Developing Filter Gradation Specifications from Current Guidance

Join us on Tuesday, September 8, 2026, from 12:00 PM - 2:00 PM for Developing Filter Gradation Specifications from Current Guidance. The current guidance on aggregate soil filter gradations is based on research conducted by the U.S. Department of Agriculture in the 1980s. Subsequently, various federal agencies (Natural Resources Conservation Service, Bureau of Reclamation, U.S. Army Corps of Engineers, and FEMA) published step-by-step guidance for aggregate filter gradation design based on that research. The resulting guidelines represent a great advance in filter gradation design, but not all practitioners understand the reasons for the various steps in the process and the latitude available in translating the results of the process into project specifications. This situation can result in the specification of filter gradations that are hard to find or are excessively expensive.

This webinar will 1)briefly review the history of aggregate soil filter gradation criteria, 2) explain the purposes of the various steps in the current guidelines, 3) illustrate with examples the latitude available to designers in developing project specifications from the results of the step-by-step guideline calculations, and 4) explain how some of the steps in the calculations may need to be modified for the coarser zones in multi-stage filter drain systems.

Learning objectives attendees will receive from this webinar:

• An understanding of the history of aggregate soil filter gradation criteria.
• An understanding of the desired characteristics of an aggregate soil filter.
• An understanding of the purposes of the various control points determined in the current step-by-step procedures for establishing aggregate filter gradation requirements.
• An understanding of the latitude available to a designer in developing an aggregate filter gradation specification using the control points.
• An understanding of adjustments to the calculation procedures that may be needed for multi-stage filter/drain systems.

PDHS AVAILABLE:

• This course qualifies for 2 PDHs.

REGISTRATION FEES:

• Member Rate: $99
• Non-Member Rate: $130 - Join ASDSO before registering and save!