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Constructing IDF Curves from ISOPLUVIALS

Constructing IDF Curves from ISOPLUVIALS

Constructing IDF Curves from ISOPLUVIALS

I have isopluvial maps of my state but what I really need is to determine intensity for various time periods.  Is there a way to use the isopluvial value for a given spot and adapt it to a synthetic storm curve Type II in this case?

Does anyone have the numbers used to assemble the SCS storm type curves handy?


RE: Constructing IDF Curves from ISOPLUVIALS

Before you do all that work try checking with your State Highway Department or local ( County ) road departments. They almost certainly have already developed IDF curves for various regions of the State.

Also, don't reinvent the wheel The NRCS type storm distributions are available free with the program WINTR55.  Do a web search for it and download it. It will save you a lot of time.

good luck

RE: Constructing IDF Curves from ISOPLUVIALS

Unfortunately this particular county does not have any of that info and it is not on the NOAA web site for that area.  The only requirement they have is 2 inches in 90 minutes.  In talking to Haested Methods they say I have to come up with a curve in order to use Storm Cad.


RE: Constructing IDF Curves from ISOPLUVIALS

Even if the County does not have IDF curves, surely the State does ?  What state are you in ?

RE: Constructing IDF Curves from ISOPLUVIALS

I am in Washington State.  That is one of the states that has yet to be added to the NOAA web site for t his kind of data.  The NOAA web site also mentioned that data is scarce for this area because the collecting stations are widely dispersed.  

I have searched the WSDOT web site for hours with no luck.


RE: Constructing IDF Curves from ISOPLUVIALS

I live in Oregon and sometimes work in Washington.  The Washington DOT has a Hydraulics Manual which you can buy. It is excellent and has IDF curves for every part of the State.  They also include equations for all the curves and even for small ephemeral streams in eastern Washington.  The Manual is probably not on their website but try calling them in Olympia.

Also check,


good luck,


RE: Constructing IDF Curves from ISOPLUVIALS

Thanks RWF7437,

   Guess I was looking at the wrong web sites.


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