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Coastline intervention tool  - Holland Coast (ITHC)

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Type: Model

Project Phase: Initiation, Planning and Design

Purpose: Communication tool for stakeholder engagement - simple modelling of different scenarios

Requirements: user-friendly (no extensive modelling skills required), knowledge on coastal processes

Relevant Software: OpenEarth Viewer (web application) or OpenEarth (requires Matlab)


 

About

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The Interactive Design Tool for the Holland Coast (ITHC) is a Interactive group modelling (- MapTable) application aiming at assisting decision makers, project developers and stakeholders in the early development stages of coastal maintenance strategies for the Holland Coast. The Holland Coast, i.e. the coast of the provinces South-Holland and North-Holland, the Netherlands, is a sandy dune coast characterized by a wide variety of economical, ecological and recreational functions, hence a large and diverse group of (potential) stakeholders. For the successful implementation of coastal maintenance strategies, the support of these stakeholders is of vital importance. With the Interactive Design Tool users can easily and rapidly evaluate the consequences of various coastal interventions (e.g. nourishments, coastal structures) for indicators such as coastline development, dune development and habitat suitability. The tool has the ability to evaluate (mutual) interactions between new interventions and existing coastal structures in both space (small- vs. large-scale) and time (short- vs. long-term). This enables users to get insight into the consequences of their choices, to determine their position, and to provide input into the design process.

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Building with Nature interest

The ITHC is a platform for interaction of knowledge from different disciplines (coastal engineering, marine & dune ecology, ecosystem services, cost-benefit analysis) and people with different roles in the development process (policy makers, stakeholders, professionals). It can be used to gain insight into the effects of human interventions and changes in environmental conditions (such as sea level rise), as well as their interactions with user functions. In this way it facilitates interaction between eco-dynamic project developers and stakeholders, which is one of the three main eco-dynamic development & design principles of Building with Nature.

 

In principle the Interactive Design Tool can be applied in all project phases . In the current (2012) version, however, the limitations of the underlying model practically restrict its use to the initiation and planning & design phases, e.g. to identify and evaluate first alternative visions/designs. For more detailed design stages more detailed models could be plugged in. The Interactive Design Tool for the Holland Coast is just one example of an interactive  type of tool. The basic concept can be (and has been) applied in a wide range of other applications.

 

Although the tool now focuses on the Holland Coast, the underlying framework, consisting of an interface, pre- and post-processing software and a model, can be applied to coastal systems anywhere in the world. Any type of model can be plugged in, as long as the proper software for pre- and post-processing is available or developed. Note, however, that the current empirical relations to link coastline development to dune development, ecology and other indicators are specific for the Holland Coast and may not be applicable to other coastal systems.


How to Use

The focus of this section is on the "technical" use of the Interactive Design Tool. For more information on the setting in which these types of tools can best be used we refer to the Interactive group modelling (- MapTable) tool description.

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Starting point of the Interactive Design Tool is that it is easy to use, also by non-experts. Therefore, the user interface strives to facilitate intuitive use, by limiting the number of buttons, keeping the number of required user actions to a minimum and checking for erroneous input. Results are visualized in a Google Earth window, which most users are acquainted with. In its present (2012) form the tool gives a first estimate of the impact of coastal interventions. Results should be interpreted qualitatively rather than quantitatively. Although starting a simulation is relatively fast and easy, workshops in cooperation with Atelier Kustkwaliteit made clear that proper interpretation of the results requires knowledge of coastal processes, underlying model assumptions and the relations linking indicators to coastline development. Therefore, when using the tool in practice (in stakeholder workshops), it is strongly recommended to appoint a moderator with such background knowledge. This moderator can put the results into perspective and explain the possibilities and limitations of the tool.


Requirements

The Interactive Design Tool for the Holland Coast is available in two versions:

  1. As an online application accessible through the OpenEarth Viewer.
    This version is meant for end-users, i.e. users who want to use the application as is and are not interested in modifying the underlying code and models. The only requirements for using this application are an internet connection and installation of the Google Earth plug-in (indicated automatically when needed).
    Note: This application is known to encounter problems .
  2. In the OpenEarthTools repository (Matlab code & web code).
    This folder contains all the underlying codes and is meant for developers rather than end-users. Help for installing the tool can be found at the OpenEarth website. Furthermore, users need to have Matlab and Unibest-CL+ licenses.

Functionality

Setting up a scenario for the Interactive Design Tool involves the following steps:

  1. Browse to viewer.openearth.nl, open the project Building with Nature, select the case Holland Coast and navigate to the tool Interactive Design Tool Holland Coast. The following window should pop-up:

Tool window Interactive Design Tool for the Holland Coast 

 

2. The Tool panel consists of two menus, i.e. 'Scenario Input' and 'Change Map'. In the 'Scenario Input' menu, the user can select whether sea-level rise needs to be taken into account and which indicators should be processed. In the 'Change Maps' menu, the background map can be chosen, as is shown in the following screenshot:

Switching background from hybrid to street map


3. The user can add measures (nourishments, groynes or revetments) by selecting them from the toolbar and clicking the location where the measure should be implemented. Automatically, a window pops up in which the user can fill out specifications for the selected measure (see screenshot for adding a nourishment). Measures can be moved by selecting the button 'Relocate', selecting the object to be relocated and dragging it to its new position. With the 'Modify' button, the user can adjust the specification of the measures.

Adding a nourishment to a scenario


4. In the 'Scenario' menu, the user can start a new scenario (all existing measures are deleted and a default empty scenario is loaded), load a previously saved scenario, or save the scenario he/she has been working on (see screenshot).

Scenario menu


5. Once the user is satisfied with the scenario, he/she can select 'Run scenario entirely' from the 'Run' menu. This will trigger a window (see screenshot) in which the name and duration of the scenario can be selected. Upon pressing 'OK' the simulation will start.

Run a scenario


6. The results will be shown in the Google Earth Panel of the OpenEarth Viewer (see screenshot). The yellow triangle indicates the location of the nourishment, the yellow line the coastline position, and the red and green bars an exaggeration of erosion and deposition along the coast relative to the initial coastline. The icons indicate the states of the indicators. In this example, dunes (dune class, habitat richness, dynamics) and ecology (three types of benthos and nursery area for fish). Red icons indicate a worsening state, green colors an improving state and yellow/grey colors approximately equal state relative to the initial state.

Scenario output (coastline development, ecology and dunes) 


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Working principles

The Interactive Design Tool for the Holland Coast consists of the following modules:

  • User interface. The user interface of the tool consists of an OpenLayers map, which is plugged into the OpenEarth Viewer. On the OpenLayers map users can draw measures (i.e. nourishment, groynes and revetments) and adjust their specifications to develop a scenario. Results are visualized in the Google Earth panel of the OpenEarth Viewer.
  • Plug-in module. The plug-in module consists of a set of functions used for the pre- and post-processing of the (numerical) model. For this tool the plug-in consists of Matlab code, but this can be any type of programming language. In the pre-processing the model simulations are prepared based on the user input, whereas in the post-processing the model results are linked to indicators and written to the Google Earth format (kml) for the visualization. The visualizations (kml-contents) are then returned to the Google Earth panel of the user interface.
  • Coastline model (Unibest-CL+). The coastline development in time is simulated with a validated Unibest-CL+ one-line model of the Holland Coast. Matlab routines activate the model simulations.
  • Indicator modules. The indicator modules are called from the post-processing routines of the plug-in module and link the impact of coastal interventions and coastline development to indicators such as dune formation, benthic communities, coastal safety, costs, etc. The indicator scores are expressed in qualitative terms (classes/categories) and based on empirical (data-driven) relationships, rules of thumb and expert judgment. For more information on the exact implementation of these indicators in the tool is referred to the documents in the references. Below three of such modules are discussed, but others are possible.
    • Benthos module. The benthos module considers the direct impact of individual nourishments, i.e. the local burial of benthic species under a large amount of sand at the nourishment site. The indicator used for this is the relative change in population size for three species with different survival strategies. The impact of a nourishment consists of a change in local environmental conditions, leading to a reduction in local carrying capacity and population size.
    • Fish nursery area module. The nursery area module considers the impact of nourishments related to the change of the foreshore area as a result of a prograding or retreating coast. The foreshore surface area is considered a proxy for the available habitat for juvenile fish along the coast (the so-called nursery area for juvenile fish).
    • Dune formation module. The dune-formation module gives the development of the most seaward dunes with respect to the current situation, and the potential biodiversity associated with that. The module starts with the volume changes per coastal cell that Unibest calculates. Those volume changes are then distributed over parts of the profile: offshore, subtidal beach, subaerial beach (i.e. the intertidal and dry beach), and dunes. Subsequently, the cumulative dune volume classified into 5 dune classes and its associated biodiversity is calculated.


Lessons learned

  • A lack of knowledge and data on an ecosystem or parts of it (e.g. the process of benthic recolonisation) poses limitations to the model performance. Even if the mechanisms can be translated into model equations, poor parameterisation will most probably result in outcomes that are less reliable than one might need.
  • It is important to clearly communicate the possibilities and limitations of existing models used in new applications. This is especially the case when working together with people from different fields, as they may not be aware of the common assumptions or methods used in other fields. In this specific case, the assumptions and output of UNIBEST, for example, impose restrictions onto the modules that build upon it. A number of times during development of the present model system, expectations among researchers were not in line with the model's capabilities. It takes time to sort out each other's model concepts and to get fully acquainted with them.
  • Application of the IDTHC shows that relatively simple models are valuable to users when combined and presented in such a way that also non-experts can work with the results. Good visualisation is essential and deserves due attention. Moreover, the model should not be used without moderation by an expert, who can clarify the results if necessary and explain model limitations.
  • When working with the IDTHC, stakeholders tend to overestimate the spatial precision and (temporal) reliability of the model outcomes. In order to avoid this, we increased the alongshore spacing of the indicators in the visualisation in Google Earth and used classes rather than volumes to present the results of the dune model.

 

Potential future improvements on the ecological module

To improve the reliability of the IDTHC model outcomes, additions to the benthos and fish nursery modules would involve:

  • Inclusion of a benthos model that allows for a size and/or age approach based on physiological processes (for instance a DEB approach).
  • Improved parameter values on benthic population reduction and recovery. This should be done on the basis of monitoring studies on the effects of nourishments on benthic populations.
  • Coupling of benthic community recovery and fish recovery, since benthos forms the food of juvenile fish inhabiting the coastal zone.
  • More detailed information on bathymetric and sedimentologic changes within the cross-shore profile.
  • More detailed information on water and bed quality parameters such as turbidity, temperature, and sediment properties, since these affect juvenile fish and benthic organism distributions.
  • Inclusion of seasonal effects of nourishing, as nourishments in spring and summer may hamper juvenile fish and benthic organisms more than in autumn and winter.
  • More detailed information on the nourishment operations, for instance in terms of intensity and duration of dredging-induced turbidity.

 

The dune module could be improved by:

  • Including feedback between UNIBEST module and dune module, so that cross-shore profile shape changes as the result of erosion and accretion of the dunes and beach.
  • Including the type of nourishment and its consequences for the dune volume.
  • The dune model is based on a simple Bayesian Network Model of measured beach and dune topographies. The current implementation is fairly simple, but allows for future implementation of more complex approaches or estimating uncertainties in the model outcome.
  • Including storm scenarios.
  • Including the online available code for ‘foredune dynamics’ and include more foredune management options. The latter could include the presence of vehicles, beach raking and cleaning, and tourist pressure, as these have strong implications for the development of new dunes and green beaches.
  • Allowing to track dune dynamics through time, which requires more parameterisation.

 

To better inform stakeholders, a separate module on nourishment costs is being implemented in the ITHC (not covered in this report).

 

Advice

The tool is a trade-off between model accuracy and calculation time. It is based on a relatively simple but fast coastline model. Some physical processes, such as cross-shore sediment transport, are not included and the long-shore cell size is relatively large (about 250 m), whence model results need to be interpreted with care. Users (i.e. stakeholders) need to be made aware of these limitations. This model should not be used without moderation by an expert, who can clarify the results if necessary and explain model limitations. The tool is most suited in the beginning of the design process, when all possible scenarios are being explored. In later project phases (such as the final design and construction phases) a higher model accuracy may be needed. 


Practical Applications

The Interactive Design Tool for the Holland Coast has already been used in workshops, where various stakeholders made plans for the future of the Dutch coast. It is an effective tool to visualise the impact of management measures (nourishments and revetments) in both time and space. This is of great value because individual processes act as different temporal and spatial scales, and respond differently to the measures.

  1. Atelier Kustkwaliteit (AKK)
  2. Ecologically Smart Nourishments
  3. Other applications

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Use of Interactive Tool in Coastal workshop (Atelier Kustkwaliteit), 2011


1. Atelier Kustkwaliteit (AKK)

The Interactive Design Tool for the Holland Coast was successfully applied in several stakeholder workshops of Atelier Kustkwaliteit between September 2011 and June 2012 (see photo below). In these workshops stakeholders from various backgrounds (i.e. policy makers, ecologists, landscape architects, beach club owners, golf club board members, drinking water companies) got together to develop alternative visions/designs for (parts of) the Holland Coast in 2100. The designs that were developed in split sessions in the morning were evaluated with the tool and discussed in a plenary afternoon session. The contributions of the tool during the sessions on the "Stille Kustlandschappen" have been incorporated in a workbook. The results of an inquiry held during a workshop in June 2012 indicate that most respondents believe the tool provided a useful contribution. The respondents mentioned the following strengths: fast, insightful, enabling to test ideas on the fly and providing insight into the interaction between different coastal interventions. Weak points mentioned were the lack of detail (simplifications) and the absence of information on the uncertainties in the visualizations. Most respondents indicated they were happy with the choice of Google Earth for the visualizations.


Lessons learned in AKK workshops

  • Google Earth visualizations help to show that coastline evolution is a dynamic process and coastal interventions affect coastline evolution in both space and time. For most participants this was an eye-opener, as they considered the coast as a static feature where interventions only have local, short-term impacts.
  • The quick feedback on the participant's choices resulted in a learning effect. The lessons learned from previous designs were incorporated in new ones.
  • Some of the workshop participants tended to interpret the Google Earth visualizations of the model results as the truth. Participants even tried to measure coastal erosion and accretion after a 100 years simulation in meters precision (which is not the level of detail that the model is able to predict). This stresses the need for an expert moderator putting the model results into perspective.
  • Stakeholder feedback is essential when developing a functional design tool.
  • Building the tool in Matlab allowed for rapid prototyping: development of extensions and adjustments of the tool's functionality. Suggestions/demands from previous design sessions could be incorporated in the next session.

 

2. Ecologically Smart Nourishments

Within the BwN project on Ecologically Smart Nourishments, the Tool has been applied on five coastal defence scenarios to test their impact on benthos, nursery habitat for juvenile fish, and dunes:

  1. Autonomous
    Autonomous development without any measures.
  2. Minimal continuous preservation
    Specific settlements and other risk areas are protected against erosion by continuous beach and surf zone nourishments of 5.0 million m3 per year, whereas other locations do not receive nourishments.
  3. Minimal five-yearly preservation
    Minimal protection of the entire coast at coastal settlements with shoreface nourishments of 12.5 million m3 every 5 years.
  4. Seaward
    Extending the coastline gradually seawards with the help of mega-nourishments of 20 million m3 each, that are applied every ten years at five locations along the coast (Vlugtenburg, Katwijk, Zandvoort, Egmond and at the Hondsbossche zeewering).
  5. Revetments
    Revetments protecting the coastal settlements (no additional nourishments)

The results of the scenario computations with the IDTHC were used to derive guidelines for ecologically optimised nourishments. These guidelines consist of recommendations on the design of sand nourishments, in terms of frequency, location and size. The focus of such strategies in the context of this study was to improve the nursery function of the Dutch coast for commercial and non-commercial fish species, while minimising impacts on benthic populations, and enhancing dune quality.

 

From the benthos and dune modules it followed that large nourishments at long time-intervals show the best potential for benthos and dunes. They allow benthic populations to recover fully from the impact and lead to, at least temporarily, new dune formation. The dynamics in growth and erosion of the dunes in such situation give rise to repeated pioneer habitats, which is considered beneficial for the currently rather static dune area of the Holland coast. However, the potential for juvenile fish nursery areas depends on foreshore width, and thus on overall nourished volume rather than nourishment frequency, given the current fixed profile. Building the coast seaward, thereby steepening the profile, has detrimental effects on the size of the nursery habitat for juvenile fish.

 

The results further show that ‘continuous’ nourishments prevent full recovery of the benthic population, even if the reduction in carrying capacity per nourishment event may be small. Only opportunistic species such as worms are able to fully recover to their carrying capacity. It is plausible that due to frequent nourishment more opportunistic species will dominate. These potentially provide good prey and feeding conditions for juvenile fish. The autonomous scenario, without nourishments, shows considerable erosion along the coast. Consequently, the foreshore area increases slightly, which results in a larger nursery area for juvenile fish.

 

Sand nourishments reduce the carrying capacity locally and temporarily. Revetments, however, are of a more permanent nature and are assumed to result in a complete local loss of habitat for bottom dwelling organisms needing a sandy environment. Despite this loss, revetments do provide habitat for other species and communities that prefer hard substrate (e.g. polyps) or use crevices for shelter (e.g. crabs, fish). Given the assumptions in this model the net effect of a revetment is considered zero for benthos and fish. But because they stabilise the dunes completely, revetments score less on that aspect.

 

The present version of the tool is a first, necessarily using many simplifications. The results give a first estimate that is sufficiently reliable for practical use, but they don't give an in-depth analysis. The true gain of this exercise is that an easy-to-use prediction tool is conceptualised, developed and applied in workshops with stakeholders. By presenting various aspects of the impact of coastal measures together through space and time, even in a yet simple form, users obtain a better understanding of the consequences of coastal strategies. Finally, by applying the tool, it becomes clear which next steps are needed to strengthen both the underlying knowledge and the model definitions.

 

The complete report is available as Developing an Interactive Tool for evaluating sand nourishment strategies along the Holland Coast in perspective of benthos, fish nursery and dune quality. Further background on the dune module can be found in Long-term coastal dune development in the Interactive Design Tool.


3. Other applications

The tool in its current form may facilitate the communication between experts, actors and stakeholders in practically any type of initial assessment of coastal interventions on the Holland Coast and similar types of sandy dune coasts. For example, the tool may be of use to the initial coastal strategy development in the Dutch Delta Program for the Coast. As pointed out in General Tool Description, the structure of the Interactive Design Tool allows for incorporating other types of models, which makes it potentially useful for any type of MapTable application. Potentially, tools can be developed for any location in the world, any aspect (or combination of aspects) and any phase of the design process (i.e. level of detail). With adapted parameterisations, the current version of the tool can also be used for other locations.


References

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  • Baptist, M.J., Wolfshaar, K.E. van de, Huisman, B.J.A., Groot, A.V. de, Boer, W. de, Ye, Q., 2012.. IMARES report C083/12 for EcoShape Building with Nature.
  • De Groot, A.V., 2012.Report for EcoShape Building with Nature.  
  • Internal memo Deltares: 
  • Internal memo Deltares: 
  • Internal memo Deltares:
  • Summary report 


 

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