DXM, CDO estimation

Dear Sir,
i am running my first DAMBRK model and need some help with the following parameters:
1. minimum distance between interpolated cross sections (DXM), how can be estimated? i guess from the time computational step but if this is the case, then how can i approximate the time step iwthout being too large (e.g. TP/20)
2. what is the "dam overtopping discharge coefficient (CDO)" and how can i estimate it?
3. how can i estimate expansion - contraction coefficient?

in the output results i get the warning message " at cross section 7 the DXM should be changed to 0.287 due to expansion - contraction criteria " . when i change it , the warning remains.

Thank you in advance,
Aimilia Pistrika

[Chris Maeder]

Aimilia:

Note that BOSS DAMBRK will automatically figure out the interpolated cross section spacing. Simply leave the entry "Minimum distance between interpolated cross sections" blank and DAMBRK will handle the rest.

The "Dam overtopping discharge coefficient" is the length of the dam that acts as a weir, multiplied with the weir coefficient that you want to use. For example, if the weir length is 100 ft and the weir coefficient is 3.0, then you would enter (100 x 3) 300 as a value.

I generally do not worry about the expansion / contraction loss coefficients when first setting up a model. The effects from expansion / contraction are much less than that used for Mannings roughness and can be easily overshadowed by the value used for roughness.

Sincerely,

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