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Purpose and Background

This webinar will cover the concepts related to creation of a design storm for use in hydraulic software packages, along with sources of rainfall data.   Many projects require that a rainfall-runoff model be developed to determine the design flow for a storm sewer system, a detention pond, or some other hydraulic conveyance facility. This is typically completed using one of a variety of software packages, such as SWMM, HEC-HMS, or vendor software. These software packages require that rainfall information be input, usually in a time series; however, very little guidance is provided in the software packages on how to take the available rainfall information and create a time series that can be used in the software. Storm water design manuals usually include requirements such as designing for the 10-year, 24-hour event, or for the 25-year, 6-hour event, but provide no information on how to actually develop a design storm for these events. This webinar will cover the concepts related to creation of a design storm for use in hydraulic software packages, along with sources of rainfall data. The webinar will include examples of the different techniques so that attendees will be able to use them, along with appropriate rainfall data, to develop a design storm for any location.

Primary Discussion Topics

• Rainfall data sources
• SCS type I, IA, II and III rainfall distributions
• Creating design storms using blocking Techniques
• Creating design storms using Huff Distributions

Learning Outcomes

The following learning outcomes have been established for webinar participants:

• Recognize the basic tools needed to create a design storm for a rainfall runoff model
• Understand examples of several methods that can be used to develop design storms and the advantages of each method
• Understand the shape of the SCS (NRCS) design storms for different areas of the U.S., and understand how these storms can be used with site-specific rainfall data
• Learn how to develop a design storm for durations varying from one hour to 24 hours using blocking Techniques and Huff Distributions

Webinar Benefits

• Become familiar with the rainfall data publications available from the National Weather Service and other publications
• Understand the shape of the SCS (NRCS) design storms for different areas of the United States, and understand how these storms can be used with site-specific rainfall data
• Learn how to develop a design storm for durations varying from one hour to 24 hours using blocking Techniques and Huff Distributions

Intended Audience

• Civil engineers involved in designing storm water facilities or using software packages to develop rainfall-runoff models
• Regulatory agency personnel responsible for review of storm water facilities

Webinar Outline

• Rainfall data sources
• SCS Type I, IA, II and III rainfall distributions
• Creating design storms using Blocking Techniques
• Creating design storms using Huff Distributions

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