Hydraulic Analysis of Storm Drain Inlets

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INSTRUCTOR: Mark Peterson, P.E., M.ASCE

Course Length: 1 Hour

Purpose and Background

The assumption is often made that a single inlet will intercept all of the water that reaches the inlet, or that a single inlet will intercept some standard flow, such as 5 cfs or 10 cfs. This results in an expensive storm sewer system that does not perform the intended function. Actual hydraulic analysis indicates that standard inlets may actually intercept only 1 to 3 cfs.  The design concepts are becoming even more important with the implementation of Low Impact Development techniques such as bio-retention cells that depend on small curb cuts to direct water away from the street curb line.

This webinar covers the concepts related to hydraulic analysis of storm drain inlets including grates, curb openings and slotted drain, both on continuous grades and in sag locations. It also reviews the use of Federal Highway Administration software available to complete the analysis.

Primary Topics of Discussion

  • Design equations for inlets on continuous grades
  • Design equations for inlets in sag locations
  • Use of Federal Highway Administration software for inlet calculations
  • Use of curb cuts for off-street bio-retention facilities

Learning Outcomes

  • Understand the necessary parameters and the equations used to analyze the hydraulic capacity of various inlets on continuous grades
  • Determine the hydraulic capacity of inlets in sags, operating either in orifice flow or in weir flow
  • Learn the basics of the Federal Highway Administration software for inlet calculations
  • Understand how curb cuts used to convey flows to off-street bio-retention cells function 

Webinar Benefits

  • Learn how inlets on a continuous grade intercept water and the importance of frontal flow and side flow
  • Gain an understanding of how both orifice flow and weir flow calculations are necessary for inlets in sag conditions
  • Understand how to use Federal Highway Administration software for inlet calculations
  • Learn why small curb cuts used to convey flows to off-street bio-retention cells are usually inadequate

Intended Audience

  • Drainage design engineers
  • Transportation engineers
  • Government officials responsible for storm drainage design or plan review

Webinar Outline

  • Types of Inlets
  • Gutter Flow Calculations
  • Capacity of Inlets on Continuous Grades
  • Capacity of Inlets in Sags
  • Use of FHWA design software
  • Curb Openings for LID features