qs6 sediment budget and channel dynamics

Disclaimer

The authors of this quick scan have tried to collect as far as possible the available knowledge

on this subject. It is possible that the quick scan is not 100% complete. In the quickscans

proposals are made for follow-up research that is - in the view of the authors - required to

answer the policy questions within the Delta program Wadden. The “Waddenacademie” has

performed a review on this quick scan and made recommendations for follow-up research.

The project team of Delta program Wadden will prepare a work plan based on the proposals

in the quickscans, the review and recommendations by the Wadden Academy. Also links with

different other initiatives in the Wadden area will be made. This work plan will be submitted

to the steering committee of the Delta program Wadden in September 2011 for decision

making.

Juli 2011

Project team Delta program Wadden

KPP Wadden Delta Programme Quick Scan 6: Sediment budget and channel dynamics (including the outlines of a project proposal)

KPP Wadden Delta Programme Quick Scan 6: Sediment budget and channel dynamics (including the outlines of a project proposal)

1204229-000 © Deltares, 2011

Title KPP Wadden Delta Programme Project 1204229-000

Reference 1204229-000-ZKS-0004

Pages 38

Keywords Tidal systems, tidal inlet and tidal flat dynamics, sediment budget, effects of climate change, safety, international cooperation, study proposal Summary Research in the Wadden area has generated a great deal of specific knowledge that needs to be integrated throughout the trilateral area. The experience acquired needs to be incorporated for the purposes of the future. The main conclusion of this quick scan is that a great deal of knowledge has been generated over the past 20 years. This will make possible the further study of a number of selected issues, with a view to answering questions about the future development of the Wadden area during the climate change that is generally expected to affect the area. Deltares advises management improvements geared towards an integrated system approach and applied research into the sediment dynamics of the wider Wadden area. Over the next few years, this will advance our knowledge to the level that is therefore required. In particular, the level and depth of knowledge about the sediment budget and sediment fluxes across the Wadden Sea, the ebb-tidal deltas, the coastal foundation (Kustfundament) and barrier islands needs to be increased. This will allow us to understand possible climate-change-related processes that affect tidal flats, tidal marshes, barrier islands and beaches. It will also allow us to optimise management arrangements for the predominantly natural Wadden area. The sediment budget project that we envisage should generate answers to the following policy questions:

1. What is the relation between the Wadden Sea sediment budget and the primary sea defences along the Wadden Sea?

2. What consequences do sea-level rise and other climate-change-related changes in driving factors have for tidal flats, barrier islands, tidal marshes and beaches: will they drown or will their character change in other ways?

3. What will be the consequences of the changes for the primary sea defences and the associated levels of protection?

4. Do lateral channel shifts constitute a threat to primary sea defences and what can be done in terms of pro-active management?

5. Which short- and long-term measures can be taken to counteract the possible drowning of tidal flats, barrier islands, tidal marshes and beaches?

To answer these policy questions, Deltares advises focusing on the following knowledge issues:

1. How do sediment transport and the erosion/deposition system affect the trilateral Wadden Sea at the different scale levels: the overall tidal basin, the individual inlet systems and the interaction between channels and flats?

2. How and where can we document the first signs of tidal-flat drowning, if it occurs, and other climate-change related changes? Currently the Wadden Sea in general is receiving enough sediment to keep up with sea-level rise to the extent that it is locally shallowing.

1204229-000-ZKS-0004, 1 September 2011, final

KPP Wadden Delta Programme

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Contents

1 Policy issues 1 1.1 Policy issues and second thoughts 1 1.2 Policy issues analysis 2 1.3 Relationship with other parts of the Delta Programme 3 1.4 Focus 3

2 Knowledge required 7 2.1 Introduction 7 2.2 Knowledge requirements 7

3 Available knowledge and gaps 9 3.1 Available knowledge 9 3.2 Relevant knowledge developments 11 3.3 Knowledge Gaps 13

4 Governance 17

5 Planning and phases 19

6 Public involvement and communications 21 6.1 Public involvement 21 6.2 Communication and dissemination of results 22

7 Possible solutions 25

8 Ingredients for a draft proposal 27 8.1 Introduction 27 8.2 Benefits 28 8.3 Recommended research 28

9 References 33

Appendices

A Remarks and suggestions during the workshop sessions & replies A-1 A.1 Remarks and suggestions during the second workshop on 9 February 2011 A-1 A.2 Remarks and suggestions during the first workshop on 5 January 2011 A-2



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1 Policy issues

1.1 Policy issues and second thoughts During the workshops held in early 2011, the central policy issue was established: “How can the Wadden system act as a 'climate buffer' while maintaining its natural and protective functions?” The question comprises several elements that were discussed in the workshops; these elements are discussed in brief below: “the Wadden system” is not very well defined. Here, we use the term broadly on the basis of our knowledge of how the Wadden area functions and of coastal policy documents. From this perspective, the Wadden system is the entire area from MSL -20 m in the North Sea, extending to and including the mainland dikes and the entirety of the barrier islands. This definition makes it possible to include the major impact of wave decay on the barrier islands and the ebb-tidal deltas. Clearly, this definition goes further than the one that was originally assumed to underlie the question: the Wadden Sea in the strict sense. In other words, the backbarrier part of the Wadden system, the sub-, inter- and supratidal shoals and the tidal channels. “act as a 'climate buffer'” is taken here to mean: the fact that the tidal shoals and channels can keep up with sea-level rise by means of sedimentation until the rise reaches a given rate at which the shoals, tidal marshes, beaches and islands start to drown. Furthermore, in addition to sea-level rise, other climate-change-related changes causing effects on driving forces may affect the height of shoals as well as development of tidal marshes, beaches and islands. “maintaining its natural functions” is taken here to mean: its functions as a habitat for invertebrates and as a feeding ground for fish, birds and seals, as well as its natural abiotic functions, i.e. the hydro- and morphodynamics of channels and shoals, barrier islands and tidal marshes. “protective functions” is taken here to mean: the protection against flooding that the Wadden system provides for inhabited areas. It will be clear from the above definitions that the shoals are expected to drown if sea-level rise exceeds a certain critical rate. If and when this point will be reached is still unclear. To answer this long-term question, we have to identify the remaining knowledge gaps, and determine when these gaps must have been remedied and the extent to which the knowledge required can be obtained elsewhere. An important point to keep in mind is that we cannot predict sea-level rise and other climate-change-related changes in driving forces other than in the form of scenarios. This means that we do not look at specific points in time but at, for example, rates of sea-level rise as limits for the maintenance of the current situation. The topic under investigation has major policy implications. As is clearly stated by the Delta Committee (2008), securing an appropriate level of flood defence has the highest political priority in the Netherlands. At the same time, there is a strong political commitment to preserving/improving the natural functions and resources of our valuable coastal ecosystems. In the Wadden Sea in particular, both these political goals are challenged by climate change and faster sea-level rise. There is the possibility, for example, of the long-term drowning of tidal flats and salt marshes, or significant stretches of these flats and marshes.



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Such a development would have a negative impact on both flood protection standards and ecological values in the Wadden Sea area. The research assignment should therefore be changed from: "How can the Wadden system act as a 'climate buffer' while maintaining its natural and protective functions?" to “how can the Wadden Sea ecosystem be made more resilient to faster sea-level rise in order to maintain its ecological structure and functions, and its role in flood defence?”. This would allow for a more pro-active approach.

1.2 Policy issues analysis 1 Q: What measures can be envisaged and considered up-front? Answer: Examples of measures that can be envisaged are nourishment for the outer rims of the ebb-tidal deltas, sediment buffers in front of dikes, the cyclical lowering of high tidal marshes, initiating set-backs by decommissioning polders, sand damming in tidal channels, salt marsh enhancement techniques, connection dams (mainland to islands, such as in North Frisia), ecosystem engineers, etc. However, evaluation and consideration of these measures will be difficult without further study. 2 Question: What measures could make it possible to keep pace with sea-level rise? Answer: For the time being, we advise focusing on research and re-analysing data which are currently available trilaterally. Depending on the outcome of these studies: use – and if necessary deploy – appropriate monitoring techniques to provide missing information with a view to determining measures for keeping pace with sea-level rise. This approach is safe because there is still plenty of time to respond: intertidal shoal drowning is likely to be a very slow process taking decades rather than years. 3 Q: Can “soft measures” improve safety levels for mainland and/or island dikes? Answer: The first step is to investigate whether or not soft measures can improve safety levels. With respect to shoal height, it makes sense to concentrate on the future situation in which the shoals are drowning. The first question is: is shoal height crucial in these conditions for the safety of mainland and/or island dikes and for natural values? This can be calculated in simple model sessions and simple approaches looking at biomass in conjunction with height (Oost et al., 1999). If the answer is in the affirmative, the second question will be: is it possible to counter this development and what impact will this have? We advise looking at the possibility of artificially raising sandy tidal flats at crucial locations, maintaining ecology and improving it where possible. The effects of this approach should also be evaluated. To address the second question, experiments running in Zeeland (Western Scheldt with its current sediment dredging and dumping strategy and the program ANT-Eastern Scheldt with its tidal shoal nourishment field trial) and elsewhere should be taken into account. A third question is: how can the lateral movement of tidal channels threatening dikes be stopped by soft measures? Erosion by channels that undercut dikes and threaten them is already a problem due to the relative late warning system currently in place and the rapid movement of some of the channels. This problem will persist into the future. Expensive stone defences are currently used to prevent further erosion, an approach that conflicts with the aim of keeping the Wadden Sea as natural as possible.



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4 Q: What issues are not covered by this quick scan? Answer: Short-term management issues such as maintenance dredging in navigational channels that are not related to safety. These are day-to-day practices that are not covered by this programme, even though attempts should be made to identify win-win situations for the future. The possible exception here is the Ems-Dollard estuary. This area is covered by another programme. 5 Q: What stakeholders will be involved? Are there any differences in their approaches? Answer: The various groups of stakeholders differ considerably. Local policymakers and the local public will be inclined to put short-term issues on the Delta Programme agenda, while scientists and NGOs will tend more to focus on the longer-term issues. Joint fact-finding by the relevant stakeholders will enable the programme to be formulated. During the joint workshop sessions earlier this year, some stakeholders voiced the opinion that the sediment budget (as defined above) for the wider Wadden Sea is a task for national government and that the scientific institutions have a clear task to guide the scientific approach. It was concluded that the provincial and municipal governments do not feel they have a leading role to play.

1.3 Relationship with other parts of the Delta Programme Within the Wadden Delta Programme it is clear that the safety function of the Wadden area comes first, closely followed by the nature function and the function of socio-economics. The relationship with the “Delta Programme Kust” is equally clear because the coastal system as a whole is being studied, even though the Delta Programme Kust currently seems to be focusing on spatial planning. Sooner or later, however, the Delta Programme Kust will also include nature and the economy as issues that are subordinate to safety. At that point, opportunities will arise for the two programmes to learn from one another.

1.4 Focus The central issue is the possible drowning of the Wadden Sea and the implications for flood protection and nature. In this quick scan, the boundaries of the study area have been located in the North Sea at the MSL -20 m depth contour, which also includes the entirety of the ebb-tidal deltas and barrier islands. As the entire Wadden Sea is being considered, international cooperation within the trilateral Wadden Sea Committee is indispensable. In order to understand the functioning of the Wadden system and its response to sea-level rise, the following issues have to be addressed:

management practices: how can a more integrated system approach be incorporated in an efficient/cost-efficient way in the management of the area?

the possible drowning of the Wadden Sea: in what conditions, how and at what speed;

locations, directions and magnitudes of sediment fluxes (sand & mud), including overall sediment balances;

channel and intertidal flat dynamics;



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effects of ‘ecosystem engineering’ in terms of sediment dynamics (to be derived from ongoing research projects in that particular field of study);

measures required (what? where? when?) to prevent the drowning of the Wadden Sea intertidal flats;

is it possible to improve drowning predictions: can we find better indicators, make better observations, and develop more realistic models?

The data from the Wadden Sea depth soundings are quite crucial in terms of estimating the critical limit for keeping pace with sea-level rise, but the accuracy of these soundings is relatively poor and the intervals between them are relatively long (5-6 years). So as many basins as possible should be studied, perhaps after selecting data which appear to be sufficiently reliable. This would include the entire trilateral Wadden Sea and as many time slices as available. The natural dynamics of the Wadden Sea as it is now are significant considering the number of human interventions (e.g. fixing the position of some of the islands, strengthening primary sea defences along the mainland, maintaining navigation channels, intensive fishing and, in the past, land reclamation, closure of embayments and sand mining). Overall, the system is importing sediment, as it has done during the many centuries it has now been in place. Local erosion is prevalent only along the North Sea coast of the islands, in the main channels and towards the front of the ebb-tidal deltas. The Wadden Sea still responds to forcing from the North Sea, which is not expected to change in any fundamental way from the pattern seen in the past. As the system has survived periods of rapid sea-level rise before, it may well be able to act as a "climate buffer” to the expected changes in forcing. Because the process of drowning will most likely be gradual, no immediate actions are required. There is enough time to think before we act. And if measures are to be taken, they will probably be of a long-term nature. Even so, we cannot sit back and wait. We must further our understanding, design methods and test them up-front, and the monitoring of certain features and processes must start within a few years. Best practices for addressing these long-term issues need to be developed and implemented at the right point in time. This means the point at which sea-level rise reaches a certain rate. These developments need to be developed in close contact with the regular coastal maintenance research programmes. The necessity of maintaining close contact with other quick scans should be emphasised because this will undoubtedly generate numerous cross-over opportunities. The goal of the quick scan The goal of this quick scan is to briefly delineate the approach that can be taken to anticipate the effects of SLR in the context of climate change on Wadden Sea safety standards, while taking into account the large-scale natural structures and functions of the ecosystem in the area. Studying a number of back-barrier basins will probably maximise the opportunities to improve our understanding of the functioning and responses of this system, combining forces with German and Danish expertise in an international setting.



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One element involves identifying the management measures required and identifying the possibilities. Another consists of mapping out future research that may be needed to acquire the necessary insights in terms of sediment (sand and mud) fluxes in and out of the Wadden Sea, and of the mechanisms of sediment transport and – reworking active in the Wadden Sea itself. The various landscapes of salt marshes, tidal flats, channels, ebb-tidal deltas and the adjoining coastal zone, as well as their mutual interactions, will have to be considered. The islands are also part of the system. The main emphasis will, however, be on the water of the Wadden Sea. It will therefore be clear that the northern section of the North Holland coast is included the study area. The Coast, Protection and Wadden Delta Programmes have overlapping tasks here.



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2 Knowledge required

2.1 Introduction As stated above, a central role is granted to the development/deployment of management techniques which allow the system to become more resilient to sea-level rise and other climate-change-related changes in the driving forces. Knowledge relating to morphological development can be used to understand the behaviour of the Wadden Sea system and to assess the effect of policy and management options. In that sense, there is no distinction between the knowledge requirements for policy and management and those for scientific ideas. However, the principal knowledge requirements in this respect originate from the question about in which conditions, how and when the Wadden Sea intertidal flats, barrier islands and tidal marshes may drown and the implications for flood protection. Can we guarantee coastal safety while simultaneously maintaining the dynamic and natural character of the Wadden Sea region? Is it possible to maintain the present Wadden Sea system as a climate buffer to protect our coast?

2.2 Knowledge requirements Basically, the related relevant policy and management issues in the Wadden Sea region are coastal safety and protection, the degree to which the system behaves naturally, ecological values and biodiversity, economic use, and the value of natural resources. The approach chosen in this Quick Scan is a system approach and so we will briefly address the most relevant knowledge requirements for all environments. The knowledge requirements listed here are largely taken from Speelman et al. , 2009. North Sea Coasts/barrier islands Coastal integrity on the North Sea coast of the barrier islands is maintained by regular nourishment. The base coastline (BKL) is the limit beyond which the coastline is not allowed to move farther inland; the coastal foundation is required to keep pace with sea-level rise. To plan, design and execute these nourishment operations, proper knowledge of the behaviour of the coasts of the Wadden Islands, in conjunction with the morphological evolution of tidal inlets, is required at several temporal and spatial scales. Furthermore, coastal nourishment operations may have implications for the local morphology, ecology and hydrology of a barrier island. The morphological development of the coast is also relevant to evaluating and understanding the way extreme hydraulic conditions such as high waves and storm surge levels will affect the coast. Furthermore, the barrier islands are sediment depositories in their own right: during erosion they deliver sediment and, during sedimentation, sediment is stored. The main question is how the barrier islands will function in changed climatic conditions (sea-level rise, global warming, changed wind patterns, changed precipitation/evaporation patterns), and how this affects the sediment supply towards, and the shelter given to the back-barrier area.



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The inlet system and ebb-tidal delta The inlet system and the ebb-tidal delta form the gateway to the backbarrier area. A proper understanding of the behaviour of the ebb-tidal delta in relation to the need for sediment and the tidal volume of the backbarrier area at several spatial and temporal levels is required to estimate how the area will develop in the future. Furthermore, the position of, and sand transportation through, the ebb-tidal delta determines to a large extent the fate of the North Sea coasts of the islands. The backbarrier basins The unique characteristics of the Wadden Sea can be threatened by both changing boundary conditions and human interference. If the rate of relative sea-level rise exceeds a critical value the Wadden Sea may eventually drown. This implies the disappearance of the characteristic Wadden Sea intertidal shoals and mud flats, which are of great importance for the ecological system. The effects of, for instance, accelerating sea-level rise will not only occur when the critical rate is exceeded: this will be a gradual process. With accelerating sea-level rise, the morphology of the Wadden Sea could change. It is of interest to know how the morphological evolution of the Wadden Sea will be affected by sea-level rise at different rates. For the management of the Wadden Sea, the natural changes such as sea-level rise are seen as given boundary conditions. Measures that can be taken to mitigate the negative effects can be investigated. However, this will require a profound knowledge of sediment transport mechanisms in the Wadden Sea and the way in which these processes contribute to net deposition and morphological change. In summary, knowledge of morphological development under the influence of natural processes and human interference at different spatial and temporal scales is essential for policy and management objectives ( Speelman et al., 2009). Major questions at the largest scale focus on the sediment budget of the Wadden Sea: 1) Which sediment fractions will deposit in the Wadden Sea tidal basins in which conditions? 2) What amounts of each sediment fraction are imported and exported in each tidal inlet? To maintain the height of the Wadden Sea shoals, sand is of major importance, but fines may also be quite relevant for ecosystem functioning. 3) What are the most important sediment transport mechanisms and pathways in a tidal inlet system? 4) What determines the exchange of sediment between adjacent tidal basins? 5) What role do extreme events like storms play in erosion and deposition of sediment? 6) What are the consequences of various aspects of climate change (sea-level rise, global warming, changed wind patterns, changed precipitation/evaporation patterns) for net sediment transport into the Wadden Sea? At a smaller spatial and temporal scale the following questions are of importance: 1) What determines the shape and size of the ebb-tidal delta? 2) Which factors determine the characteristic tree-structure of the channels in the basin? 3) What causes the cyclical pattern in the ebb-tidal delta? 4) Is there an interaction between these patterns and development in the backbarrier basin? 5) What factors determine the location and migration of the watersheds between the basins? 6) Which processes govern the transport of sediments between tidal channels and tidal flats? To answer these questions, a fundamental knowledge is required of basic physical processes involving water movement, sediment transport and morphological response.



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3 Available knowledge and gaps

3.1 Available knowledge Data The Wadden Sea area is a tidal flat area that has been studied extensively. Data about morphodynamic development are abundant. The geological Holocene history is relatively well known in large stretches of the trilateral Wadden Sea. Historical information, including fairly accurate maps, is available from Roman times onwards. Detailed maps and depth soundings are available from the early 19th century onwards. Tide gauge measurements are locally available from the 18th century onwards and generally available from the 19th century on. Hydrodynamic measurements are available from the late 19th century onwards. Information about wildlife in the area has been collected since the 19th century and data about the interaction between biota and sedimentation have been collected since 1950. Knowledge It therefore comes as no surprise that a fairly impressive amount of knowledge is available relating to the central question addressed by this quick scan. If the various parts of the Wadden Sea at large are considered it can be concluded that: 1) Our available knowledge is limited with respect to the natural functioning of the barrier islands, because large areas had already undergone major human influences before research even started. This is an important point because there are strong indications that, in the current situation, sedimentation will be inadequate for the barrier islands to cope with fast sea-level rise. In the long term, this may lead to the drowning of the more natural unprotected areas, and therefore less shelter for the backbarrier area and mainland coasts. We know a lot about the functioning of tidal marshes and the functioning of the barrier island coasts and dune front: the problem relates mainly to active inland dunes and overwash processes, both of which seem vital to the future preservation of the barrier islands. We also know a lot about the management of the dunes, beaches and tidal marshes. We do know something about managing the active migrating dunes, but hardly anything about managing overwash in the natural areas. And nothing is really known about how to manage the barrier islands (from either the physical or wildlife perspective) as a part of the larger Wadden Sea system, for instance in terms of shelter or sediment supply to the backbarrier. 2) We know a fair amount about the development of the ebb-tidal deltas. There are some significant gaps in our knowledge about the interaction with the barrier islands, and particularly with the backbarrier area. Our knowledge about the management of the waterways in the ebb-tidal deltas is extensive, but limited when it comes to the management of the interaction between the ebb-tidal delta with the islands and the backbarrier area. 3) We know a good amount about the development of the channels and morphological development of sandy shoals and tidal marshes but less about the development of muddy shoals (Dollard, Jadebusen). Our understanding of channel-shoal interactions is still rather limited. A fair amount of knowledge is available about the management of the channels in terms of waterways and water movements, while our understanding is limited in terms of the management (which is mainly reactive in nature) of outer bends of channels moving into the dikes and of the management of tidal flats (which is also mainly reactive). We know a lot about the management of the mainland tidal marshes.



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Models A lot of this knowledge has been formalised as models. Models for the morphological development of the Wadden Sea area at large can be divided into: 1) Empirical and semi-empirical models, also known as behaviour-oriented models These models are based on empirical relations to define the morphological equilibrium. An important assumption is that, after a disturbance (through natural evolution or by human interference), the morphological system always tends to develop into a state satisfying the empirical equilibrium relations (e.g. the ASMITA model; Stive et al., 1998, Stive and Wang, 2003). Models of this type use a black-box approach and they do not specify the relevant processes. 2) Process-based models These models strive to establish the best possible description of the relevant processes. An example is the Delft3D system (Lesser et al., 2004), in which the mathematical equations representing the physical processes of water movement and sediment transport are solved numerically to determine the morphological changes based on mass-balance for sediment. Models of this kind can be used for the detailed presentation of the morphological changes. These models are particularly suitable for short-term detailed simulations to understand the system (Elias, 2006). In recent years there has also been significant progress in long-term morphodynamic modelling with process-based models (Wang et al., 1995, Hibma et al., 2003a, 2003b, Marciano et al., 2005, Van der Wegen et al., 2008, Dastgheib et al., 2008). Models of this kind are still limited in terms of practicality for long-term predictions due to practical reasons such as computing power, limited insight into the behaviour of the models and the schematisation of highly variable driving forces. 3) Idealised models Models of this kind are process-based, based on simplified physical and mathematical descriptions to analyse the behaviour of a morphodynamic system. The difference with the 'complex' models is that they do not pursue the full description of all processes, but try to reduce them to the relevant, essential components only. An example of this type of model is the conceptual model of Postma (1961) of inland sediment transport in the Wadden Sea. The different types of models should be thought of as complementing one another rather than as alternatives. To attain research objectives and answer questions relating to coastal zone management, a combination of different models is often required. Improvements in modelling should be achieved not only by making improvements in the modelling tools themselves, for example through the introduction of better physical and mathematical formulations, but also by improving the application of the models. Model schematisations of the Wadden Sea area are partly available (RWS, Deltares, Arcadis-Alkyon). A particular issue is the schematisation of driving forces which is deterministic (in the case of tides). Another driving force (wind) is a stochastic process. In models, these can only be incorporated in a simplified manner. In particular, the role of extreme events like storms is still largely unclear (Speelman et al., 2009). Furthermore, as the models become more detailed and realistic, additional data are required to fine-tune and calibrate the models. Researchers have mentioned the need for additional data (especially physical data) frequently.



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3.2 Relevant knowledge developments Wadden Sea area Various programmes that are already in progress are directly relevant to the subject of this quick scan.

The Naar een Rijke Waddenzee programme emphasises the natural values in the area.

Wadden-Fund-based projects. Dynamiek Project: The DYNAMIEK Project (Utrecht University and many other

research institutes) aims to substantially extend the knowledge relating to integrated North Sea coast and island management. However, for the moment, the project has been rejected for financing by the Wadden Fund. It is expected that some isolated components of the original proposal will be implemented in various ways.

o Feasibility study into “Mud in the Wadden Sea” conducted for the Wadden Academy by Deltares and others (results expected by 1 April 2011).

‘Ecosystem engineering’ programmes such as the re-introduction of mussel beds and sea grasses are generating a lot of insight into the functioning of tidal flat areas

The bilateral Dutch/German call for Georisk and Biorisk research proposals (issued by NWO) has led to several submissions. It is expected that the winning proposal will be of direct relevance to the programme of this quick scan (see Burchard, 2011). The Delta Programme and the Georisk proposal both focus on the effects of climate change and so active collaboration with be needed in this specific case.

The Kustlijnzorg (Care for the Coastline) ecology programme is monitoring the impact (particularly ecological) of the major nourishment operations in the central and eastern areas of Ameland. Although this programme does not have the funds to monitor the pathways of the nourished sand, it may be able, together with the monitoring of the Ameland gas extraction site, to generate clues relating to these pathways.

EIA of the effects of dike construction on Ameland (Deltares). Kennis voor Klimaat (Knowledge for Climate): this programme concentrates on the

implications for nature of artificial tidal marsh development in respect to dike safety. The results of this programme should be used.

Similar programmes in Germany and Denmark (D: KLIWAS, AufMod, HoRisk, WADE, MORAN, ImTg; Denmark: Restoration programmes and morphological research conducted by the University of Copenhagen).

National level

HR 2011 & SBW Golfonderzoek The generic programmes “Hydraulic Boundary Conditions 2011” and "Strengths and Loads of Water Defences: Wave Study". These programmes are part of the ongoing determination of the Hydraulic Boundary Conditions.

Coast Delta Programme & Protection Delta Programme The insights generated by these two programmes will largely determine the safety standards for the Wadden Sea area. The unique morphology of the Wadden, with a row of barrier islands and high tidal flats and marshes along the mainland coast, and the highly varied nature of the coastline, will make the implementation of the safety standards difficult. These difficulties need to be taken into account. The studies for the reinforcement of the Afsluitdijk and the artificial high tidal marsh (kweldernok) at Delfzijl can be considered



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to be the first attempts in this direction. This integrated approach will probably open up a new line of research.

Ecoshape Building with Nature is not yet active in the Wadden area. Many areas are being developed at present, and a lot is being learnt, particularly about the role of ecosystem engineers for freshwater systems and seagrass areas. The ongoing research into the potential erosion of tidal marshes (M. de Vries) may enhance our understanding of the future development of tidal marshes.

Ecoshape is also engaged in research concentrating on the question: “How can defence measures be carried out so that the coast is protected in the long term, while a balance between economics and ecology is maintained at the same time?”. This includes projects like the Sand Motor on the coast of South Holland. However, a different approach has been adopted in the Wadden area where, according to the stakeholders, nature must maintain itself as much as possible and spread sand from nourishment operations. In Ecoshape, the nourishment operations are the forcing factor and nature is expected to follow. It is expected that DPW5 will open up new avenues for coastal zone management in which nature will have a larger role. Furthermore, in recent years, there has been a lot of integrated work in the Zeeland area. Lessons learned, for instance in terms of smart dredging and dumping in the Western Scheldt, can easily be transposed to the Wadden area. The existence of an international (B-NL) technical secretariat has been extremely beneficial for the integrated programme. A lot of experience has been acquired with respect to dealing with the large morphological changes that occur in estuarine and tidal areas, notably in relation to safety and ecology. Examples are the trials with the nourishment of tidal flats and the establishment of oyster reefs in the Eastern Scheldt. Experiences with experiments in Zeeland (Western and Eastern Scheldt) should be taken into account. First and foremost, however, a similar type of organisation should be established for the Dutch section of the Wadden area. This is a prerequisite for clarifying the ownership of the area prior to introducing integrated management.

International level There is a massive body of knowledge available relating to similar tidal barrier areas in the world. However, this relates mainly to hurricane coasts in the USA, where the morphodynamics are quite different. The best examples are possibly the Georgia Bight in the USA and some tidal barrier systems in Australia. However, the Wadden Sea area is so unique (as was established in the studies for the World Heritage nomination) that it is felt that the bulk of the knowledge required should be derived from the trilateral studies of Denmark, Germany and the Netherlands. The research plan should focus on close trilateral cooperation. As mentioned elsewhere in this report, the Netherlands is currently leading the way in the application of climate adaptation to levels of protection in the national Delta Programme, which comprises three generic applied research streams and six study areas. The Trilateral Committee is actively interested in the outcome of the current quick scan. Contributors to the Trilateral Committee are keen to participate.



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3.3 Knowledge Gaps The knowledge gaps were identified in broad terms by the Speelman et al. (2009). They are accordingly summarised below at the various spatial and temporal scales. Large-scale sediment budget 1) Sediment budgets for the barrier islands in the longer term, especially the storage of sand on tidal flats, of mud in the tidal marshes and sand in the washover structures and the dunes. 2) With sedimentation rates in tidal basins, it is difficult to determine the net sediment transports through the various inlets, between the basins and along the North Sea coast. Unfortunately, sediment transport measurements are rare, and inadequate as sources of accurate information about these sediment flows. Moreover, sediment budget analysis until now has been based on fixed boundaries and does not incorporate the migration of the tidal watersheds. 3) Sediment budget studies indicate that sedimentation of sand and mud in the Dutch Wadden Sea basins is more or less balanced by the erosion of sand along the North Sea coast. In itself, the distinction between mud and sand reveals a lack of balance in erosion and deposition rates. Until now, sediment budget studies have usually determined the total amounts of sandy sedimentation and erosion. Particularly to further our understanding of the relevance for natural values in particular, separate budgets are required for mud and sand at least. nevertheless, sand budget studies are the most commonly occurring, hence these attract most of the attention. Generally, mud in the system is a few percent of the bulk sedimentation. Hence it seems obvious to focus on sand budget studies, and at the same time not forgetting the finer-than-sand fraction present in the system. 4) Bathymetric data constitute the basis for determining sedimentation and erosion volumes for various parts of the Wadden Sea system. However, this information is subject to errors and uncertainties. Future research has to address these errors and uncertainties to obtain a more precise picture of the morphodynamic behaviour of the system. 5) The establishment of the exact critical rate of sea-level rise and the factors that influence this critical rate. 6) The character and effect of mitigation to learn what measures can be effective in controlling undesired developments such as the local drowning of shoals and tidal flats in response to accelerated sea-level rise. Smaller temporal and spatial scales At a smaller scale, knowledge has to be developed to understand the various morphological elements, in particular their size, shape and behaviour. The following morphological elements should be considered: 1) Interaction foreshore-beach-dunes-washovers: Most of the barrier islands are drumstick-shaped, with a broad head on the updrift side. As a result, the beaches are a-typical and are very different in morphology and behaviour to “normal” North Sea beaches, as observed along the coastline of Holland. The beaches are very wide and dissipative and the wave field is highly 3D in character and very much affected by the nearshore morphology and bathymetry of the ebb-tidal delta. It results in specific refraction patterns and the convergence and divergence of wave energy. In addition, the wave field on the beach is almost always dominated by low-frequency (or infragravity) waves, waves with a wave period > 20 s. (Ruessink, 1998). The complexity of the coast means that the protection levels for this part of the islands are difficult to assess and the present methodology – as required by law – fails to determine these levels. According to this methodology, coastal stretches that are supposed to erode actually accrete, or vice-versa.



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2) Coastal nourishment and other forms of nourishment in the future: The morphological, ecological and hydrological impact of coastal nourishment operations should be determined in response to the design, dimensions and location of the operations. 3) Ebb-tidal deltas: What determines the shape and size of the ebb-tidal delta? What determines the cyclical patterns of the ebb-tidal delta? Is there an interaction between these patterns and development in the backbarrier basin? 4) Channels in basins: Which factors determine the characteristic tree-like or branching structure of the channels in the basin? What determines the shape of the cross-sections of the channels? 5) Intertidal flats: What factors determine the sizes, shapes and bed levels of intertidal flats? What determines the sediment grain size composition on these tidal flats and how relevant is the exchange of sediment between channels and shoals? 6) Watershed: What factors determine the location and migration of a watershed between two tidal basins? Driving the smaller-scale interactions, there are various physical processes and mechanisms that are essential to understanding the role of sediment transport gradients in generating morphological change for the Wadden Sea: 1) Wind-driven currents: For shallow water areas such as the Wadden Sea wind-driven currents play an important role. The same applies to waves wind-generated locally in the tidal basins. In both cases though, the impact of wind-driven processes is far from being understood 2) Mud transport processes: More knowledge is required about the erosion of mud and especially sand-mud mixtures and associated processes such as re-suspension, flocculation and consolidation. 3) Mechanisms that lead to residual sediment transport: Qualitatively, we know which mechanisms are responsible for residual sediment transport in the Wadden Sea (Van Straaten and Kuenen, 1957, Postma, 1961). However, we do not know which contribution each mechanism makes to the various inlets. Furthermore, each mechanism may have a different impact depending on the grain size involved. Another important question is: are we still missing certain processes or mechanisms? For example: the impact of density gradients due to freshwater runoff and direct atmospheric freshwater and heat fluxes on estuarine circulation and net sediment transport need to be further investigated at the regional scale. 4) Biogeomorphological processes: In recent decades, it has become clear that biological processes play an important role in the morphodynamics of the Wadden Sea. This means that it is important to know about these processes, and their variations in time and space, in detail. 5) Morphological equilibrium: There is still a gap between the theoretical and empirical knowledge relating to the existence of morphological equilibriums and the physical characteristics of those equilibriums. The groundbreaking work of Escoffier (1940) relating to the stability of tidal inlets already demonstrates that a morphological system may comprise multiple equilibriums, in this case a stable and an unstable equilibrium. These equilibriums may shift in the future under the external forcing brought about by climate change and may therefore lead to unexpected changes in the system if not understood. Modelling tools Generally speaking, a number of aspects are crucial to morphological modelling in tidal areas, and we should be able to address the following problems: 1) Morphological equilibrium: Observations suggest that morphological equilibriums exist and empirical relations have been defined linking morphological properties in equilibrium conditions to hydrodynamic parameters. However, in the case of a process-based morphodynamic model, it is far from clear that the model reproduces a morphological equilibrium.



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2) Parameters in behaviour-oriented models: Behaviour-oriented models are based on empirical relations for morphological equilibrium. The problem here is how the model parameters that describe the morphological evolution are related to the physical processes and the way we can derive these parameters. 3) Schematisation of driving forces: The forces driving morphological changes can be both deterministic (e.g. tidal) and stochastic (e.g. wind-related). A model can only include these factors in a simplified way. For example, the issue of how stochastic events like storms should be combined with deterministic processes such as tides is still under discussion and there is no standard approach. 4) Predictability and uncertainty: The stochastic nature of some components of the driving forces means that morphological development will not always be predictable. In other words: the driving forces of the future are, by definition, almost unpredictable. We can only rely on realistic scenarios that have a certain degree of probability. This probability will tell us something about the degree of uncertainty in the morphological analysis and results. 5) The interactive coupling between three-dimensional baroclinic hydrodynamic models and morphodynamic models needs to be further investigated and developed. This is a promising task in the light of the further massive increase of computer resources. 6) The proper implementation of closure models for turbulence and mixing is essential to quantitatively predict sediment dynamics and the resulting net fluxes into the Wadden Sea. Processes like settling lag depend in a sensitive way on the dynamics of turbulence breakdown and subsequent turbulence generation in the course of slack tides. The effects of turbulence damping and enhancement by stable or instable stratification respectively are key to the sediment transport processes such as the interaction between turbulence and water column stability due to high sediment loads or the dynamics of tidal straining. In addition, the consistent two-way coupling between wave models and turbulence closure models is an Important issue.



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4 Governance

The following governance issues have been identified: a. Cooperation with the active support of the Trilateral Committee (Netherlands, Germany and Denmark).

The Trilateral Committee is very interested in the potential of the Wadden Delta Programme for the all three countries involved. The Netherlands is ahead in the implementation of climate impact programmes. The Bundesland Schleswig-Holstein has indicated a strong interest, even to the extent of active participation. In any case, the Trilateral Committee has proposed playing an active part in the preparations, even during this quick-scan development stage. b. Current coastal management plans in the Netherlands

In the Netherlands, there are strong links with current plans for coastal management. Close coordination with these plans will benefit these programmes and the next phase, the Action Plan under the Wadden Delta Programme. The related programmes are: KPP-B&OKust, KPP-Kustbeleid en KPP-DPWadden. The brief background to these programmes is given below.

Due to a lack of sediment supply (from rivers, for example) and sea-level rise, most of the Netherlands is challenged by coastal erosion. Coastal retreat puts pressure on levels of protection and other coastal functions. This resulted, in 1990, in the introduction of the dynamic coastal management policy (‘dynamisch kustbeheer’). This policy is based on a sediment volume approach. Where there are structural deficits in sediment volumes, replenishment takes place in the form of sand nourishment operations. The preservation of the coastline (the "Base Coastline" adopted on the basis of the 1990 sediment volume in the near-coastal zone) is required by Dutch law (the 2009 Water Act). The preservation of the sediment volume in a wider zone (the "coastal foundation" (kustfundament), ranging from -20 m to the inner dune area) has been set out in Dutch policy documents (National Water Plan, 2009). As a result, the Dutch coast is nourished with 12 million m3 of sand on average a year.

This amount is based among other things on sediment export from the coastal foundation to the Wadden basins: the "loss" of sediment from the coastal foundation to the Wadden basin is offset by the nourishment of the coastal foundation. Studies have estimated that the sediment deficit in the coastal foundation in the Wadden area amounts to approximately 12 million m3 annually, with approximately 5 million m3 being replenished annually (in the period 2001-2009). We need to know more about sediment import to the Wadden basins to determine the proper amount of sediment that needs to be nourished to comply with the policy objectives referred to above.

Knowledge about the impact of nourishment strategies (i.e. decisions about nourishment locations, frequencies etc.) is required to determine not only the future effects on coastline migration but also the possible impact on sediment import / export to the Wadden basins. The ecological effects of nourishment operations are currently subject to evaluation. We need to learn about the cyclical patterns in the coastline of the Dutch Wadden Islands to determine whether structural erosion is endangering coastal functions or whether erosion is temporary (this knowledge will make decisions possible with respect to nourishment locations).



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A thorough understanding of sediment budgets, sediment dynamics, the effects of nourishment strategies and the implications for coastal policy and coastal management is required to define an optimal nourishment strategy.

The Centre for Water Management and Deltares work together on these subjects in the projects KPP-B&OKust (coastal management) and KPP-Kustbeleid (coastal policy, including DP-Kust). The hypotheses upon which the current nourishment strategy is based occupy a central role in these projects. The following hypotheses are the most relevant for the Wadden area, some of which still need validation and verification:

• The Wadden Sea takes sand from the coastal foundation (kustfundament). The volume is determined by the Wadden Sea surface (in km2), relative sea-level rise (including soil subsidence due to gas and salt mining) and morphological adjustments caused by the earlier closure of tidal basins;

• Nourishing the coast does not increase net sand transport into the Wadden Sea; • Nourishment IN a tidal basin does not diminish net sand imports through a tidal

inlet; • The development of barrier island coasts is influenced by developments in

adjacent ebb-tidal deltas; • The coastal erosion of barrier islands is caused by the lateral movement of tidal

channels towards the islands. Sediment management programmes in Germany Sediment management is a task for the “Küstenländer”, not for the federal government. Large-scale sediment management issues (covering the entire Wadden Sea coast) are non-existent, but regional sediment problems are present, notably in the estuaries (Ems, Elbe) as a mix of the natural accumulation of mostly fine-grained sediment (silt and mud) and accessibility for large ships, which has been increased over the years. The resulting changes in tidal characteristics have in turn altered the nature and the locations of sedimentation. Locally sandy Wadden islands (such as Sylt) are nourished once every few years. The methods used are similar to those adopted in the Netherlands. Scientifically, there is a lot of interest in modelling large-scale sediment transport into the German Bight, and into the Wadden Sea. Sediment management programmes in Denmark Denmark has local coastal erosion problems that are usually dealt with by the local nourishment of erosive coastlines down-drift of structures such as harbour moles. The amount of cubic meters supplied to all locations is ca. 1Mm3 on a yearly basis and EIA routines are applied. Dumping of sediment must in any case take place below 10 m water depth. The Danish Coastal Authority is the chief actor, while the National Environmental Agency overseas dumping and dredging operations (pers. comm., Prof. M. Pejrup).

c. Natura2000

Natura2000 is covered by the governance issue, so it is important to make clear what kind of measures will be acceptable from the point of view of the regional nature management plans. This applies equally to the trilateral countries.



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5 Planning and phases

This QS document contains a proposal for further analysis and study (Chapter 8). Once this is finished, a longer-term applied research effort will start. The following phases are foreseen: 1. The proposal as it is worked out in this QS document; 2. Drafting the full proposal “Action Plan” (second half of 2011): choice of methodology; differentiating the project from other, related projects and delineating cooperation with affiliated projects, as well as the establishment of the basic trilateral structure. Towards an Action Plan:

• Likely further developments of morphological models (process-based (D3D) & ASMITA types of models with processes incorporated and with increased resolution);

• Detailed modelling actions: these will include tidal flat-channel interactions (seasonal; long-term scale over decades; mud-sand interactions);

• Incorporate Natura2000 targets; • Test most suitable measures (if possible); • Evaluate, for instance, maintenance dredging work to get better grip on system

patterns; • Organise a scientific support programme including doctorate students.

3. Mid- to Long-term actual study (probably 5-10 years).



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6 Public involvement and communications

6.1 Public involvement The figure below shows how the project will be implemented. There are four layers:

• The financier, the stakeholders and the project team • The agreed package of measures • The modelling system • The morphological experts

Figure 6.1: Overview of the generic approach to the research The diagram above shows:

• The stakeholders and project team (with support from experts if required) produce a joint proposal of measures to be studied(red arrows);

• The measures will be proposed for inclusion in the morphological models (blue arrows);

• The results will be submitted to the morphological experts for discussion (white arrows);

• Finally, feedback is provided to the stakeholders (green arrows).

Stakeholders

Project Team

Measures

Morphological model

Morphological experts

Morphological model



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6.2 Communication and dissemination of results The communication and dissemination of the results (internally and externally) will be an integral part of the project from the outset at both the national (i.e. in the Netherlands and, potentially, Germany and Denmark) and international levels. This may include: internet, regional and trilateral workshops, stakeholder group, regular project flyers etc. During the drafting of the project proposal, specific attention must be paid to these matters. Various initiatives in this regard have been developed recently, and the methods and tools they have employed can be copied. Some of these examples have been copied from another quick scan and included below, in this case the quick scan “Effects of climate change on storm surge levels in the Eems-Dollard estuary”. Visualisation is an extremely important tool in communications and dissemination. For the Western Scheldt, much of this has been worked out (examples from screenshots below); the methods used can easily be transferred into the Wadden Sea area.

Figure 6.2: Measures: dredging (blue), dumping (red) and sand mining (green)

Figure 6.3: Bathymetry



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Figure 6.4: Maps showing the differences between two consecutive bathymetry measurements: erosion = blue, red

= sedimentation.

Figure 6.5: Calculated speed vectors and bathymetry

Figure 6.6: Cross-sections of consecutive years (different colours)



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7 Possible solutions

Promising measures that could be implemented around the Wadden Sea are set out below. Their potential implementation would initially be in pilot studies:

• Nourishment of the ebb-tidal deltas (flood-dominated areas): these areas are highly dynamic and are home to less benthic fauna than other parts of the coastal system.

• Nourishment operations for the sides of flood channels and restoration/relocation of channel patterns;

• Sand damming in “at-risk” gullies (leading to dikes or salt marshes => example “Vollerwiek near Eiderstedt, Germany) or as a means of stabilising sub-basins (by reducing or eliminating the hydrologic energy);

• Long dams following the tidal divides (example Hindenburgdamm near Sylt, Germany);

• “Smart dredging” trials: use maintenance dredging spoils for system tests (and for testing the morphological and environmental impacts of this type of dredging): select the proper season for the dredging & dumping of spoils;

• Test bio-fixation of nourishment and/or “smart dredging” materials (sea grass, Japanese oysters,…);

• Test effects of limited filling-in of deeply scoured flood channels (as sediment supplier for tidal flats, because the channel will erode again due to strong currents)

It may be necessary to combine some of these trial proposals in a major trial in order to limit the potential geographical impact, to restrict the monitoring activities in the area, and to combine monitoring activities better/more economically. Stakeholder involvement is necessary. Monitoring and evaluation at the proper level is necessary in any case.



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8 Ingredients for a draft proposal

8.1 Introduction The essential knowledge issues address resilience, i.e. the capacity of the Wadden Sea to keep pace with relative sea-level rise and other climate-change-related changes in driving forces. We need to know what we can do to determine this capacity, and how we can increase this capacity where possible. An incidental question is: what are the indicators of drowning/incipient drowning and how can we register and, if possible, quantify them? Although sea-level rise is a long-term process, and as the Wadden Sea still seems to accumulate sediment (as far as we can measure), this is suggesting that urgency is low. Nevertheless, it is still very important to start researching the effects. Many relevant issues are still underdeveloped, such as measurements (particularly automated) in the field, the monitoring required, and the nature of some effects. Fundamental to a proper analysis of the sediment budget is the availability of a well-calibrated and validated hydrodynamic model. Some models are available, but none of them cover the entire Wadden Sea. Many models include specific hydrodynamic parameters for sedimentation and erosion, but not at the scale of the entire Wadden Sea. A further version of D3D is being set up in which drying and flooding is worked out in detail, so that realistic sedimentation and erosion processes can be simulated and compared with long-term model results (such as ASMITA). An important issue for the quick-scan subject is monitoring. Current monitoring arrangements in the standard Dutch monitoring programme (MWTL) are insufficient to generate an insight into the sediment budgets as will be needed in the context of the Delta programme. It is clear that, for the Wadden Sea as a whole, new comprehensive monitoring methods need to be designed for better system analysis and system management. The monitoring infrastructure, in combination with the modelling tools, must in due course be able to represent sediment budgets comprising both sand and mud. Intensive interaction is planned with the KPP ‘Kustlijnzorg’ projects, as referred to above; these mainly carry out sand budget studies. Information about the approach to Wadden Sea mud can be found in the Action Plan “Clear as Mud" (van Duren et al., in press). During various meetings, the regional stakeholders have indicated that they see the dynamic nature of sediment movement in the Wadden Sea as characteristic for the Wadden Landscape. The ever-changing morphology is fundamental to the appeal of the area for tourists and therefore important for the economy of the area. The understanding is also that the level of dynamics should not change. It is proposed to focus at first on the extension of system understanding in relation to sand budgets. Speelman et al. (2009) have listed the current knowledge and knowledge needs on the Netherlands’ part of the system; this will need to be supplemented by German and Danish researchers for good (model) connections in the tripartite area. We work on different scales, i.e. the scale of entire tidal basins, and the scale of tidal flats with adjacent channels.



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8.2 Benefits What will be the benefits for the Wadden Delta Programme if the QS is indeed implemented?

• An overview of sandy sediment fluxes in as many tidal sub-basins as possible. Total sediment fluxes can be determined within a given bandwidth (policy issues 1, 2)

• Insights into the resilience of barrier islands, tidal basins, tidal flats and marshes given accelerated sea-level rise and other climate-change-related changes (policy issues 2, 3).

• An overview of places where the first signs may be observed of effects that are likely due to accelerated SLR and other climate-change-related changes, i.e. locations where critical thresholds will be exceeded first, at which point safety will be under threat (policy issue 3).

• As and when pilot studies will take place, with monitoring of essential parameters, extensive experience may be gained (policy issues 1, 2, 3).

• On this basis, after some years, a Wadden Sea sediment-management plan may be drafted with a mid- to long-term perspective, as is now the case for the standard sand nourishment programme for the entire Dutch coast and in some inland locations such as the Eastern Scheldt (policy issue 1).

• Involvement of local stakeholders (policy issue 5) What is specifically required? As mentioned above, flat-channel interactions are a major gap in our knowledge, as are the processes involved in sediment import into tidal basins. Sediment exchange data are required at these various scales to provide input for the models under development. System observations and initial modelling results may then improve the efficiency of the monitoring programme. Zooming in & out to different scales will be imperative as an iterative action throughout the project.

8.3 Recommended research Obviously, extensive research is required to close the critical knowledge gaps that have been identified. However, for management purposes, it is felt that the knowledge gaps individually have different priorities. The next phase, the Action Plan, will include a presentation for the recommended research that is required. However, this research should first address the question of the relevance of the height of shoals, barrier islands and beaches for both safety and for natural values. Once this has been determined, a better understanding of sediment dynamics can be acquired by initiating research combining the identification of relevant knowledge (this quick scan), data analysis, laboratory experiments, field surveys, theoretical analysis and numerical modelling. The required research will be a major ongoing effort involving various disciplines. Some elementary first steps are given here, and research might be extended in the future on the basis of the results.



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A desk study (using existing knowledge and expertise) that will concentrate on the following questions:

1) What will be the impact of lower shoals and islands and beaches on safety and natural values? What hydro-morphological processes (sediment fluxes) would prevail in this unstable state? (Go/no-go);

2) When (in which hydrological scenarios) will the tidal basins in the Wadden Sea start to “drown” (can this already be seen locally)?

3) How and where would the artificial measures perform optimally (from the point of view of safety and ecology)?

Analysis of the available data about the morphodynamics of the trilateral Wadden Sea system Identification of which tidal sub-basins will offer the best opportunities to develop the system knowledge that is required. In view of the major uncertainties in the bathymetric data, all tidal sub-basins of the entire Wadden Sea should be considered for as long a period of time as possible. Later, the focus may shift to a limited number of areas that are expected to yield the most relevant information when they exhibit ‘signs of drowning’. At first, an analysis of the supposed drivers behind tidal flat sedimentation and sedimentation in tidal basins is made using relatively simple existing elevation data and tidal data. The tidal flats To collect as much elevation data as possible about small- to medium-sized tidal basins in the trilateral Wadden Sea (10 to 100 km2) and analyse these data in conjunction with other data (cf. Elias, 2006):

• MLW, MSL, MHW and SHW levels in the year preceding the analysis and at some prior moments in time (to understand the trend);

• Storm surge history for the year (or years) preceding the analysis; • Barometric history for the year (or years) preceding the analysis; • Prepare a cumulative sediment transport scheme (c.f. Kohsiek et al., 1988).

A comparable analysis should be conducted for the channels in these areas in order to trace channel-flat exchanges and possible imports/exports from the areas. This analysis could serve as a basis for establishing a good picture of which indicators are important to register early response to relative sea-level rise and of which indicators should be included in the models to improve the capabilities of the models.

4) Identification of early indicators of changes in the system that are relevant to safety and natural values.

5) Inventory of lateral channel shifts, the resulting threats to dike safety and possible management approaches that should be considered

6) Inventory of new measurement techniques, especially remote sensing techniques, that can be used to obtain, for example, a synoptic picture of the relevant processes/parameters.

7) Inventory of international knowledge and inventory of the knowledge (both scientific and managerial) and the knowledge structures in Denmark, Germany and the Netherlands with the aim of incorporating the latter in the final research plan.

8) Development of a trilateral-based final research plan Towards the International Wadden Sea: future sediment dynamics and sediment budgets, addressing the relevant questions which have been summed up in 3.2. This plan will include a good combination of the identification of relevant knowledge, data analysis, laboratory experiments, field surveys, theoretical analysis and numerical modelling.



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Phase 1 Drafting the Action Plan A small committee will draft the Action Plan jointly in a central location, with data on hand to test hypotheses. The set-up of the Plan and demarcation with respect to other (active) projects will be discussed and agreed. International cooperation requires proper funding. A phased project budget needs to be set up and allocated. Once agreed, funding agencies in the trilateral countries need to have their budgets ready at the same time and resource persons need to be available. Allowing gaps in the programme is needed (at go/no-go decision moments), must be discussed and decided in good time. Kick-off meeting A kick-off meeting is held, bringing together scientists and managers from NL, D and DK. At this meeting, presentations are given demonstrating the potential feasibility of the methods, availability of data, determination of hot spots, etc., leading to the results outlined in the draft project plan. At the end of the meeting, a joint conclusion about the feasibility of the project will be drafted and recommendations will be listed. Local relevance must be clear at this stage. A go/no-go moment will follow. A decision needs to be taken for the following phase (1-2 years), not for the main project work (5-10 years). Phase 2 Establishing the project structure and drafting the Action Plan This phase starts with the elaboration of the project plan. The same group as in Phase 1, with help from the trilateral working group, elaborates the results from the KO meeting to produce an Action Plan for the entire project. In fact, monitoring of maintenance works can start earlier, as and when suitable opportunities arise. The problem is that, for this type of monitoring, which is more wide-ranging than usual, the required budget is larger than for straightforward monitoring. The management authorities have to be willing to undertake and invest in monitoring of this kind. It needs to be developed in close cooperation with the Wadden Fund Project WaLTER and any other projects relating to monitoring in the Wadden Sea, such as the fine sediment Action Plan, in order to streamline data acquisition and data accessibility. A selection of appropriate tidal basins is taking place in the trilateral countries. Trilateral meetings are being held to investigate the feasibility of the project design. Suggestions and ‘recipes’ for monitoring and modelling need to be listed in the slipstream of the desk study and fed back into the overall monitoring stream in close cooperation with other efforts focusing on monitoring and sediment dynamics. At the same time, the project needs to be in touch and interact with other quick-scan studies and to borrow from them or contribute new insights to them. At the end of this desk study, there will be another go/no-go moment. A decision will have to be taken about the implementation of the full project (5-10 years).



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Phase 3 Modelling New insights need to be worked into the most important available models (such as Estmorf, ASMITA and the 'new version' of Delft3D). Weaknesses in the current monitoring arrangements must be exposed and indications must be generated about where and when the first signs of the impact of sea-level rise will be visible, and what indicators must be followed. Models may also generate insights into potential test locations for measures that will help the Wadden Sea to keep pace with SLR. Start with a limited number of test locations and expand when successful. Iterative modelling actions required when data collected under the project justify this. Monitoring On the basis of iterative model research and field tests, monitoring will have to be revisited to enhance the quality of our system views of sedimentation and erosion in the Wadden Sea. Depending on the degree of additional monitoring and the results it generates, further improvements may be made in terms of predicting the future of the Wadden Sea. Designing methods for nourishing the Wadden Sea: where and when On the basis of the project work, while incorporating incoming views from directly relevant projects, methods will be designed to help the Wadden Sea to maintain its shape and safety levels while respecting ecological values. Throughout the project Stakeholder involvement In view of the project's importance, an independent committee of scientists, local management authorities, and a representative of the NGOs should be established (in NL, i.e. Wadden Academy, Wadden Area & Rich Wadden Sea Delta Programme, Wadden Association) to safeguard the necessary flow of information to stakeholders and the incorporation of local views where possible. Using feedback loops It will be very important to maintain feedback loops with other ongoing quick scans (in NL) and other projects in D and DK, and with regular maintenance works, for two reasons: to learn from these activities (from extended monitoring, as explained above) and to introduce new insights to regular activities and general monitoring programmes (WaLTER & Wadden DP). The flexible management and allocation of resources to the project are indispensable. Annual reviews will be required for the reallocation of budgetary resources. Planning First 1-2 years Desk Study: Data analysis of “all data” available in the trilateral Wadden Sea. Pilot studies for tidal channel management Dollard, Balgzand, Pinkegat and Zoutkamperlaag. Next year (depending on outcomes of the first years) Model studies looking at the impact and at locations where effects are recorded in order to improve monitoring.



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9 References

Borsje, B. W., M.B.De Vries, S.J.M.H.Hulscher, and G.J.de Boer 2008: Modeling large-scale cohesive sediment transport affected by small-scale biological activity. Estuarine Coastal and Shelf Science 78:468-480. Bouma, T. J., M.B. De Vries, E. Low, G. Peralta, C. Tanczos, J. van de Koppel, and P.M.J. Herman 2005: Trade-offs related to ecosystem engineering: A case study on stiffness of emerging macrophytes. Ecology 86:2187-2199. Burchard, H. et al., 2011: The future of the Wadden Sea sediment fluxes: still keeping pace with sea-level rise?. Proposal submitted to NOW/Bundesministerium für Bilding und Forschung. Rostock, pp n.n. Dastgheib, A., J.A. Roelvink and Z.B. Wang, 2008, Long-term Process-based Morphological Modeling of the Marsdiep Tidal Basin, Marine Geology, doi:10.1016/j.margeo.2008.10.003.

Deltacommissie, 2008:: Samen werken met water. Bevindingen van de Deltacommissie, Den Haag, 134 pp. Deltaprogramma Waddengebied, 2010: Plan van Aanpak (definitief concept) & Basisrapport voor Plan van Aanpak. Leeuwarden, 38 pp & 164 pp. Duren, L.A. van, Ridderinkhof,H., Winterwerp, J.C., van Prooijen, B.C., and Oost, A.P., in press.: Clear as Mud: understanding fine sediment dynamics in the Wadden Sea - Plan of Action. Elias, E., 2006: Morphodynamics of Texel Inlet. PhD thesis TU Delft, pp 262. Elias, E.P.L., Stive, M.J.F. and J.A. Roelvink, 2005, Impact of back-barrier changes on ebb-tidal delta evolution, Journal of Coastal Research, 42(SI), 460-476.

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A-1

A Remarks and suggestions during the workshop sessions & replies

A.1 Remarks and suggestions during the second workshop on 9 February 2011 remark/suggestion Reply Monitoring sediment pathways thru RS in the QS Morphological consequences of nourishment for Wadden Sea (WZ) (height, sediment characteristics)

in the QS

What is contribution of WZ system to general safety

undertake jointly with other QSs

Connect to Coast DP/use system view (wet & dry)

Incorporated into the design of QS

Is the WZ similar to the Coast system? no, although some parts/themes are similar Channel mobility and sediment budget in relation to fixation of islands/non-fixation of islands

unique to the Wadden and Zeeland open channels systems around non-fixed boundaries

What is our target for the WZ? It is not sensible to choose a target from the past: the WZ IS a dynamic coast. Neither is it sensible to choose some target in the future for the same reason.

Need to know more about channel mobility? to be incorporated into monitoring Channels threaten current primary sea defences

local feature; careful monitoring: learn from it

measurements = firm knowledge footing; modelling=learning

always true, but not feasible for rolling out to the entire Wadden Sea

Define tidal sand flats done; to be worked out further Define sediment budget all sediment that is contained in the Wadden

Sea and beyond Marking of individual sand grains ? not recommended while not feasible and

expensive How to deal with the long-term aspects that predominate in this QS subject?

Decision to be made that monitoring long-term aspects is crucial to survival of the Wadden Sea. Not an issue in this QS

What role for the research institutes? Provide them with budget; they will be more than happy to respond to complicated system issues. Not an issue in this QS

What role for data collection/analysis? Prominent role; to be incorporated in the second stage

How to deal with low urgency of measures (as seems to be the case at present)?

Political decision. Not an issue in this QS.



A-2

A.2 Remarks and suggestions during the first workshop on 5 January 2011 remark/suggestion reply sediment pathways largely unknown, including those from nourishment operations

inclusion in long-term monitoring programmes

improve bandwidths by studying multiple sub-basins

inclusion in proposal

better understanding of channel dynamics inclusion in proposal ASMITA study to refine/enhance long-term predictive capacity (100-200 years)


Influence of wave heights on sedimentation/erosion regime

learn from SBW project

tidal amplitude increases in the German Wadden Sea: why not in NL?


Link with ongoing monitoring programmes along the NL coast

learn from KLZ (now) and Coast DP (in due course)

Harbour siltation included? not a part of this QS How do intertidal flats ‘work’ in relation to channels? >> this is part of the wider issue of sediment dynamics, like many other questions brought up

sediment (sand + mud) dynamics (coast, ebb-tidal deltas, channels, shoals, flats) prominently to be included in proposal

Stakeholders: who? inclusion in proposal Which locations to be used for nourishments? a follow-up of sediment dynamics study Accessibility islands 24/7 under all conditions not an issue for this QS>> different

discussion Effects of historical measures inclusion in long-term approach in proposal How best to influence lateral channel migration?

is a regular maintenance issue at most times>> not an issue for this QS, only when safety levels of dikes are at stake: part of proposal

feasibility of measures such as nourishment operations (if large scale, long-term, repeated)?

if MER/EIA will be obligatory, then these issues will be studied in a EIA context.

qs6 sediment budget and channel dynamics

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