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Hydraulic constraints ensure a proper operation of the sewer networks. They establish bounds for the constraints exhibited in Table 1. The minimum allowed diameter prevents obstructions in the system. The maximum filling ratio precludes surcharge problems and ensures ventilation in the system to avoid environmental difficulties. The minimum wall shear stress and velocity ensure a cleaning process inside the pipes; while the maximum velocity prevents problems such as erosion, cavitation, air entrapment, hydraulic jumps, among others. The minimum and maximum slope constraints are limited by the minimum and maximum velocities, respectively.

Table 1

Hydraulic design constraints

ConstraintValueCondition
1 Minimum diameter 200 mm Always 
2 Maximum filling ratio 0.7  
0.8 0.7 ≤ ≤ 1.5 
0.85 Other cases 
3 Minimum wall shear stress 2   
4 Minimum velocity 0.75   
5 Maximum velocity 5   > 0.0001 
10   < 0.0001 
6 Minimum slope The one for which the minimum velocity and shear stress are obtained 
7 Maximum slope The one for which the maximum velocity is obtained 
ConstraintValueCondition
1 Minimum diameter 200 mm Always 
2 Maximum filling ratio 0.7  
0.8 0.7 ≤ ≤ 1.5 
0.85 Other cases 
3 Minimum wall shear stress 2   
4 Minimum velocity 0.75   
5 Maximum velocity 5   > 0.0001 
10   < 0.0001 
6 Minimum slope The one for which the minimum velocity and shear stress are obtained 
7 Maximum slope The one for which the maximum velocity is obtained 

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