Reservoir surface area warning message

Dear Dan :

Surface area is the preferred method of defining reservoir volume since the reservoir storage (level-pool) routing uses area in its computations, and the volume to surface area conversion algorithm used in the program does not always provide an adequate conversion.

If you have any additional questions or need any further information, please contact me again.

Sincerely,

Chris E. Maeder, M.S.
Senior Technical Engineer
chris.maeder@bossintl.com

From: INTERNGEN1@ci.tacoma.wa.us

Chris,
I'm working on the Cowlitz River Dam Break Study for Tacoma Power. Your program continually gives us the following warning on our models:

Warning:
Surface area table entries below entry no. 1 is not exactly compatible with the volume table. The volume table should be checked for possible errors. If possible, use a surface area table rather than a volume table. This warning appears in the analysis output just after the reservoir volume table is shown and just before a reservoir surface area table is shown (The model must have developed the surface area table since it was not entered.) We have no Surface area data available to us. We need to be able to enter volume.

Can you please explain the meaning of this warning, and whether or not it is significant? ----------

Chris,

The resulting outflow hydrograph seems reasonable but the reservoir volume shown in Analysis Results is much higher than actual. I am comfortable using volume rather than surface area as long as this bogus volume calculation is irrelevant.

We are also having another problem. Even though our inflow hydrograph lasts for 80 hours and the boundary condition for the routing hours is left blank, the model always ends at 30 hours. How can we get the model to run longer? We confirmed that the inflow hydrograph is smooth and have tried numerous other approaches with no success. I would like to show how long it takes for the flow to return to normal - probably several days. Note: The peak flow at the last cross section is reached at 24 hours and then the slope is very gradual. I look forward to your response to the above questions.

Thanks,
Dan Rottler

Chris,

I changed the initial time step size to 0.02 from 0.01 and doubled the routing period to 60 hours. Since this model covers 50 miles of river, I guess this time step was too small for the time period we desired.

Please still answer the reservoir volume question.
Thanks,
Dan
DROTTLER@ci.tacoma.wa.us

Dear Dan :

There are only a finite number of times steps available in DAMBRK. It is written in FORTRAN, so it uses fix arrray sizes. BOSS DAMBRK Professional Version has been compiled for 3,000 time steps. We have one that has been sized at 9,000 time steps, which could quite possibly model the entire reach of your river. Alternatively, you can break the model into pieces, only modeling a portion of it (i.e., upper reach, middle reach, etc.).

As far as computing the volume is concerned, I guess I would need more information from you. Are these numbers in metric or English units? Did you enter the data as volume or surface area? Where is this data being reported--in an echo print of the input data? It is quite possibly a simple reporting error, where it is using the correct data internally. Note that DAMBRK does all of its calculations in English units, and converts from and to metric units when dealing with metric data.

If you have any additional questions or need any further information, please contact me again.

Sincerely,

Chris E. Maeder, M.S.
Senior Technical Engineer
chris.maeder@bossintl.com