Sewer Junction Total Loss and Total Loss (Smooth)
The Total (head) Loss is estimated using the methodology
described in the “Hydraulic Grade Design Procedure”
section of the “Model Drainage Manual - 1991” from
AASHTO, pp. 13.66-13.69. Using uniform pipe velocities the
contraction, controlling expansion and greatest bend losses are
computed and then totaled for each specified junction. This is
the unadjusted Total (head) Loss. If the junction catchment (inlet)
flows and known flows are greater than 10% of the mainline flow
the total (head) loss is increased by 30% giving the Total Loss.
If you select to use the Total Loss (smooth) method this adjusted
Total Loss value is then reduced by 50%.
| Total Loss | Total Loss (smooth) |
| Ht = Ho + Hi + Hb | Hts = 0.5*(Ht) |
Ho = 0.25*(Vo^2 / 2g)
Hi = 0.35*(Vi^2 / 2g)
Hb = K*(Vi^2 / 2g)
where:
Ht = Total Loss, head loss
Hts = Total Loss (smooth), head loss
Ho = Contraction (head) Loss
Hi = Expansion (head) Loss
Hb = Bend (head) Loss
Vi = inlet pipe velocity
Vo = outlet pipe velocity
g = acceleration due to gravity
The bend head loss accounts for the deflection angles of incoming
pipes. The loss is calculated using values for K from the
following table. Each incoming pipe is computed and the greatest
head loss value is then used. User Input for Kj is not required.
The values of K are linearly interpolated for absolute angles
between 0 and 180.
Each K is calculated as follows. Refer to the AASHTO table on
pages 13.54 and 13.55.
| K value | Absolute Deflection Angle |
| 0 | 0 |
| 0.19 | 15 |
| 0.35 | 30 |
| 0.47 | 45 |
| 0.56 | 60 |
| 0.64 | 75 |
| 0.70 | 90 |
| 0.70 | 180 |