R. ter Hofstede

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Master thesis (2)

2 records found

Systematic investigation of the coral-inclusive potential of marine infrastructure

Master thesis (2022) - J.C. van Arkel (author), M. van Koningsveld (mentor), R. ter Hofstede (mentor), M.Z. Voorendt (mentor), Michel Ruijter (mentor), M. Kershaw (mentor)

Ecosystems are under pressure worldwide, due to both natural and anthropogenic stresses. Stresses on ecosystems can cause a decline in biodiversity, a loss of habitat and a deterioration in ecosystem services. To avoid further pressure on ecosystems caused by advancing economic development, new infrastructure projects should be integrated into the ecosystem. Environmental Impact Assessments (EIAs) are now mandatory for projects that are likely to have significant environmental effects. EIAs have primarily focused on mitigating negative impacts. However, recently new design philosophies have emerged such as ‘Engineering with Nature’, ‘Working with Nature’ and ‘Building with Nature’ which also focus on promoting positive impacts.
Constructively realizing nature-inclusive projects is complicated due to involving stakeholders with dif-fering perspectives. Therefore, in an integrated approach towards new marine infrastructure devel-opment, the next step is to promote constructive collaboration between stakeholders to systematically investigate the nature-inclusive potential of infrastructure. This thesis describes a proposed strategy for doing so, within the context of nearshore infrastructure development located in or nearby coral ecosys¬tems. The focus is on how nature-inclusive potential of new marine infrastructure might be maximised, taking into account the local ecosystem.
The aim of this research is to find an optimal approach to develop coral-inclusive infrastructure. This is done by structuring the required discussions between stakeholders considering socio-economic, ecolo¬gical and engineering perspectives regarding the nature-inclusive design potential of new marine infra¬structure. For this purpose, a method was developed that proposes a step-by-step strategy to promote constructive collaboration between relevant stakeholders, consisting of the following five steps:

1. project description, outlining the basic challenge at hand

2. project location analysis, involving a systematic assessment of the relevant ’natural system’ as well as the ’anthropogenic system’

3. Development of marine infrastructure design applications, involving an inventory of project elements that can have negative or positive effects on the overall ecosystem

4. inventory and ranking of potential measures, objectively outlining feasibility and potential effectiveness of measures and design modifications

5. summary of sustainable design recommendations, leading to a systematic ranking of potential measures proposed to support further decision making.

We have investigated the effectiveness of the systematic method, by applying it to a case study in Sint Eustatius that investigates whether the intended extension of a breakwater in Sint Eustatius can be designed as a coral-inclusive project. Sint Eustatius was chosen because Rijkswaterstaat offered research opportunities on location. In an ideal case, the use of long-term consistent data maps the nat¬ural factors over a longer period of time. This provides greater certainty of results and recommended actions. However, the values that were reported for the Sint Eustatius case were not derived from long term systematic data collection. Furthermore, the substrate from the existing breakwater looks to be promising for coral recruitment. However, there is not a lot of coral development evident on the existing breakwater. Possible negative factors hindering coral development on the existing breakwater are: 1) poor water quality; 2) high hydrodynamic circumstances with high wave action in shallow waters which limits the type of coral species; 3) inconsistent larval supply through ocean currents.
Coral reef connectivity seems sufficient and potential substrate is already present in the existing break¬water. Extension of the breakwater will lead to substrate increase which could improve the chance for coral recruitment in a hurricane-risk area as Sint Eustatius. A valid next step that could be proposed to aid a better understanding of this habitat is to invest in an extensive and dedicated data gathering campaign.

In conclusion, the main improvements derived from the application of the systematic approach for nature-inclusive potential for infrastructure projects are:

· providing an overview of the steps required to create coral-inclusive infrastructure,

· instigating the investigation of the status or the possibilities for coral development,

· assisting ecologists and engineers to structure the discussion on coral-inclusiveness,

· lowering the barrier to use (new) design philosophies,

· and stimulating coral development and decreasing negative effects by providing design recommendations.

Bringing stakeholders with different perspectives together in one nature-inclusive project plan remains challenging. Environmental data can play a role in arriving at a realistic approach supported by ecologists and civil engineers to realize nature-inclusivity for infrastructure. This requires knowledge, money and time and could provide insight into the threats and opportunities. The systematic approach, derived in this thesis, has been proven to support stakeholders in assessing the nature-inclusive potential of marine infrastructure.

Droppable oyster brood stock structure

Experimental study on the design for a flat oyster brood stock structure, that can be installed at the scour protection of Dutch offshore wind farms, via dropping from a vessel

Master thesis (2022) - E.J.S. Siderius (author), Bas Hofland (graduation committee member), M. van Koningsveld (mentor), R. ter Hofstede (coach)

In 2050, the entire energy consumption in the Netherlands is foreseen to come from renewable sources. Offshore wind energy has the potential to enable this transition to a CO2-emission-free energy supply. Consequently, the development of offshore wind farms in the Dutch North Sea ...

In 2050, the entire energy consumption in the Netherlands is foreseen to come from renewable sources. Offshore wind energy has the potential to enable this transition to a CO2-emission-free energy supply. Consequently, the development of offshore wind farms in the Dutch North Sea has been expanding enormously in the last decade. The Dutch Government is also ambitious to achieve biodiversity goals in the Dutch North Sea, by restoring ecosystem functions. The European flat oyster is identified as a key species when restoring the biodiversity in the North Sea, because they embody a distinctive benthic community that provides a range of valuable ecosystem services. The environmental conditions in offshore wind farms have shown to be suitable to act as a habitat for the European flat oyster reefs, because of hard substrate and undisturbed areas. Multiple oyster recovery initiatives have been introduced in offshore wind farms, to kick-start oyster reef restoration. No larvae source is nearby, therefore oysters need to be introduced for oyster reefs to develop in offshore wind farms. These oysters are introduced by applying oyster brood stock structures, which are structures to which adult oysters are attached. The brood stock structures are installed by onboard cranes present at vessels, on the scour protection at offshore wind farms. This crane installation method has shown to be complicated and costly, due to the vessel type and equipment required. These complications result in a challenging and therefore limited application. Hence, there is a need to look for an alternative installation method, that ensures a simple and cost-effective application. Deployment of brood stock structures via dropping from a vessel manually is selected, which ensures easy deployment, because it does not require a crane (and a vessel that can hold this crane). This would decrease the engaged expenses significantly. Such a new installation method requires a different design for the brood stock structure. Research is needed into a new design for a flat oyster brood stock structures, which is appropriate for the drop installation method. This leads to the following research objective for this master thesis;

What is the design for a flat oyster brood stock structure, that can be installed at the scour protection at offshore wind farms, via dropping from a vessel, such that it will be stable and integer during deployment and operational lifetime?

Based on literature study and consultation sessions with experts, a set of design criteria for the
droppable brood stock structure are set. Behavioural predictions are made for the performance of the concepts during the lifetime of the droppable broodstock structure by performing calculations.. which are used to select the most suited concept parameters (e.g. volume, dimensions) for the six basic concepts by an iterative process. Ten concepts emerged.

Physical model tests were performed to test the behaviour of the ten selected concepts during the
relevant situations. Three types of tests are executed; fall test, land test and stability test. The physical model tests are performed in the wave flume in the Hydraulic Engineering Laboratory at TU Delft.
The fall test investigated the fall of the structure from the vessel onto the scour protection, to define
the dropping accuracy during the fall.
The land test investigates the landing of the structure on the scour protection, by analysing the
interaction between the prototypes and the stone layer after dropping them in the wave flume. The
interaction observation is used to get insight in the amount of oyster damage encountered during the landing.
The stability test investigates the stability of the concepts during extreme hydraulic conditions, by
generating storm conditions in the wave flume.

To select the design for a droppable flat oyster brood stock structure, the ten concepts are analysed
and assessed, using two methods. The first method entails a requirement analysis and a multi-criteria analysis. Two concepts have been selected as suitable based on these methods, A Tetrapod concept and an Open Table concept.