intro story Coast / Estuary

Coast / Estuary

Coastal systems are among the most dynamic physical systems on earth and are subject to a large variety of forces. The morphodynamic changes occurring to coastlines worldwide are of great interest and importance. These changes occur as a result of the erosion of sediments, its subsequent transport as bed load or suspended load, and eventual deposition. 
Estuaries are partly enclosed water bodies that have an open connection to the coast. Estuaries generally have one or more branching channels, intertidal mudflats and/or salt marshes. Intertidal areas are of high ecological importance and trap sediments (sands, silts, clays and organic matter).
Within the Delft3D modelling package a large variation of coastal and estuarine physical and chemical processes can be simulated. These include waves, tidal propagation, wind- or wave-induced water level setup, flow induced by salinity or temperature gradients, sand and mud transport, water quality and changing bathymetry (morphology). Delft3D can also be used operationally e.g. storm, surge and algal bloom forecasting. 
On this discussion page you can post questions, research discussions or just share your experience about modelling coastal and/or estuarine systems with Delft3D FM. 




Sub groups
D-Flow Flexible Mesh
Cohesive sediments & muddy systems



Message Boards

question about the sigma grid distribution

Federico Posada, modified 7 Years ago.

question about the sigma grid distribution

Youngling Posts: 5 Join Date: 11/30/12 Recent Posts
hi all,
Im trying to see the currents and waves interactions, and i was using a sigma grid distribution with four layers, 1% at surface, 10%, 10% and 79%, i don't know, if this hard changes in the layers generates problems.
Qinghua Ye, modified 7 Years ago.

RE: question about the sigma grid distribution (Answer)

Jedi Council Member Posts: 610 Join Date: 3/2/11 Recent Posts
Hi Federico,

If the sum of all vertical layer thickness is 100%, Delft3D will not give any error message. But, you must be aware of that, if the thickness difference is too big, there might be some consequences. Refer to the Delft3D-FLOW manual, version 3.15 Revision: 18392, Page 32:

To resolve the logarithmic pro le of the horizontal velocity components in the vertical the thickness of the bottom layer should be small. It is recommended to choose the bed layer
thickness to be about 2% of the water depth. The variation in the layer thickness should not be large, i.e. the layer thickness must have a smooth distribution. An indicative value for the
variation-factor for each layer is 0.7 to 1.4. Going from bottom to surface the suggested layer thickness should not exceed 3%, 4.5%, 6.75%, etc. of the water depth. For a ten -layers
example the suggested layer thickness is 2, 3, 4, 6, 8, 10, 12, 15, 20, 20%. If wind is one of the important driving forces also the layer thickness near the surface should not exceed 2% of the water depth. Thus, going down from the surface the layer thickness should not exceed 3%, 4.5%, 6.75% etc. of the water depth. A similar argument holds when you want to resolve sharp density gradients in the vertical: you must have a sufficient fine grid to resolve the vertical profi le.

Furthermore, in the lastest release of Delft3D-FLOW, the 3D wave-current interaction has been activated. Wave effects are combined not only in the surface layer any more, but also being distributed along the vertical layers. Thus the layer thickness might be somewhat important to be similar or to a limited ratio.