ULTRA 4 INSTRUCTION MANUAL 
 
90 
Rectangular Flume Calculations 
Absolute 
If the flow calculation is to be absolute P702 = 1 the flow will be calculated 
using the formula:  q = (2/3)
1.5
gn
0.5
C
s
C
v
C
d
bh
1.5
   
Where:   
q  = flowrate                   
gn = gravitational acceleration  (nominal value = 980.66 cm/s
2
)                                                                              
C
s
 = shape coefficient (value = 1)                 
C
v
 = velocity coefficient calculated by Ultra 4 (P721) 
C
d
 = discharge coefficient calculated by Ultra 4 (P722) 
b    = throat width P711     
h    = head   
Ratiometric 
If the flow calculation is to be ratiometric P702 = 2 the flow will be 
calculated using the formula:  q= q
cal
(C
v
/C
vcal
)(C
d
/C
dcal
)(h/h
cal
)
1.5
 
Where:   
q  = flowrate      
q
cal 
= flowrate at maximum head P705         
C
v
 = velocity coefficient calculated by Ultra 4 (P721)  
C
vcal
 = velocity coefficient at maximum head    
C
d 
= discharge coefficient calculated by Ultra 4 (P722)  
C
dcal 
= discharge coefficient at maximum head   
h  = head 
h
cal 
= maximum head P704