Triangular Rainfall Distribution

[hydro50]

I'm a new user of HydroCad v10. How or where can I load or use the Triangular Synthetic Distribution form the Corps of Engineers or the Frequency Based Hypothetical Storm (HEC-HMS).
For small basins, the SCS Type II distribution generates very high peak discharges.

 

[psmart]

You may be confusing the rainfall distribution (e.g. Type II) with the Unit Hydrograph, which can be curvilinear or triangular. The peak runoff is effected by both curves.

In HydroCAD, you can change the Unit Hydrograph peak factor by selecting a different UH table. HydroCAD-10 includes tables for a number of different peak factors from 200 to 600. The default SCS UH has a peak factor of 484. Triangular UH tables can be used, but there is really no need, since they will produce peak flows consistent with the curvilinear UH with the same peak factor.

You can also select a different rainfall distribution. The Type II storm has a peak that is somewhat higher than the Type III. The storm you choose depends on the project's location. You can also define custom rainfall distributions, and HydroCAD-10 can generate a custom synthetic rainfall distribution based on local Precipitation Frequency Data from NOAA, NRCC, and other sources.

So, if you're trying to reduce the peak runoff, have a look at the UH and Rainfall selections. You'll find them on the Rainfall and UH tabs of the Settings|Calculation screen. For further details please see

http://www.hydrocad.net/rainfall/

If you have further questions, please post the project location and we can provide more specific recommendations.


Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[psmart]

I should add: If you want to create a custom rainfall distribution (perhaps to match the one you used in HEC-HMS) you'll find details at

http://www.hydrocad.net/rainfall/faqs.htm

Peter Smart
HydroCAD Software

http://www.hydrocad.net