initial surface elevation in mike 21

i am modelling an area 50kmx50km in mike 21. my bathymetry file contains elevation from 3m to 53m. i choose land value as 60. no i have to create open boundary. for that i changed land value (60) to some elevation depending on the neighbor point's elevation. the problem is with initial surface elevation.

what is your question?

what value i have to choose as initial surface elevation?

Hi Vadlamudi Premkumar,

are you still struggling with the surface elevation problem?
(i) You know that you are free to set the initial surface elevation at any level you want, and you can do that by providing a constant value and a spatially varying surface elevation. Your bathymetric heights suggest that you are somewhere inland. So, to have any water in your model, for the initial surface elevation you would select a value larger than 3m. That should be easy, if you are sure that the vertical reference datum of your bathymetry is the same as your initial surface elevation.
(ii) Then, I noted that your land value of 60m is 7m above the highest part of your model. The setting is ok as long as you will have no water travelling higher up than 60m.
So in the case as you describe it, your initial surface elevation should be set somewhere between 3m and 60m.
Best regards
Stefan

thank you stefan,
i had given my bathymetry data it self as the initial elevation. but for every grid value in bathymetry i increased value by 0.01m so the initial water depth will be 0.01m.

thanks again.

Hi Vadlamudi Premkumar,

oh, you put a pretty thin layer of water over an arbitrary terrain at the beginning. As soon as you start the model, the water will flow into the next nearby "whole" and form some puddles, some water might manage to flow out. This situation remains until water from the top rushing over the partly dry bathymetry.

I suggest to start the model with the inital surface elevation which matches the inlet BC. In case that your inlet BC is varying, then I suggest a two step approach:
Model Simulation 1:
Use a constant initial surface elevation and keep the inlet boundary condition constant. Let it run long enough until you have a stable surface elevation in your entire model domain. Use the last timestep for your initial surface elevation of your final simulation
Model Simulation 2 (final simulation):
You can use the result of simulation 1 as a starting point (initial condition) for your final simulations. Change back to you original inlet condition and run your simulation.

Hope this helps!

Best regards
Stefan

what should i do if i have multiple boundary conditions??

Hi Vadlamudi Premkumar,

you would usually have multiple boundary conditions. Not sure what you mean. Can you specify? It would also be good to know which kind of model application you are looking at (long river, lake, or?).

Best regards
Stefan

hii stefan,

my model is related to inland application that study how overflowing from rivers are inundating the floodplain.

Hi Vadlamudi Premkumar,

did you try specifying a discharge at the upstream boundary and a water level at the downstream boundary? You may also try free outflow at the downstream boundary.

Cheers
Stefan