`I = (b) / (t_c+d)^e`

Enter a value for all fields

The Rainfall Intensity Calculator finds the average rainfall rate for a specific duration and a selected frequency, where:

• I = average rainfall intensity
• t_c = time of concentration 
  • time required for an entire watershed to contribute to runoff at the point of interest for hydraulic design
• e, b, d = coefficients based on rainfall IDF data

The Math

I = b / (t_c + d)^e 

where:

I = average rainfall intensity

t_c = time of concentration 

e, b, d = coefficients based on rainfall IDF data

References

OnlineManuals (http://onlinemanuals.txdot.gov/txdotmanuals/hyd/rational_method.htm)