Person | TU Delft Repository

E. M.M. van Eekelen

2 records found

Authored

Beneficial use of dredged sediment to enhance salt marsh development by applying a ‘Mud Motor’

Journal article (2019) - Martin Josephus Baptist, Theo Gerkema, Bram van Prooijen, D.S. van Maren, D.S. van Maren, I. Colosimo, Kelly Elschot, A. V. de Groot, J. Cleveringa, E. M.M. van Eekelen, None More Authors

We test an innovative approach to beneficially re-use dredged sediment to enhance salt marsh development. A Mud Motor is a dredged sediment disposal in the form of a semi-continuous source of mud in a shallow tidal channel allowing natural processes to disperse the sediment to nearby mudflats and salt marshes. We describe the various steps in the design of a Mud Motor pilot: numerical simulations with a sediment transport model to explore suitable disposal locations, a tracer experiment to measure the transport fate of disposed mud, assessment of the legal requirements, and detailing the planning and technical feasibility. An extensive monitoring and research programme was designed to measure sediment transport rates and the response of intertidal mudflats and salt marshes to an increased sediment load. Measurements include the sediment transport in the tidal channel and on the shallow mudflats, the vertical accretion of intertidal mudflats and salt marsh, and the salt marsh vegetation cover and composition. In the Mud Motor pilot a total of 470,516 m3 of fine grained sediment (D50 of ∼10 μm) was disposed over two winter seasons, with an average of 22 sediment disposals per week of operation. Ship-based measurements revealed a periodic vertical salinity stratification that is inverted compared to a classical estuary and that is working against the asymmetric flood-dominated transport direction. Field measurements on the intertidal mudflats showed that the functioning of the Mud Motor, i.e. the successful increased mud transport toward the salt marsh, is significantly dependent on wind and wave forcing. Accretion measurements showed relatively large changes in surface elevation due to deposition and erosion of layers of watery mud with a thickness of up to 10 cm on a time scale of days. The measurements indicate notably higher sediment dynamics during periods of Mud Motor disposal. The salt marsh demonstrated significant vertical accretion though this has not yet led to horizontal expansion because there was more hydrodynamic stress than foreseen. In carrying out the pilot we learned that the feasibility of a Mud Motor depends on an assessment of additional travel time for the dredger, the effectiveness on salt marsh growth, reduced dredging volumes in a port, and many other practical issues. Our improved understanding on the transport processes in the channel and on the mudflats and salt marsh yields design lessons and guiding principles for future applications of sediment management in salt marsh development that include a Mud Motor approach.@en

Contributed

Integrating coral habitat potential and coastal protection services in design of artificial reefs

A case study in Addu City, Maldives

Master thesis (2023) - A.B. Douwes, S.G.J. Aarninkhof, Marcel Zijlema, M.C. Onderwater, E. M.M. van Eekelen

This research focuses on the implementation of the Building with Nature (BwN) approach in the design of artificial coral reefs. The goal is to explore environmental preferences and design tools for coral development, considering both coral habitat potential and coastal protection services. The research also aims to optimize artificial reef design for a case study in Addu City, Maldives.

A conceptual model is developed based on an extensive literature review, incorporating critical engineering and ecological variables relevant to coral habitat potential and coastal protection services. This conceptual model serves as a practical design tool, fulfilling three primary purposes: identifying variables that require further examination to explore coral habitat potential, identifying variables that require analysis to explore coastal protection services, and identifying design variables that influence physical-chemical and biological variables for potential integral solutions.

The research also utilizes OpenFOAM, a numerical modeling tool commonly used in coastal engineering, to design artificial reefs. OpenFOAM accurately models flow and turbulence regimes, crucial for the ecological and biological functioning of coral reefs. An OpenFOAM numerical model is set up, calibrated, and validated for the case study in Addu City. Three design alternatives with different slopes are evaluated using a multi-criteria analysis (MCA), considering criteria such as coastal protection, coral habitat potential, and costs. The numerical model is applied to assess flow regimes and wave transmission for different design variables.

Based on the MCA results and the evaluation of criteria, an artificial reef with a mild slope of 1:3 is selected as the optimal integral solution for the case study. This design performs well in terms of coastal protection, coral habitat potential, and costs. The research demonstrates that the conceptual model and OpenFOAM numerical model are valuable design tools for assessing and optimizing artificial reef design, adhering to the principles of the BwN approach.

In conclusion, this research contributes to expanding knowledge and developing tools for implementing the BwN approach in artificial reef design. By considering both coral habitat potential and coastal protection services, the design of artificial reefs can be optimized to provide multiple benefits, including environmental and socio-economic values. The conceptual model and numerical modeling tool offer practical assistance in the design process, promoting the integration of nature and engineering for sustainable coastal solutions.