Stability of intertidal and subtidal areas after Delta21 plan Evaluating the consequences for the morphological development produced by the intervention Mayra I. Zaldivar Piña October 21st, 2020 Stability of intertidal and subtidal areas after Delta21 plan Evaluating the consequences for the morphological development produced by the interventaion by Mayra Ithzel Zaldivar Piña in partial fulfillment of the requirements for the degree of Master of Science in Civil Engineering at the Delft University of Technology, to be defended publicly on Tuesday October 21st, 2020 at 12:00 PM. Student number: 4899962 Project duration: April 2nd, 2020 – October 21st, 2020 Chair committee: Prof. dr. ir. Z.B. Wang, TU Delft & Deltares Committee members Dr. ir. J. Bricker, TU Delft Ir. A. Colina Alonso, TU Delft & Deltares Ir. S.G. Pearson, TU Delft & Deltares An electronic version of this thesis is available at http://repository.tudelft.nl/. Cover: View of Kwade Hoek and the Haringvliet sluices in the Haringvliet mouth. Photography by Jacques van der Neut. Acknowledgements This thesis concludes a long trip away from home. This document reflects the conclusion of my studies in the Master of Science in Hydraulic engineering program. This research was conducted as part of the Delta21 initiative in collaboration with the Delft University of Technology. I am grateful for the opportunity to work on this ambitious and challenging project. I want to express my complete gratitude to my committee for their great support and time during this process. I know it was a challenge for everybody under the new 2020 circumstances. Zheng Bing Wang, I am very grateful for your enthusiasm in this project since the first time I came to you, it meant a great motivation for me. Thank you for the insights and feedback, all your comments were always challenging and made me think further. Jeremy Bricker, thank you for introducing me to the Delta21 project, it gave the perfect balance between the requirements for my graduation project and what I really wanted to do. I am also grateful for your observations in our meetings, they help me move from my coastal-engineering comfort zone (at least a bit). To Ana Colina and Stuart Pearson, thank you both for all the time I took from you, for always encouraging me to go further. All our discussions helped me to shape this project into what it became. Ana Colina, thank you for sharing all your experiences with me. Your advice was always key in the decision-making process in the different stages of the research. Thank you for always offering a friendly hand but always demanding the best of my effort. Stuart Pearson, thank you for being so enthusiastic since I first brought the project to you, it gave me the motivation I needed at the moment I needed it. I am very grateful for all our discussions and all your advice, they really meant the difference for the outcome. Thank you even more for introducing me to the deeper world of the ebb-tidal delta dynamics. I learned a great deal. Thank you also for always cheering-me up! Additionally, I want to thank Huub Lavooij and Leen Berke for conceiving the Delta21. Despite the challenges and the long path still ahead, I believe this project has a lot of potential in learning about the implications for natural ecosystems when taking action against climate change. I want to express my special gratitude to the CONACYT-SENER sustainability trust fund for granting me the opportunity to study at the Delft University of Technology. I also want to thank all my fellow Hydraulic friends who also shared this path of the thesis-making. Your company helped in moments of need. I am especially grateful to the Lati-thesis friends, with whom I shared most of my frustrations and happy moments during the second half of this process. Thank you for joining the ride and making happy memories with me regardless of the COVID-times. Thank you to my greek girls for always being very supportive. Janko, I am grateful for your company during this journey and all your support, help, and advice. Thank you for your patience in my most stressful times and for being happy for me in every little success. Thank you for being my personal cheerleader. Last but not least, I want to give all my gratitude to my family. Gracias a mis padres por siempre apoyarme e impulsarme a perseguir mis sueños por más lejos que estén. Les agradezco sobre todo la paciencia en mis momentos de mayor estrés y la fortaleza que me dan a la distancia. Al resto de mi familia, gracias por sus buenos deseos siempre. A Hilda de la Longa Valle, quien siempre me regala una sonrisa a través de la cámara, a quien más extraño. El resultado del sacrificio de que estemos lejos está en este documento. Los quiero a todos. Mayra I. Zaldivar Piña Delft, October 2020 i Summary In recent years, there has been an increasing need for solutions against the threats that SLR and climate change represent for coastal systems, especially in low lying areas like the SW Dutch coast. Simultaneously, awareness of the impacts that human activities have on natural environments has surged. Integrated and sustainable solutions are necessary. The Delta21 plan proposes an integrated plan for flood-protection, energy storage, and natural ecosys- tem restoration for The Netherlands, specifically for the Haringvliet estuary. This large-scale interven- tion will produce large disturbances in the system. Despite the resilient character of tidal basin systems (Z. B. Wang et al. 2009), the evaluation of the intervention’s effects, in terms of the initial response and the variations in the mechanisms driving morphological changes is compulsory. Assessing the bed level changes is especially important, considering the valuable intertidal and subtidal ecosystems present in the Haringvliet mouth. It is essential to guarantee their preservation despite the large dis- turbances. The evaluation of the Haringvliet mouth response is performed employing a long-term morphodynamic 2DH computational simulation to forecast the response of the system. The models implemented for the simulation are the Delft3D-FLOW and Delft3D-WAVE. To reduce computational times, the modeling approach applies input reduction and acceleration techniques. The hydraulic forcing is schematized (morphological tide, waves, and discharges) while maintaining the seasonal character of the input. A variable morphological acceleration factor (MF), depending on the wave condition is applied. The variable MF allows us to employ low values during strong-episodic conditions and larger during more regular conditions. The approach is especially beneficial in the presence of oscillating forcings that are also enhanced by the MF. Finally, the impact of the D21 plan on the Haringvliet mouth is assessed by studying the alterations to the hydrodynamic regime, the related net sediment transport pathways, and the observed bed level changes. The analysis of the resulting morphological evolution focuses on the variations of the inter- tidal and subtidal zones and the mechanisms behind them. We showed that the tidal regime shifts again towards a long-basin regime once the D21 is imple- mented. The intervention also causes the emergence of new subtidal and intertidal areas, mostly within the Tidal Lake, resulting from the redistribution of the material from the main channel. The original intertidal and subtidal areas, formed by the Hinderplaat and Slikken van Voorne, are almost undisturbed. This behavior guarantees the preservation of the intertidal and subtidal ecosystems. The results also show that despite the initial dredging activity necessary for the D21 plan implementation, which decreases the extent of shallow areas, the emergence of intertidal and subtidal features bal- ances the negative effect as long as no further dredging is performed. The TL shows a net sediment export of material at both control cross-sections (the Haringvliet Dam and the new TL inlet). The findings of the morphological development agree with the known morphology and processes of mixed- energy tidal inlet systems, despite the large-scale intervention. This study provided the opportunity to evaluate the emergence of typical tidal features in a highly disturbed system, where the tidal inlet is shifted further offshore. To achieve an accurate forecast, an- thropogenic forcing signals also had to be considered and extrapolated to long-term morphodynamic simulations. The forecasting of large-scale anthropogenic interventions in sensible systems, such as tidal estuaries, is performed successfully by adapting an existing model. The development of this type of study will be increasingly relevant in the future for the evaluation of measures against SLR during conceptual project stages. ii Samenvatting In de laatste jaren was er toenemende behoefte aan oplossingen voor de bedreigingen die zeespie- gelstijging en klimaatverandering voor kustsystemen vormen, vooral in laaggelegen gebieden zoals de Nederlandse zuidwestkust. Tegelijkertijd is het bewustzijn van de impact die menselijke activiteiten op natuurlijke omgevingen hebben enorm toegenomen. Geïntegreerde en duurzame oplossingen zijn nodig. In het plan Delta21 wordt een integraal plan voorgesteld voor hoogwaterbescherming, energieopslag en natuurlijk ecosysteemherstel voor Nederland, specifiek voor het Haringvliet-estuarium. Deze groot- schalige ingreep zal tot grote verstoringen in het systeem leiden. Ondanks het veerkrachtige karakter van getijdenbekkensystemen parencite Wang2009, de evaluatie van de effecten van de interventie in termen van de initiële respons en de variaties in de mechanismen die morfologische veranderingen aansturen is verplicht. Het beoordelen van de bodemveranderingen is vooral belangrijk, gezien de waardevolle intergetijden en subgetijden ecosystemen in de Haringvlietmonding. Het behoud ervan ondanks de grote verstoringen is essentieel. De evaluatie van de Haringvlietmonding-respons is uitgevoerd met behulp van een lange termijn mor- fodynamische 2DH-computersimulatie om de respons van het systeem te voorspellen. De modellen die voor de simulatie zijn geïmplementeerd zijn de Delft3D-FLOW en Delft3D-WAVE.