You are here

Home › Forums › W2 Forum › Hydrodynamics

w2.err in water quality model

Wed, 08/06/2014 - 5:19pm — Alma
Hello, I am modeling two separate lakes, I setup the hydrodynamic model and the model runs fine, with no errors or warnings. When I turn ON the constituents computations and include all the files of constituents, the model does not run and gives the following error: Unstable water surface elevation on day 200.696 negative surface layer thickness using minimum timestep at iteration 6706527 Segment, Surface layer thickness, m, Flow m3/s, U(KT,I) m/s, ELWS, m 3 0.03 -0.05 -0.02 95.03 4 0.03 -0.07 -0.03 95.03 5 0.02 -0.06 -0.04 95.02 6 -0.00 0.00 0.00 95.00 Why do I have this error if I have not changed anything? Just I included the water quality part. Thanks for your help Alma
Forums: 
Hydrodynamics
Thu, 08/07/2014 - 4:14pm — Amir

Hi Alma Based on the information you provided, it seems the layers are so small (a few centimeters) Try using larger layers maybe 0.25 m at least.
Fri, 08/08/2014 - 10:32am — Alma

Thank you Amir, I have one question: What is the maximum layer depth to be used without having unstability problems? Because I have one system with reservoirs with depths > 15m and smaller reservoirs with depths of 2 m, so I dont know how many layers should I set up? Thank you!
Fri, 08/08/2014 - 12:54pm — Amir

Your welcome Alma, I don't have a theoretically based definition. But based on my experiences, it depends on the system your are modeling. When you define the layer thicknesses very small (e.g. 10 cm), with a small inflow /outflow the water level will change too much compare to the layer thickness (e.g. 25 cm). This means you add/ drain water to/from 3 layers . The model terminates since the changes in active layer are more than 2 layers in one iteration.
Fri, 08/08/2014 - 12:59pm — Amir

I would use a layer thickness of at least one meter for the deeper lake and 25-40 cm for the shallower lake. But again it depends on the changes in the lake water level in your simulation time.
Fri, 08/08/2014 - 1:51pm — Alma

Thank you Amir, based on your comments, I'm going to try with different options, since the changes in inflows/outflows are big, especially in winter time. Alma