User Forum of Software BASEMENT

Reyhaneh

User

Registered: 2014-12-05

Posts: 3

OUTLET_Boundary_WEIR

Hi,

My problem concerns the use of the  WEIR boundary condition as the downstream boundary condition. Actually, what I know from the downstream conditions is the discharge value as well as the water depth which is the critical depth. I used these two to calculate the C  coefficient. But I don't know what is the relationship between this C value (formula page 128 of the BASEMENT_REFERENCE) and the ''my factor'' which I should define for the weir boundary condition. I also have issues regarding defining the text file of weir time-elevation. your ideas would be highly appreciated.

Reyhaneh

Christian Volz

User

Registered: 2014-09-04

Posts: 31

Re: OUTLET_Boundary_WEIR

the weir formula is implemented exactly as described in the BASEMENT reference document. The weir flow is computed as:

q = 2./3. * C * sqrt(2. * g * ((wseLeft - weirHeight_)^3 )

with

C = my factor = poleni factor (note that the factor "2./3." is not included in C, as it is in some textbooks!)
wseLeft = water surface elevation of the element associated with the boundary edge
weirHeight = elevation of the weir crest

q is a specific discharge [m2/s] here. It is computed for each edge of the string_def seperately and is finally multiplied with the edge length [m] to obtain the discharge Q over the edge [m3/s].

If your water level at the outflow boundary is nearly constant, then you can assume that BASEMENT computes the total outflow discharge as:

Q = 2./3. * C * sqrt(2. * g * (wse - weirHeight_)^3 ) * length_stringdef

I hope this is enough information for you...

Unfortunately I do not know what your problems are with the definition of the text file with the weir elevations? In this file you can set up varying weir levels over the time. If your weir level is constant during the simulation, just set constant values.