1Design Rainfall (IDF)

Search a place or coordinates, or click a point in Texas to pull live NOAA Atlas 14 data — or switch to manual entry.

Search or click a point in Texas to fetch its NOAA Atlas 14 (Vol. 11) point IDF.

Intensity by duration in/hr @ min

Intensity must decrease as duration increases; values 0–40 in/hr.

2Rational Parameters

Peak discharge by the Rational Method. Intensity i is read from the IDF above at duration = Tc for the chosen return period.

Runoff coefficientC =–

Time of concentrationTc =min

Drainage areaA =acres

Return periodTr =yr

Q = C · i · A → —

Design storm

—yr

return period

Rainfall intensity · at Tc

—in/hr

i at duration = Tc

Peak discharge · Q = C·i·A

—cfs

Log–log rainfall intensity vs. storm duration. Hover or tap the plot to read every curve; the marker shows i used for Q.