How to Model Spillway ?

[kaustubhsohoni]

Dear All
I am trying to model a gated spillway in Hecras.
but from the Hydraulic Reference Manual, It can be seen that Hec Ras does not account for the side contractions at the opening and hence instead of Effective Length, it is using the net overflow length ,without accounting for contraction due to pier and abutment. Thus it increases the discharge capacity of the spillway
How can it be modelled for getting the accurate results?

[toge_civil]

i think generaly, ineffective area have calculate it.
ussualy, I use smaller Cd for each gate, but it needs gauge data from phisical model to clarify and kalibrate.