. However, with regards to the flood safety, it is not expected to flood to the extent that affects the residents of the area. The farmers around Holwerd are another key stakeholder part as there are a number of potato cultivations at certain parts of Holwerd area (Figure 7). However, surrounding the proposed navigational channel and the buffer lake there are no such agricultural areas nearby and there are few further towards the city. Hence, the farmers will be concerned of
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any salt-water intrusion into their farms. As a solution, a canal lock is proposed to prevent the intrusion of saline water to the agricultural areas in the city and therefore provide fresh water to the farms without any disturbance. The local people in the area are another segment who will be affected by the upgrading of Holwerd as a tourist city. The objective is to attract more people to Holwerd and this will certainly change the calm and quiet life style of the locals. With the introduction of water parks, hotels and other infrastructure facilities, the city would obtain a buoyant mood and hence these frequent crowds throughout the day will affect the general public around the area. Also as a result of the project, many people would be encouraged to live in Holwerd, so that the population in the area would increase as well. Further, it can be pointed out that the project will create number of job opportunities, which will invariably benefit the local people. As the ultimate objective of the project is to attract more tourists, the tourism industry in Holwerd area will benefit immensely. Arguably, the tourists coming to Holwerd wield the most power on the long-term success of the project, as they will be the end users. The project of ‘Rehabilitation of Holwerd’ would make Holwerd a popular holiday destination, and the expected tourists have to be provided with what they are looking for. The Ameland islands nearby already attracts number of tourists, and hence an attractive plan is required to convince them to stay at Holwerd and enjoy its beauty. For an instance, by the inclusion of bicycle lanes and bird-watching sites along with the water environment, more tourists would be interested to visit the place. Therefore, it is clear that a reliable execution plan is essential in attracting more tourists by adding unique features to the area. Consequently, an economic boost in the tourist industry can be expected. In any project, the environmental considerations need to be given proper attention and in this project the case remains the same. The proposed measures need to be designed in such a way that that would minimize the impact to the environment. The main potential environmental problem would be the salt-water intrusion into the irrigation canals nearby. However, a sufficient mitigation plan incorporating a canal lock is proposed for this matter. Further, it is prudent to invite environmental groups and ONGs to discuss about the mitigation measures. Finally, as the project progresses towards the detailed design stage a focused attention will be given to incorporate the needs and issues of the related parties which would ultimately lead to a sustainable project.
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3. Preliminary Research
A preliminary research was conducted in order to analyze the data, which will be input to the further design of the sluices and navigation channel. Topics that will be described in this section are: tides, wind, currents, design ship, and vessel’s traffic.
3.1. Astronomical Tide The astronomical tide is important to define the variation in the water level. Data from Holwerd Station in Rijkswaterstaat was acquired and are shown in Appendix B. The harmonic components obtained were used to describe the tide near Holwerd area.
The form factor number obtained was 0.13, which determines semidiurnal predominant tide. With this information, an astronomical tide prediction for one year was made using T-Tide Program. In Figure 11 it is presents the prediction for the city of Holwerd. As it can be seen, the astronomical tidal range is 3.5 m.
Figure 11: Tide Prediction for Holwerd.
3.2. Wind The wind data for the Holwerd area was taken from BMT ARGOSS WaveClimate database (grid resolution 50 km x 50 km) with. The extraction point is 53¡30’N and 5¡50’E (closest point to Holwerd’s coordinates) and the period acquired was 1992-2014. The database of “Wind Speed Altimeter” gave an average wind speed of 6-7 m/s, with North-Northeast as the predominant wind direction. Figure 12 and Figure 13 provide a visual representation of the aforementioned information.
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Figure 12: Detailed Wind Speed Data around Holwerd.
Figure 13: Wind Rose diagram around Holwerd.
3.3. Currents According to numerical simulations of storm and extreme storm events (Dogeren et al. 2011) wind driven circulation dominates the tidal currents in Ameland inlet during extreme events. The simulated velocities in our area of interest showed a maximum velocity of approximately 2 m/s in extreme storm conditions while tidal currents are in the range of 0.2-0.4 m/s and non-extreme wind driven currents are 0.8-1.0 m/s. (Figure 14).
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Figure 14: Tidal currents velocities, wind-driven currents, and extreme wind-currents velocities.
3.4. Waves The waves in Holwerd are dominated by wind-growth, currents effects, and depth-limitation (Dogeren et al. 2011). The ebb tidal delta of Ameland inlet refracts and dissipates most of waves incoming from the North Sea. Therefore, in our area of interest the incoming waves in general have low energy, except during extreme events.
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3.5. Sea Level Rise Ð Estimation from IPCC AR5 Intergovernmental Panel on Climate Change (IPCC) in its Fifth Assessment Report (2013) pointed out some of the research done on SLR. Figure 15 below is taken from the report (13.20b).
Figure 15: SLR estimation An SLR estimate of 60 cm in the Netherlands in 2100 can be made from this figure. Nonetheless, this is just an estimate based on a model, and some models also predict SLR of as low as 20 cm in 2100. Due to the variation of these models, a safety value of 1 m rise for 100 years it is assumed.
3.6. Design Ship The design ship type implemented in this project is a recreational craft, which has different sizes and models as it can be seen in Table 2. The design ship adopted in this project was sailing yacht with length, beam, and draught of 15 m, 4.0 m, and 2.10 m respectively.
Type of Length (m) Beam (m) Draught (m) Air Draught recreation craft (m) Open boat 5.5 2 0.5 2.0 Cabin boat 9.5 3 1.0 3.25 Motor yacht 15 4 1.5 4.0 Sailing yacht 15 4 2.10 30.0 Table 2: Recreational craft dimensions (According to ECEIRVW2011).
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3.7. Traffic Analysis Nowadays, vessels are not navigating near Holwerd, thus a traffic analysis is difficult to conduct. For a rough prediction of the future traffic using the new Holwerd facilities, Ameland’s current traffic was taken into account. It is known that an average of 0.5 million passengers per year according to MarineTraffic.com. More passengers travel during spring-summer time than in the fall-winter time, hence there is more schedule trip during peak months (March-September) especially during the weekends. It is also known that there are several types of vessels including pleasure crafts and fishing vessels that arrive in this port as it is shown in Figure 16. Holwerd’s project neither will receive the same type of vessels, nor will be design for them, so this information will not be taken into account once the estimation of the future traffic is made.
Figure 16: Type of vessels arriving/departing Ameland’s port
The gravity model is much like Newton's theory of gravity. The gravity model assumes that the trips produced at an origin and attracted to a destination are directly proportional to the total trip productions at the origin and the total attractions at the destination.
!! ! !!" !!" !!" = !! ! !!! !! ! !!" !!" • Tij = trips from I to j
• Ti = total trip production at i
• Aj = total trip attraction at j
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• f(Cij) = a calibration term for interchange ij, (friction factor) or travel time factor • C= calibration factor for the friction factor
• Kij = a socioeconomic adjustment factor for interchange ij (calibration parameter) The calibrating term or "friction factor" (f) represents the reluctance or impedance of persons to make trips of various duration or distances. The general friction factor indicates that as travel times increase, travelers are increasingly less likely to make trips of such lengths. Calibration of the gravity model involves adjusting the friction factor. In this case, it is assumed that it will increase for the ferry since there is a previously established schedule so the travel time is bigger. Also, depending on the type of vessel and existing facilities, it might be cheaper for passenger to use their own boat if possible. The socioeconomic adjustment factor is an adjustment factor for individual trip interchanges. For this specific situation, it is assumed that this factor equals to 1 since people that already have a craft can use it, otherwise, they can use the ferry as they being doing it during this period.
Based on the gravity model mentioned above, and assuming that 1% of the passengers currently have a pleasure craft, it was calculated that 8.2 trips would be made through the new channel per day. Figure 17 provides a scope of the daily average departures and arrivals from Ameland’s port.
Figure 17: Average arrivals and departures by hour of Ameland Port
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4. Conceptual Design
4.1. General objective The main objective of this project is to revitalize Holwerd. A lot of things can be build but it does not mean that this will actually attract tourism. In order to make a proper analysis, first several questions were made and some of them are mentioned below:
- What makes a city attractive? - What is the main reason you would visit a place? - What would make Holwerd unique?
4.2. Possible Alternatives 4.2.1. Survey In order to know what would attract more tourists to Holwerd a survey was performed. From the survey, not only an idea of what people like but also events, public transport, and cost related opinion is obtained. This information is very helpful for the management of the city and makes the development process of alternatives more efficient. In Appendix G the results of the survey analysis are presented.
4.2.2 Alternatives The following elements are taken into consideration in order to develop the alternatives: • Proximity to the sea (channel and buffer lake) • Parks and open spaces • Restaurants & Bars • Museum, art and culture center • Hotel/Resort • Natural attractions • Shopping malls • Modern Buildings The alternatives considered in the analysis are described below: Alternative 1 For this proposal only recreational elements are considered to be implemented. Therefore, proximity to the sea, restaurants and bars, hotels and shopping malls are the relevant factors.
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Alternative 2 In this case the natural elements such as the creation of parks and open spaces and the implementation of natural attractions (pathways, high viewing points, etc.) are considered. Alternative 3 This alternative is based on the enhancement of cultural elements. The construction of a museum/art and culture center, invest in keeping the architecture style of the site and adding new modern buildings are the factors considered. Alternative 4 Both recreational and natural elements are proposed as alternative. Alternative 5 Both recreational and cultural elements are proposed as alternative. Alternative 6 Both natural and cultural elements are proposed as alternative. Alternative 7 Every single factor is included in this alternative. Alternative 8, 9 and 10 These alternatives include every single factor from the 3 main elements, apart from shopping malls, investment in architecture and modern buildings. The construction cost makes a distinction between them. Alternative 8 is the cheapest one and alternative 10 is the most expensive one, while alternative 9 has the cost higher than alternative 8 and lower than alternative 10.
A summary of the different alternatives is presented in Table 3.
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Natural Recreational elements Cultural elements elements
bars spaces Architecture Hotel/Resort culture center culture Park and open open and Park Shopping malls Restaurants and Museum, art and and art Museum, Modern buildings Modern Natural attractions Natural Proximity to the sea the to Proximity Alternative 1 x x x x Alternative 2 x x Alternative 3 x x x Alternative 4 x x x x x x Alternative 5 x x x x x x x Alternative 6 x x x x x Alternative 7 x x x x x x x x x Alternative 8 x x x x x x Alternative 9 x x x x x x Alternative 10 x x x x x x Table 3: Summary of Alternatives
4.3. Evaluation of Alternatives Following the process, an evaluation of the alternatives was performed and is presented in Figure 18.
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Figure 18: Evaluation results
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4.3.1. Analysis of Results For the analysis and evaluation of the previously mentioned alternatives, the 'Joint Ecological and Socio-economic Evaluation of Water resources development’ (JESEW) model was used. With this model, the alternatives were weighted according to the survey. The most optimal option will be the one closest to the top right corner. An alternative that would satisfy every single stakeholder is an impossible task, but the best approach to this problem is to choose an alternative that will have the majority of the stakeholders’ acceptance. Among the options, option 7 includes every single element, which results in the most attractive option but the most expensive as well. In order to optimize the final solution, the alternatives were divided in phases and analyzed.
4.4. Master Plan and Phasing 4.4.1. A Door to the Wadden Sea Architecture students have studied the area and designed a master plan of the project based on the idea of interconnecting all the villages along the Wadden Sea coast establishing Holwerd as a centre of the system. This is depicted in Figure 19.
Figure 19: Regional scale of the proposal In order to attract people to Holwerd and activate the town, the willingness is to reduce the distance between the sea and the city by opening the dike and creating a buffer lake.
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Figure 20: Local scale of the proposal In addition, due to the connection to the sea, the mixture of salt and fresh water will create new flora and fauna of the area as is shown in Figure 21. This can bring new job opportunities and attraction to the town.
Figure 21: Ecological scheme Several recreational points are set such as dobbens, islands, bird watching places and the possibility of swimming in fresh water. Camping sites, restaurants and hotels are also considered as valuable items to boost the tourism. A better boat and road connections is needed it to get an optimal implementation of the plan.
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Figure 22: Recreational scheme In Appendix C, the master plan poster is enclosed.
4.4.2 Phasing The project ‘Rehabilitation of Holwerd’ has an objective with a broader perspective into the future, which emphasizes on the effective phasing to achieve various project sub-goals. The conceptual design of the project mainly indicates the overall design concept incorporating four phases that the project needs to accomplish in chronological order.
Phase 1 Alternative 8, also shown in Section Error! Reference source not found., represents the first phase in the rehabilitation project. This phase includes: • Proximity to the sea • Restaurants and Bars • Hotel • Park and open spaces • Art related events • Natural attractions • Dobben/island
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For the proximity to the sea action, it includes creating a channel and a buffer lake connecting the city to the Wadden Sea. This way, the city will have that feeling of a beach city but in a different positive way since one will get the perks of being in a city and a beach as well. For the restaurants and bars, the idea is to optimize the existing ones by making it more attractive and if the worst case, locate 1 or 2 new ones at some strategic places (yet to be defined). The more authentic and different they are; more people will be attracted to them. The hotel aspect of this phase is to analyze if it is enough or not for the amount of people that will be visiting Holwerd. It also known that at the very beginning people will be only spending the day but by not providing the service will not attract more tourist and it will only make them go to a place where they actually can sleep or spend more than one day. Natural attractions, and parks and open spaces will be, once again, an adaptation of the existing areas, and constructions will only be undertaken as needed. The dobben/island development is described in section 0. Events like concerts, festivals, among others, should be considered along this phase given that was one of the biggest attractions obtained from the survey previously mentioned. Other activities such as races, local artist showcases, etc. will also allow Holwerd to become known, appealing tourists to come. As a recommendation, since the most traveled season is summer, it should be considering when deciding on the starting date for the project. This phase is estimated to last 10 months.
Phase 2 In Phase 2, a small harbor could be developed subjected to public demand. The harbor is planned at the buffer lake side of Holwerd, as shown in Figure 24. Among the options to be included in phase 2 are: • Small marina • Market square • Restaurants and bars • Camping area As previously mentioned, each phase must have an economical and environmental impact so it is known that the development of the city is positive.
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Figure 23: Plan made by one of the Architecture Groups: A door to the Wadden Sea
Figure 24: Possible harbor, market square and camping sites
There have been plans by the Dutch Government to create a system made by the freshwater from the rivers in the Netherlands. Unfortunately, Friesland and the northern area close to the Wadden Sea (the mud flats) are not well connected to this water system. In this phase the connection of Holwerd to the bigger water system can be explored. This will increase the freshwater supply to the area in question, which will be helpful for the next phases to follow.
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Figure 25: Intended ecological wet network The previous figure indicates the intended ecological wet network from the Delta Region to Lauwersmeer, while the figure below indicates the blue network, which is the water network in Friesland. By developing the water system network, a brackish lake may develop accomplishing one of the main goals of this project.
Figure 26: Blue network Phase 3 At this point, main changes have been made hence this phase is more of an analytical and experimental phase, in which the development process should be analyze and correct if something is not working properly. With the brackish water and the fresh water system, nature is expected to flourish. By bringing in brackish water and creating various spaces and natural areas, activities such as brackish water cultivation, brackish water flower farming and cultivation of various saline resistant crops, among others can be proposed.
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Theoretically, and basing our analysis on the artificial Peberholm Island created during the construction of the ¯resund Bridge between Denmark and Sweden, the lake should develop naturally however, further analysis should be made in order to have a better comprehension of the development of the area. In the saltwater side, the salt marshes that are currently present will be disturbed by the construction of the channels in the first phase. However, it is predicted that the area will flourish again with the same or variations of this species. Figure 27 shows a schematic overview of the salt marshes as per the exposure regions. A Saltmarsh Observation-cum- Research Centre can be considered to be developed to make tourists more knowledgeable of this delicate but effective means of preventing inundation by natural forces.
Figure 27: Schematic section of saltmarshes
Ecological interventions, like green slopes (embankments with mild slopes, so that flora and fauna are able to flourish on it -Figure 29), can be considered in the created water network.
Figure 28: Interventions to strengthen the ecological network
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Figure 29: Mild slope for flora and fauna to flourish
Phase 4 In this phase the introduction of otters in the ecosystem can be considered. Eurasian Otter (Lutra lutra) is a representative species in the sense that it is at the top of the food chain. So, its presence would be an indication of the thriving success of the project. An important remark is that, all of these projections depend on several factors but mainly it depends on nature, which only makes the uncertainty higher. Theoretically, once the water system and the brackish water from the lake it’s fully developed, otter from the southern Friesland area could migrate to the Holwerd area since the habitat is quite appropriate. Having said this, it would also be good to work along with other cities in the area to create a bigger and better habitat for this species to migrate.
Figure 30: Otter and its relation to food chain
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5. Overview of the main elements
5.1. General Objective In this chapter, the attention is mainly focused on the sea and land connection (from Wadden Sea to the vicinity of Holwerd city) where more specific engineering design interventions can be applied. As part of revitalizing Holwerd, it is proposed to construct a navigational channel through the dike connecting to a buffer lake. Together with the channel, a sluice in connection to the sea (opening of the dike) and another sluice in connection with fresh water (canal in the city side) are considered. The scope of this part of the project is to analyze alternatives for the overview which consists both the navigational channel and the sluices in the connection to the sea (opening of the dike) and in the connection with fresh water (canal in the city side). In Table 4 the project requirements and the implications of it in the design of the channel and sluices are enlisted. Requirement Design value Calculated value Buffer lake (recreational space) Surface area of inner Surface area of inner channel = 350,000 m² with a maximum of 35 channel = 351,900 m² ha Minimal Depth = 3.1 m; Channel navigable for Minimal Depth = 3.25 m; Minimal Width for one-way traffic= 13 m; recreational boats Width = 30 m; Minimal Width for two-way traffic= 28 m;
hLW= 3.25 m; h =2.7 m; water depth in low water in the channel HW Minimal maintenance a/h=0.35; (h )
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Control of saline intrusion in the canal (not in the scope within this project) - further in the city à canal lock Table 4: Project Requirements
5.2. Boundary Conditions In Table 5: Boundary Conditions the boundary conditions applied in the design of channel and sluices are presented. Boundary Conditions Source Tidal Range TR=3.5 m Tide data from Rijkswaterstaat Mean Low Water MLW = - 1.75 m NAP Tide data from Rijkswaterstaat (MLW) Mean High Water MLH = +1.75 m NAP Tide data from Rijkswaterstaat (MHW) Design (Storm)water Hydraulische Randvoorwaarden WL=+4.9 m NAP level 2006 Design (Storm )Wave Hydraulische Randvoorwaarden Hs=1.65 m Height 2006 Sea Level Rise SLR = 1m in 100 years IPCC Table 5: Boundary Conditions
5.3. Channel 5.3.1. Alternatives Basically three different alternatives are considered for the overview of designing the channel and the positioning of the sluices.
Alternative 1 The first alternative was thought in such a way that it can be connected to an existing marina located at the south of the city, this way, new berth facilities will not be needed for the time being. Since the aim is to attract boats, a mooring place for them should be considered for the near future, otherwise, vessels can only navigate through the new features but cannot visit the city of Holwerd. Another important feature of this alternative is that, by connecting the inner channel and the buffer lake with this part of the city, a controlled mixture of water can be provided by installing a lock, described further in this report. Alternative 1 is presented in Figure 31.
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Figure 31: Alternative 1
Alternative 2 The second alternative provides a longer route so tourists can enjoy navigating through the new facility. In this alternative, the inner channel is directly connected to an irrigation canal, which lies parallel to the dike. Hence, the salt-water intrusion is a likely adverse effect with related to this alternative. The alignment of the inner channel is designed in such a way that its path lies closer to the city so that the tourists get a glimpse of the Holwerd city as well during their journey. As it can be seen in Figure 32 the two locks are positioned at the dike as well as at the intersection between the proposed inner channel and the irrigation canal.
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Figure 32: Alternative 2 Alternative 3 The third and last alternative is a straight inner channel, reducing dredging volumes, and facilitating the convenient navigability since it does not have curves. However, the connection between the proposed inner channel and the main city is somewhat distant so it can be perceived as a drawback. In addition, similar to the second alternative a potential salt-water intrusion can occur due to the direct connection to the irrigation channel. Similar to Alternative 2, two locks are proposed as shown in Figure 33.
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Figure 33: Alternative 3
5.3.2. Evaluation of Alternatives Generally, in the context of engineering solutions to certain problems at hand, it is possible to present number of alternatives, which satisfy the desired objectives with certain degrees. Although a number of options exist to address the problem, only one alternative can be introduced as the most appropriate one. Therefore, it is essential to compare the various alternatives based on number of related aspects. Such comparison often facilitates more effective and informed decisions eventually leading to economic and sustainable designs. For the project of ‘Rehabilitation of Holwerd’, engineering designs are proposed mainly for the channel that connects Wadden Sea to the Holwerd city and for the gate at Holwerd dike. A careful and a thorough analysis of the proposed alternatives need to be performed in order to arrive at the best alternative. For this purpose, a multi-criteria analysis (MCA) is conducted for the selection of the best alternative. A Multi-Criteria Analysis (MCA) method enables the combination of the different indicators to the final outcome corresponding to its significance by weighing the various aspects relative to
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each other. If a suitable method of assessing the indicators is established, the method is very straightforward. 5.3.3. Multi Criteria Analysis (MCA) There are basically two channels considered in the project namely outer channel and inner channel. The outer channel connects the Wadden Sea to the Holwerd dike while the inner channel runs from the dike to the Holwerd’s city center. Only one alternative path is proposed for the outer channel. However, for the inner channel three different outlines are proposed based on various reasoning. The positioning of sluices is basically dependent upon the channel path. A multi-criteria analysis is performed in order to select the best inner channel alternative for the project and thus deciding on the locations of sluices. In performing the MCA, four main criteria are identified covering all the phases of the project namely designing, construction, and operation. These primary criteria are further divided into relevant indicators which are defined in such a way cumulatively they can capture the full scope of the project outcomes in different related areas. Figure 34 below gives a summary of the selected main criteria and their respective indicators.
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Total dredging volume
1. Construction Aspects
Channel length
Connectivity to Holwerd City
Aesthetic framework for 2. Effectiveness tourists
Availability of infrastructure facilties (eg: marina)
Future adaptability of the
Multi-Criteria Analysis Multi-Criteria solution
3. Sustainability
Public acceptance
Possible salt water intrusion
4.Social and Environmental Impact Time scale required for the construction process
Figure 34: Main criteria and corresponding alternatives Most of those indicators are of inherent qualitative nature and hence difficult to assign a quantitative value. This particular attribute of the given indicators could be perceived as a drawback.
Allocation of Weight Factors for Main Criteria and Indicators Weight factors are assigned accordingly using a scale from 0% to 100% depending on the relative significance of each criterion and their corresponding indicators. Each of the criteria
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and their indicators are explained in detail below with related to overall design. Also, the respective weight percentages are mentioned in brackets.
Criterion 1: Construction Aspects (50%) This criterion mainly affects the total cost of the project. Since being economic is an essential part of any project this criterion is given a high weight of 50%. Total dredging volume (75%) The total dredging volume comprises of the volume of inner channel and the volume of buffer lake. Higher the dredging volume, higher the costs associated with the dredging operations. Based on these reasoning, this particular indicator is assigned a weight of 75%. Channel length (25%) It is expected to utilize the maximum area available for the project. By having longer channel incorporating the beauty of the landscapes around would give higher value for the money of a tourist. However, due to the directly proportional relationship, higher the channel length higher the total dredging volume is. Despite the cost influence, channel length need to be sufficient and hence a weight of 25% is allocated for this indicator.
Criterion 2: Effectiveness of the selected alternative (30%) This criterion describes the extent to which the proposed solutions are capable of achieving the main objective of the project. Therefore, a weight of 30% is given for this. Connectivity to the Holwerd city (20%) The primary objective of the project itself is to achieve effective connection between the Wadden Sea and the Holwerd city. Hence, it is necessary for the inner channel to directly connect to the city. This direct connection is important for the tourists in ship tour to enjoy the attractive architectural masterpieces in the city center in addition to the natural scenery. The importance of this indicator is emphasized by the fact that Holwerd possess some unique cultural heritage comprising of buildings and other constructions. Therefore, the weight for the connectivity to the city indication is 20%. Aesthetic framework for the tourists (50%) Since the project is all about making Holwerd a tourist attraction, the ship tour along the channels must accomplish this objective by navigating through the best path along which the eye-catching sights are located. Hence, the alignment of the inner channel need to be designed in such a way it maximizes the aesthetic prospect that a tourist can experience in a
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ship tour around the area. Due to the higher significance of this indicator for the success of the project a weight of 50% is assigned. Availability of infrastructure facilities, e.g.: marina (30%) The ships arriving the Holwerd city centre need to be provided with relevant infrastructure facilities in order to maintain an undisturbed and smooth service to the tourists who are visiting Holwerd. For this context, the channel needs to maintain sufficient navigable depth at all times. Further, at least a small marina with basic amenities is required for the ships to be moored as well as to input fuel/oil for further excursions. The weight of this indicator is 30%.
Criterion 3: Sustainability of the selected alternative (10%) This criterion mainly attributed to the long-term success of the project. With the estimation of less future impacts from the proposed solution of channel and the gates, a relatively low weight of 10% is assigned for this. Future adaptability of the solution (50%) For a sustainable solution, a development done at the current timeline should be easily incorporated in a future development as much as possible. For the channel design in Holwerd, it is required to design it with flexibility for future expansion due to potential high demand that could be arisen from increased popularity among tourists. For an instance, a requirement of additional marina of large scale can be expected subjected to the increasing number of ships, boats etc. Thus, the weight factor of this indicator is 50%. Public acceptance (50%) The general public living in Holwerd would be greatly affected by the project. Thus, in order to implement a sustainable solution, the acceptance of the public is of utmost importance. Further, people who conduct businesses in the area as well as the farming community are other segments who would be directly affected, as the project would impact their livelihood by significant proportions. Hence, when designing the channel profile and the gates, it is imperative to avoid any public protest and this particular criterion plays a vital role in deciding the most sustainable solution to the problem at hand. Thus, the weight of this indicator is 50%.
Criterion 4: Social and Environmental Impact (10%) In order to launch a successful project, it needs to fulfil certain requirements in terms of positive social impact and minimum adverse environmental impacts. Taking those into account, a weight of 10% is assigned for this criterion.
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Possible salt water intrusion (75%) Minimum adverse environmental effects are always a major criterion for the approval of any design. Therefore, the alignment of the inner channel need to be selected such that it causes as minimum disturbance to the existing natural features as possible. Saltwater intrusion to the nearby irrigation canal is the key factor in this scenario since the saline water would enter the buffer lake. As a result, the potatoes cultivations near the city area would be affected negatively and the yield could reduce dramatically. In this scenario, effective positioning of the canal gate becomes vital in achieving required stoppage of salt-water mixing to irrigation canals nearby. Thus, the weight of this indicator is 75%.
Time scale required for construction process (25%) Any construction would cause disturbance to residents in the area and higher the period of time it takes for the completion of channel construction more the inconvenience it would cause for the nearby residents. In this context, the noise, dust and other relevant issues need to be taken into account. Even though, the period of construction is just confined only to a very small time period compared to the lifetime of the project, if this is not taken into consideration, the project may come to a halt at the very beginning if large social disapproval is built up. However, due to the less significance of this indicator for the proposed channel construction a lower weight of 25% 1 is allocated.
Evaluation of Indicators with respect to each alternative The next step of the Multi-Criteria Analysis is the evaluation of the indicators with respect to each alternative. As mentioned before, the Multi-Criteria Analysis performed for the selection of the best alternative is predominantly a qualitative investigation. Based on valid justifications, a score varying between 1-3 is assigned for each indicator (1 being the lowest/worst case and 3 being the highest/best).
Total dredging volume As the exact dredging volumes can be calculated, giving a score for each alternative based on this indicator is rather straightforward. The total dredging volumes of inner channel (incl. buffer lake) are as follows; • Alternative 1 Ð 627,640 m3 • Alternative 2 Ð 1,157,073 m3 • Alternative 3 Ð 865,405 m3
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Based on the above values, scores of 3, 1 and 2 are given for Alternative 1, Alternative 2 and Alternative 3 respectively.
Channel length Similarly, as above, a score could be assigned based upon calculated inner channel length. • Alternative 1 Ð 851 m • Alternative 2 Ð 1567 m • Alternative 3 Ð 1172 m Scores are given as 1, 3 and 2 for Alternative 1, Alternative 2 and Alternative 3 respectively.
Connectivity to Holwerd city Alternative 1 provides a direct connection to the city. In alternative 2 also the inner channel goes along a path that gives a glimpse of the city. However, in alternative 3, this connection is somewhat distant as the channel path lies quiet far away from the vicinity of Holwerd city. Hence, scores of 3, 2 and 1 are assigned for Alternative 1, Alternative 2 and Alternative 3 respectively.
Aesthetic framework for tourists The view of surrounding natural greenery landscape contributes to the aesthetic prospect that a tourist can experience. This also depends on the architectural concept that is to be adopted on either side of the channel. The aesthetic appearance of the gates also contributes to this particular factor. Thus, based on the path of channel and gate types scores of 3, 2 and 1 can be given to Alternative 1, Alternative 2 and Alternative 3 respectively.
Availability of infrastructure facilities (e.g.: marina) Only in alternative 1, the inner channel is connected to a small marina (mooring place) while other two alternatives require some kind of mooring facility to be built for the implementation of the project, as it is mandatory to have one. Hence, it can be pointed out that only in the alternative 1, the initial phase of the project can be implemented without investing on new marina. Thus, in accordance with this reasoning, scores of 3, 1 and 1 are assigned to Alternative 1, Alternative 2 and Alternative 3 respectively.
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Future adaptability of the solution This indicator attributes to the flexibility of the solution presented. For an instance, a reserved area for a new large-scale marina is important that need to be built in the future. In alternative 1, the existing mooring place can be expanded accordingly to cater the demand in the future. When all three alternatives are considered, the flexibility for future modifications varies only by insignificant amounts. Thus, scores of 1, 3 and 2 are assigned to Alternative 1, Alternative 2 and Alternative 3 respectively.
Public acceptance When it comes to public acceptance, a wide variety of segments in the society need to consider. Firstly, if the channel were to occupy the farming lands, the farmers would express their protest on the project. This scenario is mostly applicable to alternative 2 and 3 since their channel paths lie more towards the agricultural parts of the area. Further, in those two alternatives (2 and 3) the inner channel directly connects to an irrigational canal, which would definitely lead to some sort of objection from the locals who use that irrigation canal. Consequently, scores of 3, 2 and 1 can be given to Alternative 1, Alternative 2 and Alternative 3 respectively.
Possible salt water intrusion As mentioned in the above indicator, both the alternatives 2 and 3 connect directly to an irrigation canal. Thus, there is a higher potential of saltwater intrusion to the agricultural lands nearby resulting in an adverse and critical environmental impact. However, alternative 1 does not cause such acute negative effect when it comes to salt water intrusion. Accordingly, scores of 3, 1 and 1 are proposed to Alternative 1, Alternative 2 and Alternative 3 respectively.
Time scale required for the construction process This relates to the inconvenience encountered by the residents of the area during the construction phase of the channel due to noise, dust etc. This indicator directly related to the channel length. Since alternative 1 has the lowest channel length, it is the option with least time consumption while alternatives 3 and 2 are second and third based of construction time respectively. Therefore, scores of 3, 1 and 2 are assigned to Alternative 1, Alternative 2 and Alternative 3 respectively.
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Summary of Results Table 6 below summarizes the results. The alternative with the highest score would be selected as the best alternative. Weight Criteria Indicators Factor Alt 1 Alt 2 Alt 3 Dredging Volume (75%) 0.375 3 1 2 Construction (50%) Channel Length (25%) 0.125 1 3 2 Connectivity to city (20%) 0.06 3 2 1 Effectiveness (30%) Aesthetic Framework (50%) 0.15 2 3 1 Infrastructure facilities (30%) 0.09 3 1 1 Future adaptability (50%) 0.05 1 3 2 Sustainability (10%) Public acceptability (50%) 0.05 3 2 1 Social and Salt water intrusion (75%) 0.075 3 1 1 Environmental (10%) Time for construction (25%) 0.025 3 1 2 Sum 1 2.5 1.8 1.6 Table 6: Multi- Criteria Analysis for selection of channel
It can be seen that Alternative 1 gives the highest score and is the clear front-runner in terms of most of the vital aspects considered. Thus, it can be concluded that, after taking all the related components that are connected to the channel construction into account, Alternative 1 is the most viable and sustainable solution as it causes the least adverse impact on the system compared to the other two alternatives. In further justification of the selected alternative, that it can be connected to a fresh water source more easily as there is already some existing canal and Marina connecting the system. Moreover, this part can be further developed to a fresh water source for the buffer lake creating a brackish water environment, which is one of the desirable conditions by the client. The alignment of the inner channel of the first proposal includes a mild bend to locate the buffer lake closer to the city as well as to utilize the maximum allowable land that is reserved for the project.
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Figure 35: Schematic figure of selected Alternative
5.4. Sluices Sluices, in the hydraulic engineering sense, can be defined as an artificial channel for conducting water often fitted with a gate at the upper end for regulating the flow. The main functions of a sluice are: § Water retention § Water locking § Water discharge § Shore connection A lock is part of the sluice family. It consists of an enclosed chamber in a waterway used to transport vessels from one to another water level. Three type of locks were considered in this project:
5.4.1. Navigational Lock This type of lock connects two sections of a waterway (river, sea or channel) with different water levels. The lock enables the transfer of the ship from one to the other section of the waterway by admitting or releasing water. The key parameter of the navigational lock is the lift: the water difference between both sides of the lock.
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5.4.1 Guard Lock/Storm Surge Barrier Guard locks and storm surge barriers has two main functions: § Passage of vessels § Retention of water As long as it is possible to allow ship passage, the gate of the guard lock will remain opened. Obviously, while it is opened the guard lock will not be retaining water. In case of a water level too high or too low that compromises safety during ship navigation, the guard lock may close its gate.
5.4.2 Canal Lock The function of the canal lock is to control the intrusion of saline water, coming from the connection to the sea, to the existing canal. Therefore, the main function of this lock is to separate body waters.
5.4.3 Types of Locks Selected There are two different connections to implement. One connection will be made by opening the dike and connecting the city of Holwerd with the Wadden Sea. This connection requires a lock to protect the city from flooding and storm events. Another connection will be form he buffer lake (to be designed) and a canal with fresh water located in south of Holwerd (to be expanded). This connection requires a lock to stop the mixing of the saline water and freshwater.
Lock for the opening of the dike Navigational lock was firstly considered as an option for the opening of the dike. However, due to the small traffic predicted (section 3.7) was been discarded as a suitable alternative. Guard lock was selected as the most appropriate option since it matches with the scale of the project and fulfill the requirements of ship passage and defense against extreme events. The lock will be a one-way retaining guard lock, which means that in normal conditions, the lock will remain open, allowing the passage of recreational craft and only in extreme high water conditions (storm surge) it will be closed working as a flood defense together with the present dike. The Guard lock is composed of gates and lock heads. Different types of gates were analyzed in order to define the alternatives for the guard lock of Holwerd.
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Lock for stopping the mixing between saline water and freshwater The canal lock is the only alternative suitable in this case since it enables to control the intrusion of saline water to the inner part of the city. The fresh water in the canal is used for agriculture and connects to other bodies of fresh water considered heritage. Therefore, it is highly importance the lock fulfills the requirement of prevention of saline water. Besides, it also allows vessel’s passage. The location of these two locks is presented in Figure 35. The further design of the canal lock is not within the scope of this project, only the analysis of possible gates.
5.4.4 Alternatives for Guard Lock Gate selection type is a key stage in the design of the barrier due to the fact that the choice will have important consequences in the operational, financial and other aspects of the project that are more critical than the detailed engineering. Besides, it should be noticed that it must have given a more carefully look to the design of weir gate (than a fixed ground-based structures) because: • They are movable • Loads are difficult to calculate particularly hydrodynamic effects, varying loads, fluid structure interactions) • Shapes can be complex (3D stiffened shells) which make stresses difficult to calculate • These structures are mainly under-water and often difficult to inspect and to maintain • They are subject to deterioration from various causes: vibration, corrosion, wear, flow, • Structures are typically kept in use significantly longer that their design life. Therefore, robust solutions and high safety factors are required. To achieve a higher level of confidence the design procedures needs to be integrated with risk assessment, maintenance, control of operation and environmental impacts and aesthetics: • Maintenance: it is one of the most important aspects of a weir design since it has a considerably affect in the costs. A higher efficiency/cost ratio will be reach if maintenance is taken into account in the early design stage. • Control of operation: it is recommended to duplicate all the critical elements of the control system so that reach a higher reliability.
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• Risk assessment: the different possibilities of failures and the current probability of their appearing with their respective consequences must be evaluated. • Environmental impacts and aesthetics: it is important to consider the environmental impacts that can occur during the construction and the operation of the barrier in order to minimize its effects.
According to the requirements of the project (section 5.1), different alternatives for the guard lock were investigated, and a description, advantages and disadvantages of each type can be found in Appendix D. First, a pre-selection of the type of gate that fits the demands were carried out. Three options were selected and evaluated in the Multi Criteria Analysis. These are: Single-Leaf Gate, Sector Gate and Folding Gate.
Single-Leaf Gate Some of the advantages of the single-leaf gate are that it is suitable for locks with small width, thus is applicable for the project since it is only expected recreational vessels. Among the disadvantages are a long recess area in lock head, large water displacement while opening and closing, and width restriction. For this project, the disadvantages evaluated against the advantages of this gate are not significant, so the single-leaf gate would be considered as one possible alternative.
Sector Gate The sector gate was also considered as a possible alternative for the lock since it is recommended for storm surge barriers. Although there are some negative aspects, such as the usage of large amounts of material, large size of lock head, among others, they do not overshadow the compensations it offers to the project.
Folding Gate The folding Gate was selected as a possible alternative for the Guard Lock of Holwerd because it is an innovative alternative, it is more resistant to loads than mitre gates, moreover due to its shape can resist to storm surge. Besides, it requires relatively small area and has no draught limitation. The disadvantages are increase in the length of the lock and it relatively new applications, however the disadvantages did not seem to overlap the advantages.
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5.4.5 MCA for Guard Lock Gate As described in the previous section, more than one option is suitable to solve the problem presented in this project. Different criteria should be considered during the selection of the gate, therefore a multi criteria analysis was completed. The criteria used are: cost, usability, maintenance, and environmental. The criteria were weighted and graded according relevance for the project and the client’s requirements and it can be seen in the sections below. As a result, cost, usability, maintenance, and environmental has a weight factor of 40%,35%,15% and 10% respectively. Costs (40%) The guard lock is one of the most important structures in the project Holwerd and Sea. However, the project has a budget of 1.5 million of euros for its entirety, which includes others structures such as the navigation channel, buffer lake, etc. Therefore, the cost was considered as the main criterion with 40% of the overall weight. Usability (35%) The guard lock has many functions: exchange of water between sea and the future buffer lake, transport of recreational vessels and protection of the city against storm events, among others. Thus, the usability of the lock is an important aspect to be considered and, therefore, has a weight of 35%. In the Usability Criteria are consider the reliability and adjustments of the structure. The reliability is related to the resistance and stability of the structure. Therefore, reliability has a weight of 75% with resistance and stability with equal weights (50% each). Locks design lifetime is generally 100 years and so is this one. During the lifetime of the lock, changes in the area may occur. An increase in the traffic, an increase in the size of the ships using the lock, a sea level rise, an increase of frequency and/or intensity of storms or an increase of rainfall and subsidence of soil are some possible situations that can appear in the future. Therefore, adjustability refers to the capacity of adaptation of the structure to all these kind of changes that may occur in the future and has a weight of 25%. Maintenance (15%) Maintenance is evaluated regarding three aspects: frequency of maintenance, the level of difficulty to perform the operation itself and the sensibility to the accumulation of sediments. This last point is included since the seabed of the area is composed by fine sediments, mainly clay. Moreover, the lock of Holwerd is projected to be opened for most of the time. Thus, sediments will be transported through the lock due to the tide propagation and the
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channel flow. These sediments can be accumulated in the gates and influence their functionality in the moment of closing doors to prevent storm events. During the maintenance of the lock, no passage of vessels will be available. Therefore, maintenance is an important aspect to be considered. Maintenance was weighted with a 15%. The frequency and the operation aspects have a weight of 40% each, while the sensibility to sediments aspect have a weight of 20%. Environmental (10%) The overall environmental impact is expected to be positive once the entire project is finished (including the connection to the canal, which will induce the mixture of fresh and salt water) since the project leads to an improvement from the ecological point of view. Therefore, in this section, it will be only considered the visual impact of the gates. Thus, the weight of the environmental criterion is 10%.
MCA Results This item presents the results of the Multi Criteria Analysis for the three possible alternatives of gates for the guard lock: Single-Leaf Gate, Sector Gate and Folding Gate. Table 7 presents the Multi Criteria Analysis results. The grading (1,2 and 3) refers to lowest/worst, medium and highest/best. Therefore, the option with the highest grade will be the selected one. Single- Sector Folding Criteria Weight Leaf Gate Gate Gate Cost (40%) 0.4 2 1 2
Resistance 0.13125 1 3 2 Reliability (50%) Usability (75%) Stability (35%) 0.13125 1 2 2 (50%) Adjustments (25%) 0.0875 3 2 3 Frequency (40%) 0.06 3 2 3 Maintenance Operation (40%) 0.06 3 2 3 (15%) Sensibility to sediments 0.03 3 2 2 (20%) Environmental Visual Impact (100%) 0.1 2 1 3 (10%) Sum 1 2.0 1.6 2.3
Table 7: Multi Criteria Analysis of the gates possibilities for the Guard Lock of Holwerd
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According to the Multi Criteria Analysis, the best option for the gate of the Guard Lock of Holwerd is the Folding Gate.
5.4.6 Alternatives Canal Lock As it was done for the guard lock, different alternatives for the Canal Lock were investigated. First, a pre-selection of the type of gate that fits the demands of the Canal Lock were carried out. Four options were selected as possible alternatives for this lock: Mitre Gate, Single-Leaf Gate, Inflatable Gate and Folding Gate.
Mitre Gates The Mitre Gates are considered as a possible alternative to the Canal Lock since they are described as a relatively good solution for small widths and have relatively low costs. One of the disadvantages of the mitre gates is that it cannot be opened or closed under water head difference, so the operation of the gate would be limited to low water levels only.
Single-Leaf Gate Some of the advantages of the single-leaf gate are that it is suitable for locks with small width. The listed disadvantages are: a long recess area in lock head, large water displacement while opening and closing and width restriction. The disadvantages of this type of gate do not excel the advantages of this gate, so it is a conceivable alternative.
Inflatable Gate Although the inflatable gate presents risks of leakage, this type of gate could be suitable for the canal lock since this lock will be in relatively calm area. Also, this gate presents very small aesthetical impact. Thus, the inflatable gate was considered as possible alternative for the canal lock of Holwerd.
Folding Gate The folding gate was considered as a possible alternative for the canal lock since it requires relatively small recess area and it is an improvement of the mitre gate, which is also feasible for this type of lock.
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5.4.7 MCA Canal Lock Gate More than one option is suitable to solve the problem presented in this project, but there is more than one criterion that needs to be considered in order to choose the best alternative for the canal lock, therefore a multi criteria analysis was completed. The criteria used are: cost, usability, maintenance, and environmental. The criteria were weighted and graded according the relevance for the project and the client’s requirements and it can be seen in the sections below. As a result, cost, usability, maintenance, and environmental has a weight of 40%, 35%, 15%, and 10% respectively. Costs (40%) The canal lock is also one of the most important structures in the project Holwerd and Sea since its main function is separate the saline water from the freshwater. The fresh water in the canal is used for agriculture and connects to other bodies of fresh water considered heritage. Therefore, the separation of the saline water and the fresh water in the canal is important. However, the project has a budget of 1.5 million of euros and that accounts for others structures as well such as the navigation channel, buffer lake, etc. Therefore, the cost was considered the main criterion with 40% of the weight. Usability (35%) The canal lock has many functions: connect the city canal with the buffer lake and sea, transport of recreational vessels and control of the saline intrusion in the canal, among others. Thus, the usability of the lock is an important aspect to be considered and has a weight of 35%. In the Usability Criteria are considered the reliability and the adjustments of the structure. The reliability is related to how efficient the gate is to separate water bodies is, for instance the risk of leaking. If the canal lock fails, it will allow the saline water to penetrate further in the fresh water that is used for agriculture, besides of reaching heritage water bodies causing a huge environmental impact. So reliability is an important aspect to be consider. Therefore, the structure has to be efficient in separating water bodies, and hence reliable, in order to protect the fresh water from the city and other areas from saline intrusion. Locks design lifetime is generally 100 years and so is this one. During the lifetime of the lock, changes in the area may occur. An increase in the traffic, an increase in the size of the ships using the lock, a sea level rise, an increase of frequency and/or intensity of storms or an increase of rainfall and subsidence of soil are some possible situations that can appear in the future. Therefore, adjustability refers to the capacity of adaptation of the structure to all these kind of changes that may occur in the future.
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Reliability and adjustments have a weight of 75% and 25%, respectively. Maintenance (15%) Maintenance is evaluated regarding two aspects: frequency of maintenance and the level of difficulty to perform the operation itself. During the maintenance of the lock, no passage of vessels will be available. Therefore, maintenance is an important aspect to be considered and has a weight of 15%, with frequency and operation with 50% each. Environmental (10%) The overall environmental impact of the canal lock expected is positive since it will allow the connection between the fresh water and salt water creating new habitats but with the control of the intrusion of salt water. Therefore, in these criteria it will be only considered the visual impact of the gates. In addition, the visual impact is also related to the objective of attracting people to the city of Holwerd. The weight of the environmental criterion is 10%.
MCA Results This item presents the results of the Multi Criteria Analysis for the four possible alternatives of gates: Mitre Gate, Single-Leaf Gate, Inflatable Gate and Folding Gate. Table 8 presents the Multi Criteria Analysis results. The grading (1, 2 and 3) refers to a lowest/worst, medium and highest/best. Therefore, the option with the highest grade will be the selected one. Mitre Single-Leaf Inflatable Folding Criteria Weight Gate Gate Gate Gate Cost (40%) 0.4 1 2 3 2 Reliability 0.2625 (75%) 3 2 1 3 Usability (35%) Adjustments 0.0875 (25%) 3 1 1 1 Frequency Maintenance (50%) 0.075 2 3 1 3 (15%) Operation (50%) 0.075 2 3 1 3 Environmental Visual Impact (10%) (100%) 0.100 1 1 3 2 Sum 1 1.9 2.0 2.0 2.3 Table 8: Multi Criteria Analysis of the gates possibilities for the canal lock. According to the Multi Criteria Analysis, the best option for the gate of the Canal Lock is the Folding Gate.
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6. Channels
6.1. Basis of Design A navigational channel is to be designed connecting the Wadden Sea with the city of Holwerd. From the dike, an inner channel will be designed along with a buffer lake to facilitate a storage area. Previous analysis and data collected which are stated in previous sections of this report, are crucial to a successful design. All the information mentioned before gives a more detailed overview of the situation, making the requirements, restrictions, and boundary conditions easier to define. The hydraulic boundary conditions (Section 5.2) were based on the Hydraulic Conditions for Primary Flood Defenses (HR 2006) with a return period of 1/4000. The lifetime of the guard lock of Holwerd is 100 years with a probability of failure of 2.5% and it was defined based on the return period of 1/4000 by the formula:
! = 1 − exp (−!"#$) Where: p = probability of failure; f = frequency of design conditions; TL= lifetime;
6.2. Design of Channel Elements 6.2.1. Embankment of the Channel For both the outer channel and the inner channel, a two-lane channel is proposed. In order to provide the adequate discharge through the dike (which facilitates flushing via the gate), the outer channel section connecting the dike is designed narrower than the rest of the channel. There are two different channel types that are proposed based on the channel embankments.
Channel with a sloping embankments covered in vegetation In Figure 36 is presented a cross-section scheme of a channel with sloping embankments. On one hand, the sloping embankments have more stability. Therefore, hard revetments are not needed and vegetation can be used to reduce possible erosion. However, this type of embankment implies higher dredging volumes.
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Maneuvering Lane
Figure 36: Channel with a sloping embankment.
Channel with vertical hard embankment Vertical embankments need less dredging than the sloping ones. However, this option presents some disadvantages due the turbulence generated by recirculation and secondary circulation around the sharp edges. Therefore, this alternative of embankment requires stronger bed protection and stronger material for the construction, which ultimately leads to an increase of the project cost. At this point, Alternative 1 seems more suitable for the project since it has more stability and matches with a “building with nature” perspective. However, since the dredging aspect is a key factor, we will continue evaluating Alternative 2 so we have a broader view of both options. In Figure 37 is presented a cross-section for a channel with vertical embankment.
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Passing Distance Bank Bank Clearance Clearance
Maneuvering Maneuvering Lane Lane
Channel Width Figure 37: Channel with vertical hard embankment.
6.2.2. Width of Channels Based on the above proposals, the dimensions of the channel are calculated incorporating the site conditions and other related factors according to PIANC recommendations. Both navigational channel and inner channel will have the same width and type of embankments. The proposed navigational channel can be also considered as an ‘Inner channel’ since it lies in a relatively sheltered area. Due to the effect of the surrounding islands of Ameland, the effect of waves is negligible regarding the width of the channel. However, tide effect has to be taken into account with accurate estimation since the area is characterized as a tide- dominant area.
Alignment According to PIANC, the channel alignment should be calculated with regards to: • The shortest channel length; • The existence of any condition or basin at either end of the channel; • The need to avoid obstacles or areas of accretions which are difficult or expensive to remove or require excessive (and hence costly) maintenance dredging; • Prevailing winds, currents and waves; • Avoiding bends close to port entrances; • The edge of the channel should be such that ships passing along it do not cause disturbance or damage. If possible, it is preferable to align the prevailing longitudinal currents so a cross-current condition is minimized. In the case of wind and waves, the same analysis applies, although
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these may come in several different directions. Information about currents winds, and waves can be found in section 3.
Width of the Straight Sections (For two-lane channel): Considerations In approach channels, vessels are influenced by several conditions, which include, among others, maneuverability, navigation aids, and environmental factors. The conditions that were considered the most significant and influential for this project are stated below. Basic Maneuverability In approach channels, vessels under manual control tends to sweep a path, which relates to the response speed of the handler/ship to the visual indicators and the response speed of the ship to the actions of the rudder. The most important elements on which the maneuverability lane dependent on are: • The inherent maneuverability of the ship (dependent on the water depth/draught ratio); • The ability of the ship-handler; • The visual indicators available; • The overall visibility. Figure 38 describes the real and theoretical maneuverability path of a vessel.
Figure 38: Width of the maneuverability lane. Environmental Factors These environmental factors were lightly mentioned in the alignment section above. In this section, a deeper analysis will be conducted.
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Wind Crosswind will affect the ship trajectory at all speeds but its greatest impact will occur during low speed since it will cause the ship to drift sideways as it can be seen in Figure 39.
Figure 39: Impact of the environmental factors on the vessel path.
Currents Currents influent deeply in the ship’s path as well. Cross currents affect the ships ability to maintain a straight path but longitudinal currents disturb its maneuverability and ability to stop, which indicates that currents are one, if not the most, influential environmental factor in a vessels path. If needed, operational limits should be stated in order to provide a secure channel, which are specified further along of this document.
Waves Naturally, waves affect the channel design entirely, width and depth equally, and in case of big waves locations, are a cause of concern. Detailed information about waves should be obtained and analyzed in order to determine the impact on a channel design, and can be found in section 3.4. Passing Distance Since the navigational channel is set to be a two-way channel, preparations should be made to provide a secure passage. Distance between passing vessels should ensure that the ship- interaction is reduced to a minimum or, at least, an acceptable amount. In Figure 40 it illustrates the passing distance.
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Figure 40: Passing distance.
Bank Clearance Bank interaction can cause a boat to sheer uncontrollably. By allowing an additional width to the maneuvering lane, bank interaction can be avoided depending also in the ship speed, bank height and slope, and depth/draught ratio.
Calculations ! ! ! = 2!"# + 2 Wi + !"# + !"# + !" !!! !!! In Table 9 are presented the meaning of the terms in the equation above.
Wbm Width of the maneuverability lane
Wi Additional width due to specific site conditions
Wbr and Wbg Additional widths for Bank Clearance
Wp Additional width for passing distance in Two-way traffic Table 9: Definition of the elements in the equation.
The calculations of the above terms are shown in the Appendix E. By taking all these factors into account the approximate width for the proposed navigational channel can be estimated as follows:
Alternative 1: Sloping Channel Edge and Shoals ! ! ! = 2!"# + 2 Wi + !"# + !"# + !" !!! !!!
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! = 2 ∗ 1.3! + 2 ∗ 1.3B + 0.3! + 0.3! + 1.0! ! = 6.8! = 6.8 ∗ 4.0 ! = 27.2 !
For the convenience of construction, the bottom channel width is proposed to be 30 m. Also for the slope on either side of the channel it is proposed to have 1:4. In Figure 41 is presented the dimensions of the width of the channel for Alternative 1.
4m
1.6m 1.6m 11.4m 11.4m
30 m Figure 41: Dimensions of width of the channel in Alternative 1.
Alternative 2: Steep and Hard Embankments Structures
In case of having steep and hard embankments structures, the total with of the channel would be: ! ! ! = 2!"# + 2 Wi + !"# + !"# + !" !!! !!! ! = 2 ∗ 1.3! + 2 ∗ 1.4B + 0.4! + 0.4! + 1.0!
! = 7.2! = 7.2 ∗ 4.0 ! = 28.8 !
Figure 42 presents the dimensions of width of the channel for Alternative 2.
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4m
1.6m 10.8m 1.6m 10.8 m
28.8m
Figure 42: Dimensions of channel in Alternative 2.
6.2.3. Depth of Navigational Channel Navigational Aids It is proposed to provide reasonable navigational aids and also sound depth guarantee for the ships using the channel. According to the PIANC, this attributes to the following group: Depth Guarantee: - Group B (Satisfactory navigational aids for day navigation only where given depths are guaranteed.
Fully Restricted Channel (canal) The proposed channel falls under the category of ‘fully restricted channel’ (Figure 43) where the either side of the channel is constrained by embankments.
Dredged Channel
Figure 43: Fully Restricted Channel. Considerations Tide Height Since Holwerd’s future waterway is subject to tidal action, a decision was made that it will be usable even during the low tides, being compatible with depth, squat, and speed. Although, a traffic increment due to a shorter usable window for the channel is a viable option since
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currently traffic is not a problem, it was decided that it was more beneficial to allow ship navigation all the time, as long it is secure (not during extreme conditions). Operational Limits There are certain limits beyond which operations become unsafe. For instance, handling a ship in bad weather conditions, the currents too strong or the wind speed too great. The pilot may not be able to control the vessel safely. Therefore, it is important to estimate these limits. Marine Traffic and Risk Analysis In order to fulfill the safety and navigability requirements for the shipping traffic, a marine traffic analysis and risk analysis should be carried out. On the one hand, marine risk is related to the risk to life, damage to the marine environment and occasionally the potential commercial loss to a port in the event of an accident. On the other hand, overall risk is defined from the frequency with which a particular type of accident may occur combined with some measure of its consequence. Consequence may be measured as the number of casualties, damage to the environment or potential loss of revenue.
Calculations In designing the depth of the channel, three factors are given consideration to provide a navigable channel with a convenient maneuverability. The draught of the design ship Since the design ship is a sailing yacht, the proposed draught is 2.1m. The underkeel clearance It is important to provide sufficient underkeel clearance taking all the factors related to depth variability into account. Hence, the proposed underkeel clearance is 0.7m. Tolerance for sedimentation Except during LW tide, the water level within the channel would increase. Since no maintenance dredging will be carried out, sedimentation will be present over years. Therefore, a tolerance for sedimentation is essential. This tolerance proposed is 0.3m as a freeboard. Consequently, the total required depth of navigational channels is 3.1 m NAP
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Squat The vessel speed is considered to be 5-8 knots. Due to this low speed the resulting Froude depth number is relatively low. The underkeel clearance is taken as 0.7m. With these limitations the squat can be controlled and hence not taken into account.
6.2.4. Selection of Embankment Finally, after determining the dimensions of the channel we can analyze more accurately the two proposed alternatives by calculating the volume per unit area to dredge. • Alternative 1: Sloping embankments 3 V1=109.74 m /m • Alternative 2: Vertical embankments 3 V2=84.32 m /m
Although the first alternative implies more dredging, it provides higher embankment stability. Thus, since sloping embankments has a higher stability and are suitable for growing vegetation to counteract the erosion problems that may occur, option 1 will be selected as the design alternative.
6.2.5. Dimensions of the Outer and Inner Channel The inner and outer channels were designed in order to obtain an ebb-dominant geometry so the ebb velocities can be higher than the flood velocity, which is favorable to export sediments. In order to obtain such geometry, the water depth during low water must be higher than the water depth during high tide. This can be achieved by designing the buffer lake with extensive intertidal areas (wet during high tide and dry during low tide) and a deep main channel. According to these considerations, the following dimensions of the inner and outer channel were obtained. Therefore, the dimensions of the inner channel are,
• Width of the main channel - !! = 30 ! • Width of intertidal area - ! = 400 ! • Slope of embankment = 1:4;
• Water depth in low water - ℎ!" = 3.25 ! • Water depth in high water - ℎ!" = 2.7 ! • Length of inner channel - !! = 850 !; • Length of outer channel - !! = 1690 !; The slope adopted was defined based on clay stability, so no hard embankment is needed. Instead, salt marshes can develop in the intertidal areas, contributing to the stability of the channel.
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Another method of ensuring ebb-dominant geometry is through the ratio between tidal amplitude and mean water depth of the channel: ! 1.75 (1) = = 0.35 ℎ 5 For small ratios of tidal amplitude and channel water depth such as the above, an ebb- dominant behavior of the channel is expected.
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From Figure 44 to Figure 46 is presented the cross-section of the inner channel, cross-section of the outer channel and a longitudinal section, respectively.
Figure 44: Cross- section inner channel.
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Figure 45: Cross-section outer channel (zoom close to the opening).
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Figure 46: Longitudinal section of the channel.
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6.2.6. Water Level in the Outer and Inner Channel Tidal Influence According to the tidal information presented in section 3, it is assumed that the tide cycle is semi-diurnal (form factor = 0.13). Hence the tide period is 12 hours and 25 minutes (earth rotation plus the moon rotation around the earth).
The outer channel is designed in a way that it has a seaward end and runs until the main dike. From that point onwards, the inner channel is constructed until it connects the waterway to an existing small water body (to be expanded) located in the south of Holwerd. The entrance of the inner channel, which comprises a storm surge barrier, acts similar to a tidal inlet. Therefore, the inner channel can be considered as a basin with tidal influence.
Basin Length/Tidal Wave Length Since tidal propagation can be approximate as shallow water wave propagation due to their long wavelength when compared to the general depth of oceans, the tidal wave length (λ) can be calculated from the equation of wavelength for shallow water (linear wave theory):
! = ! . ! (2) where ! = phase velocity, and in shallow water approximation: ! = !ℎ; ! = wave period, in this case, tide period, ! = 12ℎ25 min = 44700 !; ℎ = mean water depth in the inner channel, ℎ = 5 !; This yields a tidal wave length of λ = 241,286 m. The inner channel extends from the opening on the dike to the vicinity of the Holwerd city. Therefore, the length of the basin is approximately 850 m. In order to determine the basin characteristics, the basin length/tidal wavelength ratio must be analyzed in order to verify if the basin behaves as a short basin or a long basin: !"#$% !"#$%ℎ 850 = = 0.35% < 5% !"#$% !"#$ !"#$%ℎ 241,286 As the basin length is smaller than 5% of the tidal wave length, the inner channel can be categorized as a ‘Short Basin’. For design purposes, it is assumed that the inner channel depicts inherent characteristics of a short basin. Those can be summarized as follows: i. The water level in the basin immediately follows the water level in sea; ii. It behaves in the pumping mode where the water level throughout basin goes up and down at the same time (Uniformly oscillating water level)
!" iii. There is no variation in the tidal amplitude along the channel axis. i.e = 0 !"
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With the use of the assumption of short basin, the friction in the basin is neglected. Even though, zero-friction is generally an unrealistic situation, by assuming negligible friction the design becomes more conservative. Thus, that particular assumption could be justified with respect to safety.
6.2.7. Storage Area Approach In order to calculate the respective water levels inside as well as outside of the basin, the storage area approach is incorporated. Figure 47 below depicts the storage area of the basin considered.
Figure 47: Storage area sketch The following equations constitute the storage approach: !ℎ (3) ! = !" !" Where: ! = flow rate through the opening; !" = surface area of storage area (basin); ℎ = water depth; Furthermore, the total flow rate can be described as: !ℎ (4) !! ℎ . ! = ! ! ! ! !" Where: ! =flow contraction coefficient;
!! = width of the opening;
!! =river discharge;
ℎ! = water depth in the opening defined as: 3 (5) ℎ = max ℎ , ℎ ! ! 2 ! Where:
ℎ! =water depth outside and ℎ! = water depth inside;
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! =velocity through the gap which is defined from the potential energy transformed in kinetic energy when flow passing through an opening: 1 (6) ρgΔh = !!! 2 This yields a flow velocity:
! = 2!"ℎ (7) Where: ! = gravitational acceleration; !ℎ = water depth difference from inside and outside the opening:
!ℎ = (ℎ! − ℎ!) (8) The following values are used for the parameters mentioned above: !" = 351900 !²;
!! = 30 !; ! = 0.6; ! = 9.81 !/!²;
!! = 0
A 1D model was simulated with a time-step of 0.01 hrs for 24 hrs. In order to obtain the water level inside and outside the basin, the mean water depth was subtracted from the water depth results of the simulation. In Figure 48, the results of the water level in the inner and outer channel are depicted. It can be observed that there almost no phase difference on the tide propagation in the inner channel as expected for a short basin as well as no damping of the water level in the inner channel due to the non-friction assumption. In reality it will occurs friction, however the non-friction assumption is more conservative once the water levels inside the buffer lake are used to determine the height of the inner dikes.
Figure 48: Water Levels in Channels
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6.2.8. Wind Induced Wave Growing In order to check for wave generation due wind in the buffer lake, the dimensionless fetch and wave height formulas were applied (Holthuijsen, 2007): !" (9.81)(900) ! = ! = ! = 138 !!" (8)
!! !.!" !!/! = 2.88!10 ! = 0.03
! ! !!/!!!" 0.03(8) ! = = = 0.2 ! !/! ! 9.81 Thus, waves of 0.2 m height can be expected to occur in the buffer lake if NW winds of 8 m/s occurs. Other directions of wind will imply less fetch, and hence, smaller wave heights. The velocity of the wind was determined as the maximum wind velocity observed in the wind data from BMT ARGOSS Wave Climate database (53¡30’N and 5¡50’E, 1992-2014). In addition, a risk of overtopping analysis was carried out for the inner dikes. More information about can be found in Appendix F.
6.2.9. Velocity in the Channel In order to check for the exporting of sediment, velocities were calculated in the opening of the dike (gate) and in the inner and the outer channel. To estimate the velocity in the opening, the storage approach approximation was applied where potential energy is transformed in kinetic energy when flow passing through an opening (Section 6.2.6). The velocity calculated in the opening is 0.9 m/s, which is a good approximation for the equilibrium velocity for keeping an inlet opened according to Escoffier’s model (Bosboom & Stive, 2015). For the inner and outer channel, the velocity was estimated based on continuity equation for a short basin: !" !" (9) + ! = 0 !" !" Where ! = tidal discharge in the channel cross-section; ! = with of the channel; ! = water level;
!" = volume change due to in-going and out-going transport; !"
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!" ! = volume change due to water level change; !"
Equation 9 can be rewritten as: !" !" (10) − = ! !" !"
The tidal discharge in a certain cross-section of the channel can be determined from the integration along the channel axis from a location x to the end of the basin (!"): !" !" (11) ! !, ! = ! !" ! !" The tidal discharge in a cross-section depends on the amount of water that is necessary to fill the basin landward of the cross-section under consideration (tidal prism). In a short basin, !" there is no variation of the tidal amplitude along the channel axis !" = 0 , thus the water level in the basin follows immediately the water level seawards. These consideration yields: !" !" !" (12) ! !, ! = !!!! = !"# = !! !" ! !" From equation 12 is possible to obtain the velocity in the flow-carrying cross-section of the channel:
!" !! (13) !!(!, !) = !" !! Where:
!! = basin surface area upstream;
!! = channel cross-section area; Figure 49 depicts the water level and velocity in the inner channel and it can be observed that the velocity leads the water level with a phase difference of 90¼, which is also a resultant of the short basin assumption. The maximum velocity observed in the inner channel is 0.06 m/s.
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Figure 49: Water Level (left axis) and velocity (right axis) in the inner channel. Figure 50 below illustrates the velocity for the outer channel. The maximum velocity observed in the outer channel is 0.12 m/s.
Figure 50: Velocity in the outer channel Both maximum velocities from the inner and outer channel are higher than the threshold the start of motion of fine sediments (!∗ = 0.02 !/!). The minimal velocity for transport of fine sediment was obtained from the initiation of motion modified Shields diagram (Parker, 2006) and the shear formula: !∗! (14) !∗ = ℎ!" Where: !∗ = shear velocity; ℎ = mean water depth; ! = gravitational acceleration; ! = grain size; From the diagram we obtained the value of shear stress for silt (! = 0.04 !!), !∗ = 0.2 !!!. Then, the shear velocity is obtained by manipulation of Eq. 14:
!∗ = !∗ℎ!" (15) Where:
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!∗ = 0.2 m-1 ℎ = 5 m; ! = 9.81 m/s²; ! = 0.04 mm; In this way, the shear velocity for initiation of fine sediments is !∗ = 0.02 !/!
Figure 51: Modified initiation of motion Shields diagram (Parker, 2006). Obtained from lecture notes of Sediment Dynamics course. It is important to note that the velocities were calculated from a one-dimensional model with a sinusoidal symmetric tide and that is the reason there is no residual negative velocity in the results as expected from the ebb-dominant geometry of the channel. However, in reality the tidal wave that reaches Holwerd has an asymmetry due the shallow water depths of the region and the geometry of the channel will also induce tidal asymmetry. Moreover, the discharge from the connection of the buffer lake with an existing water body (to be expanded) is not considered in this model and this also affects the velocity in the channel. Therefore, these results should be considered as first estimates of velocities and more detail calculation (3D simulations) should be carried out in order to check for more accurate velocities.
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7. Sluices
7.1. Design of the Lock According to PIANC (inCom, Report of WG, January 2006) the design procedure of barrier structures includes the following steps: • Site parameters, as the selection of the site (depends on the positioning of the structure, easy access during construction and maintenance, requirements for extensive foundation works, among others) • Required information such as bathymetry, water discharge and wind magnitude, and the necessary loads for the technical analysis and the structure design • Navigation and operational requirements such as navigation safety, sedimentation. • Design criteria to assess the degree of applicability of each type of structure to the proposed project site In Figure 52 a flow chart of the design procedure of a barrier structure is shown.
Figure 52: Flow chart of the design of a barrier.
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Gate selection type is a key stage in the design of the barrier due to the fact that the choice will have important consequences in the operational, financial and other aspects of the project that are more critical than the detailed engineering. Besides, it should be noticed that it must have given a more carefully look to the design of weir gate (than a fixed ground-based structures) because: • They are movable • Loads are difficult to calculate particularly hydrodynamic effects, varying loads, fluid structure interactions) • Shapes can be complex (3D stiffened shells) which make stresses difficult to calculate • These structures are mainly under-water and often difficult to inspect and to maintain • They are subject to deterioration from various causes: vibration, corrosion, wear, flow, • Structures are typically kept in use significantly longer that their design life. Therefore, robust solutions and high safety factors are required.
To achieve a higher level of confidence the design procedures needs to be integrated with risk assessment, maintenance, control of operation and environmental impacts and aesthetics: • Maintenance: it is one of the most important aspects of a weir design since it has a considerably affect in the costs. A higher efficiency/cost ratio will be reach if maintenance is taken into account in the early design stage. • Control of operation: it is recommended to duplicate all the critical elements of the control system so that reach a higher reliability. • Risk assessment: the different possibilities of failures and the current probability of their appearing with their respective consequences must be evaluated. • Environmental impacts and aesthetics: it is important to consider the environmental impacts that can occur during the construction and the operation of the barrier in order to minimize its effects.
7.2. Basis of Design The first step in the design, and the most important one is, to fully understand the purpose and requirements of it, which means that it is imperative that the location, stakeholders, main problem, and budget and known in fully details (all of this information can be found in
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previous sections of this report). The requirements and boundary conditions applied for the design of the guard lock are described in Section 5.2. In order to follow the requirements and boundary conditions, the gate presents the following dimensions: • Top of Structure = + 8 m NAP; • Bottom of Structure = - 5 m NAP; • Height = 14 m; • Width = 30 m;
The material of the gates considered is timber and the cost estimated is €100,000 per gate, in total €200,000. More information about cost estimation and the material is presented in Appendix H.
7.3. Closure of Gates The gates should be closed when the water level is higher or equal to +2 m NAP. Based in the water level data from Rijkswaterstaat of Holwerd station (53¡23'43"N, 5¡52'44"E) from 02/25/2012 to 03/10/2016 that means a probability of exceedance of (of past events) of 0.5%. Table 10 and Figure 53 presents the statistical analysis of the water level data. However, this analysis represents the statistics of individual events from past events. To obtain the frequency of the gates, the peak over a threshold analysis (PoT) was carried out, where the threshold was defined was 2 m and a Gumbel distribution was adopted. From this analysis, the frequency of closing the gates is approximately 5 months. More details of the analysis can be found in Appendix J.
Wave height Accumulated Probability of Probability of classes Frequency frequency occurrence exceedance Lower Upper 0 0.5 47139 47139 0.409 0.591 0.5 1 50223 97362 0.844 0.156 1 1.5 16133 113495 0.984 0.016 1.5 2 1521 115016 0.997 0.003 2 2.5 259 115275 0.999 0.001 2.5 3 73 115348 0.999 0.001 3 3.5 44 115392 1.000 0 Table 10: Statistical properties of water level data from Holwerd station from Rijkswaterstaat
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Exceedance of Water Level 3.5 3 y = -0.322ln(x) + 0.3033 R² = 0.98288 2.5 2 1.5
Water Level 1 0.5 0 1 0.1 0.01 0.001 0.0001 Probability of Exceedance
Figure 53: Probability of exceedance of water level from the database of Rijkswaterstaat.
7.4. Material and sections For this analysis, the material used was pine sand wood and the sections were: • HSS20x12x5x5/16 • Pipe 12XS • PXX8 The HSS20x12x5x5/16 section was adapted when defining the elements for it to be a full piece instead of a hollow section, which resembles the material in a better way. The pipe’s material is a Fy 50 psi steel since it would make the structure more resistant, although this corrosion protection most be considered. This sections and materials might not be available in the location of the project so a study of the availability of material must be done in order to make a more precise design.
7.5. Analysis of Forces Two cases had been considered for this analysis and are shown below:
Figure 54: Storm surge scenario
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Figure 55: Flushing scenario
7.5.1. Storm Surge Scenario Figure 54 is in case of a storm surge while the gate is closed. The purpose of this analysis is to check the strength, stresses, and momentum of the gate while having the biggest head difference possible. The higher water level is in the inner side of the arc-like shape while the lower (inner channel) water level is in the outer part. The angles and lengths of the model used for the calculations are based on other samples that were encountered during this research; hence a deeper analysis along with the manufacturer of the gate should be produced to ensure the safety of the gate since it is the primary defense of the city (and the country). For this analysis, water pressure was taken into account but loads such as, accidental boat crashes, ice, among others, should be included in further analysis.
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Figure 56: Water pressure distribution Below the results of the analysis are presented.
Figure 57: Maximum momentum As seen in Figure 57, the maximum momentum occurs at the bottom center of the gate, which allows us to check that the model behaves properly since the biggest pressures are at the bottom and this will be the furthest point from the supports. The maximum momentum is 33.75 kN¥m while the minimum momentum is 6 kN¥m.
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Figure 58: Maximum shear stress Shear stresses are shown above in Figure 58. The maximum shear stress is 17.037 kN and the minimum is 0.112 kN.
Figure 59: Deformed shape Maximum deformation occurs at the bottom of the gate since it is the zone that carries most of the load. The maximum deformation is 3.232 cm, which can be said that is reasonable and would not cause any unwanted damage.
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7.5.2. Flushing Scenario The second situation is for the flushing process of the inner channel. As it can be seen in Figure 55, the inner channel’s water depth is greater than the outer channel.
Figure 60: Hydrostatic pressure distribution As previously mention in Section 6.2.9, the flow velocity is 0.6 m/s. Hence, the new velocity due to the transfer of potential energy to kinetic energy is:
! = 2!∆ℎ = 8 !/! Therefore, the dynamic pressure caused by the water is: 1 ! = !!! = 32.8 !"# ! 2 With this information, the analysis was conducted providing the following results:
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Figure 61: Shear stresses Figure 61 above indicates the shear stresses cause by the combination of the hydrostatic pressure and the hydrodynamic pressure from the water running. It is important to mention that the operation time of the gate is no greater than 50 seconds and the water differences is not as high, which allows us to think that this will be the worst case scenario while opening the gate for flushing. The structure does not fail according to the provided analysis but a deeper examination with the exact sections, material, and information will help have a better understating of the structural behavior of this configuration.
Figure 62: Forces
Figure 62 provides an image of the resulting forces. In the bottom right section of the gate, the force is not 0 as it appears to be in the graph. Since it is in the opposite direction Ðfrom
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the landside to the seasideÐ the resulting forces is -88.48 kN, which makes it less than 0 obtaining the magenta shade. The maximum deformation is 4.32 cm, which is still under the allowable deformation.
7.6. Foundation of the Lock In order to have a stable structure, a good foundation is critical and, therefore, a complete soil analysis. Soil analysis is outside of the scope of this report and project, nevertheless, it is known that clay is the predominant sediment in Holwerd and the nearby areas. Clay is a fine-grained natural rock or soil material that combines one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure. Properties of clay minerals include plasticity, shrinkage under firing and air- drying, fineness of grain, color after firing, hardness, and, most importantly, cohesion. Each of the properties of the clay can lead to a different classification. Thus, it may be classified according to their color, cooking temperature, its plastic properties, porosity, chemical composition, etc. There are several types of foundations that will be appropriate for the soil in the area, but for this project, piles would be considered. After the design, all the necessary verifications should be made, especially the bearing capacity and shear stresses since they are clay weaknesses.
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8. Dredging Operation
The total volume to be dredged is 2,494,583 m³ consisting 627,640 m³ from the inner channel and 1,866,943 m³ from the outer channel. Part of the dredging volume (~290,000 m³) can be used for the construction of the inner dikes. For the remaining volume of 2,203,843m³, two alternatives are proposed:
1) Nourishment and development of salt marshes in Visbuurt (Figure 64) and
2) Silt islands and development of salt marshes in Holwerd( Figure 65).
8.1. Alternative 1 Alternative 1 is designed in order to increase the development of salt marshes area of the Wadden Sea. The alternative proposes nourishment in the region of Visbuurt where it can be visualized currently no growth of salt marshes. Furthermore, the nourishment helps in coastal protection due the damping of wave energy and the ecosystem receives a nesting site, adding ecological value to the Wadden Sea. One must note that this is a conceptual design and the effectiveness of this measure must be assessed by numerical morphodynamic modelling in the following stages of the project. The dimension of the nourishment provides conditions to the development of the following ecological zones: mud flat, pioneer zone, and low zone. The species of the mud flat zone (Zoster sp and Diatomophyceaesp) will naturally establish themselves by local currents. In the pioneer zone, Salicornia sp and Spartinasp will be artificially colonized. Moreover, as in the pioneer zone, in the low zone, Puccinellia sp. and Halimionesp will be artificially colonized. The time scale of the process of growing of species after colonization of the different zones is in the order of 1 year. According to (Esselink, 2014), after 1 year, in the Wadden Sea, it already happened some development of pioneer species, and a similar development is expected for the islands. It is recommended to colonize with more than one species in each zone, once an ecosystem with more biodiversity is more stable and productive. Regarding the creeks, it is expected that they will be created naturally by the water flow. In Figure 63 it is presented a schematization of the ecological development expected in the nourishment. More information about development of salt marshes can be found in Appendix I.
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Figure 63: Schematization of ecological zones for Alternative 1 The boundary conditions adopted to design the nourishment are: • Available volume of sediment = 2.2M m³; • Bottom level = 0 (estimated); • Tidal amplitude = 3.5m; • Loss of sediment during discharge = 10%. • The underwater slope stability of silt in active water is in order of 1V:10H, according to the Handbook of Geotechnical Investigation and Design Tables (Look, 2014).
To make it possible to create a low zone area, the nourishment should be built with a minimum level of +4.5 m NAP, assuring that the species have around 9 h of dry period. Given the volume of sediment, the existing slope, and the required crest level, the final design comprises around 4,500 m², around 1.5 km wider and the slope of the nourishment extends around 300 m to the sea. In Figure 64 is presented the location of the nourishment proposed in this alternative.
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Figure 64: Alternative 1 for disposal - Nourishment and development of salt marshes in Visbuurt.
8.2. Alternative 2 Alternative 2 proposes building of two silt islands in the Wadden Sea that will provide ideal condition to develop a salt marsh ecosystem. These silt islands will work as tidal flats in shallow areas east of the outer channel. In Figure 65 is presented a top view of the area with the suggested position for the islands. The salt marsh traps sediment, so for the region, it can help on the reduction of sedimentation in the channel along the years, thus, reduction of costs due to dredging activities. This phenomenon of sediment trap generated with salt marshes is describe as positive feedback which a perturbation in the system grows in time. For the ecosystem, the salt marsh provides a nesting site, especially for birds, adding ecological value to the area by increasing biodiversity. The dimensions of the islands provide conditions to the development of the same ecological zones as in alternative 1: mud flat, pioneer zone, and low zone. Therefore, the same development of species described in the previous alternative is expected to occur. The boundary conditions adopted to design the island are: • Available volume of sediment = 2.2M m³; • Water depth in low water = - 1.75 m NAP; • Tidal amplitude = 3.5 m; • Loss of sediment during discharge = 10%.
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• The underwater slope stability of silt in active water is in order of 1V:10H, according to the Handbook of Geotechnical Investigation and Design Tables (Look, 2014). To make it possible to create a low zone area, the islands should be built with a minimum level of +4.5 m NAP, assuring that the species have around 9 h of dry period. Given the volume of sediment, a slope of 1V:50H (milder than the required for stability underwater) and the required crest level of the islands, the final design is two islands with approximately 1.6 km² (circle with 500 m diameter at the bottom and 250 m diameter at the top) at +4,5 m NAP. The position of the islands should be chosen taking in to account relatively shallow water depths and low flow velocities, because if the islands are located in a region where hydrodynamics are high enough to transport sediment then the islands can become a source of sediment for the region, which already faces sedimentation problems. Therefore, morphodynamic simulations are necessary to evaluate this alternative and are not included in the scope of this project. For this reason, alternative 1 is used to estimate the dredging cycles. However, the dredging operation will be similar for both alternatives, except from small differences in time of transporting the dumping material. Thus, the dredging and disposal plan of alternative 1 can be used as reference for alternative 2.
Figure 65: Alternative 2 for disposal Ð 2 Silt islands and development of salt marshes in Holwerd.
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8.3. Dredging Operation Ð Alternative 1 The dredging operation for the inner channel consists of 5 excavators with a productivity of 70m³/oh to dredge the material inland and 5 trucks with capacity of 10 m³ to transport the material to the dumping area. For each excavator, 5 trucks are necessary in order to obtain a non-stop dredging activity. The dredging operation for the inner channel and buffer lake consists of 5 excavators and 25 trucks and the duration is approximately 16 weeks, with 112 working hours per week (16h/day and 7 days per week). Table 11 presents the details for the calculation of the dredging operation in the inner channel. Cycle - Inner Channel Dredging volume 627,640 m³ Excavator capacity 70 m³/oh Truck capacity 10 m³ Soil expansion factor 1.2
Truck capacity with soil 8 m³/oh expansion Cycle
Filling time (1 truck) 0.12 h Full truck velocity 40 km/h Empty truck velocity 60 km/h Travel distance 5.2 km Travel time - truck full 0.13 h Travel time - truck empty 0.09 h Dumping time 0.17 h Total cycle 1 truck 0.50 h Efficiency 75%
Total cycle 1 truck + 0.67 h efficiency 40 min Trucks necessary for 1 5 - excavator
7 days/week Work time 16 h/day 112 h/week Productivity Excavator 7840 m³/week # Backhoe 5 - # Trucks 25 - Total Productivity Excavators 39200 m³/week Total operation duration 16 weeks Table 11: Calculations for the dredging operation for the inner channel For the outer channel, the dredging equipment chosen was a Cutter Suction Dredger (CSD) due to the ability of the equipment to open a front of work in shallow water depths. A pipeline
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will be coupled to the dredger in order to transport the dumping material. To build the islands, one more equipment will be added to the construction methodology: a spreader pontoon. Spreader pontoons discharge the dredged mixture with low velocities very close to the bottom, minimizing the dispersion and loss of sediment during the discharge. The total duration of the dredging operation for the outer channel is approximately 41 weeks. In Table 12 is presented the details for the calculation of the dredging operation for the outer channel. Outer Channel Dredging volume 1,866,943 m³ 1250 m³/oh CSD production 120 oh/week 150,000.00 m³/week Solids in the mixture 30% Volume of solids 45,000.00 m³/week Total operation duration 41 weeks Table 12: Details of calculation for the dredging operation in the outer channel The estimated cost for the dredging and disposal operation is 39 M euros and the total duration of the operation estimated is 41 weeks (10 months). In Table 13, the details of the cost estimation are presented.
Estimated Costs Excavator 30,000 euro/week Truck 10,000 euro/week Inner 5 excavator 150,000 euro/week Channel 25 trucks 250,000 euro/week Total - Inner 6,404,490 euro
CSD 400,000 euro/week Outer Pipeline 150 euro/m Channel Pipeline 4,000 m Total - Outer 20,514,059 euro
Site cost 30,000 euro/week Fill area cost 45,000 euro/week Mob/Demob 8,000,000 euro Salt marsh (colonization + 3,000 euro monitoring)
Total 39,135,771 euro Table 13: Cost Estimation of dredging and disposal operations
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9. Environmental Impact Assessment
The purpose of this Environmental Impact Assessment (EIA) is to analyze the potential effects the project may have on the environment and provide mitigation and/or compensation measures for reducing them. The EIA is implemented to the chosen alternative, already described in Section 5, by using the Conesa Method (Conesa, 1993) for quantifying the environmental impacts. However, before the implementation of the project, is recommended to develop an extended EIA by environmental experts.
9.1. Wadden Sea Conservation Area The Wadden Sea is considered a conservation area as Figure 66 shows. Therefore, the project must have a low impact in the area and mitigation measures must be a priority. Quality level can be described by certain characteristic structures, the presence of certain organisms, the absence of disturbance and toxic effects and by the chemical condition of the habitat.
Figure 66: Conservation area of the Wadden Sea
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The Trilateral Wadden Sea Plan (2009) specify ecological targets needed to be adopted with the objective of maintaining and enhancing the area which is natural, dynamic and undisturbed, including targets for birds and marine mammals (Table 14).
Landscape and Culture Identity Ð to preserve, restore and develop the elements that contribute to the character, or identity, of the landscape. Variety Ð to maintain the full variety of cultural landscapes typical for the Wadden Sea landscape. History Ð to conserve the cultural-historic heritage. Scenery Ð to pay special attention to the environmental perception of the landscape and the cultural-historic contributions in the context of management and planning. Water and Sediment A Wadden Sea, which can be regarded as a eutrophication non-problem area. Background concentrations of natural micropollutants in water, sediment and indicator species. Concentrations of man-made substances as resulting from zero discharges. Salt Marshes An increased area of natural salt marshes. An increased natural morphology and dynamics, including natural drainage patterns, of artificial salt marshes, under the condition that the present surface is not reduced. An improved natural vegetation structure, including the pioneer zone, of artificial salt marshes. Tidal Area A natural dynamic situation in the Tidal Area. An increased area of geomorphologically and biologically undisturbed tidal flats and subtidal areas. An increased area of, and a more natural distribution and development of natural mussel beds, Sabellaria reefs and Zostera fields. A favourable food availability for migrating and breeding birds. Beaches and Dunes Increased natural dynamics of beaches, primary dunes, beach plains and primary dune valleys in connection with the Offshore Zone. An increased presence of a complete natural vegetation succession. Estuaries Valuable parts of estuaries will be protected and river banks will remain in and, as far as possible, be restored to their natural state. Offshore Area An increased natural morphology, including the outer deltas between the islands. A favourable food availability for birds. Viable stocks and a natural reproduction capacity of the common seal, grey seal and harbour porpoise Rural Area Favourable conditions for flora and fauna, especially migrating and breeding birds.
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Birds Favourable conditions for migrating and breeding birds: - A favourable food availability; - a natural breeding success; - Sufficiently large undisturbed roosting and molting area; - Natural flight distances. Marine Mammals Viable stocks and a natural reproduction capacity of the common seal, grey seal and harbour porpoise in the tidal areas and the offshore zone. Table 14: Targets to maintain and enhance the conserved area
9.2. Potential Impacts The potential impacts can be classified in three groups: 9.2.1. Physical Impacts Noise invasion During the construction phase noise is generated. The amount of noise depends on the type of equipment, the performed operation, the distance from the source of noise, the topography, among others. Noise can be a disturbance for local people and fauna. Vibration The equipment used for construction generates vibrations. Depending on the type of equipment used, an appropriate level of vibration may occur affecting residents’ quality of life and fauna. Air quality Fume emissions, dust, and pollution due to waste material can affect the air quality. This factor is also dependent on the type of equipment used. Water quality The dredging process required by the implementation of the navigational channel and the buffer lake, leads to some potential effects on the water quality such as the increase in the turbidity. The discharge of pollutants is also taken into account. Soil quality Contamination of soil due to pollutants generated by the construction machinery needs to be considered.
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9.2.2. Biological Impacts Flora Due to the waste disposals and temporary occupations, the vegetation cover can be affected. Disturbance, modification, or destruction of any vegetation area is analysed as well as the creation of new vegetation areas Fauna Some of the present species can be affected by the development of the construction works. However, this impact can be considered as minor since one of the objectives of the project is to create new brackish fauna in the area by the interaction between salt and fresh water.
9.2.3. Socio-economic Impacts Landscape quality Since the main purpose of the project is to attract people to visit Holwerd, it is important to assess the aesthetic effects of the chosen alternative. The presence of rubbish and debris after the construction phase is also considered as a potential effect. Disruption of infrastructure and services The analysis of the roads and pathways that could be affected due to the implementation of the alternative has been carried out. The impact on irrigation channels is also considered since it can affect agricultural activities. In Table 15 is presented the analyzed potential effects. POTENTIAL EFFECTS Noise invasion due to construction equipment Vibration caused by the construction equipment
impacts Air quality Fume emissions and dust due to construction process
Water Increased turbidity in water caused by the dredging process quality Discharge of pollutants on the water
Physical Soil quality Discharge of pollutant on the soil
Disturbance, modification or destruction of any vegetation Flora area or natural area Damage or alteration to the present biodiversity and habitat
impacts Fauna Biological Introduction of new species
- Landscape Aesthetic effects quality Rubbish or debris Socio
impacts Disruption of infrastructure and services economic Table 15: Summary of the potential effects
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9.3. Mitigation Measures POTENTIAL EFFECTS MITIGATION MEASURES Noise invasion due to Constant maintenance of the equipment and motor construction equipment Vibration caused by the Constant maintenance of the equipment and motor construction equipment Air Fume emissions and dust Constant maintenance of the equipment and motor quality due to construction process Monitoring air quality
Increased turbidity in water caused by the dredging Continuous monitoring water turbidity process impacts Water Use sediment traps when working near waterways. quality Ensure harmful materials are stored in proper Discharge of pollutants on facilities (ex. gasoline). the water Physical Have contingency plans in case of an accident. Continuously monitoring effluent discharges in area. Constant maintenance of the equipment to ensure they are in good working condition. Soil Discharge of pollutant on Ensure harmful materials are stored in proper quality the soil facilities (e.g. gasoline). Have contingency plans in case of an accident. Restoration or revegetation of the site may be necessary. Disturbance, modification Educate staff and clients on low impact techniques or destruction of any and why they should keep to the existing pathways. Flora vegetation area or natural Since it is a conservation area, it should be restored area to the same condition as before project impacts implementation or even improved in some degree as a compensation measure. Damage or alteration to the Concentrate activities into areas that can sustain use
Biological present biodiversity and during specific time periods when impacts can be Fauna habitat minimized Ensure new species are not harmful for the present Introduction of new species ones Necessity to look into alternative locations in case of
Aesthetic effects Landsca negative impacts
pe Provide garbage bags and appropriate waste quality Rubbish or debris containers. economic
- Educate staff on eco-friendly solutions.
impacts Provide temporary roads and access to the affected Disruption of infrastructure
Socio areas. Choose the optimal period to implement the and services project to minimize disruptions. Table 16: Mitigation measures
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9.4. Quantification of Environmental Impacts In order to quantify the environmental impacts, the simplified Conesa Method is applied. This method is base in the following criteria: CRITERION MEANING Defines if a specific action has a positive or negative Sign +/- impact on the considered factors Intensity IN Level of incidence of the impact in the affected area Area of influence of the impact in relation to the area Extension EX in which the effect is manifested Indicates how long the effect of the impact is going to Persistence PE be present Evaluates the possibility of returning to the initial Reversibility RV conditions by natural means once the activity causing the impact is no longer present Evaluates the possibility of returning to the initial conditions, fully or partially, by human intervention Recoverability RC once the activity causing the impact is no longer present Table 17: Criteria for Conesa method
All those criteria are evaluated as follow: SIGN INTENSITY (IN) Positive impact + (Level of incidence) Negative impact - Low 1 Medium 2 High 4 Very high 8 Total 12 EXTENSION (EX) PERSISTENCE (PE) (Area of influence) (Permanence of the effect) Local 1 Transient 1 Partial 2 Temporal 2 Extensive 4 Permanent 4 Total 8 REVERSIBILITY (RV) RECOVERABILITY (RC) (Reconstruction by natural means) (Reconstruction human intervention) Short term 1 Immediately recoverable Medium term 2 Recoverable in medium term 1 Irreversible 4 Mitigatable o compensable 2 Irrecoverable 4 8 Table 18: Evaluation of criteria
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9.4.1. Environmental Importance (I) Based on the criteria previously presented, the environmental importance (I) can be calculated by applying the following algorithm: I= (3IN+2EX+PE+RV+RC) Regarding the environmental importance, impacts can be classified as follow: IMPACT I Compatible <15 Moderate 15-35 Severe 35-50 Critical 50 Table 19: Importance of impacts
9.5. Evaluation of the Chosen Alternative Applying the simplified Conesa method, each impact is analyzed and the results are summarized in Table 20.
IMPACT SIGN IN EX PE RV RC I Noise invasion due to - 2 1 1 1 1 11 Compatible construction equipment Vibration caused by the - 2 1 1 1 1 11 Compatible construction equipment Fume emissions and dust due to Air quality - 4 2 2 1 2 21 Moderate impacts construction process Increased turbidity in water
ysical - 4 4 2 1 1 24 Moderate Water caused by the dredging process Ph quality Discharge of pollutants on the - 2 2 4 4 4 22 Moderate water Soil quality Discharge of pollutant on the soil - 2 2 4 4 4 22 Moderate Disturbance, modification or Flora destruction of any vegetation - 4 4 4 4 8 36 Severe
impacts area or natural area
Damage or alteration to the - 2 2 2 4 4 20 Moderate Fauna present biodiversity and habitat
Biological Introduction of new species + 2 4 4 4 8 30 Moderate Landscape Aesthetic effect + 8 4 4 4 8 48 Severe
quality Rubbish or debris - 2 1 2 4 2 16 Moderate economic
- Disruption of infrastructure and
impacts - 2 2 2 4 2 18 Moderate services Socio Overall (-) 20,1 Moderate
Overall (+) 39 Severe
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Average overall 29,6 Moderate Table 20: Method’s result
From the Environmental Impact Assessment, it can be concluded that the project implementation implies a moderate level of impacts. In addition, by applying mitigation measures the impact of the activities will be reduced. Due to the construction of the navigational channel and buffer lake, the impact of the project on the vegetation area is severe. However, dobbens are planned to be built as a compensation. The aesthetic effect is also severe (in a positive way), so a good visual impact is expected by the implementation of the project.
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10. Further Recommendations
It is recommended to build two gates. Not only for safety measures but also for maintenance of the gates. So when one is being maintained, the other one could be used if necessary. It is important to perform check-ups of the gate performance and status constantly to prevent a failure in times of need. During the opening of the gates, eddies will appear as it is shown in Figure 67. Therefore, some level of scour is assumed to take place. In order to mitigate this effect a study of the turbulence generated by the gate should be developed so the required bed protection is applied, if necessary.
Figure 67: Scheme opening of the gates For the opening of the dike is recommended to build a temporary cofferdam (Figure 68) in order to have isolation from water and keep dry the working area so the dike can be broken in safety conditions. A further study needs to be developed in order to ensure acceptable workability and safety against flood.
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Figure 68: Scheme of a cofferdam. Source:http://www.sepa.org.uk/media/150997/wat_sg_29.pdf
In order to evaluate the design proposed in this report, it is highly recommended the performance of morphological numerical simulations of average conditions as well as of storm events with the future scenario for the channel and disposal alternatives in order to verify the morphological response of the channel as well the possible disposals. Usually, current pattern in tidal inlet areas are highly complex. The tidal asymmetry occurred due the presence of shallow areas generates complex 3 dimensional currents patterns (also called inner basin phenomena) such as bathymetry induced tide-average current, secondary flows, horizontal circulations (due to water level differences in bends), curvature-induced secondary transport and so on. The current velocities of the area affect directly the stability of the disposal. Therefore, morphological simulations can contribute to a better understanding of the response of the channel and disposal.
In the intertidal section of the outer channel embankments, for the prevention of erosion, wooden piles can be considered to be installed in those locations. This is because the salt marshes may not successfully grow in these areas. The wooden piles can be made of hardwood to minimize the replacement rate, since they have long life expectancy in exposed conditions. Figure 69 presents the location where wooden piles may be considered to be installed.
Figure 69: Wooden Piles in the Intertidal Area of Outer Channel Embankments
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11. Conclusion
In this report entitled ‘Rehabilitation of Holwerd’, it attempts to present a comprehensive solution by addressing the main prerequisite of providing an effective plan of action to revitalize the city of Holwerd. The proposed solution is presented incorporating four major phases in chronological order. As these four different phases when combined together, capture the full scope of the proposed solution, it enables the development of Holwerd as a unique tourist city equipped with a number of attractive features. The framework of design mainly deals with the connectivity between Wadden Sea and Holwerd city by means of a navigational channel with a sluice at the opening of the dike. This connection is assumed to serve as the major boost Holwerd requires to blossom as a tourist destination. Thus, a thorough analysis of those design elements is carried out as a first step in the broader scope of the project. Furthermore, the existing natural landscape features, eco-systems (eg : salt marshes) and distinctive species habitation (eg: otters) are incorporated in adding unique value to the conceptual design provided. In addition, the implementation of well- planned recreational facilities is anticipated to play a vital role in the context of attracting tourists to visit the place. With this particular plan of action, it is expected to materialize the following goals in its path to revitalizing Holwerd. • An exponential economic growth • A positive social impact on the residents of the area via adding value to their home city • Combination of natural features around Holwerd with artificial developments to accomplish a sustainable arrangement for the years to come As a whole, the project team firmly believes with the attainment of the above-mentioned goals, the flourishing of Holwerd as a popular tourist destination is inevitable.
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12. References
Bosboom, J. and Stive, M.J.F., 2015, Coastal Dynamics I Ð Lecture Notes CIE4305. Delft Academic Press, Delft, The Netherlands.
Church, J.A., P.U. Clark, A. Cazenave, J.M. Gregory, S. Jevrejeva, A. Levermann, M.A. Merrifield, G.A. Milne, R.S. Nerem, P.D. Nunn, A.J. Payne, W.T. Pfeffer, D. Stammer and A.S. Unnikrishnan, 2013: Sea Level Change. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.- K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
Conesa (1993). Guía metodologíca para la evaluación del impacto ambiental. Vicente Conesa Fernandez-Vitoria. Editorial Mundi-Prensa.
Davis, John P. HYDRAULIC DESIGN OF NAVIGATION LOCK.
HYDRAULISCHE RANDVOORWAARDEN PRIMAIRE WATERKERINGEN. Ministerie van Verkeer en Waterstaat. 2006FLORIS Ð Flood Risk and Safety in the Netherlands. 2005. Floris study Ð Full report. Published at www.projectvnk.nl
Kanning, W., van Baars, S., van Gelder, P.H.A.J.M. & Vrijling, J.K. Lessons from New Orleans for the design and maintenance of flood defence systems. Delft University of Technology, Delft, The Netherlands 2007
Leo H. Holthuijsen. Waves in Oceanic and Coastal Water, Cambridge (2007)
Look, B. (2014). Handbook of geotechnical investigation and design tables. London: CRC Press/Balkema.
Loon-Steensma, J. M. (2016). Salt marshes for flood protection. Lecture Slides - Building with Nature Course. Netherlands.
Lumber and Timber Prices - Tropical Logs & Sawnwood Market Reports 01-15 May 2016, http://www.globalwood.org/market/timber_prices_2016/aaw20160501.htm. Retrieved 01/06/16
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Marinetraffic (2016). Retrieved from http://www.marinetraffic.com/en/ais/details/ports/1758/port_name:AMELAND
PIANC Ð Design of movable weir and storm surge barriers, inCom, Report of WG Ð January 2006
PIANC Ð Innovations in the navigational lock design, Report No. 106 Ð 2009
PIANC Ð Approach Channels. A guide for design, Report of working group II-30
Rijkewaddenzee (2016) Retrieved from http://www.rijkewaddenzee.nl/nieuws/nieuws/prw- verkent-mogelijkheid-%E2%80%98holwerd-aan-zee%E2%80%99
Rotterdam (2016). Retrieved from http://www.rotterdam.nl/gelsluisCitg.tufelft (2016). Retrieved from http://www.citg.tudelft.nl/nl/over-faculteit/afdelingen/hydraulic- engineering/latest-news/artikel/detail/development-of-the-gesluis/
RoyalHaskoningDHV 1 (2016). Retrieved from http://www.royalhaskoningdhv.com/en- gb/news-room/awards-and-nominations/20140320-innovation-award-folding-lock- gate/2308
RoyalHaskoningDHV 2 (2016). Retrieved from http://www.royalhaskoningdhv.com/en- gb/innovation/international-innovation-day/unique-folding-lock-gate-design-gains- recognition
TAW Ð Technical Advisory Committee on Water Defences. 1998. Fundamentals on Water defenses, published on http://www.tawinfo.nl/asp/uk.aspdocumentID=112.
TAW Ð Technical Advisory Committee on Water Defenses. 1989. Guideline for the design of river dikes Ð part 2: Lower river branches Ð appendices. Waltman, ’s Graven- hage, the Netherlands.
Tropical Marine Timbers Ð Ekki Hardwood http://www.tropicalmarinetimbers.com/ekki/. Retrieved 03/06/16
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WL|Delft Hydraulics and Alkyon (2007). Hindcasting of Waves and Wave Loads on Dutch Wadden Sea Defenses. 2007. Authors: Ap van Dongeren, Jacco Groeneweg, Gerbrant van Vledder, André van der Westhuysen, Sofia Caires and Jeroen Adema. Wpd (2016). Retrieved from:
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Appendix A. Field Report
Holwerd is a Dutch town in the province of Friesland towards the northwest of the Netherlands. The project ‘Rehabilitation of Holwerd’ is oriented near the border of Holwerd with Wadden Sea accompanying number of natural landscape features surrounding the area together with restoring the connection with the sea. As the group of civil engineers engaged in this project, the first task was to have a site visit to the specific location to gather the information. Therefore, together with the Architecture students, all six members of our team went on a field visit to Holwerd on 12th February, 2016. The objective was to visit the specific location where the project is to be executed in order to get an understanding on the surrounding area and gather information as much as possible from the personnel associated with project of ‘’Holwerd aan Zee’’. First, we reached the city of Dokkum, which is in the municipality of Dongeradeel, and visited number of places on our way to Holwerd from Dokkum. There we witnessed many green dikes built to keep the water away from the city, a circular dike system to catch fresh water from rain and the canal system incorporated with gates, etc. Figure 70 below depicts a canal with a gate, which is quite common around the area in Dokkum.
Figure 70: Canal with a gate in Dokkum
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A presentation about the project ‘Holwerd aan Zee’ was done by a person associated with the project. The information collected regarding the aspects related to our scope of the project during that presentation can be summarized as follows; Ø Holwerd is mainly a trading village and it is not connected with the sea anymore. So the main objective of this project is to restore the connection between the Wadden Sea and the hinterland Ø A buffer lake is suggested to be built to flush away the mud from navigational channel with the intention of avoiding maintenance dredging Ø The improvement of the existing dike to a wide multi-functional green dike is one of the major attributes of the project Ø There is a proposal of building new pumping station which is considered to be an alternative option only Ø Recreational boats are to be implemented facilitating a method to attract more tourists to experience the unique landscape features in the area Ø Due to the connection of the sea to the canal system, it will be prone to salinization and this can be perceived as a problem Ø In the tourist aspect, the ecological elements surrounding the area are to be used to bring about an economical value to the village and the region During the latter part of the site visit, we visited the pier at the other end. illustrate the existing pier.
Figure 71: The Pier Showing the Water Level (left) and The Pier Top (rigth).
The area around the connecting roads between the pier and the dike was observed. The presence of salt marsh was evident and Figure 72 and Figure 73 demonstrate the plantation on both sides of the road. After checking the soil by hand it was initially observed by us as the soil type to be clay.
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Figure 72: Salt Marsh and Old dike near the pier
Figure 73: Salt Marsh formation near the Dike of Holwerd
The existing dike expands several kilometers. Figure 74 and Figure 74 depict the dike in Holwerd. It is evaluated that this dike is not up to the required standards, which calls for an upgrade during the project.
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Figure 74: Existing Dike for protection of Holwerd
Figure 75: Dike from the distance.
The site visit has given us the general overview of the project area regarding some critical conditions that we may encounter during the planning and design phases of the project. For an instance, for the channel design it is much prudent to utilize any natural channel path if there is any rather than following a completely new path. Further, after visiting the site, we have come to know the typical site conditions in general which will be very useful for the fulfillment of the objectives of the project and client successfully by adding value to those existing features.
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Appendix B. Table of Harmonic Components of Holwerd’s Area
Amplitude Phase Components (m) (¡) SA 0.1014 223.2 SM 0.0433 32.9 Q1 0.03068 175.21 O1 0.08347 239.84 M1C 0.0092 198.77 P1 0.02442 19.96 S1 0.01082 16.9 K1 0.07112 29.56 3MKS2 0.01734 149.29 3MS2 0.02091 132.74 OQ2 0.01405 155.97 MNS2 0.01675 352.23 2ML2S2 0.01118 175.74 NLK2 0.03576 206.41 MU2 0.09768 21.05 N2 0.15638 270.81 NU2 0.05555 249.81 MSK2 0.00911 163.72 MPS2 0.03661 326.62 M2 0.95354 295.35 MSP2 0.00634 320.48 MKS2 0.01229 313.98 LABDA2 0.03378 323.07 2MN2 0.08404 129.71 T2 0.01056 312.38 S2 0.24036 2.5 K2 0.06853 2.28 MSN2 0.01374 185.58 2SM2 0.01944 231.8 SKM2 0.0141 211.79 NO3 0.00481 36.67 2MK3 0.01588 75.18 2MP3 0.00304 91.71 SO3 0.01094 149.27 MK3 0.0127 238.19 SK3 0.00581 315.18
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4MS4 0.00554 260.49 2MNS4 0.00769 119.87 3MS4 0.02218 154.09 MN4 0.04191 52.87 2MLS4 0.01839 224.63 2MSK4 0.00857 351.73 M4 0.13644 80.49 3MN4 0.01468 266.86 MS4 0.0836 153.23 MK4 0.01596 158.66 2MSN4 0.00849 347.06 S4 0.00819 294.2 MNO5 0.00701 10.44 3MK5 0.0079 80.32 2MP5 0.00705 215.1 3MO5 0.00988 244.41 MSK5 0.00325 338.08 3KM5 0.00055 139.44 3MNS6 0.01173 224.69 2NM6 0.01228 117.7 4MS6 0.01787 258.46 2MN6 0.03551 151.17 2MNU6 0.01609 142.82 3MSK6 0.00613 46.46 M6 0.07143 184.34 MSN6 0.00695 215.98 MKNU6 0.00376 210.07 2MS6 0.06701 251.88 2MK6 0.0155 247.96 3MSN6 0.01179 83.09 2SM6 0.01084 350.6 MSK6 0.00693 349.25 2MNO7 0.00473 164.31 M7 0.0032 26.67 2MSO7 0.00715 318.78 2(MN)8 0.00729 220.92 3MN8 0.01634 259.08 M8 0.02203 298.19 2MSN8 0.00871 328.95 2MNK8 0.00853 342.67 3MS8 0.03521 0 3MK8 0.00908 3.06 2(MS)8 0.01142 90.97 2MSK8 0.00596 96.1
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3MNK9 0.00344 137.15 4MK9 0.0023 176.29 3MSK9 0.00454 235.4 4MN10 0.01015 38.02 M10 0.00886 85.83 3MSN10 0.00951 105.24 4MS10 0.02115 135.16 2(MS)N10 0.00167 322.51 3M2S10 0.01151 215.13 4MSK11 0.00182 28.96 M12 0.00225 253.56 4MSN12 0.00462 247.9 5MS12 0.00705 277.99 4M2S12 0.00654 349.04 Table 21. Harmonic components The form factor was calculated according to the formula: !1 + !1
!2 + !2
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Appendix C. Master Plan Poster Ð A Door to the Wadden Sea
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Appendix D. Types of Gates
Mitre Gates Mitre gates consist of two leaves, symmetric to the centerline of the lock and the rotation axis of both leaves is vertical. The mitre gates can only retain water in one direction because of its shape. Therefore, in order to retain water from both sides, two sets of gates are necessary. Mitre gates should not be exposed to significant current or wave actions when partially open; hence it is unsuitable for storm surge barrier. In some cases, hydraulic cylinders can be used to open and close the gates allowing the mitre gates to resist a small headwater difference. When opened, the mitre gates are positioned in recesses walls of the lock heads. In Figure 77 a scheme of mitre gates is presented.
Figure 76: Mitre gates scheme. The advantages of Mitre Gates are: • Low cost, effective solution for relatively small navigation locks. It is considered a relatively light gate structure; • No air draught limitations; • The equipment for mitre gates does not have to carry the weight of the gate; the centre of gravity remains in a horizontal plane during opening and closing; • Short time for closing and opening the gate. The disadvantages of Mitre Gates are: • The length of the lock itself needs lengthening as well as the upper lock head due to the recesses of the gates; • Mitre gates cannot be opened or closed under a water head difference; • Not suitable for flood defences.
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Single-Leaf Gate The single-leaf gate is one leaf with rotation around the vertical axis. It can be considered as a half mitre gate, however the mitre gate transfers the hydrostatic load mostly by normal forces while the single-leaf gate transfers by bending moments. Also, the recess in the wall for the repose of the leaf gate has a different shape compared to the mitre gate, which is better for streamlining water flow. The single-leaf gate is most frequently used for lock with small width as locks for recreational craft. Figure 77 presents a scheme of a single-leaf gate.
Figure 77: Single-leaf gate scheme.
The advantages of Single-leaf gates are: • Suitable for lock with small width; • No air draught limitations; • Forces on the gates are transferred parallel to the lock wall (when the closed leaf gate is perpendicular to the lock axis). The disadvantages of Single-leaf gates are: • Long recesses in wall of the lock head are necessary (longer than mitre gates); • Large water displacement during closing and opening; • Width limitation.
Sector Gates Sector gates are also name radial gates and have a vertical rotation axis. The gate is composed by a skin plate, which has a curved shape of part of a cylindrical circle. The skin plate has to be stiffened in order to resist the hydrostatic pressures. Besides the skin plate, the sector gate has the lower and upper arms (triangular shaped trusses in the horizontal plane), which support vertically and horizontally the stiffened skin plate.
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Due to the shape of the skin plate, the resultant force has its working line through the attachment point (pivot). Sector gates can resist reverse head and can be operated with a water head. They are more expensive than single-leaf and mitre gates due to their weight. Due to the large layout of the gate, they require deep and large recess in the lock heads. Sector gates are more often used for guard locks or storm surge barriers where closure under free flow and unlimited air draught is needed. Hydraulic jacks are required to move the gate, similar to mitre gates. The gates will slide trough the water, making them operative when there is a head difference and reducing the water displacement. In Figure 78 a scheme of a sector gate is presented.
Figure 78: Sector gate scheme.
The advantages of a sector gate are: • The possibility to close the gate in flow conditions (head water differences, currents); • Opening and closing relatively easy because it cuts through the water with a small surface; • No air draught limitations; • Short-time to opening and closing. The disadvantages of a sector gate are: • Relatively large amount of material; • High support loads at the pivots resulting in heavy cast-in items in the lock head wall due to weight of the gate; • Large size of the lock head due to the necessary recess.
Tainter Gates Tainter gates are radial gates with horizontal axis of rotation. A single tainter gate spans the whole width of the lock head opening. Generally, two sector gates are used. The gate can be
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either stored in upward position or in a recess in the bottom of the concrete superstructure, both allowing the passage of vessels however the former has an air draught limitation to the passage of the vessels while the latter has a higher cost once a deeper foundation and recess in the lock head are necessary. It is possible to use this type of gate for guard gates, flood defense or storm surge barriers, hence the gate body is designed high and strong enough to resist underflow or/and overflow. In Figure 79 a scheme of a tainter gate is presented.
Figure 79: Tainter gate scheme.
The advantages of a tainter gate are: • Radial gates are often referred to as esthetical nice structures; • No air draught limitations when stored in the recess; • Suitable for guard locks. The disadvantages of a tainter gate are: • Limitation in air draught when stored in upward position; • Heavy construction required since the gate is moved vertically (along a circle).
Lift Gate The lift gate is composed by one door that spans the entire width of the lock and translates in the vertical direction. The translation in the vertical direction of this type of lock enables the hydrostatic load to be transferred to the lock head. The deadweight of the gate is balanced by counterweights in order to reduce the operating forces of the equipment. High gantries or guide towers are required to guide the gates during opening and closing operation. Figure 80 presents a scheme of a lift gate.
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Figure 80: Lift gate scheme.
The advantages of lift gate are: • No need of recess in the wall of lock head, thus enables the total lock length to be reduced to a minimum; • It is possible to open the gate under a water head because considering the driving gear the force directions are in different planes; • Easy to control and repair; • The support system of the gate is statically determinate and therefore largely insensitive to differential settlement. The disadvantages of lift gate are: • Air draught limitation of vessels; • It has a large and heavy structure due to the lift towers or columns; • Generates a strong underflow when opening (lifting) the gate; • Very sensitive to wind loads when in upward position; • Big esthetical influence due to the high and large superstructure.
Submersible Lift Gate The submersible lift gate is composed by one door that translates in the vertical direction and it is accommodated in a recess deep in the ground. During the closing of the lock the gate is lifted upwards. Most of the horizontal loads on the gate are diverted to the side recesses; a small amount is transferred to the bottom support. This type of gates takes little horizontal space and has no air draught limitation. However, it requires a large recess deep into the
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ground to accommodate the gate and its construction and maintenance costs are high. Figure 81 presents a scheme of a submersible lift gate.
Figure 81: Submersible lift gate scheme.
Rolling or Sliding Gates The rolling or sliding gates are composed by one door that spans the entire width of the lock and translates in the horizontal direction on underwater rails or sliding tracks. This type of gate can only be used when sufficient space exists besides the lock since the width of the lock head structure is about two times the door’s length. The rolling gates have a high risk of getting jammed in the sliding tracks due to accumulation of sediments or debris on those tracks, especially if the gate frequently remains in the open position it should be considered to wipe the rail or track clean before or during gate operation. In closed position, the rolling gate can be considered as a simply supported beam; in fully opened position, there are hardly any horizontal forces on the door. Therefore, in those positions stability of the gate is not a problem. During the opening or closing process, the ‘upper’ corner of the gate is completely unsupported. A force on this door area, for instance due to a remaining water level difference or large flow, may result in significant stability problems. Figure 82 presents a scheme of a rolling or sliding gate.
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Figure 82: Rolling or sliding gate scheme.
The advantages of rolling or sliding gates are: • Suitable for locks of large width. • No air draught limitation; • Easy to maintain. The disadvantages of rolling or sliding gates are: • Requires a lot of space besides the lock (head); • Requires a large recess or lock head. • Cannot be opened or closed under water head conditions; • Accumulation of debris in the tracks of the sliding gates implies in risk of jammed gates and therefore cleaning operations in the tracks. • Inflatable Barrier In contrast with the other type of gates mentioned above, this gate is an innovative type of gate. The inflatable barrier consists of a strong fiber stored in a concrete foundation and connected longitudinally to the both sides of the lock. To close the lock, water and air are pumped into a closed system, which causes the fiber to partly float forming a barrier. To open the barrier, the water and air are pumped out of the system causing the fiber to sink to the bottom. In Figure 83 a scheme of an inflatable barrier is presented.
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Figure 83: Inflatable barrier scheme.
The advantages of inflatable barrier are: • Very small aesthetical impact; • Possible absorption of the dynamic effect due to waves. • Only tensional forces in the superstructure; • No air draught limitation; • Relatively fast closing operation. The disadvantages of inflatable barriers are: • Risk of leakage; • High maintenance cost due to the relatively short lifetime of the fibber; • Vulnerable to water and wave overtopping; • Vulnerable connection between concrete and fibber.
Folding Gate This type of gate is also taken as an innovative type of variation to the mitre gate developed by Royal HaskoningDHV. The folding gate consists of two components connected to each other by mean of a hinge. When the gates are closed, they adopt an arc shape and when opened, they are folded and accommodate in a recess in the wall of the lock head. Figure 84 depicts a scheme of the folding gate.
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Figure 84: Folding gate scheme. The advantages of the folding gate are: • No air draught limitation; • Relatively small recess area; • More resistant to loads than mitre gates. The disadvantages of the folding gate are: • The length of the lock itself needs lengthening as well as the upper lock head due to the recesses of the gates; • Relatively new applications.
Gelsluis The Gelsluis is a sluice without doors in which ships go through a gel dike (mainly made out of gelatin and some barite) without a waiting time of opening/closing the gates or filling/emptying processes. Although, it can resist a water head of 5 meter, which indicates that it can resist a representative amount of pressure, it is mostly recommended in places with high ship traffic to replace navigational locks. For the dimension of this sluice, it should be considered that the length of the dam should be three times the ship length in order to being able for the gel to close again and also to prevent damage to the ship hull. The gel has a unit weight of approximately 12 kN/m3 and efficiently prevents intrusion of salt water. This innovative gate has been developed in 2011 by dr. Ir.J.G.de Gijt and it is an option for the Nieuwe Waterweg Rotterdam. Tests in small hydraulic flume have been carried out to check the feasibility of the project. However, more research is required into the behavior of the gel itself. In Figure 85 and Figure 86 schemes of Gelsluis are illustrated.
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Figure 85: Gelsluis scheme (yellow part represents the gel).
Figure 86: Operation with a Gelsluis scheme (yellow part represents the gel).
The advantages of the Gelsluis are: • No air draught limitation; • Reduces operational time; • Filling and emptying system is not required, opposite to other types of navigational lock. The disadvantages of the Gelsluis are: • Requires a centre of production of gel in the area, close to the lock; • Lengthens of the lock structure; • Relatively new concept, which indicates a lack of information and a necessity of extensive research prior the design and construction; • High maintenance cost due to the relatively short lifetime of the gel.
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Appendix E. Calculation of the Channels’ Dimensions
WBM (Width of the maneuverability lane):
It is assumed that the ship maneuverability is good. Hence WBM = 1.3B
Wi (Additional width due to specific site conditions): Category type is taken as ‘Low’ as the selected design ship is for passengers, therefore the coefficients are stated as: • Vessel speed: slow, 5-8 knots Ð 0.0B • Prevailing cross-winds: moderate >15-33 knots Ð 0.5B • Prevailing cross-currents: negligible < 0.2 knots Ð 0.2B • Prevailing longitudinal currents: moderate > 1.5-3 knots -0.2B
• Significant wave height Hs and length λ: 1 Alternative 1: Sloping channel edge and shoals ! • !!! Wi = 0.5! + 0.2! + 0.2! + 0.1! + 0.1! + 0.2! = 1.3! • Alternative 2: Steep and Hard Embankments structures ! • !!! Wi = 0.5! + 0.2! + 0.2! + 0.1! + 0.2! + 0.2! = 1.4! Wp (Additional width for passing distance in Two-way traffic): Vessel speed (slow 5-8 knots) Ð 1.0B Encounter traffic density: light -0.0B Therefore, Wp = 1.0B 119 WBr and WBg (Additional widths for Bank Clearance): Alternative 1: Sloping channel edge and shoals Ð 0.3B Alternative 2: Steep and hard embankment structures Ð 0.4B 120 Appendix F. Risk of Overtopping for Inner Dike The failure risk for overtopping is investigated for the 1/2000-year design storm. To determine the overtopping risk of the dike section during the design storm of 1/2000 years the maximum overtopping discharge for the design storm conditions is calculated. Significant Wave Height The significant wave height are mainly due to wind and for each wind direction was calculated using the Young and Verhagen equations (see Eq. 1-6) a description of the variables within these equations can be found in Table 22. Northerly wind directions were not assessed due to the effective fetch being limited and as such wave heights irrelevant in terms of max overtopping discharge. !.!"# !.!"∙!"!!!!.!" Eq.1 ! = ! tanh (0.343!!.!") ∙ tanh ! !"#$ (!.!"#"!!.!") !.!"# !.!!∙!"!!!!.!" Eq.2 ! = ! tanh (0.10!!.!") ∙ tanh ! !"#$ (!.!"!!!.!") !!!! !!! Eq. 3 ! = ! Eq.4 ! = !!" !!" !" !" Eq.5 ! = ! Eq. 6 ! = ! !!" !!" Variable Symbol(units) Value Gravity g(ms-2) 9.81 Dimensionless wave height deep water !!(-) 0.24 Dimensionless wave period deep water !!(-) 7.69 Water depth d(m) See Table 23 Fetch F(m) See Table 23 Wind Speed !!"(m/s) See Table 23 Peak Wave period !!(s) See Table 23 Significant wave height !!!(m) See Table 24 Table 22: Equations 1-6 variables 121 The characteristic values for the wind speeds were determined using the 95%-quartile value for the Weibull distribution as this is considered a load factor. The input variables that are dependent on wind direction can be found in Table 23 Wind Depth Peak wave Fetch(m) U (m/s) Direction (m) 10 period(s) W 1989 9.69 19.8 2.66 WSW 1885 9.99 23.5 2.83 SW 1567 8.83 26.7 2.86 SSW 1141 7.02 27.8 2.67 S 633 6.98 20.1 1.96 Table 23:1 in 2000-year event wind direction dependent variables From the analysis it was found that the significant wave heights from the North West were the largest at 0.84m (see Table 23). Wind Direction Significant wave height(m) W 0.67 WSW 0.79 SW 0.84 SSW 0.76 S 0.41 Table 24: Significant wave height Determination of Maximum Overtopping Discharge Utilising the significant wave heights calculated with Table 24 the maximum overtopping discharge for each wave direction was calculated. This angle of incidence is incorporated using equation 8 within the overtopping calculation as it reduces the force per unit area along the dike face. Eq. 8 !! = 1 − 0.0022! A crest height of 3m NAP was determined using the MHW of 1.75m NAP. The roughness factor for the dike was determined to be 1.0 as it is assumed to be normal grass covered slope which results in negligible roughness. The maximum overtopping discharge was then calculated using inputs in Table 25, and equation 9. Variable Symbol (units) Value Gravity g 9.81 Significant wave height H!" See table 25 Crest Height R! 1.25 122 Friction factor γ! 1.0 Angle of approach factor γ! See table 25 Table 25: Wind direction independent Inputs !.! ! ! Eq.9 = 0.09!"# − 1.5 ! ! !!!!!!! !!!! Wind Significant wave Angle of approach Direction height(m) factor W 0.67 0.95 WSW 0.79 0.85 SW 0.84 0.835 SSW 0.76 0.8515 S 0.41 0.802 Table 26: Wind direction dependent variables Wind Overtopping Over topping Direction discharge (m/m2/s) discharge(l/m/s) W 0.0026 2.631 WSW 0.0044 4.430 SW 0.0059 5.920 SSW 0.0035 3.467 S 4.94776E-06 0.005 Table 27: Overtopping discharge The maximum overtopping discharge was calculated to be 0.0084m3/s or 5.92 l/m/s. A safe level used within the Netherlands is 5 l/m/s and this would also be a valid discharge to take due to the irregularities on the slope. Probability of Overtopping Failure With a critical overtopping discharge of 10 l/s/m and a standard deviation of 3 l/s/m the probability of failure of the dike section was calculated utilizing a Monte Carlo simulation. The 5%-quartile value for the log distribution for the critical overtopping was calculated to be 5.9 l/m/s and was used within the limit state function in equation 10. The following failure probability is expressed with equation 11. Eq. 10 ! = 5.9 − ! Eq. 11 !! = !(! < 0) The results of the Monte Carlo analysis can be found within Table 28. The resultant probability of failure for the dike section in a 1/2000-year design storm was calculated to be 123 3.99% by summing the failure probabilities from all wind directions. Again the main wind direction that is likely to result in the failure of the dike is the SW direction with a failure probability of 2.13%. The second most likely direction for failure of the dike is the WSW direction with 1.85%. Wind Direction Probability of failure W 2.13% WSW 1.85% SW 0.0028% SSW 0.0054% S 0.002% ALL Directions 3.99% Table 28: Probability of failure 124 Appendix G. Management Survey Survey Model 1. What is your age? o 10 to 25 o 26 to 50 o 51 to 75 o 75 or older *2. Do you like to travel? o Yes o No *3. During which season do you like to travel the most? o Winter o Spring o Summer o Fall *4. Based on what factor(s) do you choose your vacation destination? o Cost o Hotel-Resort o Entertainment o Shopping o Relaxation (like spas, spiritual activities, etc.) o Museums and History o Other (please specify) *5. How important is cost when choosing a vacation destination? o Extremely important o Very important o Moderately important o Slightly important 125 o Not at all important *6. How important is the environmental aspects, and green buildings in the decision-making? o Extremely important o Very important o Moderately important o Slightly important o Not at all important *7. What attracts you the most in a new city? (Festivals and concerts, open spaces, parks, view from high points in the city, party and ambiance, people, architecture, etc.) *8. Where is your favorite vacation destination? Survey Analysis Considering the boundary conditions previously mentioned, the brainstorming process started. Although a lot of ideas were given, it was almost impossible to know which alternative would attract more tourists to Holwerd, which led us to create a survey in which people would not only select from the possible options but were able to answer from previous experiences. A lot of questions could be asked, but it was chosen the ones that will not only give us an idea of what people like but also events, public transport, and cost related opinion which will be very helpful for the management of the city. It is important to mention that there is a difference between what one would think one would pay or like, and what would one actually would pay or like. This means that, it could be said that an appropriate cost for a trip would be €100 at the moment of asking but at the instant of 126 actually paying the trip, several aspects play a role so it is possible that €100 is too high of a price making it impossible to truly buy it. As a result, the following graphs were obtained from survey presented above: Travel Season 6% 6% Winter Spring 34% Summer 54% Fall Figure 87: Preferred travel season Figure 87 tells us when people will travel the most, which allow us to design and prepare the city better for this months. Hence, it will be more profitable to do a public pool than a ski center. Basis of decision-making 10% 26% Cost 16% Hotel-Resort Entertainment 10% 7% Shopping Relaxation Museums & History 26% Other 5% Figure 88: Basis of the decision This question allows us to know how each person decide on where to spend vacations or where to go for the weekend. As previously mentioned, it not only depends on what the person wants to do, but in several other factors. In Figure 88 we have a better linking of the opinion of the travelers. 127 Importance of cost 4% 3% 17% Extremely important 21% Very important Moderatly important Slightly important 55% Not at all important Figure 89: Importance of the cost Some people prefer luxury, some others they prefer nature and so on. This question provides us insight on how much people are prepared to pay. Even if Holwerd is the best place in the world, if it’s really costly, then not a lot of people will be able to visit the city so we have to really consider options that would be of interest but with a low cost. (Figure 89) Importance of environmental aspects 9% 6% Extremely important 22% 26% Very important Moderatly important 37% Slightly important Not at all important Figure 90: Importance of environmental aspects One of the client’s requirements was that any change made to the city has to be as environment friendly as possible. From Figure 90 it can be known that people do not have the environment as a priority but it is still important for the decision-making process, therefore the proposed alternatives have to include either a mitigation plan or to be as environmental as possible. 128 Attractiveness of a destination Architecture & View 5% 4% Festivals 14% Nature 10% Museums 11% Historical sites 19% Cuisine 5% 5% Proximity to the sea Night life and ambiance 10% 7% 5% Shopping Parks & open spaces 1% 4% Culture Art Adveture activities Figure 91:.Attractiveness of a destination Figure 90 and Figure 91 are considered the most important graphs since they create a more clear view of what needs to be done to revitalize the city. It is important to mention that a budget is considered as well, so all the constructions and project cannot be done at once. In this figure it is shown what attracts most people are parks and open spaces. This is an important reference because not all the cities in the world have an area in which people can just walk and enjoy a sunny day hence that different situation calls the attention of a lot of tourists. The second attractive thing is the architecture of a city and points in which you can have a clear and nice view of the city. This is an advantage since Holwerd already has a charismatic architecture, which will only require that the new constructions stay within the same architectural style. Other common answers were festivals, concerts, and cuisine. For this, there is no need to construct more structures but to manage and to organize what’s already in Holwerd. Therefore, part of this can be included in the first phase of the project and increase as the city develops. 129 Favorite Destination 22% 28% Beach Food 15% Modern city History 11% 24% Night life Figure 92: Favorite destination As it can be seen in Figure 92, results from the previous question do not change as much with the exception of the beach option. What can be inferred from this is that tourists might not think of the beach as their first location to visit in a weekend or for vacations, but they do enjoy better and it can be concluded that it’s the combination of things which make a city attractive and not a single item per se. 130 Appendix H. Timber as a Construction Material for Hydraulic Gates Operating Conditions The life expectancy of timber gates depends highly on the operating conditions; particularly the amount of traffic on the channel and mechanical damage are influential factors. Generally, a lifetime of 30 years can be expected for hardwood gates. In some cases, hardwood (in frames) and softwood (in sheeters) are combined in a single gate. The sheeters are replaced every 10-15 years but the frame may last for over 50 years. Joints and fittings need more attention as the decay is likely to take place first in these areas and thus progressive failure will occur. The replacement rate of Ekki (Lophira alata), a hardwood timber species, is low, thus eliminating the need for frequent replacement. This greatly reduces the associated labor costs and the amount of material used. Applicability of Timber in Holwerd Timber structures are generally used in Holwerd area for groynes. Below is a picture depicting the pile groynes near Holwerd. So, timber is a natural choice for the gate. Also since it is a natural product, it increases the aesthetic value of the gate and more tourists will be attracted to see it. Figures 94 and 95 show pictures of the existing pile groynes near Holwerd, taken on the field trip of 12/02/2016. Figure 93: Pile Groyne near Holwerd, From field trip (12/02/16) 131 Figure 94: Pile Groyne near Holwerd (another view), From field trip (12/02/16) Timber Prices As per the recent report of Global Wood, the log export price of Ekki (from West and Central Africa) is around €230 per m3. This is for the use in frames. If softwood is used (in sheeters), then Pitch Pine can be used. This is imported typically from Brazil, the export price being around €179 per m3 (kiln dried). As per the dimensions of the gate, the volume (30m X 14 m X 0.60 m) is 252 m3 and so the approximate price per gate is around €58,000 without any connections and sheeters. If all these additional structures are put into consideration and also maybe the import duties, the price of a single gate can be about €100,000. For two gates, it will be €200,000. But this is a very basic estimation. Actual costs can vary due to various non-predictable situations. 132 Appendix I. Salt Marshes The dredged sediments from the Holwerd are mainly composed by fine sediment (silt/clay) which presents a potential to the development of salt marshes ecosystems. The development of salt marsh ecosystems contributes to the nature by increasing local biodiversity. Besides the 3 typical species :Salicornia sp., Avicenniasp and Spartina sp., salt marshes also provides room for other animals such as benthonic species, invertebrates, birds and etc. Salt marshes can develop from tidal flats if there is enough soil expose during high water and low water allowing pioneer species to colonize this intertidal flats. The establishment of pioneer species causes more sedimentation in the tidal flat (positive feedback), allowing secondary species that are not so salt tolerant to colonize the tidal flat initiating in this way the ecological succession of the development of salt marshes. In general, the ecological succession of salt marshes occurs from mud flats, which are areas that are submerged all the day and habitat mainly by algae such as Zosterasp and Diatomophyceae sp. The mud flats are considered the first stage. The second stage is called pioneer zone and it develops in the intertidal zone. Species characteristic of this stage are the pioneer species: Salicornia spand Spartina sp. This species are salt tolerant and can handle 3 hours per day of inundation, thus they require 9.4 hours of dry periods to develop (Erdinger in Dijkema et al. (2001) apud (Loon-Steensma, 2016)). This hours range is based in a semidiurnal tide. The next stage is denominated low zone and it located above the mean water level (MSL). The typical species of this region are Puccinellia sp. and Halimione sp. These species are less salt tolerant and can tolerate around 400 hours per year of inundation (Erdinger in Dijkema et al. (2001) apud (Loon-Steensma, 2016)). The next stage is the middle zone where even less salt tolerant species are present such as: Festuca sp. and Juncus sp. The frequency of inundation in this region should be around 100 hours per year in order to propitiate ideal condition to this species develop. The final stage of the ecological succession of salt marshes is the high zone where mature plant communities intolerant to salt are establish. This zone is located more inland where do not occur inundation unless during extreme storm/flooding events. 133 Appendix J. PoT Analysis Peak over a Threshold method defines a storm as a water level higher than a threshold. In this project, the threshold selected was 2 m once the gate should be closed when the water level is higher than 2 m, thus, water levels higher than 2 m are considered storm. In Table 29 the statistics of storms are presented. In the 5 years wave data, there is a total of 20 storms. Dividing the number of observed storms for the period of observation (5 years), the average number of storms per year is Ns=4. The probability of exceedance of a storm in a year (Qs) is then the probability of exceedance (Q) times the number of storms per year. Qs represents the number of storms in a year. The Gumbel extreme value distribution was applied with regression linear in order to get the period of return of a storm with water level = + 2 m. In Figure 95 is presented the Gumbel Distribution of the storm water level as well the linear regression. Wave level Probability Probability Probability of Axis transformations classes Accumulated of of exceedance of a Frequency Frequency occurrence exceedance storm per year - lower upper ln(Q) ln(wl) ln(qs) G - P - Q Qs 2.00 2.25 14.00 14.00 0.70 0.30 1.20 1.20 0.81 0.18 1.03 2.25 2.50 1.00 15.00 0.75 0.25 1.00 1.39 0.92 0.00 1.25 2.50 2.75 1.00 16.00 0.80 0.20 0.80 1.61 1.01 -0.22 1.50 2.75 3.00 1.00 17.00 0.85 0.15 0.60 1.90 1.10 -0.51 1.82 3.00 3.25 2.00 19.00 0.95 0.05 0.20 3.00 1.18 -1.61 2.97 3.25 3.50 1.00 20.00 1.00 0.00 0.00 1.25 Table 29: Statistics of PoT analysis Gumbel DistribuLon 3.60 3.40 y = 0.4795x + 1.9288 R² = 0.85335 3.20 3.00 2.80 2.60 Water Level (m) 2.40 2.20 2.00 0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 Gumber reduced variable Figure 95: Gumbel distribution for water level 134 Therefore, the Probability of exceedance of a storm (water level > 2 m) per year Ð Qs is: !! 4 !! = !! − !!!" = 4 − !.!"##!! = 2.3 exp !"# exp !"# ! !.!"#$ A !! = 2.3 means a frequency of 0.43, which is once in every 5 months, approximately. It is important to note that the correlation between the data and the linear regression performed with the Gumbel Distribution is not very high (!! = 0.8533). This can be explained by the short period of data (5 years). Even though, the frequency of closing the gates obtained from this analysis is valid. 135 Appendix K. Consultation fees Time Rate Serial Category Quantity Cost (Euro) (hours) (€/hr.) Human Resource Requirement 1 Architect/ Project Planner 1 130 75.00 € 9,750.00 € 5 Design Engineer 6 260 100 € 156,000.00 € Office Equipment and Software 1 Computer 6 - - 6,000.00 € 2 Printing/Photocopy/Binding - - - 2,000.00 € 3 Mailing/Courier - - - 1,000.00 € 4 Software - - - 5,000.00 € Others 1 Data Collection - - - 5,000.00 € 2 Site Visit/ Travel Cost - - - 1,000.00 € 3 Miscellaneous - - - 2,000.00 € Total Cost 187,750,00€ Table 30. Consultation fees 136