This course presents criteria for determining the grain-size distribution (or gradation) of sand and gravel filters needed to prevent internal erosion or piping of soil in embankments or foundations of hydraulic structures. These criteria are based on results of an extensive laboratory filter study carried out by the Soil Conservation Service at the Soil Mechanics Laboratory in Lincoln, Nebraska, from 1980 to 1985. Topics: Basic purpose of filters and drains Permeability and capacity Determining filter gradation limits Intended Audience: This course is intended for Geotechnical, Civil, Environmental, Water Resources, and other engineers whose job description requires a comprehensive knowledge of geotextile applications and design procedures.