Thesis: Modelling tidal currents in mangroves with 3Di

Partners
Universiteit Twente
Researcher
Berend ten Booij
Mangrove forests are unique ecosystems found in tropical regions. These forests thrive in intertidal zones, providing a habitat for a wide variety of animal species. During each tidal cycle, the trees are alternately exposed to air or submerged in water, forming a transitional zone between sea and land. Due to this unique position, mangroves also serve as natural coastal protection by dissipating incoming wave energy and reducing its impact. In this way, mangrove forests contribute to mitigating coastal erosion. Additionally, they are capable of trapping sediment, which helps to stabilize the coastline.

This master’s thesis by Berend te Booij, conducted at the University of Twente, aims to shed light on the complexity of mangrove ecosystems. The research focuses on how modeling techniques can be best applied to account for the significant variation in mangrove vegetation within a hydrodynamic model. A case study was carried out for the mangrove area of Lac Bay on Bonaire.

The challenge

Mangrove forests are often inhospitable, densely vegetated areas where conducting measurements to understand hydrodynamic processes is challenging. In Lac Bay, only limited measurement campaigns have been conducted, providing restricted insight into the hydrodynamics. This also complicates the validation of model simulations. Gaining an understanding of the hydrodynamics of the mangrove forest with limited measurements, supplemented by hydrodynamic simulations, presents a complex challenge.

Our solution

To address this challenge, this study combines field measurements with advanced numerical modeling techniques. Previous measurements of water levels, tidal creek flows, and vegetation characteristics were provided; however, flow measurements within the mangrove forest itself are lacking. This research bridges the knowledge gap with hydrodynamic simulations, providing a clearer understanding of how the mangrove forest influences tidal dynamics.

Three methods were applied to incorporate vegetation into the hydrodynamic calculations:

  1. Increased bed roughness,
  2. The Baptist method, which accounts for the vertical influence of roots on drag, and
  3. The porous layer method, which models flow through dense root networks using a diffusion equation.

The simulation results demonstrated that vegetation in mangrove areas plays a crucial role in shaping tidal patterns, particularly within the dense root zones of the forest. While the hybrid model performed well, some discrepancies during low tide were observed, potentially due to factors like evaporation, which were not fully integrated into the models. These variables, along with the influence of creek profiles on water flows, are critical for future model improvements.

The outcome

This research highlights the importance of a detailed, multi-methodological approach to modeling complex ecosystems like the mangroves of Lac Bay. The combined use of vegetation methods in the model, tailored to the specific characteristics of red and black mangroves, proved most effective in simulating tidal exchange and water levels.

The model provides valuable insights for conservationists and ecologists aiming to enhance the health and resilience of mangrove ecosystems. It can also be utilized to develop effective management strategies for the sustainable restoration of mangroves in Lac Bay.

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