Tidal power saving the day?

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Tidal power saving the day?

Assessing the financial feasibility of a pumping turbine system in

the Brouwersdam as a water management solution.

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Author: Ing. Dirk Andries de Jong Student number: s1660748

E-mail: dirkdejong@gmail.com

Telephone number: 0624696449

Study program: University of Groningen

Faculty of Economics and Business MSc Technology Management

Company: ARCADIS

Company Supervisor: P.L.M. Jansen University Supervisors: 1st Drs. F.P. Bakker

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Abstract

This master thesis is the final report of a study which was conducted for Arcadis. Alkyon, a daughter company of Arcadis, demonstrated in the beginning of this century that production of electricity by using tidal energy in the South Western Delta area of the Netherlands is possible. In the study presented here this production of sustainable energy is combined with a reduction of the water level in the Southern Delta area. This solution is based on a number of pumping turbines in the Brouwersdam, which can be used on the one hand to produce electricity using the tidal range and on the other hand to reduce the water level in the adjacent area by pumping water to the sea.

The main goal of the study was to examine the financial feasibility of implementing this solution in the area of the Grevelingen & Krammer-Volkerak based on its influence on the Leading High Water level (LHW)1 in the surrounding area.

To come to a statement regarding the financial feasibility of the overall solution the following research steps were taken: Determination of future requirements, conceptual design of the system,

determination of the LHW effect and an economic analysis/feasibility assessment.

Future requirements first follow from the water level in the South Western Delta area which will be subjected to change due to a sea water rise and an increment of water flow from the larger rivers before the year 2100. Other requirements follow from the evidence that the Grevelingen and the Volkerak to encounter several problems on the ecological level.

The next major influence on the financial feasibility of the overall system is the system itself. The system under consideration is based on a maximum amount of 195 horizontal bulb turbines made suitable for pumping with a turbine diameter of 3.5 [m] and a discharge of 48 [m3/s] per turbine. These

characteristics lead to a maximum power output of 410 [GWh/year], which would be enough for approximately 111.000 households.

Following this basic design the effect of the measure on the water level was determined. This is effect was investigated by performing computer simulations, for which a number of different scenarios was developed in which the river discharge and several other parameters were varied. For interesting locations like Dordrecht and Rotterdam a maximum water level reduction of respectively 30 and 12 centimeter can be achieved by installing 7500 [m3/s] of pump capacity. The same pump capacity leads to reductions up to 80 centimeters at the Hollands Diep and Haringvliet.

Using the design characteristics and simulation results an economic analysis of the tidal power station was made, which indicated that a power station on its own is not feasible. Next the returns from power production were combined with the additional returns from the LHW effect and ecological effects. From this could be concluded that the financial feasibility of implementing a pumping turbine system as a water management solution in the area of the Grevelingen & Krammer-Volkerak is positive.

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The economic analysis indicates a breakeven point after 30 years and it reaches a Net Present Value of more than 200 million euro after 100 years. Besides these quantitative financial factors there are also several qualitative factors that could make the solution more attractive and should be taken into account. First there is a large area of outer dike regions that are prevented from flooding. Second this solution has an the immediate effect on the LHW level and does not lead to extreme water levels on the Grevelingen and Volkerak, which would be the case when implementing other water management solutions. Thirdly tidal energy is sustainable and thereby contributes to political goals (national and international). And last but not least the solution provides knowledge, expertise and innovative capability, which contributes to the knowledge economy that the Netherlands wish to be.

In essence the solution seems to be financially feasible, however the sensitivity to changes in the initial investment and the electricity price does suggest that more research is needed to reduce the risks. Furthermore optimization of the tidal power station and the LHW parameters could make the financial feasibility of the solution even more positive.

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Preface

This master thesis is the result of a half year of study and research for Arcadis. At the same time, the report is the final part of my master Technology Management at the Rijksuniversiteit Groningen. At first glance this thesis can interpreted as an extensive feasibility study, a standard thesis project or a combination of both. But for me this thesis brought many of my interests together, since it gave me the opportunity to combine water and technology on a level which I could never have reached as a

graduated naval architect.

Completing an academic thesis would however been very difficult without the help of several other people. Therefore I would first like to thank Mr. Bakker for his patience and guidance during my graduation period. Next my gratitude goes out to Peter Jansen, my company supervisor from Arcadis, for both an exceptional interesting research subject and his valuable feedback on all subjects that came around. In addition I would like to thank my temporary colleagues at Alkyon for the facilities and guidance provided in Marknesse, and in particular to Gerrit Hartsuiker, who enlightened the world of water flow simulations for me.

Finally this thesis could never have been completed without the everlasting support and feedback of my girlfriend during these long and turbulent months. For her, my parents and everybody else that has been waiting for so long I would like to promise that seven and a half year of studying is enough. Now the time has come to do something useful with all this knowledge.

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Table of Appendices

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1 Introduction

The production of sustainable electricity is growing steadily in the Netherlands. Numbers from 2008 show a share of 7,5% of the total electricity production. The Dutch government is striving for a share of 9 % in 2010 and 20% in 20202, which corresponds with 10 million [MWh/year]. This means that a duplication of the capacity is needed in the next decennium. Unfortunately the amount of sustainable energy sources in the Netherlands seems to be small since solar and wind energy both demand a lot of the scarce space available in the Netherlands. Furthermore both cannot account for a constant and predictable energy production.

A sustainable source of energy that has had little attention in the Netherlands is tidal energy. Tidal power is not a new technology, evidence has been found of tidal mills in Northern Ireland from before 1000 B.C., these ancient tidal mils were mostly used for grinding grain. Tidal power used for electricity production was not introduced on a large scale until 1964, when the power station in La Rance, France, was completed. Tidal power seemed to be unprofitable for small tidal ranges, which was the assumption in all studies until recently. However due to recent technological developments in the turbine industries, it is now possible to install turbines that work efficiently at lower tidal ranges. Alkyon, a daughter company of Arcadis, demonstrated in the beginning of this century that that production of electricity by using tidal energy in the South Western Delta area, in particular at the Brouwersdam, is possible (Delta-Synergie, et al., 2001). Other more recent studies confirm these early conclusions (Natuur- en

Recreatieschap Grevelingen, 2006; Vrijling, et al., 2008(I)) , nevertheless such an installation would require huge investments and in some cases even a subsidy on the selling prices.

This economic disadvantage could however be reduced when combining such an investment with other developments. One recent development that could lead to promising results is combining tidal power with water management, since the Delta Commission came in 2008 with several important suggestions for the same area.

According to the advice from the new Delta Commission several measures have to be taken to prepare for a rising sea level and an increasing flow of water from several major rivers. This includes many future adjustments to current dikes and other weirs in the entire South-Western Delta area. Furthermore there are several urban areas with critical weirs that need alternative solutions (for example Dordrecht).One measure recommended by the Commission was using the Krammer-Volkerak and the Grevelingen to store excess water from the rivers Rhine and Meuse. In addition to this measure the commission suggested to reintroduce the tide in the Grevelingen to recover several important ecological values. There are however other areas in the Netherlands that face problems with water management, one of which is the area surrounding the Afsluitdijk. As a result of the advice that the ‘Delta’ commission gave in 2008 a market exploration was assigned by the Dutch ministry of transport and water management for this area. ARCADIS, the company for which this report was made, has participated in a consortium that performed this market exploration for the Afsluitdijk in the 21st century. One interesting outcome of this study was to use a pumping system which can handle excess water in the Ijsselmeer in case of

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extremely high water levels. During normal operation, when no emergencies occur, the pumping system can be used as a turbine to produce electrical energy from the tide (the difference between high and low water). These energy producing properties could have a significant positive influence the feasibility of the overall emergency water management solution. The outcomes of this study seem to be suitable for other locations like the Brouwersdam in Zeeland, which divides the lake of Grevelingen from the North sea. The lake of Grevelingen is situated at the border between the provinces Zeeland and Zuid-Holland. It is limited in the West from the North Sea by the Brouwersdam and in the East from the Krammer-Volkerak by the Grevelingendam. The lake Krammer-Volkerak is limited in the West by the Grevelingendam from the Grevelingen, in the Southwest from the Zoommeer by the Philipsdam and in North from the Haringvliet/Hollands Diep by the Volkerakdam.

By placing pumping turbines in the Brouwersdam it could be possible to combine electricity production and water management. The possible water management solution in this area is to enlarge the storage capacity of this buffer by pumping water from the Grevelingen, and potentially the Krammer-Volkerak, into the North Sea in case of alarming water levels. Again these pumps can be used as electricity producing turbines during normal operation, more than 99 % of the time.

1.1 Research solution

The overall solution which will be analyzed in this report is thus a combination of two solutions. First a water management solution (Figure 1), which will use the pumps in the Brouwersdam to pump water away from the Northern part of the Delta area leading to a reduction of the water level in that area. The second solution is power production (Figure 2) by the pump turbines in the Brouwersdam using the tidal range between the sea and the Grevelingen.

Figure 1 Overview of the area under consideration for the water management solution

Brouwersdam

Grevelingendam _Volkerak Volkerakdam Grevelingen

Zoommeer

Rotterdam

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Figure 2 Overview of the tidal power production at the Brouwersdam

1.2 Research goal

ARCADIS wants to make clear which water management solutions are suitable for further development. This should be done with a strong focus on the impact of several options on the overall water

management in the area and their financial feasibility.

ARCADIS provided an option which is based on a number of pumping turbines in the Brouwersdam. These pumping turbines can be used on the one hand to produce electricity using the tidal range and on the other hand to reduce the water level in the adjacent area by pumping water to the sea.

This option provides a solution for both production of sustainable energy and a possible reduction of the water level in the surrounding area and therefore it seems to be a very attractive option. Unknown is however what the related costs and returns of this option are and what the costs of other possible measures are. Other uncertainties are the ecological and social impact of such a (radical) solution, although these uncertainties will not be investigated in detail in this research. So this research should deliver insight in related costs & returns combined with its impact on the water level in the surrounding area. And thereby providing an indication of the overall feasibility of the solution.

The main goal of this research will thereby be to examine the financial feasibility of implementing the discussed solution in the area of the Grevelingen & Krammer-Volkerak based on its influence on the Leading High Water level (LHW)3 in the surrounding area.

Using the insights provided by this study it should for example be possible for ARCADIS to compare several solutions for high water reduction with a similar safety level .

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Leading high water level (LHW) or hydraulic constraint is a water level that occurs once during several years at a specific location. This is the water level for which water management solutions are designed.

Brouwersdam

Grevelingendam

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2 Research design

This chapter will introduce the research question for this report, followed by several sub questions and their relation with the research question. Furthermore the research methodology will be discussed, in which the chosen approach for each question will be explained.

2.1 Research question

Feasibility can be split into several components like; technological feasibility, environmental feasibility, financial feasibility etc. A directional choice for the financial feasibility is made for this study, which is based on several considerations. First technologically the implementation of the system is assumed to be feasible on the one hand because of the experiences from Nijhuis Pompen B.V. at the Afsluitdijk project and on the other hand because of the experience that the Netherlands has with adjusting large hydraulic structures. Next the financial feasibility is chosen because it can provide an overview of the majority of cost and benefits of a design, hereby incorporating several other feasibility components. Based on these considerations the following research question is developed:

What is the financial feasibility of implementing a pumping turbine system as a water management solution in the area of the Grevelingen & Krammer-Volkerak?

The outcome of this research question will give an indication of the overall feasibility, but further research will probably be required to assess financial, environmental and other effects in detail.

2.2 Conceptual model

A Conceptual Model is developed to gain insight in the variables that are relevant for the research question. Based on this model relevant sub questions can be developed in the following paragraph.

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2.3 Sub questions

To make a verdict about the financial feasibility of this new water management solution first several sub questions have to be answered.

The financial feasibility of both the LHW measure as the power station solution will be analyzed for a basic design. As any other design it should be based on design constraints, which are for a significant part based on requirements for the water management in the given area. The requirements of a new water management solution follow both from problems that might arise due to the present condition of weirs as from expected developments in the future, for example a rising sea level. The design

parameters of a new water management solution should therefore be based on a complete set of future requirements, which leads to the following question:

1. What are the future requirements of water management in the given area?

The answer to this question determines the requirements and constraints on which the water

management solution should comply. And thereby influences the cost that have to be made to comply and the (financial) benefits that can be acquired by complying to these requirements and constraints. This combination of cost and benefit will then influence the overall financial feasibility.

Another major influence on cost and returns of the presented water management solution is the pumping turbine system itself. To present realistic financial information about this system, basic parameters of the system have to be determined. To do this first an analysis of tidal energy in general and its implementation in the Brouwersdam has to be conducted. Next a preliminary design has to be made to obtain the basic parameters of the system, which can then be translated in related cost and benefits. Since this report will not deal with all design aspects it will be important to reflect how this basic design relates to the actual situation. This reflection should also indicate which impact this deviation could have on the financial feasibility. All these considerations lead to the following sub questions:

2. What are the basic design characteristics of a projected pumping turbine system in the Brouwersdam?

3. To what degree is the basic design comparable to the actual situation? 4. What are the additional cost and returns of this pumping turbine system?

The answers to these questions provide the relevant data to assess the cost and returns of tidal energy at the Brouwersdam. It should also give insight in the preliminary adjustment cost that would make the water system suitable for the Leading High Water level reduction.

Since one goal of the preliminary design is to reduce Leading High Water level during extreme water conditions an effect analysis of the true reduction has to made. The main obstacle in this approach is however to assign a monetary value to a certain water level reduction. In essence the ideal outcome of this problem would be to demonstrate a relation between the water level reduction and associated cost (and or benefits). This relation depends however on many variables and is very complex or even

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5. What is the effect of the design on the Leading High Water level in the surrounding area? 6. How can a reduction of the Leading High Water level be monetized?

The answer to these questions should provide insight in the returns from the LHW reduction and thus the percentage of cost that could be assigned to the LHW reduction, which could lead to a higher financial feasibility of the overall solution. The returns or value of the LHW reduction are however difficult to assess, which could make the returns incommensurable. This incommensurability would mean that (a part of) the LHW reduction value cannot be used within the economic analysis which would have a negative effect on the financial feasibility. For the aspects at which this

incommensurability plays a role a qualitative analysis should be conducted.

Both the tidal power station as the Leading High Water solution have a significant impact on the interests in the water system. One important interest that is not always included in water management projects is the ecosystem. Bouma and Schuijt (Bouma, et al., 2001) propose that the effects of projects on the ecosystem may be included in the water management decision making process by placing an economic value on ecosystem functions. Ecosystem functions recognized by Bouma and Schuijt are for example fish production, recreational opportunities and natural retention capacity. In the presented solution the economic value of the ecosystem could have a positive impact on the net returns of the tidal power station since previous reports (Witteveen&Bos, 2009) state that returning the tide has positive impact on several ecological aspects. On the other hand the intrusion of salt water in the Grevelingen and Volkerak could also have a negative impact on for example the fresh water supply. This leads to the following sub question:

7. How can the remaining effects of the presented solution be monetized?

The answer to this question does not necessarily have an impact on the overall financial feasibility since the analysis should indicate if the value of for example the ecological effects can be monetized at all or that it will only act as a constraint on the preliminary design.

Summarized the following sub questions need to answered in this study: 1. What are future requirements of water management in the given area?

2. What are the basic design characteristics of a projected pumping turbine system in the Brouwersdam?

3. To what degree is the basic design comparable to the actual situation? 4. What are the related cost and returns of this pumping turbine system?

5. What is the effect of the design on the Leading High Water level in the surrounding area? 6. How can a reduction of the Leading High Water level be monetized?

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2.4 Research methodology

The results will be based on a research methodology to structure the manner at which the questions are answered. The required information will be partly collected through literature research and interviews. Another major part of the research data will be collect through series of calculations and simulations at Alkyon Hydraulic Consultancy & Research. The end result will be a written report with a clear advice to ARCADIS regarding the financial feasibility of the given solution. This financial feasibility will be described using a discussion of the Net Present Value of the overall solution combined with several qualitative aspects. In the following paragraphs there will follow a short explanation of the method that will be used to obtain an answer on the particular sub question.

2.4.1 What are the future requirements of water management in the given area?

To assess the feasibility of the overall solution it will be important to analyze the current situation and describe its future requirements. This description will be mainly based on extensive desk research regarding published reports and literature. When necessary, several interviews will be conducted to reveal missing information. This will result in an overview of required changes and improvements for the water management in the given area, the solution under consideration should comply with (a part of) these requirements. Within this research should also become clear what other solutions have already been developed.

2.4.2 What are the basic design characteristics of a projected pumping turbine system in the Brouwersdam?

For this report all important elements of the actual system will be investigated. First a literature study of the operation of a tidal power station will be conducted, followed by a detailed description of the solution under consideration. Next the relevant location properties (e.g. tidal difference, flow speed) will be translated into operational parameters (e.g. number of pumps, efficiency). This will be done through several calculation steps and by consulting pumps/turbine supplier and civil and hydraulic engineers.

2.4.3 To what degree is the basic design comparable to the actual situation?

This question will be answered by indicating the differences between this basic design and the actual situation, followed by a short analysis of the influence this could have on the feasibility and possibly how this difference can be overcome.

This report is however structured according to several main subjects which all contribute to the

difference between the approach in this report and the actual situation, therefore this sub question will be answered as a reflection at the end of several of the main subjects.

2.4.4 What are the related cost and returns of this pumping turbine system?

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Next the financial feasibility of the power station can be assessed, which will be greatly influenced by the returns of the electricity production, for which data is gathered through interviews with the turbine supplier and data gathered from existing research reports. From this analysis will follow in how far the power station can be feasible on its own.

This analysis will be followed by an examination of the additional cost that should be made to include the LHW solution, which will be based on general available reports and consulting experts.

The financial feasibility of the pumping turbine system can then be assessed in comparison with other solutions, for which it will be important to describe the benefits and expenses of alternatives. It will be useful to create a financial overview over time through one or more financial modeling methods, the applicability and validity of these methods will be assessed through literature research.

2.4.5 What is the effect of the solution on the Leading High Water level in the surrounding area?

The effect of the implementation on the LHW in the surrounding area will be of great importance for the outcome of this research, since the height of the LHW-reduction is directly linked to several important factors. In agreement with experts from ARCADIS and Alkyon is decided to split this effect into two separate problems. The first is the amount of water that can be stored in the Grevelingen / Volkerak, which can be calculated by hand using existing data, collected through desk research or database extraction. This water volume together with several other variables determines the throughput of water in the Volkerak sluices. (from the Hollands Diep & Haringvliet to the Volkerak)

This throughput is then the key input for the second problem, the LHW reduction in the surrounding area. This will be investigated by performing computer simulations with water flow models at Alkyon Hydraulic Consultancy & Research BV, a daughter company of ARCADIS. To execute these simulations it will probably be necessary to get familiar to some degree with the theory and algorithms behind these simulations.

2.4.6 How can a reduction of the Leading High Water level be monetized?

The financial value of a particular LHW reduction generally used by governments is mainly build up out of components like flooding risk. Since determining this value could be a study on its own, a coarse estimation is presented in this report. This estimation will be based on a discussion of a few methods to monetize water level reductions, one of which will be used in this report. Next a presentation to a group of experts will be used to assess the validity of the monetization.

2.4.7 How can the remaining effects of the presented solution be monetized?

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2.5 Reading structure

The reading structure of this report is based on the sub questions as stated in the previous paragraphs. Some questions are however coupled in a single chapter because they contribute to a single subject. An overview of the reading structure is provided as a roadmap in Figure 4. After the conclusion chapter 8 will provide a glossary of the abbreviations and variables used in this report. Chapter 9 will give an overview of the references used for data and literature. And finally chapter 0 contains all appendices referred to in this report.

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3 Water management requirements

This chapter will provide inside in (future) problems related to the water management in the South-Western Delta area. Future requirements of water management should be based on these problems. Most water management requirements are mainly focused on the water level, although this could be seen as most important from a economic point of view, relevant problems related to the ecological condition play a vital role as well. The water management solution as discussed in this report should (partly) reduce the effect of the problems discussed in this chapter. It thereby influences the cost that have to be made to comply and the (financial) benefits that can be acquired by complying to these requirements and constraints.

3.1 Water level

After the flood in 1953 a safe height for all dikes and dunes in the Netherlands is laid down by the former Delta Commission, based on a 1/4000 norm. This norm comprehends that weirs are able to withstand a storm that occurs once every 4000 years. In practice this meant changes for a total of 160 kilometer of weirs, these changes were finished in ‘90s. In 2007 a new Delta Commission looked at the protection of the Netherlands against the water and came with an extensive advice in 2008

(Deltacommissie, 2008).

According to this advice there are several developments in the South-Western Delta area that need attention. The first is the rising sea level, according to the Delta Commission there should be accounted for a sea level rise of 0,65 to 1,30 [m] in the year 2100. There are however many different views at the different scenarios, which are difficult to judge. This rising sea level could have major impacts on the main weirs in the Netherlands. For example every 50 [cm] rise of sea level multiplies the chance of flooding by ten in the Rotterdam area. Another issue related to the sea level rise is the inland

penetration of salt water which could endanger the fresh water supply in the west of the Netherlands. A second development is the increasing flow of water from the rivers Rijn and Meuse in the winter periods. According to the Delta Commission there should be accounted for a maximum water flow from the Rijn and Meuse of respectively 18.000 m3/sec and 4.600 m3/sec in 2100, which is a total rise of 2.800 m3/sec with respect to the current numbers. Next to these major developments there are other

problems related to several ecological aspects which will be discussed below.

2001 2050 2100

Leading flow from the Rhine[m3/s] 16.000 17.000 18.000 Flow from the Meuse [m3/s] 3.800 4.200 4.600 Expected sea level rise [cm vs. 1990] +5 +20 / +40 +65 / +130

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3.2 Ecological condition

Returning the tide and estuary conditions(salt water intrusion) generally lead to more ideal ecological situation and better water quality. There are several sources that confirm these statements which will be discussed below.

According to a development sketch from 2006 (Natuur- en Recreatieschap Grevelingen, 2006) the area of the Grevelingen is hard to reach for several organisms due to the separation from the North Sea. Furthermore several coastal birds are leaving the area due to lack of suitable breeding places. Finally the development sketch pays attention to the water quality in the area, which is gradually deteriorating due to stratification4 and lack of flow and dynamics at ground level in the water.

According to Rijkswaterstaat the water quality in the Grevelingen has become worse since it was separated from the North Sea in 1971. Former lack of oxygen was partly solved by an opening in the Brouwersdam, but the ecosystem is still vulnerable. This could have major consequences for the fish, oyster farming and plant life. A similar problem applies to the Volkerak, in which the ecosystem is not functioning properly and blue algae is returning yearly.

An exploration from Witteveen & Bos (Witteveen&Bos, 2009) concluded that there are several solutions with similar effects on the oxygen level. The first three solutions, the current provision, reusing the scour sluice in the Grevelingendam and doubling the capacity of the scour sluice in the Grevelingendam are not sufficient in raising the oxygen level. The other solutions discussed in the exploration are based on new drains in the Northern and/or Southern part of the Brouwersdam and all have a similar effect on the oxygen level . In Figure 5 a comparison of these solutions based on the oxygen level is presented. This diagram shows per solution the area (in hectares) that contains less than 3 mg/L of oxygen for a period of 7 days.

Figure 5 Oxygen level per solution

In several reports is proposed to recover dynamic estuary5 in this area, which would improve water quality substantially. In the development sketch from 2006 (Natuur- en Recreatieschap Grevelingen, 2006) is proposed to recover the estuarine dynamics of the Grevelingen by :

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Water stratification occurs when water of high and low salinity forms layers that act as barriers to water mixing.

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An estuary is a transition area between rivers and the sea, in this area the water is in constant movement due to river

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1. A connection to the Oosterschelde by an opening in the Grevelingendam in the east; 2. A connection to the North Sea by an extra opening in the Brouwersdam;

3. A connection to the (fresh water) river system by an opening to the Volkerak.

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4 Design of a pumping turbine system

This chapter will first provide an insight in tidal energy and the two different approaches of harvesting tidal power. Next the characteristics of the pumping turbine system at the Brouwersdam will be discussed, followed by a determination of its basic parameters. Based on these parameters a first estimation of the amount of power will be discussed. At the end of this chapter the basic parameters will be compared to the actual situation. The parameters and the amount of produced power

determined in this chapter are the leading variables in the analysis of cost and benefits needed to answer the main research question.

4.1 Tidal energy

Tidal energy is generated by the gravitational pull of the moon, to some extend from the sun and the relative motion of the earth. The relative position of the moon to sun influences the hight of this gravitational pull. When the moon is in line with the earth and the sun a spring tide occurs, at which the tidal range is at its maximum (higher high water and lower low water). When the moon is at its first or third quarter a neap tide occurs, at which the tides are less extreme (See Figure 6).

In most areas ebb and flood occur twice a day (semidiurnal) but in some places there is only one tide a day(diurnal). In case of semidiurnal tides there is a difference between the high waters on a given day, called the daily inequality.

Tidal energy is practically inexhaustible and its forecast can be realized several years in advance, which gives it an advantage above other renewable energies. Exploitation of tidal energy is not a recent development, there are records from tidal mills from before the year 700, which were mainly used to grind corn. New technologies do however make it possible to harvest tidal energy from a smaller tidal range and with a higher efficiency. A tidal power station uses this energy to generate electricity, for which two types of tidal energy can be distinguished:

 The kinetic energy from tidal currents, originating from narrowing seas;

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4.2 Kinetic energy from tidal currents

To produce energy from tidal currents underwater turbines are placed in areas with high tidal

movements, these turbines work in much the same way as wind turbines. The design and configuration of tidal current turbines varies extensively and no dominant design has emerged yet.

Figure 7 A few water current power technologies: (a)1.2MW SeaGen Tidal System, (b)VIVACE Slow water current energy

In the following table the main (dis-)advantages of tidal stream turbines are displayed, the formulas required to calculate the power output of these turbines can be found in Appendix B .

Advantages Disadvantages

Simple installation Low effective power output Low installation costs Cannot be used for pumping Low visual pollution High maintenance costs Low noise pollution High power distribution costs

Table 2 (Dis-) advantages of tidal stream turbines

4.3 Potential energy from the tidal range

The amount of potential energy from the tidal range is defined by the tidal range, the basin surface area and the flow of water. The first requirement to use potential power from the tidal range is a dam or ‘barrage’ across a tidal bay or estuary, which will function as the water basin. In the dam several openings are made in which turbines and gates are installed. The amount of natural energy available in the tide is defined by the size of the basin and the available tidal range.

Several authors (Charlier, 2003; Harn, 2007; Fay, et al., 1983)claim that producing energy using a tidal range of less than 7 meters is unprofitable, which was the assumption in all studies until recently. Due to recent technological developments in the turbine industries, it is now possible to install turbines that work efficiently at lower tidal ranges. Nevertheless there are several disadvantages of retrieving power from the tidal range using a barrage like:

 It is expensive in construction and maintenance;

 It only provides energy for about 10 hours out of a day;

 It has large environmental effects (fish, silt deposits and local tide change-effects)

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La Rance tidal power plant in Bretagne -France, which is also the only commercial sized plant so far. A schematic overview of this plant and one of its turbines can be found in Appendix A . Some other locations with similar installations are shown in Table 3.

Table 3 Overview of important tidal power plants

4.4 Tidal power in the Brouwersdam

This paragraph will provide inside the basic design parameters of a tidal power station in the

Brouwersdam, followed by an estimation of the possible energy production of this power station. This information can then be used to calculate the cost and returns of the power station in chapter 6. To determine the basic design parameters of a tidal power station in the Brouwersdam several key decisions have to be made. First the decision to use power from the tidal range instead of power from tidal current will be explained. As was mentioned in paragraph 4.2 a tidal current turbine has a lower effective power output, or energy production per square meter of guide vanes. A simple calculation that supports this statement was mentioned by Vrijling (Vrijling, et al., 2008(II)).

Figure 8 Output calculation tidal output

Location La Rance (France) Kislaya Guba (Russia) Annapolis (Canada) Jiangxia (China)

Year 1966 1968 1984 1980

Average tidal range 8 [m] 2 [m] 6 [m] 7

Basin area [km2] 17 [km2] 2 [km2] 5 [km2] 2

Turbine type Bulb Bulb Straflo

# of turbines 24 [-] 1 [-] 1 [-] 5

Total output 240 [MW] 0 [MW] 18 [MW] 3

Total discharge 6600 [m3/s] 0 [m3/s] 378 [m3/s]

-Yearly output 540 [GWh/year] 1 [GWh/year] 30 [GWh/year] 11

= 0.5 ∙ 0.47 ∙ 1025 ∙ 2 ∙ 5.52_∙𝜋

4∙ 2.413= 160 𝑘𝑊

𝑃 = 𝜂2∙ 𝜌 ∙ 𝑔 ∙ 𝐻 ∙ 𝑄

𝑃 = 1090 𝑘𝑊

Tidal current turbine

If one would place two turbines with a propeller diameter of 5,5 [m] in an channel of the Brouwerssluis (dimensions w x h: 12.8 x 8 [m]) With a local speed would be 2.41 [m]/s and

η=0.47. Than the power output would be: 𝑃 =1₂∙ 𝜂1∙ 𝜌 ∙ 𝐴 ∙ 𝑣3

Tidal range turbine

A bulb turbine (tidal range turbine) with a diameter of 3,5 [m] would have in a similar situation a power output of:

with:

𝜂2= 0.75, 𝐻 = 2.0 𝑚 and 𝑄 = 1.2 ∙ 3.52∙𝜋₄∙ 2𝑔𝐻 = 72.28 𝑚

3

𝑠

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4.4.1 Constraints

First several constraints are applicable to the usage of tidal power in the Brouwersdam, these constraints are mainly setup to minimize impact on the surrounding area:

 an average tidal range at sea of 2,5 [m] is used;

 a maximum range at the Grevelingen (Rg)of 1,5 [m] is maintained since this is considered as the maximum achievable in the area, a closer examination of this constraint should be conducted at a later stage;

 at first Hg is concentrated around the current standard water level of AOD6 -0,20 [m], the water level at which the Grevelingen is currently maintained, although this water level could be adjusted in a later stage in case it leads to higher energy production. The mean sea water level at the other side of the Brouwersdam varies between AOD +1,43 and AOD -1,02 [m].

(See Figure 9)

 to comply with the overall water management solution of the turbine type should be able to be used for pumping.

Figure 9 Current water levels at the Brouwersdam 4.4.2 Tidal power plant layout

The first choice that has to be made with regards to a tidal power plant is the layout and in particular the number of basins:

 A single basin, the most simple and common option;

 Multiple basins, which makes it possible to continuously produce energy .

The second option seems to be valuable since normal energy generation is predictable but does not necessarily go together with fluctuations in energy demand. According to Harn (Harn, 2007) this second option is however less attractive since its power output is less than 50% of the output with a single basin. This in combination with the higher project cost, due to an extra barrage between the basins, make it a non-feasible solution for the power station in the Brouwersdam.

6

AOD is the abbreviation of ‘Amsterdam Ordnance Datum’ in Dutch known as the NAP or ‘Normaal Amsterdams Peil’, which is the reference height for height measures in the Netherlands. The AOD is somewhat higher than the mean sea level.

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4.4.3 Generation mode

The second choice relates to the generation mode of the tidal power plant, since energy production can take place during ebb (low tide), during flood (high tide) or during ebb and flood. For ebb generation the water flows through sluices into the basin until high tide at which the gates are closed. When the height difference (or head) is large enough the water flows through the turbine back into the sea. At flood generation the basin is filled through the turbines during high tide.

For the last generation mode a turbine that can operate in both directions is needed, which are however generally less efficient. In this mode the water generates energy during high and low tide. During high tide the water flows from the sea to the basin and during low tide the water flows back to sea. Both water flows can drive the same turbine, in this case called a TT-turbine which can operate in two

directions. A schematization of the different generation modes can be found in Appendix B , the figures also indicate at which moments energy can be generated (the grey areas).

Pump turbines can also be powered in reverse, to operate as pumps, to increase the water level in the basin artificially. This energy input is more than returned when operating as a turbine again, this phenomenon is explained by the non-linear correlation between tidal range and potential and results in extra available time to generate electricity. Another feature of these pumping capability as used at the la Rance power plant is to raise the basin level when electricity is cheap and recover this energy with the turbines when electricity prices are higher (Mooyaart, 2009). An overview of the operational modes at the la Rance tidal power plant can be found Appendix B . Making the pumps suitable for power

generation does however effect the turbine/pump operating efficiency, which will drop 7 to 10 % due to the blade shape and this loss is not likely to be improved in the nearby future.

Since the solution discussed in this report requires pumping capacity it is obvious that a pumping turbine is chosen. According to several authors a flood generating mode is economical less attractive, which is supported by numbers from Vrijling. Therefore an ebb generating mode and a generation in both directions are under consideration. According to Mooyaart (Mooyaart, 2009) the latter is more effective when the difference in tidal range for ebb and flood is small. Furthermore in case of a TT-central no extra sluices are required according to Vrijling (Vrijling, 2008(III)), since it can produce energy during both tides which could lead to a significant cost reduction. The choice for a particular generation mode will be made when the power production per generation mode is calculated.

4.4.4 Turbine types

For low head and relatively high flow rates in hydro electric plants axial flow turbines are used, which are therefore suitable for tidal energy barrages. Some examples of these turbines are discussed by Braitsch (Braitsch, et al., 2006):

 The Bulb turbine

 The Straflo turbine

 The tubular turbine

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turbine cannot be used for pumping. Another consideration with regard to the turbine type is the available tidal range (and the resulting head), since the currently available tubular turbines are not suitable for low pressure heads. This means that a bulb turbine is the only remaining option for this site, since recent developments have made it possible to use the Bulb turbine with relative low tidal ranges this type is chosen to be used for this research. A short description of the other types can be found in Appendix B .

In the horizontal Bulb turbine (Figure 10) the blades are directly connected to the generator, which is mounted inside the water passageway as an integral unit with the turbine. This type of turbine can furthermore be made suitable for pumping and can be fitted with adjustable blades.

Figure 10 Bulb turbine (Copyright Gevorkian, 2006) 4.4.5 Number of turbines

Before the number of turbines can be calculated, several turbine/power station parameters have to be determined. Ultimately the number of turbines is limited by the turbine dimensions and the available space at the Brouwersdam.

Worldwide there are almost no turbines in use for tidal ranges smaller than 5 meters, only the power station in Kislaya Guba (Russia, also see paragraph 4.3), in this pilot project there was accounted for a tidal range of 3 meter. The main reason for this lack of low tidal range turbines is that the needed technology was simply not available until recently. Research for the Afsluitdijk project indicated that a efficient turbine for small tidal ranges had a diameter of 2,5 [m] and a capacity of 25 m3/s. This diameter was calculated as follows:

The above situation was however based on an existing scour structure and therefore no extra space had to be reserved for the surrounding powerhouse. For the Brouwersdam the lower limit is determined by the existing bottom structure of the dam, which is according to van Westen (Westen, 1987) situated at AOD -10,0 [m] (See Figure 12). The upper limit is determined by the minimum water level (at sea or basin, whichever is lower) decreased with the tolerance for air intake. For now the minimum water level

The bottom of the current water channels is positioned at AOD -4,3 [m]. The minimum water level is AOD -0,3 [m]. With 1,5 [m] tolerance to avoid air intake during power

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is assumed to be AOD -1,0 [m], which leads to an upper limit of AOD -2,5 [m]. This indicates a total vertical space ≈ 7,5 [m]. To account for a good water flow (the surrounding power house) a vertical factor of 2,2 is used which would lead to a turbine diameter of ~3,5 [m]. This is roughly the same diameter as Vrijling (Vrijling, et al., 2008(I)) used. In case of the ebb generating mode a possibility could be to place the needed sluices above the turbine, this could decrease the cost for the turbine/sluice caissons.

The number of turbines is then determined by the available horizontal space at the Brouwersdam. There are two locations available in the Brouwersdam, the first is the dam section Goeree, the northern part of the Brouwersdam. The second location is the Southern part of the dam, is the dam section Schouwen. An overview of the entire dam can be found in Appendix Appendix A . In the section Goeree 12 caissons are placed, which gives an available space of 824 meter (see Figure 11).

Figure 11 Placement plan caissons northern closure gap (Westen, 1987)

Figure 12 Northern closure gap. Cross section bottom protection, sill and caisson (Westen, 1987)

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Figure 13 Dumping pattern of concrete blocks Southern part of the Brouwersdam (Westen, 1987)

Since little information is currently available about the distance between two adjacent turbines (𝑊𝑡), for

now a distance equal to the turbine diameter (𝐷𝑡) is assumed to account for the free flow of water and

the powerhouse construction. The above results in the following overview for the possible number of turbines (𝑁𝑡) in one layer:

Available length North 824 [m]

Available length South 550 [m]

Max # of turbines Northern section 117 [-]

Max # of turbines Southern section 78 [-] Table 4 Number of turbines

As stated in Table 4 these numbers relate to the maximum number of turbines that can be installed, which is 195 turbines in total. This number could be increased by applying a smaller distance between the turbines, ARCADIS recommends to use 20 % of the diameter (=0,7 [m]) as the absolute minimum.

4.4.6 Tidal calculations

The main objective of this paragraph will be to assess the amount of power produced by a tidal power station in the Brouwersdam. To do this first several intermediate results will be calculated and

discussed. An more extensive discussion of the calculations that were used for this project can be found in Appendix B-4.

The first variable needed is the tidal range. Generally the tidal water level follows a sinus shape during approximately 12 hours with a distance between the maximum and minimum water level called the tidal range (R). The sea water level (Hsea) with respect to the Mean Sea Level (MSL) at a given moment (t) with angular velocity (ω) can then be approached by formula [1].

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A rough estimation of the potential power of the water mass at a given tidal range can be calculated by the following simple energy balance7:

Alkyon Hydraulic Consultancy & Research provided series of data regarding volumes and areas of the Grevelingen at several depths. This data can be used to determine the volume of water mass that will shift during a tidal cycle with a chosen Tg. Next an estimation can be made of the potential tidal power at the Brouwersdam using formula [2]. In which a tidal range of 2,5 [m], an average basin area of 111 x 106 [m2] and a time between the tides of 12 [hrs] results in a potential tidal power P of 80 [MW].

Figure 14 Tidal barrage

The true power P differs from the value above due to several reasons. First not all the energy of the tide can be used because the turbine is designed to work in a certain tidal range, as soon as the range is to low the turbine will not function (optimally), which means in practice that only a certain fraction (

𝑓

𝑇) of

the tidal period can be used to turbine. In calculations the working range of the turbine is interpreted as a starting and stopping head of the turbine, which leads to an average head during power generation (𝑕𝑚𝑒𝑎𝑛, see Figure 14).

Secondly power is lost due to losses during the transition of the pressure difference to electricity, which is known as the mechanical efficiency of the turbine (𝜂𝑡), this efficiency is estimated at 0,85 [-].This

number can vary in time due to several turbine and environmental characteristics, for example the

7

This calculation was adopted from http://www.oup.com/uk/orc/bin/9780199281121/andrews_jelley_ch04.pdf Considering a basis with an area A in m2 as shown in Figure 14. The total mass m of

water in the basin above the low water level is:

𝑚 = 𝜌𝐴𝑅

where R is the tidal range in meters.

The height of the centre of gravity is h, so the work done in raising the water is:

𝑚𝑔(

1₂

𝑅) = (

1₂

)𝜌𝑔𝐴𝑅

2

Which leads to a power output of

𝑃 =

𝜌∙𝑔∙𝐴∙𝑅 2

2∙𝑇

Where T is the time between tides.

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pressure difference which is not constant in time. For this project the efficiency is however assumed to be constant which leads to formula [3].

𝑃 = 𝜂 ∙

𝑓

_𝑇∙ 𝜌 ∙ 𝑔 ∙ 𝑕𝑚𝑒𝑎𝑛 ∙ 𝑄/106 [MW]

The potential energy of the water mass at a given tidal range can be calculated by:

𝐸 = 𝑄 ∙ 𝜌 ∙ 𝑔 ∙

𝑕_{𝑚𝑒𝑎𝑛}

∙ 𝑓

_𝑇

∙ 𝑡 ∙ 𝜂 [GWh/year]

Or

𝐸 = 𝑃 ∙ (365 ∙ 24) [GWh/year]

The resulting water flow through the dam depends on the tidal range and the number and diameter of the turbines. But when the flow enlarges the tidal range at the basin will become smaller, which would mean a lower energy production(Vrijling, et al., 2008(I)). This energy production depends on the water level in the basin at a given time. Main constraints for this water level are the maximum allowable tidal difference (Δhmax) the time at which the turbine starts/ends and the generation mode.

Vrijling (see Appendix B-6) optimized the tidal range and the starting water level for the maximum energy production per year for a given throughput. These optimizations are summarized in Figure 15, in which can be seen that when a larger throughput than 5500 [m3/s] is aspired a two-way generation mode has a higher energy production but is again limited by a maximum energy production of ± 400 [GWh/year].

Figure 15 Optimization of turbine parameters (used data can be found in appendix B-6)

A turbine with a diameter of 3,5 [m] results in a throughput of 48 and 43 [m3/s] for respectively a ebb and two way generation mode, with these numbers it is possible to estimate the yearly power output

[3]

[4]

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for a specific number of turbines using Figure 15. Since the maximum number of turbines is 195 (117 + 78), the maximum throughput is 9360 [m3/s] and the associated power output per year is roughly 410 [GWh]. This amount corresponds with the electricity usage of roughly 111.000 households.

The solution producing the maximum amount of electricity is not automatically the most efficient due to several reasons. First the cost do not necessarily have linear relationship with the number of turbines. Secondly the investment for the maximum possible number of turbines might be too high. Third for flow purposes it might be better to cluster groups of turbines, which would result in a smaller overall number of turbines. Following these arguments the power output is determined for four different throughputs, see Table 5.

No. [m3/s] # of turbines Energy [GWh/year]

I 3000 63 150

II 4500 94 210

III 7500 157 360

IV 9100 190 400

Table 5 Power station output 4.4.7 Summary

In the previous paragraphs the basic design characteristics were divided in the plant layout, generation mode and the dimensions, type and number of turbines. Summarized this resulted in the following turbine parameters:

 a range at sea of 2.5 [m] is available and a range at the Grevelingen of 1.5 [m] is maintained;

 a tidal power plant with a single basin of 11.100 hectare;

 an ebb- or two way generation mode, depending on the chosen discharge;

 a horizontal bulb turbine made suitable for pumping with a turbine diameter of 3.5 [m] and a discharge of 48 [m3/s];

 a maximum amount of 195 turbines with a power output varying from 150 to 400 [GWh].

4.5 Reflection

Although the previous paragraphs provide a simple overview of the possibilities, the design of the tidal power station at the Brouwersdam should be reviewed in more detail. In chapter 2 was stated that it is important to assess the above preliminary power station parameters with respect to the actual

situation. Differences between the basic design parameters and the actual situation will mainly be based on a number of parameters and properties which were simplified.

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5 Leading High Water

The main goal of this study is to assess the possibilities of reducing the water level at several locations in the Southern Delta area in case of extreme water levels. The solution proposed in this report is to use pumps in the Brouwersdam to create a basin at the Grevelingen and the Krammer-Volkerak for temporary storage of excess water from the Hollands Diep/Haringvliet. These pumps can also be used during rising water levels, this increases the total amount of water that can be discharged from the Hollands Diep/Haringvliet. The impact of this solution, is assessed with a simulation study which will be discussed in this chapter.

5.1 Simulation design

5.1.1 SIMONA

To assess the water levels in the Southern Delta area before and after using the LHW-measure the software package SIMONA8 is used. SIMONA is a knowledge system for water flow analysis, which is based on mathematic simulation models which describe hydrodynamic processes. Within this software package one specific component was used for the simulation of water movement in two dimensions (2D), which is known as the model ‘WAQUA’. The simulations are build up out of a schematization of the water area, a set of representative constraints and a variable discharge of water at the Volkerak sluices.

Water level at location

x at time t

Constraints

(Time frame, sea conditions, river discharge etc.)

Schematization of the area

(Edges, bed elevation etc.) Discharge Volkerak sluices

(Throughput area, storage capacity G&VZ, pump capacity BD, etc.)

Simulation of scenario i

Figure 16 General representation of the simulations

The basis of the simulation is made by a schematization of the area, in which the edges are defined and the bottom shape and elevation of the river bed are included. The schematization used in this research is developed based on the Zeedelta model version 8 (Zeed-v8). Zeed-v8 is limited inland at the Lek by Hagestein, at the Waal by Tiel and at the Meuse at Lith and its limited at sea at 60 kilometers out of the coast between Zandvoort and the Brouwerhavense gat. At the overview in Appendix J can be seen that the area of the Grevelingen and the Volkerak-Zoommeer is not included in the model, this is done to reduce the complexity of the simulations and thereby the time in which these could be conducted. The

8

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LHW-measure of this project is therefore simply dimensioned as a water discharge at the Volkerakdam, which is the most important variable in the different simulations.

Figure 17 Overview of the simulation design

As mentioned above, the LHW measure is dimensioned by the discharge at the Volkerak dam. This discharge is however not a fixed magnitude since it depends on several variables like:

 Throughput area

 Pump capacity

 Pressure head

 High tide wave and storm conditions

 Storage capacity

The throughput area and pump capacity

The throughput area and the pump capacity at the Brouwersdam, determined by the number of pumps, are the two main variable for the scenario analysis. The throughput area is determined by the water flow area at the Volkerakdam. The Volkerakdam, is 7 kilometers long and built entirely from sand. This dam contains the Volkeraksluizen, one sluice for yachts, three sluices for industrial vessels and four scour sluices (See Appendix I ). Since the normal sluices are not suitable for this purpose only the scour sluices can be used. The following dimensions for the scour sluices are used for the initial calculations:

a. Total width: of 120 [m], each opening is 30 [m] wide; b. Sill height: AOD -4,25 [m];

c. Maximum opening height: AOD +1,5 [m], which leads to a total opening of 5,75 [m]). The above dimensions lead to an initial throughput opening of 690 [m2].

Rotterdam

Dordrecht

Middelharnis

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The pressure head

The pressure head, or the difference in water level between Hollands Diep and the Volkerak, is determined by the amount of water already stored at the G&VZ and the varying water level at the Hollands Diep.

The maximum water levels at the Grevelingen and Volkerak-Zoommeer are described in several sources. First the hydraulic constraints as issued by the Ministry of Transport (HKV-Lijn-in-water, et al., 2008) which describes the water level that weirs should be able to withstand in a specific area. Exceeding these preconditions thus not necessarily lead to breakthroughs, since all weirs surrounding the Volkerak date from before the Delta works and are thus capable of withstanding sea water levels exceeding AOD +2,0 [m] as stated in the MER9-study ‘Water storage at the Volkerak-Zoommeer’ (Projectbureau-Waterberging-Volkerak-Zoommeer, et al., 2009)

Another source that describes maximum water levels is the Treaty of Belgium, which are several agreements between Belgium and the Netherlands that are mainly based on sufficient water levels for shipping transport. The water levels described in this treaty state a maximum water level of AOD +0,5 [m]. Since the discussed measure will only be applied in case of extreme storm and river conditions, it will not be likely that the shipping sector is operational at all. Based on these considerations there a no binding constraints for a water level of AOD+1,5 [m], although several adjustments will have to be made to some of the new weirs.

The Treaty of Belgium also prescribes a minimum water level of AOD -1,0 [m]. Despite of the fact that the same reasoning as above applies to this minimum, a water level reduction of more than a meter will have several other consequences. When a reduction leads to a minimum water level of more than a meter far-reaching effects in several areas will occur. First from an ecological point of view, since a extremely low water level in combination with large amounts of fresh water could have significant impact. In how far this impact is permanent depends on the recovering capacity of nature. A second impact is related to the marinas and harbors in the area, since a strong reduction of the water level will have consequences for all ships in the area. This impact can however be put in perspective since the occurrence of the measure can be forecasted and necessary arrangement can be made in advance. A third impact could relate to existing dikes and artworks, for now is assumed that water levels in this range will not have a significant influence on strength or stability of dikes and artworks.

For all effects discussed above should however be noticed that this is a exceptional measure, which will only be introduced sporadic. Furthermore the realization of the discussed measure will take many years to complete, which gives plenty of time to take impact reducing measures.

9

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High tide wave and storm conditions

The water level in the Southern Delta area is determined by a combination of sea water levels and river discharges from the rivers. A significant high water wave from this rivers in combination with storm conditions at sea should represent an extreme high water condition would lead to the LHW level.

The high water wave from the rivers is determined by the discharge from the Rhine and Meuse. The shape of the Rhine discharge is standardized in the ‘Hydraulic Constraints for Primary Weirs (V&W, 2007)’ (Figure 18) a more detailed calculation of river discharges can be found in Appendix F . The storm condition is determined by three parameters: Maximum sea water level (Hs), storm period (Ts) and the phase (Fs) between the tide and the storm condition. A general representation of this storm condition can be found in Figure 19. In which Ts is taken equal to 35 [hrs] and Fs is taken equal to zero, in other words the storm maximum is taken equal to the tidal maximum. This storm condition in

combination with the normal tide at sea leads to the condition used in the simulations. Figure 20 shows a standard relation between normal sea and storm conditions.

Figure 20 Normal sea and storm conditions Figure 18 Standard discharge of the Rhine at Lobith

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The storage capacity

The maximum and minimum water level as discussed above water level determine the total available storage capacity at the Grevelingen and Volkerak-Zoommeer using the volumes as indicated in Appendix E . A minimum water level of AOD -1 [m] and a maximum of AOD +1,5 [m] leads to a total storage capacity of 294 and 161 million [m3]. at respectively the Grevelingen and the Volkerak-Zoommeer, which gives a total storage capacity of 455 million [m3].

This storage capacity can on the one hand be used to calculate the time needed empty this buffer using the available pump capacity at the Brouwersdam. And on the other hand the time needed to fill the buffer using a specific scour capacity in the Grevelingendam and the Volkerakdam.

5.1.2 Scenarios

To make an effective comparison between the possible configurations scenarios are developed. As discussed before these scenarios are designed using different pump capacities and different throughput areas at the Volkerak sluices. The functionality of the pumps can be split into two, on the one hand the pumps are used to create a basin which is then used to store water when needed and on the other hand the pumps can be used to pump water directly into the sea during alarming water levels.

First a reference simulation is performed with only a maximum prescribed river flow. This condition leads to a water level of AOD +1,9 [m] at Reach North, while the hydraulic constraint or LHW at that specific point is AOD +2,8 [m] (HKV-Lijn-in-water, et al., 2008). This difference can be explained by the assumption that the water level at Reach North is for the greater part dominated by the sea conditions. Since the LHW-measure will probably have the largest effect on extreme water levels the remaining reference simulations are performed using a significant river flow and a storm condition.

In theory this combination should both lead to the hydraulic constraint or LHW at Reach North and represent a reasonable chance of occurrence. Since little time was available to calculate all relevant combinations of storm and river discharges, a single combination was chosen after assessing several reference simulations. The choice has been made to use a maximum sea water level of ± 3,0 [m] and a river flow at the Rhine of 12000 [m3/s]. (For reference, the storm of 1953 had a significant sea water level of 2,9 [m] which is the most extreme storm occurred in Holland ever).

When looking at the Hydra-B database10 it becomes clear that there are other combinations which lead to similar LHW levels, therefore it is recommended to investigate these combinations in a follow-up study.

Next the several scenarios are constructed, the first two scenarios are based on an existing solution and thereby provides an alternative for the solution presented in this report. This solution is called “Water storage Volkerak-Zoomeer” for which effects are analyzed in (Thermes, 2006), which resulted in water level reductions between 1 and 30 centimeters. Currently an environmental effect study is conducted to explore further ecological consequences (Projectbureau-Waterberging-Volkerak-Zoommeer, et al., 2009).

10

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These two scenarios are not based on a pumping system in the Brouwersdam and do not require changes at the Grevelingendam and Volkerakdam. In this case the water flow is limited by the currently available scour sluices in the Volkerakdam. The only variable that is adjusted in scenario 1 &2 is the storage capacity of the basin (Abasin), scenario 1 only makes use of the Volkerak-Zoommeer and scenario 2 uses the Volkerak Zoommeer and the Grevelingen. Since scenario 1 and 2 are only included to

compare the impact on the water level and are already reviewed in other studies, they will not be analyzed in detail for their financial feasibility in this report.

The remaining scenarios (3-9) are configured as displayed in Table 6 in which:

 Athroughput is the throughput area of the Volkerak sluices (=_{(𝜇∙ 2∙𝑔∙𝛥𝑕)}𝑄𝑚𝑎𝑥 );

 Qpumps BD, max is the maximum pump capacity in the Brouwersdam;

 H is the start and end water level at the Grevelingen and Volkerak-Zoommeer;

 Abasin is the surface area of the basin in use;

 Vtotal is the total volume of water that is discharged through the Volkerak sluices.

The throughput area at 100% is calculated by the total width of the scour sluices multiplied by the available height (120[m] x 5,75[m]).

Table 6 Overview of the different scenarios 5.1.3 Location

To determine the effect of the solution it will be necessary to choose one or several locations at which the water level can be measured in simulation during extreme water flows. The design of the simulation study is mainly based on the water levels at Reach North, which is a measuring point at the Hollands Diep nearby the Volkerak Sluices. To assess the effect of the measure several reference points are appointed (see Appendix J ), these points are chosen to represent important locations and /or locations where a large effect may be expected.

sc i Name Athroughput,V. [m2] % QPumps BD,max

1 Storage@ VZ 690 (=100%)

-2 Storage@ VZ & Gr. 690 (=100%)

-3 100% Volkeraksluices & 40% Pumping 690 (=100%) 3000

4 100% Volkeraksluices & 60% Pumping 690 (=100%) 4500

Tidal power saving the day?