Hydraulic Calculations


Rainfall Intensity Values

The Rainfall Intensity Values are based on NOAA Atlas 14 Point Frequency Estimates for each county’s centroid. These intensity values were used to develop Intensity – Duration – Frequency (IDF) curves with the help of the FHWA’s Hydraulic Toolbox software. The coefficients for the IDF equation and Rainfall Intensity Values for given durations and frequencies are shown in the tables by county.

Rainfall Intensity Values

SCDHEC Approved Rainfall Data

SCDHEC has promulgated two ways of determining the 24 Hour Storm Event for South Carolina. One is in Appendix F of the 2005 BMP Handbook. This appendix is attached in the pdf document below. The other method is using NOAAs Hydrometeorological Design Studies Center. This method requires the Longitude and Latitude of the project. Both of these methods are acceptable to SCDHEC.

Appendix F SC Rainfall Data

Department of Natural Resources

The Department of Natural Resources provides access to topographic, land use, and aerial maps that can be downloaded as well as information about the digital elevation and world coordinates data.

Department of Natural Resources

Natural Resources Conservation Service

The Natural Resources Conservation Service provides information you can download such as Technical Release 55, Windows Technical Release 55, Technical Release 20, and Windows Technical Release 20. Also, this site has a reference to obtain county soil surveys.

Natural Resources Conservation Service

Roadway Design Manual

The Roadway Design Manual assists technicians and engineers in selecting the needed design criteria in preparing plans for SCDOT construction projects.