Water level in reservoir

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guifranz@gmail.com
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Posts: 12
Joined: Thu Jan 01, 1970 00:00

Water level in reservoir

Postby guifranz@gmail.com » Fri Aug 12, 2011 15:05

Dear all,

It`s great to have the Mohid Forum working again. :D

I had some instability in the water level in a small reservoir with only close boundaries. The same problem happened simulating the hydrodynamic of a river with Mohid and of reservoirs using other model. I had already solved this problem earlier imposing an open boundary. So, I opened the contour of the reservoir in Mohid GIS and ran the hydrodynamic model again without changing anything else. The results of the water level in this new simulation were very better, with few oscillations in the beginning. I didn`t define any contour condition in the open boundary.

How Mohid define the contour conditions in this case?

I am running the hydrodynamic model in bigger reservoirs with only close boundaries and the instability in the water level has not occurred. So, I realized that this instability depends of the size of the domain. Do you have any considerations about this?

I am having other problem with water level in reservoirs. I have diary data of elevation of the water surface and of output discharge, and with the volume depth curve exported in Mohid Gis I calculated the input discharge with a mass balance. I am running the hydrodynamic model for one year and comparing the water level with the data. The results are the same in the early months, but a difference start to appear and increases throughout the simulation, with the model results getting smaller than the data. This error is occurring in big and small reservoirs, with close and open boundaries. I didn’t define bottom fluxes and evaporation. Bellow is an example of my hydrodynamic module.
ADV_METHOD_H : 4
TVD_LIMIT_H : 4

BAROCLINIC : 0
BIHARMONIC :1
BIHARMONIC_COEF :1e3
CONTINUOUS : 0
INITIAL_ELEVATION : 1
INITIAL_ELEVATION_VALUE : -6.46
SUBMODEL : 0
TIDE : 0
WATER_DISCHARGES : 1
ENERGY : 0

TIME_SERIE : 1

TIDEPOTENTIAL : 0
WIND : 0
ATM_PRESSURE : 0
SURFACEWATERFLUX : 0
DATA_ASSIMILATION : 0

OUTPUT_TIME : 0 86400.


RECORDING : 0

TIME_SERIE_LOCATION : ..\..\GeneralData\monitoring_stations_2D.dat

My courant is about 5 in all simulations. It could be a numerical diffusion? I don`t have velocity data to compare with the results. I`m trying other numerical schemes and decrease the courant number, but until now without success. Any suggestions?

Best regards.

frank.maretec@ist.utl.pt
MOHID Guru
Posts: 151
Joined: Thu Jan 01, 1970 00:00
Location: Technical University of Lisbon
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Re: Water level in reservoir

Postby frank.maretec@ist.utl.pt » Thu Sep 08, 2011 08:39

Dear all,

I didn't apply MOHID Water in a Reservoir since several years, so for me it's difficult to answer the question...

From what I remember, in the past I always started with an INITIAL ELEVATION equal to zero and, through discharges I emptied the reservoir to the desired intial level. This in fact should not be an issue, but several years ago this helped...

Happy MOHIDing,
Frank
In order to understand recursivity you must first understand recursivity.


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