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

 

 

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Coastal model Dissolved Oxygen (DO) boundary & computational issue

U
Danker Kolijn, modified 5 Years ago.

Coastal model Dissolved Oxygen (DO) boundary & computational issue

For my coastal scenario (3 open boundaries, large volume of water with north/south alongshore currents) I experimented with the SWRear settings where 7,9,10 (see various time-series) were recommended to compute a diurnal DO signal using temperature and cloud cover, etc. . However, when I imposed an average value of 6.7 mg/L (as a time series) at the boundary the model did not produce the proper output (dotted red line does not produce amplitude expected) when compared to measured (black line). It seems almost as if the flow of DO from the boundary damps the computational process (I confirmed this in a video of the simulation). When I implemented a -999 DO time-series at the boundaries I found that this is equivalent to introducing 0 mg/L of DO (red dots on plot), where the model seems to be initially inundated with low DO. However, it then starts to the generate the proper signal (in phase and somewhat reasonable amplitude) when compared to my measured data.



I feel like i'm missing something very simple. I don't want to impose a measured DO boundary condition. I want the model to compute DO on it's own given the temperature and climatic conditions I feed the model. Does anyone know why when I input a higher average DO at the boundary, the computational process of generating a diurnal DO concentration seems to be damped?
many thanks in advance
AA
Anonymous Anonymous, modified 5 Years ago.

RE: Coastal model Dissolved Oxygen (DO) boundary & computational issue

Jedi Master Posts: 333 Join Date: 7/30/20 Recent Posts
Hi Danker,

It looks indeed like your boundary conditions are dominating the solution here.
What is the average age of water in your domain?
Is the flow direction at the boundaries mainly constant or does it change regularly?
Are you using any timelags with your boundary conditions?

The fact that your runs with zero DO at the boundaries yield a signal with more amplitude is likely due to the fact that the reaeration rate also depends on the difference between actual and saturation DO concentrations.

Christophe