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. 
 

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

 

 

Message Boards

3D z-model: Different free surfaces in FLOW and DELWAQ

JB
Javier F Bárcena, modified 3 Years ago.

3D z-model: Different free surfaces in FLOW and DELWAQ

Youngling Posts: 10 Join Date: 1/4/12 Recent Posts
Hi all,

I'm trying to model a reservoir using a 3D z-model configuration with Delft3D-FLOW and DELWAQ, applying the tag_6118.

Firstly, I ran hydrodynamics using the z-model and 12 layers with a Zthreshold of 0.1 m. As displayed in the attached figure 'flow_Zthr_10cm.png', hydrodynamics results of the free surface look fine. At the beginning (0 to 6 km), a free surface elevation above 0 m is observed due to the flow discharge and the river bathymetry and, after this section, a free surface drop around 0 m is observed because of the reservoir bathymetry.

Secondly, I ran water quality with two configurations of the Z-layer model processing:

1) Using the same threshold as in the FLOW, this is 0.1 m. The attached figure 'delwaq_Zthr_10cm.png ' shows the free surface and segments obtained by DELWAQ:
CONSTANTS ACTIVE_Emersion DATA 1.0 ; switches process 'on'
CONSTANTS ZThreshold DATA 0.1 ; threshold in m.

2) Using a non-threshold, this is 0.0 m. The attached figure 'delwaq_Zthr_0cm.png ' shows the free surface and segments obtained by DELWAQ:
CONSTANTS ACTIVE_Emersion DATA 1.0 ; switches process 'on'
CONSTANTS ZThreshold DATA 0.0 ; threshold in m.

According to these results (all of them are for the same date), it looks like DELWAQ is not able to handle free surface elevation above 0 m, or at least, in the way I'm setting up my model. On the one hand, if the Zthreshold is activated to 0.1 m, DELWAQ is avoiding the free surface above 0 m. In fact, results show a kind of flipping of the free surface in the river section. On the other hand, if the Zthreshold is activated to 0.0 m, the free surface is biased to 0 m along the whole model domain, generating a fictitious free surface and, consequently, fictitious diffusion gradients.

Following these comments, do you have any idea to preserve the free surfaces (water elevations) computed by Delft3D-FLOW in DELWAQ when these are above and below 0 m at the same time in the same domain?

Thanks in advance and regards,
Javier
MJ
Michel Jeuken, modified 3 Years ago.

RE: 3D z-model: Different free surfaces in FLOW and DELWAQ (Answer)

Jedi Knight Posts: 154 Join Date: 1/21/13 Recent Posts
Hi Javier,

> According to these results (all of them are for the same date), it looks like DELWAQ is not able to handle free surface elevation above 0 m, or at least, in the way I'm setting up my model.

I think this is just something going wrong in QuickPlot. Elevation above zero is somehow fliped into the negative again. I have no idea why this is. One idea that comes into mind, in QP there is an 'Operator' that could be switched from none to abs. Maybe this got in the way?

In Delwaq itself there is not a known absolute position in the vertical, only the order of segments in the vertical. You might want to look at 'LocalDepth', as the depth from the water surface to the bottom of this segment at this layer. You could try to plot this in this side view.

Michelle
MJ
Michelle Jeuken, modified 3 Years ago.

RE: 3D z-model: Different free surfaces in FLOW and DELWAQ (Answer)

Jedi Knight Posts: 154 Join Date: 1/21/13 Recent Posts
P.S.: cant look into this without data