Update Hydraflow Rainfall Distribution

[shdhd07]

When developing an SCS hydrograph in Hydraflow, we have the option to use multiple rainfall distribution curves.  NRCS Type I, II, IIA, and III are the most commons I've used in my career.  These curves are based partly on Technical Paper 40, released in 1961.

New distribution models were developed based on NOAA Atlas 14 rainfall data.  They were updated because the original curves were based on 50-year-old data.  NOAA Rainfall Distribution Curves Type A, B, C, and D were released as early as 2013.

It's been 12 years, yet we have not seen these curves available in the SCS Runoff Hydrograph tab in Hydraflow.  Many jurisdictions are beginning to require this be used in models and have rejected using the earlier ones.

[Molly_Thomson]

I found a reddit post that was helpful. Looks like on the NOAA Atlas 14 page, you can select your station and then click on the supplementary information tab and download the temporal distribution. Then you should be able to import it into Hydraflow as a custom distribution.

[markv5DV4A]

My question is what to do with that data.  The temporal data is in 120-minute blocks for a 24-hour duration storm and I don't think that Hydraflow's autointerpolate feature is accurate enough to convert that into a 1-minute or 2-minute interval that you need to generate hydrographs or route storms.  I tried AI-assisted data management and interpolation and the curve I get from there doesn't show the steep rise at 40% - 60% of the unit duration; it's gradual from 0% to 25% then rises linearly to 75% before the gradual approach to 100%.  Essentially it's taking the same increase and having it between 25% and 75% versus between 40% and 60%. 

From what I understand, you still need the 24-hour duration; but if that data for the 24-hour duration cannot be accurately used by modeling software due to interpolation inaccuracies, I 'm not sure to do.