Hydraulic Design of Highway Culverts - DOT On-Line Publications

English Units Calculations
By calculation, the design headwater depth, HWd, equals 885 - 878 = 7 ft. The outlet invert
elevation is:
ELo = ELi - LSo
= 878 - (200)(.05) = 868 ft
Figure V-16--Inflow Hydrograph, Example Problem (English)
1. Perform Hydrologic Calculations.
The SCS Tabular Method was used to generate the inflow hydrograph depicted in Figure V-16.
The results are shown in tabular form in Table 5 (English). The unrouted peak flow (Qp) is 220
ft³/s. The time to peak is 75 minutes.
For the routing interval, use tp/10.
∆t = tp/10 = 75/10 = 7.5 minutes.
2. Check Approximate Routing effects.
The storage behind the highway embankment will reduce the flood peak. Calculate the routed
peak flow using the approximate method. (See item 2 on the example Flood Routing Form,
Figure V-17). The peak flow of 220 ft³/s is reduced to 176 ft³/s.
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