Questions about the hydstrucmod.f90 text

I read hydstrucmod.f90 text,then I have some questions that I would like to discuss with you. Formula: "ZHU = BELV(LU) + HP(LU), ZHD = BELV(LD) + HP(LD),

HUD = ZHU - USINV,HDD = ZHD - DSINV "I do not understand the meanning of the "ZHU,BELV(LU), HP(LU),ZHD,HUD,USINV,HDD and DSINV’.What physical quantities do they represent?What pLooking forward to your reply, thank you!

Hi Cui Zhen Yong,
Definition of the variables that you were looking for can be found in the attached photo.
Culvert_exp

For the details of an upstream cell:
ZHU: Upstream water surface elevation of the hydraulic structure (m)
BELV(LU): Bottom elevation of the cell upstream of the hydraulic structure (m)
HP(LU): Water depth at the upstream cell upstream of the hydraulic structure (m)
USINV: Upstream invert elevation of the hydraulic structure (m)
Similar definitions are applied for the downstream.

Sincerely,
Kien