Creating a HydroCAD Rainfall file
Creating a HydroCAD Rainfall file
(OP)
I ran into a problem when trying to create a rainfall file for in HydroCAD v9.10. I want to create a 24 hour Chicago storm using a,b,c coefficients. The formula HydroCAD uses calculates depth = t*a/(b+t)^c. This is depth = time*intensity. The problem is that the a, b,c coeffs I have require t, to be in minutes, but generate an intensity in mm/hr. Therefore the t, on the top needs to be in hours, while the t on the bottom in minutes. Is it correct to adjust the a and b coeffs so that they use a t in hours? Or will this alter my Chicago storm. Or should I leave the coeffs as they are and manually input a depth when executing the rainfall file in HydroCAD. (The default depth is grossly incorrect).
Note, adjusting the coeffs allows HydroCAD to accurately provide a default rain depth.
Thanks for the help!
Note, adjusting the coeffs allows HydroCAD to accurately provide a default rain depth.
Thanks for the help!





RE: Creating a HydroCAD Rainfall file
These are the default IDF units, as shown in the sample IDF file:
depthunits=inches
timeunits=hours
duratunits=minutes
In your case you can use:
depthunits=mm
timeunits=hours
duratunits=minutes
In brief, just add "depthunits=mm" to your file.
Please note that the resulting IDF file can be used with a HydroCAD project that is configured for Metric or English - HydroCAD will make the units conversions automatically.
For further details please see www.hydrocad.net/rainfall/idf.htm
Peter Smart
HydroCAD Software
www.hydrocad.net
RE: Creating a HydroCAD Rainfall file
Let me clarify by reiterating my question. I'm trying to create a rainfall file, I have a working IDF file. I need to create a 24 hr Chicago storm distribution. I was using the file: Sample D 24-hr to create a 24hr Chicago storm based on IDF coefficients.
Can I add duratunits to this file? I haven't been successful so far.
Thanks
RE: Creating a HydroCAD Rainfall file
For a rainfall distribution (HCR file) the answer to your questions is contained in the "Sample D" file you referenced. Specifically, you will need to include:
timeunits=minutes
depthunits=mm
duration=24*60
peaktime=12*60
The *60 factor converts the duration and peaktime values from hours to minutes.
This will create a dimmensionless rainfall distribution. If you want to automatically preset the total rainfall depth you can also include:
stormdepth=xx.xx
If you have further questions please post the file or email it to HydroCAD support.
Peter Smart
HydroCAD Software
www.hydrocad.net