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Lake

Lakes and reservoirs are important resources for communities around the globe. They provide food, drinking and irrigation water and can also offer spots for recreation. Under certain conditions lakes can also represent a threat for local communities, such as flooding or limnic eruptions. The ecological state of shallow lakes may be hampered by suspended sediments due to wind driven currents and waves. In deep lakes, stratification can cause undesirable anoxic conditions in the deeper areas. Understanding these systems is crucial to enable a sound management of these water bodies.

 
Delft3D is the state-of-the-art modelling framework for hydrodynamics, water quality, ecology, waves and morphology.
 
Here, in this space, we share knowledge & experiences, and discuss issues related to modelling of lakes.

 

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Difficulty with transport boundary conditions: free outlet

AC
Adrian Csibran, modified 4 Years ago.

Difficulty with transport boundary conditions: free outlet

Youngling Posts: 2 Join Date: 9/9/15 Recent Posts
Dear All,

I have some difficulty with open boundary conditions in case of transport processes. I have a lake with 2 open boundaries: an inflow (total discharge) and an outflow (water level). I know the concentration at the inflow, but I have no information about it near the outflow. I would like to adjust an open boundary with free outflow, without adding any transport boundary condition. I tried to adjust zero concentration for outflow, but it reversed back on the domain. I also tried to use the Thatcher-Harleman lag, though this function was not designed for this kind of condition, but it didn’t solve the problem either. As the exact concentration near the outflow is very important to me, I am looking for a way to overcome this problem. Does an option exist in Delft3D-Flow which provides free outflow for transport, or could you suggest me any other method to fix this problem?

Thank you in advance,

Adrián Csibrán
AC
Adrian Csibran, modified 3 Years ago.

RE: Difficulty with transport boundary conditions: free outlet (Answer)

Youngling Posts: 2 Join Date: 9/9/15 Recent Posts
Dear All,

The answer for my question can be found in the Flow Manual, I have not noticed it before. In case someone would face a similar problem:
„When you specify a negative value for the time lag (Thatcher and Harleman time lag) the boundary treatment for constituents, salinity and temperature will be the same as at outflow, but now for all times. Thus, the solution for these parameters will be fully determined by the processes inside the model area. „

Best regards,

Adrián Csibrán
Qinghua Ye, modified 3 Years ago.

RE: Difficulty with transport boundary conditions: free outlet

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

Great you find the answer from the Manual.

Cheers,

Qinghua
VM
Vahid Mohammadian, modified 3 Years ago.

RE: Difficulty with transport boundary conditions: free outlet

Youngling Posts: 5 Join Date: 1/29/16 Recent Posts
Hello and thank you for your helpful solution about outflow!

I have more or less the same issue with modeling of salinity intrusion into an estuary.

The problem is that I have to define a constant salinity at the mouth of the estuary. During the flood tide, there is no problem and the saline tides intrude into the estuary from the bay. But the issue is that during ebb tide, the free outflows should be flushed out from the estuary into the bay/ocean. But the fixed constant value for the salinity (let say 30 ppt) does not allow us to have a free outflow with real salinity. In the other word, the salinity value at the mouth is confined to be constant and does not change freely, while I expect to have less saline ebb tides at the mouth.

I highly appreciate if anybody can help with comments.