Dear EFDC team and users:Why is the velocity in the simulation result like this? Why not follow the flow of rivers?

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sr Shen,You should provide more details about the problem you are trying to address with this model. For example, there may be issues arising from the extreme aspect ratio of your cells. Are the results the same if you refine your cells in the downstream direction so that your cells have a more conservative aspect ratio?From what you have provided, it is hard to determine the nature of the problem.Please let me know if you can provide more information about this problem.Tom

Dear Mr. Mathis： This picture describes my model.As shown in the picture,I set up 5 open conditions with water level data of water conservancy hubs and 2 flow conditions. And the general direction of the flow is shown in the picture.About initial conditions, I set up the bottom elevation with the poly file and xyz file. I also set up the water level with the data of several water conservancy hubs on the first day.I think the density of some cells is really high and it may influence the convergence but why is the velocity perpendicular to the river?

So are there actually velocities associated with those vector directions, or is the water just not moving? If the water velocity is zero, then the vector direction is not really meaningful since the vector has a length of zero.I recommend drawing a flux section along one of your canals and seeing what the discharge rates are in the N-S direction vs. the E-W direction. That way you can be sure that what you are seeing is actually a problem and not just a function of how the vectors are being drawn.Also, your model will work better if you can restrict the cell aspect ratio to less than 4:1. Some of your cells have pretty extreme aspect ratios from the looks of it.I think the model you are working on is very interesting. I assume it is an agricultural area, or maybe a city with a canal system? I’m curious to know where this is!Thanks!

Thank you for your advice. I modified some cells of the grid and set up more flow boundary conditions,now the problem have been solved.And this is a famous city rich in water resources in the plain area of the Yangtze river delta（and near Taihu lake）.The beijing-hangzhou grand canal runs through the city which has a complete water control system. Maybe you can take a guess!

Glad to hear you have worked it out. Yes, after looking at a map I figured out what the city was.Do you have any plans to couple this model to one of Taihu Lake as well?Very cool model!

At this stage ,I only work on this area’s model. Maybe I will try to consider more conditions of Taihu Lake later,and make a larger system. Ha ha!

Dear Mr. Mathis： Would you please read my latest question and I’m looking forward to your suggestions. I’m really worried about these problems.I read the user’s manaul and water quality manual but can’t solve these.