Bentley StormCAD CONNECT Edition Help

Q/Qp Hydrographs

Note: For some localities, different templates may be used for different ranges of Tc.

This method computes a hydrograph by using a dimensionless hydrograph template that has values for T/Tc versus Q/Qp. Time for any given ordinate can be computed by:



  T/Tc = Value in Q/Qp template
  Tc = Time of concentration for the drainage area

Any given ordinate flow can be computed by:



  Q/Qp = Value for Q/Qp corresponding to T/Tc
  Qp = Peak flow for the drainage area


Q/Qp versus T/Tc

Note: Q/Qp templates are entered with the Rational Method Enter Q/Qp Template option.

Example

Computing a Hydrograph Given Tc = 15 minutes Q = 60 cfs for the 100-year storm Compute A Q/Qp hydrograph Computing Hydrograph Solution

Hydrograph Time   Hydrograph Flow  
T/Tc T (min.) Q/Qp Q (cfs)
0.00 0.00 0.00 0.00
1.00 15.00 0.15 9.00
2.00 30.00 0.20 12.00
3.00 45.00 0.28 17.00
4.00 60.00 0.44 26.00
5.00 75.00 1.00 60.00
6.00 90.00 0.34 20.00
7.00 105.00 0.27 16.00
8.00 120.00 0.19 11.00
9.00 135.00 0.12 7.00
10.00 150.00 0.00 0.00
Parent topic: Hydrograph Methods