modified rational modified rational johnhan76 (Civil/Environmental) (OP) 25 Apr 03 23:18 I am about to develop a spreadsheet to route a modifed rational hydrograph. Just making sure no one has one that they would like to share - Thanks RE: modified rational mroberts (Civil/Environmental) 23 Jun 03 12:31 I have done several of these to calculate needed detention volume based on a triangular hydrograph from Modified Rational. email me at email@example.com and I will forward some to you. They usually have to be customized to each City's criteria. It involves some sort of lookup function for Intensity values for different time values so it really helps if you have an IDF formula.