Data Sources

Used 5% and 1% here instead of spelling out because the precision 0.01% cannot be spelled out, the concept is scientific, and for consistency.

The rainfall time-distribution data given here are obtained from Circular 173 (Huff 1990). Wherever the tabular data was available in Circular 173 it was used to develop rainfall tables. However, tabular data in Circular 173 is given only for every 5% of the time distribution. The tables available in the engineering catalogs give data for every 1% of the rainfall time duration. The data in between tabular values have been obtained from the figures in Circular 173. Due to the interpolation procedure used to develop graphs, a slight discordance between tables and figures occurs in the tails of the distributions. Where this was the case, higher precedence was given to the tabular data.

Additional differences between the data presented here and the Circular 173 tables comes from the precision used in Circular 173. While Circular 173 rounds the data to the first 1%, the data presented in the Bentley StormCAD engineering libraries has a precision of 0.01%. However, due to the statistical nature of the data presented, these differences are negligible.