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The effects of planimetric and altimetric changes on tidal amplification in coastal plain estuaries

Warmerdam, M.T.M. (2018) The effects of planimetric and altimetric changes on tidal amplification in coastal plain estuaries.

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Abstract:Estuaries are unique coastal features that occur all over the world. Many estuaries are surrounded by densely populated areas and are very important to the local economy, because they provide easy access to shipping ports inland. At the same time they often contain abundant and vibrant ecosystems with unique flora and fauna which are threatened by the expansion of shipping routes in estuaries. Dredging operations are performed to guarantee access to ports for larger ships by widening and deepening the main channels. Recent studies have shown that the structural widening and dredging of main channels in funnel-shaped coastal plain estuaries leads to an increase of the tidal amplification. The increased tidal range is often accompanied with decreased water levels during low tide, endangering shipping access. Additionally, the increased water levels during high increase the risk of flooding and endanger the ecosystem. The goal of this research is to increase understanding of the processes behind the amplification of the tidal wave in a tidal basin caused by changes in planimetry and altimetry, to predict the effects of certain interventions on the tidal ranges in estuaries. To this end, an idealized hydrodynamic model has been designed using Delft3D-FLOW to analyze the tidal dynamics in a simplified funnel-shaped estuarine tidal basin. The model has been set-up using the Scheldt Estuary in the Netherlands and Belgium as a case study. This estuary has a typical exponentially decreasing width profile. It also subject to heavy dredging operations to allow access to the port of Antwerp. A systematic analysis of several planimetric and altimetric characteristics has been performed to assess their influence on the tidal range profile in a tidal basin. Results from the analysis show that the amplification and damping of the tidal wave depends on a combination of the rate of convergence, the length of the converging tidal basin and the depth of the prismatic part upstream of the converging basin. These characteristics influence the tidal range through three basic processes: 1) Amplification through width convergence; 2) amplification through shoaling; 3) damping through bottom friction. Analysis of historic bathymetric profiles and several artificial interventions has shown that it is possible to increase or reduce the tidal amplification in a tidal basin through human interventions. However, in order to significantly reduce the tidal range large scale interventions are necessary. Additionally, the results show that local increases of bottom elevation hardly reduce the water levels during high tide. The results of this study show that it is possible to estimate the general effects of planimetric and altimetric changes caused by human interventions in a strongly simplified 2DH hydrodynamic model. The model designed in this study could be used for additional research of the effect of the channel-shoal system on tidal amplification and assess the effects of more detailed and localized interventions.
Item Type:Essay (Master)
Clients:
Arcadis Nederland
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Industrial Engineering and Management MSc (60029)
Link to this item:http://purl.utwente.nl/essays/74372
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