Person | TU Delft Repository

G.G. Hendrickx

3 records found

Authored

Predicting the survival of coral reefs

A biophysical modelling approach

Master thesis (2020) - G.G. Hendrickx, P.M.J. Herman, Jasper T. Dijkstra, J.D. Pietrzak, Arjen Luijendijk

KEY POINTS (I) A biophysical model framework (BMF) for corals is developed in which four environmental factors are included: (1) light; (2) hydrodynamics; (3) temperature; and (4) acidity. (II) The full feedback loop between corals and their environment forms the core of this model framework, where the morphological development is new and closes the feedback loop. (III) The developed BMF predicts the coral response to environmental input via (mainly) process-based relations within the accuracy of climate projections. (IV)- The BMF supports both the deep reef refugia hypothesis and the turbid reef refugia hypothesis. (V) The BMF contributes to the development of protection and recovery programs and is not site-specific. (VI) The BMF is developed for long-term predictions - in the order of decades to centuries - but runs on daily averages and is therefore applicable for assessing the response of corals on shorter time-scales; such as months to years. SUMMARY The increasing pressure on Earth’s ecosystems due to climate change becomes more and more evident. These pressures are especially visible at coral reefs. Therefore, a good understanding of the biophysical mechanisms controlling these ecosystems is needed, so that accurate predictions of their survival can be made. Such an understanding is also needed to develop efficient recovery and protection programs vital to the maintenance of these ecosystems. Because the research on marine ecosystems is relatively young and the phenomenon of coral bleaching is yet to be fully understood, there is no comprehensive framework in which the complex interactions between corals and their environment are combined. In this study, a biophysical model is developed in which four environmental factors are included in a feedback loop with the coral’s biology: (1) light; (2) hydrodynamics; (3) temperature; and (4) acidity. Literature from multiple disciplines is combined to find the interdependencies between the corals and their environment. These relations include coral growth, coral bleaching, storm damage, and recruitment/recolonization of corals. For the connection with the hydrodynamics, a coupling is made between the biological model developed here and Delft3D-FM. The composed biophysical model is a big leap forward in understanding the world of coral reefs, as it is the first construction of a model framework including four environmental factors in which the hydrodynamics are included in the feedback loop. Furthermore, it creates the ability to assess recovery and protection programs based on the four aforementioned environmental factors; e.g. the susceptibility of coral bleaching can be reduced by increasing the attenuation of light through the water column. Because more environmental factors have a role to play in the coral dynamics, the framework is constructed such that these can be added relatively easily.

PoDeA, Port development Argentina

Student report (2018) - D. Deckers, M.H. van Dijk, M. Grund, G.G. Hendrickx, R.T. de Koning, N.G.A. Smit, T. Vellinga, P.H.E. Arecco, J.G. de Gijt, M.Z. Voorendt

This report contains the conceptual lay-out for two possible expansions of the port of Bahía Blanca. To determine the best conceptual lay-outs, emphasis is drawn to understand the physical system to determine the effect of the expansion of the port on the natural system. The port of Bahía Blanca is situated at the end of a ria, or tidal basin. For the designs, different conceptual lay-outs are developed and simulated in a hydrodynamic model called MOHID. This is a 2D depth-averaged model (2DH), which uses a rough bathymetry grid of the ria to determine the effect of the port development. There are three mutations of the different port expansions on the environment, which are investigated using the MOHID-model: (1) the East expansion, containing reclamation of tidal flats and closure of a side channel; (2) the South expansion, containing a widening and elongation of the channel and reclamation of tidal flats; and (3) the deepening of the entire navigation channel to various minimum depths. From the results of the MOHID-model on the East expansion conclusions on the mutations of the different port expansions are drawn. For the East expansion, only small changes are predicted; only local erosion in the navigation channel near the expansion may occur. For the South expansion, the flow velocities reduce in the entire stretch and there seems to be sedimentation at the eastern part of the expansion.
As a conclusion the best and most feasible designs are chosen. The best design is the lay-out that obtained the highest score in the MultiCriteria- Analysis (MCA). The most feasible design is the design having the highest cost/benefit ratio determined by a Cost-Benefit Analysis (CBA). The east bank is located close to the current port, Ingeniero White, on tidal flats which are inundated at high-water and dry at low-water. For the East expansion, different port lay-outs are developed mainly differing in amount of reclaimed land, length of viaducts and the presence of a mooring basin. The best design on the east is characterised as being very compact and having small viaducts between the dry bulk and agribulk terminals and jetties. The main advantage of this design is the small expected increase of siltation, good safety and sufficient future expansion possibilities. The most feasible design, however, is characterised by long viaducts reducing the costs of the design. The other appointed location for the port expansion is the south bank, opposite of the current port development. This location, however, is characterised by one main disadvantage; It is far from any form of connection with the hinterland. Nevertheless, in 2013, the port authority (CGPBB) initiated the start of small reclamation works. The best and most feasible design fully utilises this reclaimed portion of land. Moreover, the best design has a small expected increase of siltation in the port area. For a final designs, all previous designs are combined to create a design in which all the advantages of each of the designs are fully incorporated. Therefore, this design has little reclamation as well as viaducts with only intermediate lengths.

Contributed

A parameter sensitivity analysis and feasibility study on the concept of the Lease Polder

Master thesis (2021) - D.M. Slagmoolen, S.G.J. Aarninkhof, G.G. Hendrickx, Bram van Prooijen, M. Klein

Ongoing sea level rise combined with significant levels of land subsidence cause the everlasting need for reinforcements of the current coastal protection measures to ensure a certain level of coastal safety. Developing countries in the Asian regions tend to suffer from even more severe levels of land subsidence and often lack the financial resources to fulfil these continuing needs for reinforcements, which put the coastal areas under the continuous tread for potential flood disasters. The Lease Polder is a new Building with Nature approach for the sustainable design of protective coastlines and can offer a durable solution to this current problem. The concept is built upon the principle of sharing a part of the land with the hydraulic system and thereby allowing the natural vertical growth of the area by siltation during in- and outgoing tide. The concept is, however, still in its infancy, causing numerous uncertainties regarding the feasibility. The critical design parameter that affects the feasibility is the Lease Polder period, denoting the duration for which the breach of the Lease Polder is kept open. This study aims to offer a quick assessment tool that can determine the optimal Lease Polder period and perform a feasibility analysis for arbitrary Lease Polder cases, based on a sensitivity analysis of influential parameters on the potential siltation process.

A simplified 2DH process-based Delft3D model was used to perform a sensitivity analysis on multiple sediment characteristics, hydraulic boundaries and dimensional parameters. The parameter sensitivity was determined by comparing the results from a set of parameter scenarios to a base-case model. This base-case model was a simplified version of the Tollesbury realignment site and was calibrated and validated on the available historical data sets. The base-case model was simplified to a square 430m by 430m basin area with a near-horizontal initial bed level 1m above average sea level and a 50m wide breach. The foreshore was assumed to be alongshore uniform with an offshore tidal boundary condition and an assigned level of suspended sediment concentration. A wave module was coupled to the flow module to include a constant input of wave forces. Processing the results consisted of exponential curve fitting through the average change in bed level of each scenario, followed by the determination of the initial sedimentation rate and the average equilibrium bed level. These two characteristics were then transformed into parameter specific functions describing the dimensionless
dependency for a given parameter value relative to the base-case scenario. A quick assessment tool called the WisLi-tool was created to predict the sedimentation curve for arbitrary Lease Polder cases, based on these parameter specific functions. It thereafter uses this curve to perform a cost-benefit analysis
on the complete life cycle of a Lease Polder, resulting in a quantitative net profit or loss. Finally, the tool will enter an optimization process by determining the optimal Lease Polder period which results in the maximum financial benefit.

The simplified model based on the Tollesbury was able to accurately reproduce the morphological changes which followed from the historical data analysis. A summary of the sensitivity of the most significant parameters is listed below.
Suspended sediment concentration The suspended sediment concentration (SSC) at the boundary showed a positive linear relationship with the initial rate of sedimentation, where the increase in SSC was directly proportional to the increase in initial sedimentation rate. The average equilibrium bed level was however independent of the SSC. Breach width The breach width showed to have a negative relationship for both the initial rate of sedimentation and the average equilibrium depth. Polder length and width The dimensional length and width of the polder showed to have an insignificant effect on the initial sedimentation rate, with differences remaining within the 10% range. The average equilibrium bed level decreased for increasing polder length and width. Initial polder bed level The sensitivity analysis on the initial polder bed level showed a dichotomy into two regimes, where the ’shallow regime’ was coherent to initial bed levels betweenODÅ1.0m andOD¡1.5m and the ’deep regime’ to the bed levels between OD ¡2.0m and OD ¡4.0m. The deep regime was characterized by the abrupt stop in sedimentation due to the high levels of wave energy entering the polder. Both regimes showed decreasing levels of initial sedimentation rate and average equilibrium bed level for increasing initial polder bed levels. Tidal amplitude The tidal amplitude showed to have a positive relationship with the initial sedimentation rate and the average equilibrium bed level for tidal amplitudes of 2.5m and lower. Higher tidal amplitudes caused high-velocity circular flow patterns within the polder, preventing further siltation. The above-mentioned relationships were translated into functions describing the dimensionless dependency for a given parameter value relative to the base-case scenario.

The analysis on the effect of sea level rise on the sedimentation process of a Lease Polder concluded that the siltation process was able to produce a local bed level change following the exact rate of sea level rise, for an average rate of sea level rise of 4.2mm/year . The Lease Polder can, therefore, be seen as a partly self-sustaining system of coastal defence. The quick assessment WisLi-tool was able to accurately predict the sedimentation curve based on case-specific input parameters using the dimensionless functions derived from the sensitivity analysis. By utilizing location-dependent financial input parameters, the tool was capable of performing an optimization process for the determination of the optimal Lease Polder period.

The final conclusion is that there is not a single uniform optimal duration for the Lease Polder period but that it may vary for each individual Lease Polder case. However, the WisLi-tool was able to assess arbitrary Lease Polder cases based on their parameter values and could determine the case-specific optimal duration of the Lease Polder period. Therefore, the WisLi-tool can act as a valuable resource during both the design and operational phases.