Background and requirements

Within the dredging industry, it is common practice to generate fluid mud layers when executing dredging projects in, for example, port areas. The fluid mud layer that is generated can flow by gravity to deeper sections where it can be trapped. During flow, the fluidized layer will interact with the ambient water column under local hydrodynamic forcing (i.e. tidal currents or waves). Interaction of the fluidized layer with the water column can lead to an increase in turbidity of the water. The turbidity plume is important to be evaluated prior to project execution to estimate and mitigate environmental impacts of the dredging activities.

The stability and fate of the fluidized layer, and therefore the impact of these dredging operations, is dependent on several factors like: bed slope, flow conditions, initial density, and thickness and momentum of the generated fluidized layer.

To make an assessment of the environmental impacts and effectivity of fluidized layers created by a moving turbidity source, insight should be obtained in:

1.         The transport path and stability of the fluidized sediment layer (location, extension, thickness and density of the layer); and complementary

2.         The entrainment of sediment from the fluidized layer into the water column (which can be used as turbidity source for environmental evaluation).

This project is a collaborative Topconsortium Kennis en Innovatie (TKI) Deltatechnologie project between Deltares and Boskalis. The goal of this joint project is to develop a rapid assessment numerical modelling tool to assess the environmental impacts of fluidized sediment layers induced by a moving turbidity source. This numerical modelling tool is designed to answer the following questions:

• Fate of the fluidized layer: what will be the stability of the fluidized layer as function of time and distance from the moving turbidity source? Will the layer be transported to deeper water (sloping bed), or will the layer be stirred up in the (whole) water column? Where will the sediment in the fluid mud layer end up?
• Turbidity source: if the fluidized mud layer is (partly) entrained in the water column, how large will the resulting source to the water column be and which turbidity levels will result from that?

The numerical tool should be applicable to different environmental conditions, like fluctuating tidal currents and water levels, and different bed slopes.  

This tool is important for quick assessment of environmental and operational implications in harbours and navigation channel maintenance, contributing to safety and quality of navigation infrastructures and water bodies. With minor modifications, the same tools can be utilized in predicting sedimentation and consolidation rates for beneficial use of dredged sediments, building with mud and nature-based applications. Finally, this tool strengthens the knowledge and competitive position of Dutch knowledge institutes and private sector (contractors) abroad.

This project will deliver (at least) a numerical tool (executable) together with the relevant background information, and a journal / conference presentation or publication.

Project Scope

The scope of this project is to develop a rapid assessment numerical tool to assess the environmental impacts of fluidized sediment layers induced by a moving turbidity source. The numerical tool provides insight in the stability and dispersion of turbidity currents and fluid mud in estuarine, tidal and harbour basin environments, especially resulting from a moving turbidity source. During development, this tool will be tested and applied to specific dredging applications.  

The project is subdivided in two phases:

• Phase I: development and verification of the numerical tool; and
• Phase II: validation and application of this tool on specific real dredging operation.

Phase I includes generic knowledge and tool development. By focussing on testing against practical applications in Phase II, high quality model development will be assured and optimum knowledge transfer from Deltares to the private sector and vice versa is guaranteed.

The numerical tool developed during Phase I will be based on the 1DV model.

Introduction

On this wiki webpage, we summarize the activities and findings of Phase I of the project “Development of a numerical rapid assessment tool to simulate fate and environmental impact of fluidized sediment layers”. This project is a collaborative Topconsortium Kennis en Innovatie (TKI) Deltatechnologie project between Deltares and Boskalis. The project is divided in two main phases:

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