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

Using the Z-model for Delft3D flow

Shawn Sim, modified 7 Years ago.

Using the Z-model for Delft3D flow

Youngling Posts: 12 Join Date: 4/29/13 Recent Posts
Hi all,

I would like to use the Z-model on my computational domian. I have tried using it for a 10 layer model, however the results I obtained are much poorer than what I obtained using the sigma model.

I can briefly describe my domain. 14 m (x-dir), 4 m (y-dir), dx = 0.005 m , dy = 2 m, water depth = 0.35m.
The coastal topography that comprise composite slopes is as folows, offshore 0 to 6m (no bottom contour),--> 6 to 6.17 m (slope of 1(V):0.68(H)) --->6.17 to 7.67 m (slope of 1:15)---> 7.67 to 14 m (slope of 1:30)

I am trying to find out the maximum inundation distance under solitary waves of different wave heights and compare it with experimental results.

So here are some of my questions:

1) Is it advisable to use the 'cut cell' option and if so, how should I go about doing it?
2) What is a recommeded number of layers that I should use? and should all layers have the same thickness? I have seen test cases with equal thickness and unequal thickness used.
Qinghua Ye, modified 7 Years ago.

RE: Using the Z-model for Delft3D flow

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

For z model in present version of Delft3D, the cutting cell algorithm is already included to deal with the irregularities of horizontal boundary. If you choose Flooding scheme for horizontal advection, it is on.

As to the layer thickness, it depends on your focus.

As to your claim that 10 layers z-model gives out worse results than sigma model, I can imagine. Since in sigma model, you have 10 layers everywhere in the computational domain, but in z layer model, you probably don't have 10 layers everywhere. The layer thickness in z layer is roughly computed as (ztop-zbot)/10. The ztop should be as high as the possible highest water surface level. Thus usually the layer thickness in z-layer model is thicker than sigma layers. So you get lower vertical resolution in z-layer model if you set the same layer number as the sigma-layer model. In summary, you need more layers for z-layer model to get the same resolution in general.

Hope this will help a bit.