It has been a long time since I used a spreadsheet to route stormwater flow.  I've been using HydroCAD since it first came out in the mid 80's.  Try their website.  I think they have a demo version that you can use.

johnhan76
I have a spreadsheet that is fairly simple for routing
through detention ponds.
It does not calculate the peak flow (the county agency
here doesn't use rational method), but it can be easily modified to incorporate that step.
It does generate a hydrograph using a method called
"Small Watershed Hydrograph Method" by Malcom of Univ of N.Carlina, and routes this through a predefined rating
curve for the basin and outlet structure.
For rectangular basins, it can calculate the storage
vs. stage curve for you.
The spreadsheet is easily modified to before specific
task, since no two jobs are ever the same.

email at kekillian@civiltecheng.com
if you are interested.

Elminer-

I have been using Hydrocad and am unsure of some data that I am supposed to enter using the Modified Rational Method.  What intensity and storm duration is usually used.  I am using a storm duration of 60 minutes.  Is this correct?

Thanks

I have never had any luck trying to get a Modified Rational hydrograph (with a peak and decline) out of HydroCAD.  I have to run one in another software, then create a link in HydroCAD and manually enter it there.  It is a pain.

With manually entered hydrograph, duration and intensity are not relevant, but I think you will still have to select something to make the program run.

You might try WINhydro from McTrans (Univ. of Fla)

http://mctrans.ce.ufl.edu/

PECPESC,

Can you tell us who wrote WinHydro and whether or not a demo version is available.  I found it at McTrans but no demo or reference to the actual authors of the program.

Not sure if this is what you want, but you might give it a try.

http://www.compusmart.ab.ca/dwilliam/hydtools/download....

HydroCAD can generate and route a rational method hydrograph with no problems.  For modified Rational method you can adjust the rate of rise and fall independently.  For complete details see www.hydrocad.net/rational.htm  If you have any questions or problems you can contact tech support using the link on that page.

HydroCAD-7 can also use custom IDF curves to perform automatic intensity lookup for any desired duration.  But the choice of the correct duration is essential to obtaining meaningfull results.

Although some localities may specify a fixed event duration, correct use of Rational method requires that the critical duration be determined for each point in the watershed.  This can be a time-consuming process, and points out the limitations of Rational method for all but the simplest situations.  Other methods that generate a full runoff hydrograph (such as the SCS/NRCS unit-hydrograph procedure) are often better and easier to use.  HydroCAD provides both techniques, making it easy to compare results and use the best approach for your situation.

WINhydro was written by

Don Grisham, Software Developer
P.O. Box 550171
Dallas, TX 75355

Also owns A&G Software which has other programs w/McTrans.

Can provide demo if written request.